主要内容:
种子光子是瞬时辐射的MeV光子。
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- · arXiv e-print (arXiv:1307.2663)
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Abstract
The most common progenitors of gamma-ray bursts (GRBs) are massive stars
with strong stellar winds. We show that the GRB blast wave in the wind
should emit a bright GeV flash. It is produced by inverse Compton
cooling of the thermal plasma behind the forward shock wave. The main
part of the
flash is shaped by scattering of the prompt MeV radiation
(emitted at smaller radii) which streams through the external blast
wave. The inverse-Compton flash is bright due to the huge e+- enrichment
of the external medium. At late times, the blast wave switches to normal
synchrotron-self-Compton cooling. The mechanism is demonstrated by a
detailed transfer simulation. The observed prompt MeV radiation is taken
as an input of the simulation; we use GRB 080916C as an example. The
result reproduces the GeV flash observed by the Fermi telescope. It
explains the delayed onset, the steep rise, the peak flux, the time of
the peak, the
long smooth decline, and the spectral slope of GeV
emission. The wind density required to reproduce all these features is
typical of Wolf-Rayet stars. Our simulation predicts strong TeV emission
1 min after the burst trigger; then a cutoff in the observed high-energy
spectrum is expected from absorption by extragalactic background light.
In addition, a bright optical counterpart of the GeV flash is predicted
for plausible values of the magnetic field; such a double (optical+GeV)
flash has been observed in GRB 130427A.
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