ON THE ORIGIN OF > 10 GeV PHOTONS IN GAMMA-RAY BURST AFTERGLOWS
- School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China)
- Institut d'Astrophysique de paris, CNRS, UPMC, 98 bis boulevard Arago, F-75014 Paris (France)
Fermi/LAT has detected long-lasting high-energy photons (>100 MeV) from gamma-ray bursts (GRBs), with the highest energy photons reaching about 100 GeV. One proposed scenario is that they are produced by high-energy electrons accelerated in GRB forward shocks via synchrotron radiation. We study the maximum synchrotron photon energy in this scenario, considering the properties of the microturbulence magnetic fields behind the shock, as revealed by recent particle-in-cell simulations and theoretical analyses of relativistic collisionless shocks. Due to the small-scale nature of the microturbulent magnetic field, the Bohm acceleration approximation, in which the scattering mean free path is equal to the particle Larmor radius, breaks down at such high energies. This effect leads to a typical maximum synchrotron photon of a few GeV at 100 s after the burst and this maximum synchrotron photon energy decreases quickly with time. We show that the fast decrease of the maximum synchrotron photon energy leads to a fast decay of the synchrotron flux. The 10-100 GeV photons detected after the prompt phase cannot be produced by the synchrotron mechanism. They could originate from the synchrotron self-Compton emission of the early afterglow if the circumburst density is sufficiently large, or from the external inverse Compton process in the presence of central X-ray emission, such as X-ray flares and prompt high-latitude X-ray emission.
- OSTI ID:
- 22118685
- Journal Information:
- Astrophysical Journal Letters, Vol. 771, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ACCELERATION
AFTERGLOW
APPROXIMATIONS
ASTROPHYSICS
COMPUTERIZED SIMULATION
COSMIC ELECTRONS
COSMIC GAMMA BURSTS
COSMIC PHOTONS
GAMMA ASTRONOMY
GAMMA DETECTION
GEV RANGE
LARMOR RADIUS
MAGNETIC FIELDS
MEAN FREE PATH
MEV RANGE
PHOTON EMISSION
RELATIVISTIC RANGE
SYNCHROTRON RADIATION
TELESCOPE COUNTERS
X RADIATION