Prompt emission mechanisms ofGRBsDimitrios Giannios

Max Planck Institute for Astrophysics

Structure of the talk Main properties of the prompt emission

Models for the GRB flow Fireballs Poynting-flux dominated flows

Reconnection model

Dissipative mechanisms for the prompt emission Internal shocks vs Magnetic reconnection

Radiative mechanisms Thomson thin vs photospheric emission

Summary

1 MeV

The prompt emission spectrum

The typical GRB spectrum hasnon-thermal appearanceBand et al 1993 Kaneko et al 2006

Low energy power law slope α High energy power law slope β Connected at ~a few hundred

keV (spectral peak)

Short bursts are harder probablybecause of steeper low energyslopePaciesas et al 2003 Ghirlanda et al 2004

E (MeV)

E f(E

) (er

gcm

2 s)

E

f(E)

GRB Variability

Short

t

N (t

)

Variability detected to as short as sub-msec timescales

Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996

The typical pulse width is δt~1sec(~01 sec) for long (short) bursts

Summary for the prompt emission Clues

The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998

Rapid variability

The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999

Big questions How is the flow accelerated What processes result in the observed spectral and

temporal properties of GRBs

Can we learn something about the central engine

General considerations Acceleration Important quantities of the flow

luminosity L mass flux Efficient acceleration can lead to γsr~η

Depending on the energy extraction mechanism the flow canbe dominated by

Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated

flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp

Blandford 2003

21

L

Mc = gtgt

ampMampBaryon loading

Fireballs

Parameters L η initial radius ro

Go through fast acceleration Converting thermal energy into kinetic

Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η

Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place

r

[Notation (L= L521052 ergs)]

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Structure of the talk Main properties of the prompt emission

Models for the GRB flow Fireballs Poynting-flux dominated flows

Reconnection model

Dissipative mechanisms for the prompt emission Internal shocks vs Magnetic reconnection

Radiative mechanisms Thomson thin vs photospheric emission

Summary

1 MeV

The prompt emission spectrum

The typical GRB spectrum hasnon-thermal appearanceBand et al 1993 Kaneko et al 2006

Low energy power law slope α High energy power law slope β Connected at ~a few hundred

keV (spectral peak)

Short bursts are harder probablybecause of steeper low energyslopePaciesas et al 2003 Ghirlanda et al 2004

E (MeV)

E f(E

) (er

gcm

2 s)

E

f(E)

GRB Variability

Short

t

N (t

)

Variability detected to as short as sub-msec timescales

Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996

The typical pulse width is δt~1sec(~01 sec) for long (short) bursts

Summary for the prompt emission Clues

The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998

Rapid variability

The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999

Big questions How is the flow accelerated What processes result in the observed spectral and

temporal properties of GRBs

Can we learn something about the central engine

General considerations Acceleration Important quantities of the flow

luminosity L mass flux Efficient acceleration can lead to γsr~η

Depending on the energy extraction mechanism the flow canbe dominated by

Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated

flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp

Blandford 2003

21

L

Mc = gtgt

ampMampBaryon loading

Fireballs

Parameters L η initial radius ro

Go through fast acceleration Converting thermal energy into kinetic

Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η

Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place

r

[Notation (L= L521052 ergs)]

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

1 MeV

The prompt emission spectrum

The typical GRB spectrum hasnon-thermal appearanceBand et al 1993 Kaneko et al 2006

Low energy power law slope α High energy power law slope β Connected at ~a few hundred

keV (spectral peak)

Short bursts are harder probablybecause of steeper low energyslopePaciesas et al 2003 Ghirlanda et al 2004

E (MeV)

E f(E

) (er

gcm

2 s)

E

f(E)

GRB Variability

Short

t

N (t

)

