On cosmic-ray positron origin and the role of

circumpulsar debris disks

Catia GrimaniUniversity of Urbino and INFN Florence

ContentsContents

Discovery of cosmic raysCharacteristics of cosmic raysElectrons and positrons (the lowest

mass particles in cosmic rays)Origin of electrons and positronsElectrons, positrons and pulsar

physics

Discovery of cosmic raysCharacteristics of cosmic raysElectrons and positrons (the lowest

mass particles in cosmic rays)Origin of electrons and positronsElectrons, positrons and pulsar

physics

The discoveryThe discovery1911-12 cosmic-ray discovery Victor F. Hess

What cosmic rays are made of?Photons? No, energetic positive charged particles (protons and ions)! Latitude effect and east-west asymmetry

1911-12 cosmic-ray discovery Victor F. Hess

What cosmic rays are made of?Photons? No, energetic positive charged particles (protons and ions)! Latitude effect and east-west asymmetry

Cosmic-ray compositionCosmic-ray composition

90% protons8% helium nuclei1% electrons1% heavy nuclei<1% positrons, antiprotons

90% protons8% helium nuclei1% electrons1% heavy nuclei<1% positrons, antiprotons

Rare particle discovery in cosmic rays

Rare particle discovery in cosmic rays

1932 Positrons (ground)1937 Muons (ground)1947 Pions (ground)1961 Electrons (Galactic cosmic rays)1964 Positrons (Galactic cosmic rays)1979 Antiprotons (Galactic cosmic

rays)

1932 Positrons (ground)1937 Muons (ground)1947 Pions (ground)1961 Electrons (Galactic cosmic rays)1964 Positrons (Galactic cosmic rays)1979 Antiprotons (Galactic cosmic

rays)

Cosmic-ray overallspectrum

Above a few GeVF(E)=AE-

Part./(m2 sr s GeV)

o the knee (3x1015 eV)o 1018 eVabove the ankle (3x1018 eV)

That special interest in e- and e+…

That special interest in e- and e+…

Electrons and positrons interact with magnetic field and background and stellar photons.

Comparison between proton and electron fluxes (rigidity and velocity propagation processes).

Exotic origin.

Electrons and positrons interact with magnetic field and background and stellar photons.

Comparison between proton and electron fluxes (rigidity and velocity propagation processes).

Exotic origin.

Electron energy lossesElectron energy lossesIonization (dE/dt)I = 7.6 10-18 n[3 ln(E/mc2)+18.8] GeV/s n=1 atom/cm3

Bremsstrahlung (dE/dt)B = 8 10-16 n E GeV/sSynchrotron (dE/dt)s =3.8 10-18 HT

2 E2 GeV/s

<HT>=3 G

H= 1.23 <HT>Inverse Compton Blackbody radiation Stellar photons (dE/dt)c = 10-16 w E2 GeV/s

w=0.7 eV/cm3

Ionization (dE/dt)I = 7.6 10-18 n[3 ln(E/mc2)+18.8] GeV/s n=1 atom/cm3

Bremsstrahlung (dE/dt)B = 8 10-16 n E GeV/sSynchrotron (dE/dt)s =3.8 10-18 HT

2 E2 GeV/s

<HT>=3 G

H= 1.23 <HT>Inverse Compton Blackbody radiation Stellar photons (dE/dt)c = 10-16 w E2 GeV/s

w=0.7 eV/cm3

These interactions imply that …

These interactions imply that …

Electrons are less abundant than protons

A spectral break is present at the source for electrons only…

Electrons are less abundant than protons

A spectral break is present at the source for electrons only…

Interplanetary electron flux

Interplanetary electron flux

Origin of electronsOrigin of

electrons

1<E<30 MeV Jupiter

magnetosphere 30<E<100 MeV Secondary Galactic

origin E>100 MeV Primary Galactic origin

1<E<30 MeV Jupiter

magnetosphere 30<E<100 MeV Secondary Galactic

origin E>100 MeV Primary Galactic originNear Earth

Above a few GeVF(E)=AE-

Part./(m2 sr s GeV)

CG et al., to be submitted to CQG

Primaries

About the e- galactic component…

About the e- galactic component…

Various authors assume electron spectrum break at the source:

Moskalenko and Strong: =2.1 E≤ 10 GeV =2.4 E≥10 GeV Best agreement to data!

