On the generation of high-energy photons detected by the Fermi Satellite from gamma-ray bursts

By Pawan Kumar, R. Duran. 2009

220 citations recorded by the source corpus.

Observations of gamma-ray bursts by the Fermi satellite, capable of detecting photons in a very broad energy band: 8 keV to >300 GeV, have opened a new window for the study of these enigmatic explosions. It is widely assumed that photons of energy larger than 100 MeV are produced by the same source that generated lower energy photons – at least whenever the shape of the spectrum is a Band function. We report here a surprising result – the Fermi data for a bright burst, GRB 080916C, unambiguously shows that the high-energy photons (≳102 MeV) were generated in the external shock via the synchrotron process, and the lower energy photons had a distinctly different source. The magnetic field in the region where high-energy photons were produced (and also the late-time afterglow emission region) is found to be consistent with shock compressed magnetic field of the circum-stellar medium. This result sheds light on the important question of the origin of magnetic fields required for gamma-ray burst afterglows. The external shock model for high-energy radiation makes a firm prediction that can be tested with existing and future observations.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/50647ab3413e42f9ca1abff16d0b4f8867b8c5f3

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Citations in the corpus

AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “A further interesting claim from the work of Kumar & Duran (2009a) is that the inferred value of the magnetic field for GRB090902B (along with several other LAT-detected events) is consistent with shock compression of a modest circumstellar field (B & 30µG).”
The physics of gamma-ray bursts & relativistic jets (2014, background): “There are several different lines of strong evidence suggesting that the high energy photons (>102 MeV) we observe after the prompt phase (t & 10 s) are produced in the external forward shock via the synchrotron process [104,105].”