Models of GRB GeV-TeV emission and GLAST/Swift synergy Xiang-Yu Wang Nanjing University, China...

Models of GRB GeV-TeV emission and Models of GRB GeV-TeV emission and GLAST/Swift synergyGLAST/Swift synergy

Xiang-Yu WangNanjing University, China

Co-authors: Peter Meszaros (PennState), Zhuo Li (PKU), Hao-ning He (NJU)

TeV Particle Astrophysics IV Sept. 24-28, 2008; Beijing, China

Xiang-Yu Wang TeVPA08

Outline

GRB high-energy observations Models for GeV-TeV emission from GRBs Swift new discoveries and high-energy predictions with G

LAST


I. GRB high-energy observations

GRB930131

GRB940217

EGRET on CGRO 1) Prompt 2) Delayed


GRB941017

−18 s – 14 s

14 s – 47 s

47 s – 80 s

80 s – 113 s

113 s – 211 s

High-energy emission lasts longer than KeV-MeV emission


A recent burst detected by AGILE GRB080514B

Similar to GRB941017, common phenomena?


GCN reports on GLAST Obs.

GRB080825C: LAT detection, photons with energy lower than 1 GeV (GCN No.8183)

GRB080916C : LAT detection, more than 10 photons are observed above 1 GeV (GCN No.8246)


E>100GeV: only upper limits

Magic: upper limits for several Swift bursts (Albert et al., 06)

Whipple: upper limits (Horan et al. 07) Milagro: upper limits fro short GRB (Abdo et a

l. 07) ARGO-YBJ array find only upper limits (Di Sc

iascio, et al., 06) HESS: upper limits of GRB060602B (Aharoni

an et al. 08)


Example: HESS GRB060602B

very soft BAT spectrum and proximity to the Galactic center

More likely to be a Galactic X-ray transient


GRB model: Internal and External shocks

Credit P. Meszaros

Rees & Meszaros 92; Meszaros & Rees 1994


Electrons- Shock acceleration: ~10 TeV

Protons (or nuclei)-1) Shock acceleration (e.g. Waxman 1995; Vietri 1995)

Candidate source of ultra-high energy cosmic rays (UHECRs)

2) Neutrinos from photo-meson and pp processes (e.g. Waxman & Bahcall 1997; Bottcher & Dermer 1998)

Particle acceleration in GRB shocks

eV10~ 20

7, 10~ Maxeacccool tt

5, 10 Maxe X-ray afterglows modeling e.g. Li & Waxman 2006


Two basic processes for high-energy gamma-ray emission1. Leptonic inverse-Compton scattering

2. Hadronic processes: 1)proton synchrotron; 2) p-γneutral pion decay; 3)secondary electrons synchrotron & IC

Prompt phase Internal shock, leptonic: electron synchrotron & SSC Internal shock, hadronic: proton synchrotron & p-γ interaction

Early afterglow phase External, leptonic: forward, reverse and cross shock SSC External, hadronic: proton synchrotron & p-γ interaction


Efficiency comparison for the two processes (I)

Prompt gamma-ray emission (Gupta & Zhang 2007)

-- Proton syn.-- synchrotron radiation produced by secondary positrons

**high energy emission is dominated by the leptonic component if є_e>0.01**

neutral pion decay


Efficiency comparison for the two processes (II)-mildly relativistic outflow

Ando & Meszaros 08


GRB high energy emission: IC processes

central internal external shocksengine (shocks) (reverse) (forward)

Internal shock IC: e.g. Pilla & Loeb 1998; Razzaque et al. 2004; Gupta & Zhang 2007

External shock IC reverse shock IC: e.g. Meszaros , et al. 94; Wang et al. 01; Granot & Guetta 03

forward shock IC: e.g.Meszaros & Rees 94; Dermer et al. 00; Zhang & Meszaros 01


Typical energies of SSC emission


(1) IC emission from very early external shocks

Shocked shell

Shocked ISM

Cold ISM

Coldshell

pressure

FSRS

CD

1) (rr)2) (ff)3) (fr)4) (rf)

Four IC processes

(Wang, Dai & Lu 2001 ApJ,556, 1010)

At deceleration radius, T_obs~10-100 sForward shock---Reverse shock structure is developed


Energy spectra---

1

0

max

min

'3 xfxdxgNdrf TIC

;1,5.2,01.0,6.0,10E a) 53 nperg Be

f

At sub-GeV to GeV energies, the SSC of reverse shock is dominant; at higher energies, the Combined IC or SSC of forward shock becomes increasingly dominated

Reverse shock SSC (r,f) IC

(f,r) ICForward shock SSC

Log(E/keV)

GLAST 5 photons sensitivity

(Wang, Dai & Lu 2001 ApJ,556, 1010)


One GeV burst with very hard spectrum- leptonic or hadronic process?

