X/ -ray instrumentation 1. Sources and processes in high-energy Astrophysics 1. Sources and Physical Processes in High Energy Astrophysics Xavier Barcons

X/-ray instrumentation

1. Sources and processes in high-energy Astrophysics

1. Sources and Physical Processes in High Energy

Astrophysics

Xavier Barcons

Instituto de Física de Cantabria (CSIC-UC)

X-ray and -ray instrumentation



An apology

• I’m an X-ray Astronomer

• I’ve prepared these lectures in 3 days, by collecting other lectures delivered in post-graduate courses and summer schools

Do not expect much -ray Astronomy



Acknowledgements• X-ray Astronomy gruop @ IFCA: Francisco

Carrera, Maite Ceballos, Silvia Mateos• XMM-Newton SSC: Mike Watson, Axel

Schwope, Roberto Della Ceca, many others • XEUS SAG: Martin Turner, Günther Hasinger,

Arvind Parmar, Johan Bleeker, many others• Spanish STJ (maybe) team: Lourdes Fàbrega,

Conrado Rillo, Fernando Briones, Carles Ferrer• Other: Andy Fabian, Fred Jansen, Tone Peacock,

Marcos Bavdaz, Alvaro Giménez, Martin Ward



Index

• Introduction: High-energy Astrophysics from space

• A guided tour through the high-energy Universe• Physical processes in X/-ray Astrophysics:

– Synchrotron radiation

– Bremsstrahlung

– Compton Scattering

– Pairs

– Nuclei



The main problem of high-energy astrophysics





Riccardo Giacconi (Genoa 1931)

1962

2002



The beginning of high-energy Astronomy

18-June-1962: Giacconi and collaborators fly an Aerobee rocket beyond 80 km altitude during > 5 minutes with 3 X-ray detectors

Goal: To detect X-rays reflected in the Moon from the Sun

Two surprising discoveries:•An extremely bright X-ray source, which is

totally inconspicuous in the optical (Sco X-1)•Diffuse radiation from all directions in the Universe (the

cosmic X-ray Background)And of course, no trace from the Moon…

… until 1990!



A short walk through the high-energy Universe



The Solar System



Venus and Jupiter



Active coronal starsCapellaAB Dor

EPIC-MOS

RGS

Sco

Pup



Star formation

HST Chandra

Chandra



Supernova Remnants (Cas-A)



N132D SNR

Fe line

OVII

OVIII



SNRs and PulsarsCrab Nebula and Pulsar

ChandraOptico

Pulsar



Isolated neutron stars

First detection of X-ray cyclotron absorption lines in an isolated neutron star: Measurement of the magnetic field

B~8 x 1010 Gauss

Bignami et al 03

Cyclotron lines



Accreting binaries



Low-Mass X-ray binariesBlackbody+Comptonising region

Church & Balucinska-Church 01

Parmar et al 2002

Cottam et al 02

Gravitationally redshifted lines



Be/X-ray binaries: High LX/Lopt

The Galaxy in Soft X-rays



The Galaxy in 26Al



Shadowing and the local ISM

• Shadowing of background soft X-rays by objects located at various distances



The Galactic Centre in X-rays



The galactic centre in rays



Normal galaxies: Diffuse emission and X-ray binaries

NGC 253M 31

Chandra



Galaxies: LMC



Diffuse emission from galaxy clusters

ComaComa VirgoVirgo



The X-ray spectra of custers

• Thermal bremsstrahlung kT=1-10 keV (107-108 K)

• Fe K emission feature at 6.7 keV: Highly ionised gas

• Other emission lines at soft X-ray energies (Fe L, Mg, Si)



Clusters: Temperature and metallicity

Coma Sérsic 159-03



Cooling flows? Not any moreFe L

O VIII

Mg XII


1. Sources and processes in high-energy Astrophysics(Chris Done, Univ of Durham)

The High-energy view of The High-energy view of AGNAGN

C. Done, Durham U



The High-energy AGN spectrume+e-annihilation

Saturated pair cascade

Compton Reflection hump

Fluorescence

Absorption

Soft excess



The X-ray spectrum of AGN

Reprocessed radiation from the disk’s atmosphere

Reflection (Fe line and Compton hump)

Absorbers

Soft excess (direct disk radiation)



Ionized absorbers



The variety of Fe K line profiles

Nandra (2001)



Relativistic line in MCG-6-30-15

Iwasawa et al. (1996, 1999)

1994 1997

< >t < >t

Mín Flare



Gamma-Ray Bursts (GRBs)



The X-ray background



The XMM-Newton observation of the Lockman Hole



Physical Processes in High-energy Astrophysics



Synchrotron Radiation (I)

Ingredients:• Magnetic field B• Relativistic electrons

(Lorentz factor >>1)



Synchrotron Radiation (II)

Cyclotron radiation:Electron with velocity vin a magnetic field Bhas a gyro frequency

B=eB

4mc

= 2.8/ MHz/Gauss

d

dt=4/3 T c (v/c)2 2 UB

Power radiated by an isotropic distributionof electrons

T=6.65 10-25 cm2

UB=B2

8

Discrete spectrum:concentrated around B and higher order harmonics



Synchrotron radiation: continuum

• Growing importance of higher order harmonics

• Relativistic beaming: Emission within a cone of opening angle <2/ around the electron’s velocity

• Doppler effect: The time lapse in which the observer receives the radiation is smaller than the pulse emission time (obs=2em)



