PROMPT GeV EMISSION FROM RESIDUAL COLLISIONS IN GAMMA-RAY BURST OUTFLOWS: EVIDENCE FROM FERMI OBSERVATIONS OF GRB 080916c

Journal Article · Wed Jan 20 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/709/1/525· OSTI ID:21392330

Zhuo, Li ^[1]

---

1. Department of Astronomy, Peking University, Beijing 100871 (China)

The gamma-rays from gamma-ray bursts (GRBs) are believed to be produced by internal shocks driven by small timescale, approx1 ms, variation in the GRB outflows, and a pair-production spectral cutoff is generally expected around the GeV range. However, the observed optical flashes accompanying GRBs suggest that the delayed residual collisions due to large timescale variation continue to accelerate electrons. We show here that the inverse-Compton (IC) scattering of the prompt gamma-rays by these residual internal shock electrons leads to a high-energy emission beyond the previously thought spectral cutoff, in agreement with the previous detections of GeV photons by EGRET in several GRBs in conjunction with MeV emission. We expect a spectral break due to the transition from the primary to residual internal shock emission at the previously thought spectral cutoff and expect systematic time delays of high-energy photons relative to MeV emission, the discovery of which would provide stringent constraint on the outflow properties, but requires large enough collection of high-energy photons by, e.g., Fermi and AGILE satellites. The recent Fermi-detected bright GRB 080916c unambiguously shows the shifting of the prompt emission toward later times as the photon energy increases. The second-scale shifting at >100 MeV is much longer than the MeV variability time, as predicted in the residual collision model. The observations imply that there should be emission above 70 GeV in the source frame, which may not be produced by primary internal shocks but by IC emission in residual collisions. With the method involving time delays of high-energy emission, the bulk Lorentz factor of GRB 080916c is determined to be GAMMA approx 300.

• OSTI ID: 21392330
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 709; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
79 ASTRONOMY AND ASTROPHYSICS
ACCELERATION
BOSONS
COSMIC GAMMA BURSTS
COSMIC RADIATION
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
EMISSION
ENERGY RANGE
FERMIONS
GAMMA RADIATION
GEV RANGE
INTERACTIONS
IONIZING RADIATIONS
LEPTONS
MAGNETIC FIELDS
MASSLESS PARTICLES
MEV RANGE
PAIR PRODUCTION
PARTICLE PRODUCTION
PHOTON EMISSION
PHOTONS
PRIMARY COSMIC RADIATION
RADIATIONS
SATELLITES
SCATTERING
SHOCK WAVES
TIME DELAY