Klein-Nishina effect on high-energy gamma-ray emission of GRBs

Klein-Nishina effect on high-Klein-Nishina effect on high-energy gamma-ray emission of energy gamma-ray emission of

GRBs GRBs

Xiang-Yu WangXiang-Yu Wang(( 王祥玉）王祥玉）

Nanjing University, ChinaNanjing University, China（南京大學）（南京大學）

Co-authors: Hao-Ning He (NJU), Zhuo Li (PKU), Zi-Gao Co-authors: Hao-Ning He (NJU), Zhuo Li (PKU), Zi-Gao Dai (NJU), Dai (NJU),

Xue-Feng Wu (PennState), Peter Meszaros (PennState),Xue-Feng Wu (PennState), Peter Meszaros (PennState),

Deciphering the Ancient Universe with Gamma-Ray Bursts 19-23 April 2010, Kyoto, Japan

Xiang-Yu Wang Nanjing Univ.

Fermi observations of Fermi observations of GRB080916cGRB080916c

Abdo et al. 09

Short GRB: T_90=~1 s

Significant high-energy emission up to T0+200s

Extended high-energy emission Extended high-energy emission of short GRB 090510of short GRB 090510

GRB090510

De Pasquale et al. 09

GRB090902B—a long GRB090902B—a long GRBGRB

t^-1.5

Abdo et al. 09Abdo et al. 09

Klein-Nishina (KN) effect Klein-Nishina (KN) effect may be important in may be important in

Prompt high-energy gamma-ray emission ( Prompt high-energy gamma-ray emission ( if it is due to synchrotron emission)if it is due to synchrotron emission)

Temporal Extended High Energy EmissionTemporal Extended High Energy Emission

Klein-Nishina IC scatteringKlein-Nishina IC scattering

Thomson IC scatteringThomson IC scattering KN IC scatteringKN IC scattering


KN effect may be important KN effect may be important in in

Prompt high-energy gamma-ray emissionPrompt high-energy gamma-ray emission



Prompt spectrum of Prompt spectrum of GRB080916CGRB080916C

a b

c d

1.Band function fits the KeV-GeV data

2. No bump is seen at high energies

Some other bursts: high-energy Some other bursts: high-energy emission consistent with the emission consistent with the

extrapolation extrapolation

GRB080825C, GRB090217GRB080825C, GRB090217

GRB090217


The synchrotron scenarioThe synchrotron scenario

1) Can the maximum syn. energy reach 70 1) Can the maximum syn. energy reach 70 GeV ?GeV ?

Yes, only when Bohm diffusive shock acceleration ( )

1d ---a parameter describing ---a parameter describing the efficiency of the shock the efficiency of the shock accelerationacceleration

1d

( Wang, Li, Dai & Meszaros 2009 )

)1000( (cf Ioka’talk)


The synchrotron scenarioThe synchrotron scenario

two assumptions: 1) equipartition magnetic field:

2) causality constraint:

Inverse Compton must be in theInverse Compton must be in the Klein-Nishina Klein-Nishina regimeregime,,

which leads naturally to which leads naturally to a low, invisible IC a low, invisible IC componentcomponent

2) Why no visible IC bump?

Tm


The synchrotron scenarioThe synchrotron scenario KN effect on the low-energy spectrumKN effect on the low-energy spectrum

e

e

ddN

e

1e

2e

)1( pe

Can makes the low-energy spectrum harder (Can makes the low-energy spectrum harder (αα= -1.02±0.02) in = -1.02±0.02) in GRB080916C GRB080916C ((also see Derishev et al. 2003; Nakar et al. 09))

Low-energy spectral index ?

The ratio of IC cooling efficiency to syn cooling The ratio of IC cooling efficiency to syn cooling efficiency is not a constant anymore, but depends on efficiency is not a constant anymore, but depends on γγ

KN effect may be important KN effect may be important in in

Prompt high-energy gamma-ray emission Prompt high-energy gamma-ray emission (some bursts Band function fit well, some (some bursts Band function fit well, some deviate from Band function)deviate from Band function)



Models for the extended Models for the extended emissionemission Hadronic cascade process Hadronic cascade process (Dermer & Atoyan 04) (Dermer & Atoyan 04)

Forward shockForward shock——long livedlong lived synchrotron: slow decay synchrotron: slow decay (Kumar & Barniol Duran09)(Kumar & Barniol Duran09) IC: rise initially and slow decay IC: rise initially and slow decay (Zhang & Meszaros (Zhang & Meszaros

01; Fan et al. 08)01; Fan et al. 08)

Reverse shock --- short lived, fast decay Reverse shock --- short lived, fast decay (Wang et al. 2001)(Wang et al. 2001)