Variability detected to as short as sub-msec timescales

Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996

The typical pulse width is δt~1sec(~01 sec) for long (short) bursts

Summary for the prompt emission Clues

The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998

Rapid variability

The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999

Big questions How is the flow accelerated What processes result in the observed spectral and

temporal properties of GRBs

Can we learn something about the central engine

General considerations Acceleration Important quantities of the flow

luminosity L mass flux Efficient acceleration can lead to γsr~η

Depending on the energy extraction mechanism the flow canbe dominated by

Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated

flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp

Blandford 2003

21

L

Mc = gtgt

ampMampBaryon loading

Fireballs

Parameters L η initial radius ro

Go through fast acceleration Converting thermal energy into kinetic

Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η

Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place

r

[Notation (L= L521052 ergs)]

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

GRB Variability

Short

t

N (t

)

Variability detected to as short as sub-msec timescales

Variable lightcurves composed bypulses Fenimore et al 1995 Norris et al 1996

The typical pulse width is δt~1sec(~01 sec) for long (short) bursts

Summary for the prompt emission Clues

The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998

Rapid variability

The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999

Big questions How is the flow accelerated What processes result in the observed spectral and

temporal properties of GRBs

Can we learn something about the central engine

General considerations Acceleration Important quantities of the flow

luminosity L mass flux Efficient acceleration can lead to γsr~η

Depending on the energy extraction mechanism the flow canbe dominated by

Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated

flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp

Blandford 2003

21

L

Mc = gtgt

ampMampBaryon loading

Fireballs

Parameters L η initial radius ro

Go through fast acceleration Converting thermal energy into kinetic

Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η

Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place

r

[Notation (L= L521052 ergs)]

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Summary for the prompt emission Clues

The prompt emission has non-thermal spectral appearance Band et al 1993 Preece et al 1998

Rapid variability

The GRB-emitting flow is ultrarelativistic (γgt100)eg Piran 1999

Big questions How is the flow accelerated What processes result in the observed spectral and

temporal properties of GRBs

Can we learn something about the central engine

General considerations Acceleration Important quantities of the flow

luminosity L mass flux Efficient acceleration can lead to γsr~η

Depending on the energy extraction mechanism the flow canbe dominated by

Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated

flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp

Blandford 2003

21

L

Mc = gtgt

ampMampBaryon loading

Fireballs

Parameters L η initial radius ro

Go through fast acceleration Converting thermal energy into kinetic

Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η

Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place

r

[Notation (L= L521052 ergs)]

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

General considerations Acceleration Important quantities of the flow

luminosity L mass flux Efficient acceleration can lead to γsr~η

Depending on the energy extraction mechanism the flow canbe dominated by

Thermal energy rarr thermal acceleration (Fireball) Paczynski 1986 Goodman 1986 Sari amp Piran 1991 Magnetic energy rarr magnetic acceleration (Poynting-flux dominated

flow) Usov 1992 Thompson 1994 Meacuteszaacuteros amp Rees 1997 Drenkhahn amp Spruit 2002 Lyutikon amp

Blandford 2003

21

L

Mc = gtgt

ampMampBaryon loading

Fireballs

Parameters L η initial radius ro

Go through fast acceleration Converting thermal energy into kinetic

Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η

Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place

r

[Notation (L= L521052 ergs)]

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Fireballs

Parameters L η initial radius ro

Go through fast acceleration Converting thermal energy into kinetic

Saturation takes place when almost all thermal energy is used γsr η at the photospheric crossing γsr lt η

Radiation and matter decouple whenτ ~ 1 Photospheric emission takes place

r

[Notation (L= L521052 ergs)]

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Magnetic (Poynting) models The field can be

axisymmetric (DC flow) Vlahakis amp Koumlnigl 2003 Lyutikov amp Blandford 2003

McKinney 2005 Uzdensky amp MacFadyen 2006

highly asymmetric (AC flow)Drenkhahn amp Spruit 2002 Thompson 2006

Acceleration is more gradualDrenkhahn amp Spruit 2002 Vlahakis amp Koumlnigl 2003

