PAIR-DOMINATED GeV-OPTICAL FLASH IN GRB 130427A

We show that the light curve of the double GeV+optical flash in GRB 130427A is consistent with radiation from the blast wave in a wind-type medium with density parameter A = [rho]r super(2) ~ 5 x 10 super(10) g cm super(-1). The peak of the flash is emitted by copious e super(+ or -) pairs created a...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2014-07, Vol.789 (2), p.1-5
Main Authors: VURM, INDREK, Hascoet, Romain, Beloborodov, Andrei M
Format: Article
Language:English
Subjects:
AFTERGLOW
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COMPUTERIZED SIMULATION
COSMIC GAMMA BURSTS
Density
DIAGRAMS
GEV RANGE
Integrated circuits
Light curve
Lorentz factor
MAGNETIZATION
MEV RANGE
PHOTON EMISSION
PLASMA
RADIANT HEAT TRANSFER
SCATTERING
STELLAR WINDS
Thermal plasmas
VISIBLE RADIATION
X RADIATION
X-rays
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Summary:We show that the light curve of the double GeV+optical flash in GRB 130427A is consistent with radiation from the blast wave in a wind-type medium with density parameter A = [rho]r super(2) ~ 5 x 10 super(10) g cm super(-1). The peak of the flash is emitted by copious e super(+ or -) pairs created and heated in the blast wave; our first-principle calculation determines the pair-loading factor and temperature of the shocked plasma. Using detailed radiative transfer simulations, we reconstruct the observed double flash. The optical flash is dominated by synchrotron emission from the thermal plasma behind the forward shock, and the GeV flash is produced via inverse Compton (IC) scattering by the same plasma. The seed photons for IC scattering are dominated by the prompt MeV radiation during the first tens of seconds, and by the optical to X-ray afterglow thereafter. IC cooling of the thermal plasma behind the forward shock reproduces all GeV data from a few seconds to ~1 day. We find that the blast wave Lorentz factor at the peak of the flash is [Gamma] [approximate] 200, and the forward shock magnetization is [varepsilon] sub(B) ~ 2 x 10 super(-4). An additional source is required by the data in the optical and X-ray bands at times >10 super(2) s; we speculate that this additional source may be a long-lived reverse shock in the explosion ejecta.
ISSN:2041-8205
2041-8213
DOI:10.1088/2041-8205/789/2/L37