High energy 20MeVTeV photon emission from Gammaray Bursts

1
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,
arXiv0805.2221)
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GRB internal-external shock model
(see Piran 1999, 2004 Meszaros 2002 Zhang
Meszaros 2004 for reviews)
UV/opt/IR/radio
gamma-ray
gamma-ray X-ray UV/optical IR mm radio
prompt emission
afterglow

central photosphere internal
external shocks engine
(shocks)
(reverse) (forward)

1E17cm for ISM 1E6cm
1E9cm 1E12-1E14cm
1E15cm for wind


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MeV-GeV observations (EGRET)
afterglow
The first afterglow detection, but no redshift
information
GRB 930131 (Superbowl Burst)
GRB 940217 (Hurley et al. 1994)
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MeV-GeV observations (EGRET) GRB 941017
Gonzalez et al. 2003
Quick evolution
Almost constant
Much longer high energy emission
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VHE(gt50 GeV) Observations

• Milagrito observation of GRB 970417 at energies
  above 0.1 TeV (3 s? Atkins et al. 2000)
• Upper limits from Magic for several Swift bursts
  (Albert et al., 06)
• Claims of detection GRAND at 2.7 s (Poirier et al
  03, but see Fragile et al 03)
• Tibet array 7s coincidence ? (Amenomori et al
  01)
• ARGO-YBJ array find only upper limits (Di
  Sciascio, et al., 06)

Only upper limits!
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The optical depth of universe to VHE
gamma-rays(Stecker et al. 2006)
z3
z5
z2
tau6
z1
z0.2
z0.5
z0.03
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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 review
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Inverse Compton (IC) processes
see Fan Piran (2008 ) for a review
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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 )
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High energy photons from Pion production
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Electromagnetic cascade of TeV photons
(Nikoshov 1962 Gould Schreder 1967)
MCB
Infrared background
TeV source
Seed photon
GeV photons
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High energy processes in GRBs and afterglows
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SSC in GRBs and their afterglows
ge1000
ge tens
ge104-10
From Piran (2003)
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SSC
Standard internal shocks (Peer Waxman 04)
Internal shocks (Peer Waxman 04)
External shock model GeV-TeV
Standard forward shock (Fan et al. 08)
Standard forward shock (Fan et al. 08)
(Meszaros Rees 94 Pilla Leob 98 Peer
Waxman 04 Gupta Zhang 07, 08 Guetta Granot
03 Wei et al. 06 Wang et al. 06 Fan et al. 08
Galli Perna 08 Wang et al. 01a,b Granot
Guetta 03 Peer Waxman 04b Kobayashi et al.
07 Dermer et al. 00 Sari Esin 01 Zhang
Meszaros 01 Wei Fan 07 Galli Piro 07 Gou
Meszaros 07 Yu et al. 07)
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IC of very early afterglow
(Both reverse shock (RS) and forward shock (FS)
exist)
IC RS emission FS electrons
SSC of RS
SSC of FS
IC FS emission RS electrons
(Wang et al. 2001a,b Granot Guetta 2003 Piran
et al. 2004)
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IC of very early afterglow
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 electronsprompt gamma-rays cool the RS
electrons)

• Prompt photon flow

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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)

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EIC in early afterglow(Wang et al. 06 Fan
Piran 06 Fan et al. 2008)
Any central engine afterglow photons
Fan Piran (2006 )
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EIC in early afterglow(Fan, Piran, Narayan Wei
2008)
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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 has to have a Gamma104 and is
electron/positron dominated
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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

z0.1 and BIGM10-20 Gauss (Murase et al. 07)

• The time-delay caused by the magnetic deflection
  is

• BIGMlt10-18 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 Wang et al. 04 Razzaque et al.
04 Murase et al. 07 Ichiki et al. 07)
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pion production

• The collision of relativistic nucleons
  (Gamma300) with a dense cloud to produce \pi0
  (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 \pi0 (Bahcall Meszaros 01
  Meszaros Rees 01)
• The neutral beam model (Dermer Atoyan 04 gt1018
  eV
• neutrons created in p\gamma process escaped
  from internal shocks and were subjected to
  further photopion processes with photons see
  also Ioka et al. 04)

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Interpretation of the EGRET data
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High energy afterglow of GRB 940217 the SSC
component of a slowly decaying X-ray light curve?
(Wei Fan 2007)
The SSC of an X-ray plateau followed by a sharp
decline?
We need to reproduce the spectrum and the
nearly constant count rate.
Afterglow emission
30MeV- 30GeV
GRB 940217 (Hurley et al. 1994)
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The 0.2 GeV hard component of GRB 941017 the
EIC of the RSFS shocks in wind medium? (Fan
Piran 08 based on Beloborodov 05 Fan, Zhang
Wei 05)
Fan et al. 08
1. The MeV-GeV plateau has a duration about 3
times that of the sub-MeV emission
The timescale favors a process relevant to the
very early afterglow (Granot Guetta 04)
Prompt emission overlaps FSRS (Sari Piran 99
Fan et al. 05) EIC works
2.The MeV-GeV emission energy is at least 3
times that of the sub-MeV emission
Suppose that a significant part of MeV-GeV
emission is powered by the RS, the reverse
shock has to be relativistic
3. The MeV-GeV emission has a very hard
spectrum Fv v0
Fan et al. 08
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What can GLAST tell us?
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Do something with GLAST detections

• 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 (Lithwick 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)

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Is there a canonical high energy afterglow light
curve?
(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.
?
?
?
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MAGIC-II, HESS-II 30 GeV photons from GRBs?
z1
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Thank you!

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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. 2006
Fan et al. 2008)or even GeV-TeV flashes (Galli
Piro 2007 Fan et al. 2008)
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SSC and 2nd IC in GRBs?
2nd IC
SSC
Syn

Stern Poutanen (2004) Naked-eye GRB
080319B energetic GeV source (Zou et al. 08)?