High energy (20MeV-TeV) photon emission from Gamma-ray Bursts

Yi-Zhong Fan (Niels Bohr International Academy, Denmark;

Purple Mountain Observatory, China )

Collaborators: Tsvi Piran, Ramesh Narayan, Da-Ming Wei, Bing Zhang(Fan & Piran 2008, arXiv:0805.2221)

GRB internal-external shock model

central photosphere internal external shocksengine (shocks) (reverse) (forward) 1E17cm for ISM1E6cm 1E9cm 1E12-1E14cm 1E15cm for wind

gamma-ray

UV/opt/IR/radio

gamma-rayX-rayUV/optical

IRmmradio

(see Piran 1999, 2004; Meszaros 2002; Zhang & Meszaros 2004 for reviews)

prompprompt t emissiemissionon

afterglowafterglow

MeV-GeV observations (EGRET)

GRB 940217GRB 940217

(Hurley et al. 1994)(Hurley et al. 1994)

GRB 930131 (Superbowl BursGRB 930131 (Superbowl Burst)t)

The first afterglow detThe first afterglow detection, but no redshift ection, but no redshift

informationinformation

afterglowafterglow

MeV-GeV observations (EGRET): GRB 941017: Gonzalez et al. 2003

Quick evolutionQuick evolution Almost constantAlmost constantMuch longer high Much longer high energy emissionenergy emission

VHE(>50 GeV) Observations

• Milagrito observation of GRB 970417 at energies above 0.1 TeV∼ (3 σ? Atkins et al. 2000)

• Upper limits from Magic for several Swift bursts (Albert et al., 06)

• Claims of detection GRAND at 2.7 σ (Poirier et al 03, b

ut see Fragile et al 03)

• Tibet array: 7σ coincidence ? (Amenomori et al 01)

• ARGO-YBJ array find only upper limits (Di Sciascio, et al., 06)

Only upper limits!Only upper limits!

The optical depth of universe to VHE gamma-rays

(Stecker et al. 2006) z=5z=5

z=3z=3

z=1z=1

z=2z=2

z=0.5z=0.5

z=0.03z=0.03

z=0.2z=0.2tau~6tau~6

Physical processes producing high energy gamma-rays

• Synchrotron radiation (Syn-Rad) of electrons/protons

• Inverse Compton processes

• Pion production

• Electromagnetic cascade of TeV gamma-rays

see Fan & Piran (2008 ) for a reviewsee Fan & Piran (2008 ) for a review

Inverse Compton (IC) processes

electrons Seed photons timescale

Synch. Self-Compton (SSC)

Shock-accelerated Synch. radiation of the electrons

Simultaneous with

Synch. Rad External IC

(EIC)

Shock-accelerated Irrelevant to the electrons and

along the direction of

outflow material

Much Longer

than that of the

seed photons

Bulk Compton Moving with a high bulk Lorentz factor

(cold in their comoving frame)

Irrelevant to electrons and

arbitrary

distributed

Determined by that of the ejecta car

rying the electrons

see Fan & Piran (2008 ) for a reviewsee Fan & Piran (2008 ) for a review

One novel feature of EIC

The EIC emission lasts much longer than the seed photons because the duration is affected by (1) the spherical curvature of the blast wave (Beloborodov 05) and by (2) the highly anisotropic radiation of the up-scattered photons (Fan & Piran 06)

Fan, Piran, Narayan & Wei (2008 )Fan, Piran, Narayan & Wei (2008 )

High energy photons from Pion production

Electromagnetic cascade of TeV photons

TeV source Infrared background

formed10~factor

Lorentz awith6

e

Seed photon

MCB

GeV photonsGeV photons

(Nikoshov 1962; Gould & Schreder 1967)

High energy processes in GRBs and afterglows

SSC in GRBs and their afterglowsSSC in GRBs and their afterglows

PromptPrompt SSCSSC

Forward Forward ShockShock SSCSSC

ee≈1000≈1000 e e ≈≈ tenstens ee≈10≈1044-10-10

ReverseReverse Shock Shock

SSCSSC

From Piran (2003)From Piran (2003)

Standard forward shock Standard forward shock (Fan et al. 08)(Fan et al. 08)

SSCSynch Energy

electron’s Lorentz Factor

SSC

energy

Duration

Prompt (GRB)

100 keV 1000 100GeV Prompt

Prompt (XRF)