−18 s – 14 s

14 s – 47 s

47 s – 80 s

80 s – 113 s

113 s – 211 s

Gonzalez et al. 03: Hadronic model

Leptonic IC model:

Granot & Guetta 03 Pe’er & Waxman 04 Wang X Y et al. 05

GRB941017

Wang X Y et al. 05, A&A, 439,957

Reverse shock SSCISM medium environment


(2) afterglow IC emissionZhang & Meszaros 01

May explain delayed GeV emission


Swift/GLAST synergy

1) X-ray flares 2) early shallow decay 3)low-luminosity GRBs 4)prompt emission


Swift: A Canonical X-ray Lightcurve(Zhang et al. 2006; Nousek et al. 2006; O’Brien et al. 2006)

~ -3

~ -0.5

~ - 1.2

~ -210^2 – 10^3 s

10^4 – 10^5 s

prompt emission


~30%-50% early afterglow have x-ray flares, Swift discovery

Flare light curves: rapid rise and decay

<<1 Afterglow decay consistent with

a single power-law before and after the flare

(1) High-energy photons from X-ray flares

Burrows et al. 2005Falcone et al. 2006

amplitude: ~500 times above the underlying afterglow

GRB050502B

X-ray flares occur inside the decelerationradius of the afterglow shock

X-ray flares: late-time central engine activity


IC between X-ray flare photons and afterglow electrons (Wang, Li & Meszaros 2006)

Cnetral engine

X-ray flare photons

Forward shock region

Cartoon

X-ray flare photons illuminate the afterglow shock electrons from inside

also see Fan & Piran 2006: unseen UV photons


IC GeV flare fluence-An estimate So most energy of the newly shock electrons will be lost into IC emi

ssion

X-ray flare peak energy


Temporal behavior of the IC emission Not exactly correlated with the X-ray flare light curves. IC

emission will be lengthened by the afterglow shock angular

spreading time and the anisotropic IC effect

Self-IC of flares, peak at lower energiesWang, Li & Meszaros 2006In external shock model for x-ray flares


IC emission from X-ray flares at VHE


(2)High-energy emission during shallow decay phase-energy injection model (Fan et al. 2008)


(3)High-energy emission from low-luminosity GRBs


GRB980425: first low-luminosity GRB identified sub-energetic GRB—GRB980425: E~1e48 erg, at d=38 Mpc Radio afterglow modeling: E>1e49 erg, \Gamma~1-2 X-ray afterglow: E~5e49 erg, \beta=0.8 (Waxman 2004)

Mildly relativistic ejecta component

In the error box of GRB980425


GRB060218/SN2006aj –Swift discovery

An unusually long, smooth burst

Low luminosity, low energy

z=0.033, second nearest GRB

Campana et al. 2006


Thermal x-ray emission from low-luminosity GRBs

SN2006aj/GRB060218

prompt thermal x-ray emission— mildly relativistic SN shock breakout from stellar wind

Campana et al. 06

Waxman, Meszaros, Campana 07


Three low-luminosity supernova-GRBs

1) Low-luminosity 2) Smooth light curves 3) Spectrum: a simple power-law with a high energy cutoff

So why they are so unusual?

Mildly relativistic hypernova?


High-energy emission from mildly-relativistic hypernova ejecta

Ando & Meszaros 08

at deceleration time ~1d


High-energy emission from mildly-relativistic hypernova ejecta

He & Wang, in preparation


Compared with relativistic jet case


(4)Prompt multi-band study by Swift/GLAST Swift can detect optical

to KeV-MeV emission GLAST can detected G

eV-TeV emission

One natural scenario: optical from syn,MeV from IC, Y>=10

2nd IC at GeV-TeV?

Naked eye burst GRB080319B


IR, opt, UV ~500keV ~500GeV

YL

YH=YL


Swift/GLAST can distinguish … SSC model or double syn. model for prompt

optical and MeV emission


Summary Leptonic vs. Hadronic

Leptonic component dominate at GeV-TeV for typical parameters Only for very inefficient bursts (may be diagnosed by coordinated GLAST/Swift obs

ervations), would one expects a significant hadronic contribution in the high energy spectrum

Prompt emission: SSC or double synchrotron model fro prompt optical and MeV emission Forward shock SSC would give extended GeV-TeV emission

Fluence peaks at hours GeV-TeV flares will accompany X-ray flares

Broader Delayed in time

Low-luminosity GRB afterglow Detectable at 30MeV-10 GeV at the peak time for e_e>0.1 Can be used to distinguish high \Gamma or low \Gamma with GLAST observations

of the light curves

Models of GRB GeV-TeV emission and GLAST/Swift synergy Xiang-Yu Wang Nanjing University, China...

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