Here I focus more on AC flow

DC

AC

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

The reconnection (AC) model

1 3

sr sr

4 3

7 3

23

diss

diss

( )

( ) 8

r r

B r

n r

BP r

t

=

$

$

= $

Magnetic field changes polarityon small scales λ = 2πcω

Magnetic reconnection proceedswith a fraction ε ~ 01 of theAlfveacuten speed Lyubarsky 2005

The dynamics of the flow havebeen worked out in detailDrenkhahn 2002 and Denkhahn amp Spruit 2002see also Lyubarsky amp Kirk 2001 for pulsar winds

Parameters L η (εω)

rsr

rph

Log(r [cm])

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

These are all fineWhere are the γ-rays in this picture

Which processes power the prompt emission

Where (at which radii) is it produced

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

General considerationsenergy source of the prompt emission The rapid GRB variability argues against the forward shock for

the prompt emissioneg Sari amp Piran 1997 see however Dermer 2007 for a different point of view

Observationally transition from the prompt to the early afterglowemission Zhang et al 2006

The prompt emission most likely comesfrom internal dissipation of energy in the fast flow

This can take place by Internal shocks Rees amp Meacuteszaacuteros 1994 Sari amp Piran 1997

Magnetic dissipation Thompson 1994 Denkhahn amp Spruit 2002 Lyutikov amp Blandford 2003-see Fan et al 2004 for a combination of the two

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Internal shocks vs Magnetic dissipation Internal shocks

Unsteady flow composed bymany fast shells

A fast shell with γ2gtγ1 collideswith a slower one dissipatingtheir relative kinetic energythrough shock waves

Magnetic dissipation Magnetic fields carry most of the

energy of the flow The magnetic energy is

dissipated internally throughreconnection

g-rays

Fk

FB

Fk

variability and dissipation are separateingredients in magnetic dissipationmodels

γ2υ2 γ1υ1

FB

γυ

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Where is the prompt emission produced anywhere between the Thomson photosphere rph and the

deceleration radius rd

Typically rph~1011cm and rd ~1017cm in this range of radii density ~12 orders of magnitude optical depth ~6 orders of magnitude

Different radiative mechanisms dependingon the location of the energy dissipation

Case 1 Thomsonthin dissipation

Case 2 Photosphericdissipation

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Case 1Internal shocks in the Thomson thin regime Internal shocks

The collision of the shells takes place at rcol~γ2ctv tv related to the central engine activity (not trivially Janka et al 2005 Aloy amp

Rezolla 2006) Each collision results in an observed pulse of gamma-rays

shocks cross the shells

In the shock front Particle acceleration takes place Magnetic field amplification due to plasma instabilitites (see next talks)

Parameters fractions єe ζe єB power-law N(γe) ~ γe-p pgt2

Fast particles + magnetic fields Synchrotron self-Compton emission

Thin synchrotron emission may explain the observed spectrum

~

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Case 1Can thin Synchrotron emission explain the spectra

Pros For tv~1 s the characteristic pulse duration and separation can be reproduced

Kobayashi et al 1997 Daigne amp Mochkovitch 1998 Nakar amp Piran 2002

The peak of the synchrotron spectrum can be in the ~a few 100 keV range

Flat high-energy power law

Cons Low radiative efficiency (though uncertain)

~ єdiss єe єBand at the ~ level

Low-energy spectra often too steep for thin synchrotroneg Preece et al 1998 Ghirlanda et al 2004

jitter radiation Medvedev 2000 The synchrotron spectrum gets distorted by Self Compton emission pair

creation for a large parameter spaceKobayashi et al 2002 Meacuteszaacuteros et al 2002

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Case 1Magnetic dissipation in the Thomson thin regime

In DC models the magnetic energy can be dissipated because of MHDinstabilities eg current driven instabilities at ~1016 cm Luytikov amp Blandford 2003 Lyutikov 2006