Stephens: =1.54 E≤ 4.5 GeV =2.54 E≥4.5 GeVPlerion-like input spectrum

Above 1 TeV descrete sources (for example nearby SNR- Vela, Monogem, Cygnus Loop -Kobayashi et al., 2004) are expected to produce electrons observed near Earth

Galactic electron flux estimates

Galactic electron flux estimates

Solar electronsSolar electrons

November 3rd and September 7th 1973 solar events

Solar electron detectioncan be used to forecast incoming SEPs

Posner, 2007

Positron flux observations and calculations

Moskalenko & Strong, 1998Stephens, 2001a,b

Positron fraction measurements before

1995

Positron fraction measurements before

1995

Protheroe, 1982

Origin of positrons Origin of positrons

Secondary particles produced in the interstellar medium as final products of proton interactions.

pp e++

pp e-

+

But possibly also…

Secondary particles produced in the interstellar medium as final products of proton interactions.

pp e++

pp e-

+

But possibly also… Primordial Black Hole Annihilation56Co decay in Supernova RemnantsSupersymmetric particle annihilation interactionPulsar magnetosphere (Polar Cap - Outer Gap Models)

POLAR CAP MODEL

Goldreich & Julian, 1969Harding & Ramaty, 1987

Figure from http://cossc.gsfc.nasa.gov/images/epo/gallery/pulsars/

•Strong electric fields are induced by the rotating neutron star

•Electrons are extracted from the star outer layer and accelerated

•Open field lines originate at polar caps (rpc= 8 x 102 m)

OUTER GAP MODEL

C. Grimani ECRS Florence August 31st - September 3rd 2004

Cheng, Ho & Ruderman, 1986*Electrons are accelerated in the outer magnetosphere in vacuumgaps within a charge separatedplasma*Electrons interact through syncrotron radiation or inverseCompton scattering*e+e- pairs are produced by interaction

Different cut-off energies are predicted by polar cap and outer gap models in the pulsed gamma-ray spectra (GLAST)!

Figures from http://cossc.gsfc.nasa.gov/images/epo/gallery/pulsars/

How to distinguish among different

hypotheses?It is mandatory to

discriminate among various models of secondary e+ - e-

calculations…

How to distinguish among different

hypotheses?It is mandatory to

discriminate among various models of secondary e+ - e-

calculations…

Solar modulation of cosmic-ray spectra

D. Hathaway and Dikpati M. http://science.nasa.gov/headlines/y2006/10may_lagrange.htm

SOLAR POLARITY

Positive SOL MIN Positive SOL MAX

Negative SOL MIN

BESS proton dataBESS proton data

Solar Modulation of Galactic Cosmic Rays

Solar Modulation of Galactic Cosmic Rays

Gleeson and Axford, Ap. J., 154, 1011, 1968

J(r,E,t) J(∞,E+)=

E2-Eo2 (E2-Eo

2

J: particle flux

r: distance from Sun

E: particle total energy

t: time

Eo= particle mass

= particle energy loss from infinity (different for each species)

Ok for positive polarity epoch data only!

Solar polarity effect on GCR p and He @ solar minimum

p

He

Boella G. et al., J. Geophys. Res. 106:355 2001

Negative Polarity

-40% @ 100 MeV(/n)

-30%@ 200 MeV(/n)

-25%@ 1 GeV(/n)

-a few % up to 4 GeV(/n)

LEE and AESOP data

A>0

A<0

Thick dot-dashed lines:Protheroe, 1982 SLBMClem & Evenson, 2004

Positron measurements during the last two solar Positron measurements during the last two solar cyclescycles

CG, A&A, 2007

Secondary calculations by M&S, 1998

A>0 A<0

PAMELA data…PAMELA data…

Best-fit before PAMELA

0.064+/-0.003CG, A&A, 2004

CG, A&A, 2007 - 550 MV/c

Positron Flux measurementPositron Flux

measuremente+

flux excess (continuous thick line) withrespect to thesecondary component (dot-dashed line-Moskalenko&Strong, 1998):same trendthan H&R87with 1/PB=35 years (dotted line)

CG, ICRC2005

Positron Flux from Young Pulsar Polar CapsHarding & Ramaty, 1987

Measurements before 1995

1/PB=60 years CG, Ap&SS, 241, 295, 1996

Maximum pulsar age for e+ production: 104 years

1/PB=30 years

Crab and Vela pulsar parameters

Le+ (E) B12 P-1.7 E-2.2 s-1 GeV-1

Rate of positron emission per pulsar

Spectral index above 20 GeV:

Positron fraction data after 1995 and calculation uncertainties

Harding & Ramaty, 1987

Top region correspondsto the secondary component+ H&R with a 1/PB of 30 yrs

Dashed region correspondsto the secondary component+ H&R with a 1/PB of 200 yrsBEST FIT:

1/PB=200+/-100 years

Bottom region correspondsto the secondary component+ H&R with a 1/PB of 250 yrs

CG, A&A, 418, 649, 2004

Positron fluxPositron flux

Spectral index above 20 GeVPAMELA datapoints:Implies 1.9-2.0at the source (?)