10 keV 300 1 GeV Prompt

X-ray flares 0.2 keV 500 0.2GeV Short

Reverse Shock

1 eV 100 10keV Short

Forward

Shock

10keV-1eV 104 -10 TeV-keV Long

(M’esz’aros & Rees 94; Pilla & Leob 98; Pe’er & Waxman 04; Gupta & Zhang 07, 08(M’esz’aros & Rees 94; Pilla & Leob 98; Pe’er & Waxman 04; Gupta & Zhang 07, 08Guetta & Granot 03; Wei et al. 06; Wang et al. 06; Fan et al. 08; Galli & Perna 08Guetta & Granot 03; Wei et al. 06; Wang et al. 06; Fan et al. 08; Galli & Perna 08Wang et al. 01a,b; Wang et al. 01a,b; Granot & Guetta 03;Granot & Guetta 03; Pe’er & Waxman 04b;Pe’er & Waxman 04b; Kobayashi et al. 07 Kobayashi et al. 07 Dermer et al. 00; Sari & Esin 01; Zhang & M´esz´aros 01; Wei & Fan 07; Galli & Piro 07; Dermer et al. 00; Sari & Esin 01; Zhang & M´esz´aros 01; Wei & Fan 07; Galli & Piro 07; Gou & Meszaros 07; Yu et al. 07)Gou & Meszaros 07; Yu et al. 07)

Internal shocks (Pe’er Internal shocks (Pe’er & Waxman 04)& Waxman 04)

External shock model: GeV-TeVExternal shock model: GeV-TeV

Standard internal shocks Standard internal shocks (Pe’er & Waxman 04)(Pe’er & Waxman 04)

Standard forward shock Standard forward shock (Fan et al. 08)(Fan et al. 08)

IC of very early afterglow

IC: RS emissionIC: RS emission+ FS electrons+ FS electrons

IC: FS emission IC: FS emission + RS electrons+ RS electrons

(Wang et al. 2001a,b; Granot & Guetta 2003; Piran et al. 2004)

SSC of FSSSC of FS

SSC of RSSSC of RS

(Both reverse shock (RS) and forward shock (FS) exist)

IC of very early afterglowThe energy of RS electrons to total energy of RS+

Fs electrons

Importance of RS IC emission

timescale

Weak RS

~0.1 (Nakar & Piran 04)

Unimportant Longer than the prompt emission

Relativistic RS ~0.5 Important but dominated by EIC

Longer than the prompt emission

Prompt photon flow

The prompt photon flow overlaps RS/FS shock regions and the cooling of RS/FS electrons may be dominated by EIC, and GeV-TeV EIC plateaus are produced

(Beloborodov 05: EIC in RS;

Fan, Zhang & Wei 05, ApJ629: EIC in RS + FS)

(in GRB 080319B: prompt optical photons cool the FS electrons+prompt gamma-rays cool the RS electrons)

Is strong reverse shock popular?

• Bright optical flashes, predicted in RS model, are detected only in a few bursts (Akerlof et al. 1999; Fox et al. 2003; Li, W. et al. 2003; Boer et al. 2006; Klotz et al. 2006; Roming et al. 2006)

• Even for these limited detections, the afterglow modeling usually suggests a weakly magnetized RS region (Fan et al. 2002; Zhang et al. 2003; Kumar & Panaitescu 2003; Wei et al. 2006; Klotz et al. 2006). A stronger magnetization may account for the non-detection in other events (Fan, Wei & Wang 2004; Zhang & Kobayashi 2005; Giannios et al. 2008).

• The IC emission of reverse shock is expected to be weak in most cases (cf. Kobayashi et al. 2007)

EIC in early afterglow(Wang et al. 06; Fan & Piran 06; Fan et al. 2008)

Fan & Piran (2006 )Fan & Piran (2006 )

Any central engine Any central engine afterglow photonsafterglow photons

EIC in early afterglow(Fan, Piran, Narayan & Wei 2008)

Bulk Compton in GRBs and their afterglows

• Shemi (94) and Shaviv & Dar (95a,b) suggested that the ultra-relativistic GRB ejecta was moving into a dense soft photon background and the electrons in the ejecta Compton scattered on the photons and boosted them to MeV-GeV (producing GRB prompt emission)

• Bulk Compton in GRB internal shocks (Takagi & Kobayashi 05), producing GeV-TeV emission (efficiency ~1E-3)

• Bulk Compton in GRB afterglows (Panaitescu 08a, b), producing flares, plateaus followed by a sharp drop, some

X-ray flattening and GeV emission

The late outflow launched by the re-activity of the central engine The late outflow launched by the re-activity of the central engine has to have a Gamma~10has to have a Gamma~1044 and is electron/positron dominated and is electron/positron dominated

Electromagnetic cascade of TeV photons• In the presence of intergalactic magnetic field (B_IGM), the magnetic

deflection angle of the electron/positron at a radius R_IC they lose

most of their energy through IC scattering the CMB )//( 2

IGMeeICB eBcmR • The time-delay caused by the magnetic deflection is

11216

56

112 )1()10

()10

sec(106)2/()1(

zG

BcRzt IGMe

BICB

• BIGM<10-18 G is needed to get detectable GeV emission signatures. It is not clear that whether such a small value is realistic within a radius ~10 Mpc to the GRB host galaxy.

