GRB 131231A: Implications of the GeV emission

Abstract

GRB 131231A was detected by the Large Area Telescope on board the Fermi Space Gamma-ray Telescope. The high-energy gamma-ray (>100 MeV) afterglow emission spectrum is F νν-0.54 ± 0.15 in the first 1300 s after the trigger and the most energetic photon has an energy of 62 GeV, arriving at t 520 s. With reasonable parameters of the gamma-ray burst (GRB) outflow as well as the density of the circum-burst medium, the synchrotron radiation of electrons or protons accelerated at an external forward shock have difficulty accounting for the data. Rather, the synchrotron self-Compton radiation of the forward shock-accelerated electrons can account for both the spectrum and temporal behavior of the GeV afterglow emission. We also show that the prospect for detecting GRB 131231A-like GRBs with the Cherenkov Telescope Array is promising. © 2014. The American Astronomical Society. All rights reserved..