Jet of electrons with Lorentz factor :

dd = B

31/2e3

mc2F(/c)

c=3eB

4mc2 sin

B

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6

x

F(x

)

Continuum centeredaround c




For an isotropic distribution of electrons with a power law in energies:

dN() -p d

dd

-(p-1)/2

Spectrum of Synchrotron radiation

Power law emission, extending to X-rayand -ray energies with index -(p-1)/2


Self-absorbed Synchrotron



Bremsstrahlung (I)

Ingredients:• Totally or partially ionised

gas • Temperature T> 106 K



Bremsstrahlung (II)

Electrons deviate from their trajectory when passingclose to an ion, accelerate and therefore radiate

b

velectron

Ion

Cutoff frequency: 0=v/2b

d

d const, for << 0

d

d e -/0, for >> 0



Thermal bremsstrahlung

For a thermal distribution at temperature T

d

dV d Z2 ni ne T-1/2 g(,T) e-/kT

Ion’s atomicnumber

Temperature (K) Gaunt factor

d

dt dV = 1.43 10-41 Z2 T1/2 ni ne g(T) erg cm-3 s-1

(1+(kT/mc2)) (relativistic correction)



Electron-positron pairs

Ingredients:

• Photons with energy > mc2

• “Compact” source




Energetic condition for two photons to give rise to an electron-Positron pair (at rest):

E1 E2 > (mc2)2

0

0.05

0.1

0.15

0.2

0.25

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7 3

3.3

3.6

3.9

4.2

4.5

4.8

(E1*E2)**(1/2) (MeV)

Sec

ció

n E

ficaz

The cross section isMaximal at ~ 1MeVAnd takes the value ~ 0.25 T




Compactness: Optical depth of photon-photon collisions

=n R > 1

Photon density at~mc2

Crosssection

Size of emission region

Compactness parameter: =L T

Rmc3

~ /60 > 1

The compactness parameter must be >> 10



Scattering Compton (I)Ingredients:

• Electrons

• PhotonsThomson classical h << mc2

Compton

Inverse h < mc2

Direct h > mc2



Scattering ThomsonPhoton-electron interaction without energy transfer

d

dt d

3

8c T U sin2 =

d

dt= T c U

* For non-relativistic electrons

* For relativistic electrons:The Klein-Nishina cross section KN is a function of =h/mc2

KN~ T{1-2h/mc2+…} if h << mc2

KN~ (3/8)T (mc2/h){ln(2h/mc2)+1/2} if h >> mc2

Decreaseswith

h/mc2



Compton effect

Transfer of energy between photons and electrons

Electron at rest: Eout=Ein

1+Ein/mc2(1-cos )

Moving electron: Eout~ 2 Ein

d

dt =(4/3) T c U (v/c)2 2

Power radiated by Compton effect



ComptonizationThe interaction of photons with a thermal electron gasChanges the photon energy at each collision

E

E

4kT-E

mc2=

The energy of the photonstends to equilibrate with thetemperature of the electrons

Compton depth: T= T dx ne

Number de collisionsper photon (Ncol):

~ T if T < 1

~ T2

if T >> 1



Comptonization

Comptonization parameter: y=kT

mc2

Ncol

After Ncol collisions Eout=Ein e4y

Comptonized radiation tends to the Equilibrium Bose-Einstein distribution:

Planck spectrum if there is radiation-matterEquilibrium or otherwise a Wien spectrum



Compton cooling

d

dt =(4/3) T c U (v/c)2 2

Compton energyloss for =mc2

For relativistic electrons ( >>1), the Compton coolingtime is:

tcool= /(d/dt)=tesc

3

In a compact source, electrons cool before escaping



A high-energy spectrum for compact sources



Atoms and ionsEmission processes in Astrophysical plasmas T < 108 K:•Bremsstrahlung•Bound-bound emission lines (dominant up to 5 107 K)•Radiation recombination continua (capture

of a free electron to a bound state T< 107 K)•Di-electronic recombination lines (capture of a free electron

giving rise to a doubly excited state)•Two-photon continuum (Simultaneous emission of two photons from a meta-stable state)

Absorption processes in Astrophysical plasmas T < 108 K:•Photoionisation (free a bound electron) •Resonance absorption lines (bound-bound transition)



Models of Astrophysical plasmas Ionisation Examples

Coronal <<1 collisions Stellar coronae SNR Intracluster gas

Nebular <1 Photo- ionisation

AGNs Planetary nebulae

Thick >>1 collisions Dense stars



The He-like triplet

1s2 1S

1s 2s 1S

1s 2p 1P1s 2p 3P

1s 2s 3S

Res

onan

ce E

1

Inter

combin

ation

E1+

M2

Forbidden M1

Nm

Nk

Coll excit

Ng



Plasma diagnostics using He-like triplets

R=P(mg)

P(kg)

Forbidden

Interchange=

R=mg

kg

(1+ne/ncrit)-1

Ncrit=Amg kg

Smk (kg+mg)

A function of density

I

Akg

kg

Amg

mg

FSmk

: recombination, A: transition probs



Photoelectric absorption

Absorption cross-section:

abs()7.8 10-18LL

( )3 Z4

n5cm2 for >LL

OVII K: 0.739 keVOVIII K: 0.874 keVFe I K: 7.1 keV



Nuclear emission lines

Solar flare



Nuclear emission lines from SNeSN 1987A

Documents

X/ -ray instrumentation 1. Sources and processes in high-energy Astrophysics 1. Sources and Physical Processes in High Energy Astrophysics Xavier Barcons