Forward shock IC Forward shock IC emissionemission

Zhang & Meszaros 01

First rise, then decay

Forward shock synchrotron Forward shock synchrotron scenarioscenario

Can easily explain the Can easily explain the simple decaysimple decay

The flux level matches The flux level matches the observations the observations (Kumar (Kumar &Barniol Duran 09)&Barniol Duran 09)

Possible problems: Possible problems: 1) maximum photon 1) maximum photon

energy energy (Abdo et al. (Abdo et al. arXiv:0909.2470; Piran & arXiv:0909.2470; Piran & Nakar 10)Nakar 10)

2) too steep 2) too steep (Ghisellini et al. (Ghisellini et al. 09), 09), see also Poster #95 (T. see also Poster #95 (T. Uehara) on 090926AUehara) on 090926A

Barniol Duran & Kumar 09

If afterglow emission, KN If afterglow emission, KN effect should be taken into effect should be taken into

accountaccount For afterglow electrons in the Thomson For afterglow electrons in the Thomson scattering, scattering,

YY

For high-energy afterglow emission, For high-energy afterglow emission, ( ) is large, inverse Compton ( ) is large, inverse Compton

scattering with synchrotron peak photons should scattering with synchrotron peak photons should be in Klein-Nishina regimebe in Klein-Nishina regime

Sari & Esin 2001:

<

Compton Y parameter depends on γ, therefore depends on ν !

One example: the slow-One example: the slow-cooling casecooling case

i) Values of compton Y i) Values of compton Y parameters parameters

(t=1 s)(t=1 s)Wang, He, et al. 2010, ApJ

Compton Y parameters (t=10 Compton Y parameters (t=10 s)s)

KN effects -summary (1) KN effects -summary (1)

For a wide range of parameters, For a wide range of parameters, Y(100MeV) is initially small, typically Y(100MeV) is initially small, typically smaller than 1smaller than 1

Leading to a high synchrotron luminosity Leading to a high synchrotron luminosity at early time at early time


Y here is dependent

of ν

Kumar & Barniol Duran 09:

ii) KN effect on the ii) KN effect on the spectrumspectrum

Slow-cooling case Fast-cooling case


The short GRB case The short GRB case (He & Wang 09)(He & Wang 09)

Spectra and Light curves under typical Spectra and Light curves under typical parameters for short GRBsparameters for short GRBs

KN effects –summary (2) KN effects –summary (2)

At very early time, synchrotron emission At very early time, synchrotron emission is usually dominant in the LAT energy is usually dominant in the LAT energy band (30MeV to tens of GeV)band (30MeV to tens of GeV)

SSC dominates only above the maximum SSC dominates only above the maximum synchrotron energysynchrotron energy


iii) Evolution of Y parameters iii) Evolution of Y parameters with timewith time

Slow-cooling caseSlow-cooling case

Wang, He, et al. 2010

The fast-cooling caseThe fast-cooling case

KN effects –summary (3) KN effects –summary (3) For certain parameter space, Y(100MeV) For certain parameter space, Y(100MeV)

increases with time--- the KN suppression effect increases with time--- the KN suppression effect of high-energy electrons weakens with time, of high-energy electrons weakens with time, so that the IC loss increases with time.so that the IC loss increases with time.

If Y(100MeV) >1 as well, leading to a steeper If Y(100MeV) >1 as well, leading to a steeper decay than predicted by the standard decay than predicted by the standard synchrotron theorysynchrotron theory

A testable prediction for this scenario: the A testable prediction for this scenario: the spectrum becomes harder meanwhile spectrum becomes harder meanwhile


GRB090510GRB090510

De Pasquale et al. 2009

Ghirlanda et al. 2009

Standard syn model: LAT should decay as

GRB090902BGRB090902B

t^-1.5


ConclusionsConclusions If the prompt high-energy emission is of If the prompt high-energy emission is of

synchrotron origin, KN is important and may synchrotron origin, KN is important and may affect the prompt low-energy spectrumaffect the prompt low-energy spectrum

KN effect is important in estimating the KN effect is important in estimating the afterglow synchrotron emission, which leads afterglow synchrotron emission, which leads toto

Early high synchrotron luminosityEarly high synchrotron luminosity Faster temporal decay in some parameter spaceFaster temporal decay in some parameter space When modeling the high-energy afterglow When modeling the high-energy afterglow

emission, emission, treat carefully the KN scattering treat carefully the KN scattering effect effect on the electron radiationon the electron radiation

Backup slide Backup slide KN effect KN effect on electron distributionon electron distribution

How the synchrotron luminosity is How the synchrotron luminosity is affected depends on the electron affected depends on the electron distribution distribution (Nakar et al. 09; Wang et al. 10)(Nakar et al. 09; Wang et al. 10)

1) slow cooling

2) fast cooling

Documents

Klein-Nishina effect on high-energy gamma-ray emission of GRBs