Yuksel, Kistler & Stanevastro-ph/0810.2784V2

PULSAR BIRTHRATE ESTIMATES

LMT-1985: Lyne, Manchester & Taylor, 1985L-1993: Lorimer, 1993H-1999: Hansen, 1999R-2001: Regimbeau, 2001CET-1999: Cappellaro, Evans & Turatto, 1999

35.7 years

Fucher-Giguère and Kaspi,astro-ph/0512585

However… middle aged pulsars are favoured over young ones in producing positrons reaching the interstellar medium as an increasing fraction of them lies outside their host remnants as a function of age.

0.0625 % of pulsarshave an age ranging between 0 and 104 years

Arzoumanian, astro-ph/0106159

What it was proposed:What it was proposed:

Positrons and electrons observed near Earth are generated by Geminga e B0656+14

Positrons and electrons fluxes are generated by galactic middle aged pulsars

Positrons and electrons observed near Earth are generated by Geminga e B0656+14

Positrons and electrons fluxes are generated by galactic middle aged pulsars

Pulsar Age (years)

Magnetic Field B (1012 G)

Period (ms)

Crab 1300 3.8 33

B1509-58 1500 15.4 150

Vela 11000 3.4 89

B1706-44 17000 1.165 102

B1951+32 110000 1.1 40

Geminga 340000 1.6 237

B1055-52 530000 0.97 197

Observed gamma-ray pulsar characteristics

Radio pulsar observedmagnetic field distribution

Figure from Gonthier et al., 2002

Observed gamma-raypulsar magnetic field(3.92 1.97) 1012 G

3.8 1012 G H&R87

Radio pulsar observedperiod distribution

Average observed gamma-raypulsar period121 29 ms

Gamma-rayPulsars from e+ measurements200-300 ms

Gamma-raypulsars from Harding&Ramaty33 ms

Figure from Gonthier et al., 2002

ELECTRON

FLUx

Different cut-off energies are predicted by polar cap and outer gap models in the pulsed gamma-ray spectra (GLAST)!

Figure from http://cossc.gsfc.nasa.gov/images/epo/gallery/pulsars/

Is the proposed scenario consistent with overall pulsar

observations?

Is the proposed scenario consistent with overall pulsar

observations?

Pulsar energy loss processes

and braking indeces

Pulsar energy loss processes

and braking indeces

n= -(d2/dt2 )/ (ddt)2

Electromagnetic (n=3)Gravitational (n=5)Supernova fallback debris disk

friction (n<3)

n= -(d2/dt2 )/ (ddt)2

Electromagnetic (n=3)Gravitational (n=5)Supernova fallback debris disk

friction (n<3)

Observed young pulsar braking indeces

Observed young pulsar braking indeces

J1846-0258 2.65B0531+21 2.51B1509-58 2.839J1119-6127 2.91B0540-69 2.140B0833-45 1.4

J1846-0258 2.65B0531+21 2.51B1509-58 2.839J1119-6127 2.91B0540-69 2.140B0833-45 1.4

Pulsar n

Pulsar gravitational wave energy losses…

Pulsar gravitational wave energy losses…

…cannot be the only answer however electromagnetic AND gravitational wave energy losses can explain observed braking indeces (LIGO shows Crab loses at most 6% of energy in gws; Abbott et al., 2008).

Debris disks lead to braking indeces compatible with observations

…cannot be the only answer however electromagnetic AND gravitational wave energy losses can explain observed braking indeces (LIGO shows Crab loses at most 6% of energy in gws; Abbott et al., 2008).

Debris disks lead to braking indeces compatible with observations

Fallback Debris disksFallback Debris disks

It was suggested that protoplanetary disks might form around pulsars from remnant fallback material

A debris disk has been observed around the young pulsar 4U 0142+61

(brightest known 8.7 s AXP)

It was suggested that protoplanetary disks might form around pulsars from remnant fallback material

A debris disk has been observed around the young pulsar 4U 0142+61

(brightest known 8.7 s AXP)

Energy losses due to Electromagnetic processes

and debris disk

Energy losses due to Electromagnetic processes

and debris disk

MP&H01

At most 12%-29% is lost by a young pulsar such as Crab because of a debris disk surrounding the pulsar

This leads to a wrong estimate of pulsar dP/dt due to em processes and therefore to wrong estimates of pulsar magnetic fields between 6% and 16% (B2 prop P dP/dt) and age. Positron flux calculations are affected similarly (Le+ prop. B).

… however, present positron measurements are still consistent with this scenario within uncertainties (a factor of two on the magnetic field).

At most 12%-29% is lost by a young pulsar such as Crab because of a debris disk surrounding the pulsar

This leads to a wrong estimate of pulsar dP/dt due to em processes and therefore to wrong estimates of pulsar magnetic fields between 6% and 16% (B2 prop P dP/dt) and age. Positron flux calculations are affected similarly (Le+ prop. B).