Fast proper plasma motions lead to the rapid observed variability

AC model dissipation near photosphere as well as outside

Significant amount of energy is dissipated in Thomson thin conditionsDG amp Spruit 2005

Particle acceleration through electric fields in current sheetseg Craig amp Litvinenko 2002 Zenitani amp Hoshino 2004

Thin synchrotron emission may be responsible for the GRB

The B-field is given directly by the model At low densities particle distributions in reconnection uncertain

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Case 2

Photospheric emission is radiationadvected with the flow that is releasedwhen the flow becomes optically thin

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Photospheric emission In the fireball the photospheric luminosity is eg Meacuteszaacuteros amp Rees 2000

Spectrum quasi thermal Goodman 1986

Energy dissipation at τ ge 1 distorts the spectraMeacuteszaacuteros amp Rees 2005 Persquoer et al 2006

In the AC model DG 2006 DG amp Spruit 2007

For this range of η the model predicts a dissipative photosphere

1 48 3 23

ph 25 o7 52

2 3

52 o7

005 1000L r L

L L r

$ lt amp

(

15 15ph 15 1552 3

52 3

25

( )016 150 ( )

L LL

L

$

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Dissipative Photosphere in a fireball Internal shocks take place below the

photosphere for tvltlt1 s

Persquoer et al (2006) - energy release close tothe fireballrsquos photosphere ndashThompson et al 2007

Injecting fast electrons Slow heating Ghisellini amp Celotti 1999

Studied the radiative transfer for variousvalues of єdiss єB єe τ

Big variety of spectra depending on τ

Dominant process Compton scattering ofphotons advected with the flow

τγe = 1

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Our suggestion photospheric emission from the AC modelMain features

AC model gradual dissipation throughout the photosphere

If fraction fe ~ 1 of the energy goes to the electrons then Hot photosphere Soft photon upscattering

Unsaturated Comptonization spectrum with DG 2006 DG amp Spruit 2007

Peak in the sub-MeV range Flat high-energy emission Steep low energy slopes

Rather high efficiency Lph ~ 003hellip03L for 100 lt η lt 1500 ~ ~

rsrrph

Log(r [cm])

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Radiative transfer analytical estimates+ Monte Carlo Comptonization

Deep in the flow radiation ampparticles are in thermal equilibrium

At req ~ rph10 radiation andelectrons drop out of equilibrium Teq ~ 1 keV Tobs=γeq Teq ~100 keV

For r gt req balance in heating andcooling determined Te

Mildly relativistic temperatures at τ ~ 1 Soft photon up scattering

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Photospheric spectra Characteristic peak at ~1 MeV

(in the central engine frame)

Flat power law high energy tails(unsaturated Comptonization)

Quasi-thermal spectrum for highbaryon loadings the spectrum May be relevant for a sub-group of

bursts Ryde 2004 2005

Analytical fitting formulas give thespectra as a function of thecharacteristics of the flowDG amp Spruit 2007

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Inferences for the central enginethe stronger the cleaner

The Amati relation explainedif in different bursts

Variability in prompt emission Reflects changes in L η

Assumption relationholds during the GRB the model predicts the observed

narrowing of pulses withincreasing energyFenimore et al 1995

06L

06L

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Summary Spectral and temporal properties of GRBs are very intriguing

The prompt emission most likely comes from internaldissipation of energy in the fast flow Internal shocks or Magnetic dissipation

Dissipation can take place in Thompson thin or thick conditions Thin case particle acceleration uncertainties єe ζe p єB

Gradual dissipation throughout the photosphere has verypromising properties The reconnection model has them

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

The peak energy and the energetics

η30 100 300 1000

η30 100 300 1000

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +

Comment

The temperature of the flow at the req in the observer frame is

The Ef(E) spectrum of this component peaks at ~4 times thisenergy

19 1 9 1 3 2 9

eq eqobs e1 52 3 25

eq

( ) ( )100 keV

1 1

r T f LT

z z

$

+ +