(Plaga 95; Cheng & Cheng 96; Dai & Lu 02; Guetta & Granot 03; (Plaga 95; Cheng & Cheng 96; Dai & Lu 02; Guetta & Granot 03; Wang et al. 04; Razzaque et al. 04; Murase et al. 07; Ichiki et al. 07)Wang et al. 04; Razzaque et al. 04; Murase et al. 07; Ichiki et al. 07)

z~0.1 and Bz~0.1 and BIGMIGM~10~10-20-20 Gauss (Murase et a Gauss (Murase et a

l. 07) l. 07)

pion production • The collision of relativistic nucleons (Gamma~300) wit

h a dense cloud to produce \pi^0 (Katz 94; to account for the 18 GeV photon detected in afterglow of GRB 940217 )

• Pions produced in standard GRB internal shocks (Waxman & Bahcall 97; Gupta & Zhang 07)

• Neutron rich GRB outflow: inelastic n, p collision produces \pi^0 (Bahcall & Meszaros 01; Meszaros & Rees 01)

• The neutral beam model (Dermer & Atoyan 04; >1018 eV neutrons created in p+\gamma process escaped from internal shocks and w

ere subjected to further photopion processes with photons……; see also Ioka et al. 04)

Interpretation of the EGRET data

4~ , , 4.0e

5.0k pttE We need

to reproduce the spectrum and the nearly constant count rate.

The SSC of an X-ray plateau The SSC of an X-ray plateau followed by a sharp decline?followed by a sharp decline?

High energy afterglow of GRB 940217: the SSC com

ponent of a slowly decaying X-ray light curve? (Wei & Fan 2007)

GRB 940217 (Hurley et al. 1994)

Afterglow Afterglow emissionemission

30MeV- 30GeV

The ~0.2 GeV hard component of GRB 941017:

the EIC of the RS+FS shocks in wind medium? (Fan & Piran 08 based on Beloborodov 05 + Fan, Zhang & Wei 05)

3. The MeV-GeV emission has a very hard spectrum

Fv ~v0

1. The MeV-GeV plateau has a duration about 3

times that of the sub-MeV emission

2.The MeV-GeV emission energy is at least

~3 times that of the sub-MeV emission

Prompt emission overlaps FS+RS (Sari & Piran 99; Fan e

t al. 05): EIC works

The timescale favors a process relevant to the very early

afterglow (Granot & Guetta 04)

Suppose that a significant part of MeV-GeV emission is

powered by the RS, the reverse shock has to be relativistic

Fan et al. 08Fan et al. 08

Fan et al. 08Fan et al. 08

What can GLAST tell us?

• Constrain the physical composition of the GRB outflow (If magnetized, no GeV-TeV excess: Giannios 08), the particle acceleration models and the radiation mechanisms

• Probe the initial Lorentz factor of the GRB ejecta (Lithw

ick & Sari 01; Dai & Lu 02; Fan & Wei 04) and the radius of the prompt energy dissipation (Gupta & Zhang 08)

• Test current various modifications of forward shock model that introduced to account for the peculiar Swift X-ray data (Fan et al. 08)

Do something with GLAST detections

Is there a canonical high energy afterglow light curve?

(Fan, Piran, Narayan & Wei 08)(Fan, Piran, Narayan & Wei 08)

??

??

??

Given the small number of high energy photons, these novel features are not expected to be identified as frequently as in X-ray band. But in some extremely bright bursts, like GRBs 940217, 941017 and 030329, more than 1000 sub-GeV photons may be collected.

MAGIC-II, HESS-II: ~30 GeV photons from GRBs?

z=1z=1

Thank you!

EIC in early afterglow(something to be clarify)

• The total energy to be emitted into GeV energies is that of the blast wave and does not strongly depend on the brightness of the central engine afterglow (e.g., X-ray flares).

• The SSC of the early forward shock also peaks at GeV energies. In the absence of EIC, the SSC will convert a significant of blast wave energy into high energy emission. So the EIC can not enhance the GeV detection significantly.

• After taking into account the SSC of the forward shock before and after the X-ray flare, the detected high energy lightcurve should be a plateau rather than a GeV flare.

The SSC of the X-ray flares can be distinguished as sub-GeV (Wei et al. 2006; Wang et al. 2The SSC of the X-ray flares can be distinguished as sub-GeV (Wei et al. 2006; Wang et al. 2006; Fan et al. 2008)or even GeV-TeV flashes 006; Fan et al. 2008)or even GeV-TeV flashes (Galli & Piro 2007; Fan et al. 2008)(Galli & Piro 2007; Fan et al. 2008)

Stern & Stern & Poutanen (2004) (2004)

Naked-eye GRB 080319B: energetic GeV source (Zou et al. 08)?Naked-eye GRB 080319B: energetic GeV source (Zou et al. 08)?

SynSynSSCSSC

2nd IC2nd IC

SSC and 2nd IC in GRBs?SSC and 2nd IC in GRBs?