… however, present positron measurements are still consistent with this scenario within uncertainties (a factor of two on the magnetic field).

An exercise:estimate of gravitational wave

emission from pulsar+debris

disk systems

An exercise:estimate of gravitational wave

emission from pulsar+debris

disk systems

Disk dimensions (theory): 2000 - 200000 km

Disk dimensions (observed): 2.02x106- 6.75x106 km

Disk mass: 10 Earth mass = 5.97 1025

kgPulsar mass = 2.8 1030 kg

Disk dimensions (theory): 2000 - 200000 km

Disk dimensions (observed): 2.02x106- 6.75x106 km

Disk mass: 10 Earth mass = 5.97 1025

kgPulsar mass = 2.8 1030 kg

Assumptions:

Might gravitational waves produced by debris disks

be detected?

Might gravitational waves produced by debris disks

be detected?Planetary systemsDisk precession

Planetary systemsDisk precession

Gravitational energy loss from pulsar planetary systems

Gravitational energy loss from pulsar planetary systems

LGW = (32/5) G4/c5 M3 2/a5

M=M1+M2

M1M2/(M1+M2)

Planetary disk dimensions > 8 105 km < 6.04 10-4 Hz

LGW < 1.24 x 1016 J/s

LGW = (32/5) G4/c5 M3 2/a5

M=M1+M2

M1M2/(M1+M2)

Planetary disk dimensions > 8 105 km < 6.04 10-4 Hz

LGW < 1.24 x 1016 J/s

LISA sensitivity curveLISA sensitivity curve

Vocca et al., CQG, 2004

Gravitational wave amplitude from pulsar

planetary systems

Gravitational wave amplitude from pulsar

planetary systems Signals might lie in the LISA band (r>c/):

ho=-1/r (G2/c4) (4M1M2/a)ho=-1/r (4.59x10-7) At 3x10-4 Hz LISA can detect gw with

amplitudes larger than 5.07x10-23 Sources will lie within a light year in 10

years of data taking

Signals might lie in the LISA band (r>c/):

ho=-1/r (G2/c4) (4M1M2/a)ho=-1/r (4.59x10-7) At 3x10-4 Hz LISA can detect gw with

amplitudes larger than 5.07x10-23 Sources will lie within a light year in 10

years of data taking

Gravitational waves from internal parts of

precessing disks (?)

Gravitational waves from internal parts of

precessing disks (?) I3= 1/2 M (R1

2 + R22)

= I3/(I1 cos

P=(2G)/(5c5)sin2 (cos2 +16 sin2 s

(0.01) x GW frequencies are similar to those produced by pulsar

planetary systems (in the LISA band).Decay time are very long! d/dt=-1/ 1/ =(2G)/(5c5)/I1

I3= 1/2 M (R12 + R2

2)

= I3/(I1 cos

P=(2G)/(5c5)sin2 (cos2 +16 sin2 s

(0.01) x GW frequencies are similar to those produced by pulsar

planetary systems (in the LISA band).Decay time are very long! d/dt=-1/ 1/ =(2G)/(5c5)/I1

Consequences…Consequences…

Even if the frequencies lie in the LISA band, ten years of integration would not allow the detection of planetary systems beyond one light years. The role of disk precession in generating gravitatonal waves must be investigated further.

ConclusionsConclusions

Electrons and positrons are unique tools for cosmic-ray and interstellar medium investigation.

Data seem to indicate the model by M&S as the best reproducing e+ and e-data trend.

A positron excess is present above a few GeV. The positron excess is compatible with a model of pair

production at the polar cap of middle aged pulsars extrapolated from a model of pair production at the polar cap of young pulsars.

The hypothesis of fallback debris disks around young pulsars is compatible with positron origin from pulsar polar cap.

Electrons and positrons are unique tools for cosmic-ray and interstellar medium investigation.

Data seem to indicate the model by M&S as the best reproducing e+ and e-data trend.

A positron excess is present above a few GeV. The positron excess is compatible with a model of pair

production at the polar cap of middle aged pulsars extrapolated from a model of pair production at the polar cap of young pulsars.

The hypothesis of fallback debris disks around young pulsars is compatible with positron origin from pulsar polar cap.

Thank you!Thank you!

ATIC electron data

Supersymmetry and the positron excess in cosmic rays

Supersymmetry and the positron excess in cosmic rays

Kane, Wang & Wells, 2001 hep-ph/0108138

Cirelli, Kadastik, Raidal, Strumia,2008

Kamionkowski and Turner, 1991Neutralino annihilation

Cheng et al, 2002Kaluza-Klein DM annihilation