GRB 131231A: Implications of the GeV emission

Abstract

GRB 131231A was detected by the Large Area Telescope onboard Fermi Space Gamma-ray Telescope. The high energy gamma-ray ($>100$ MeV) afterglow emission spectrum is $F_{\nu }\propto {\nu }^{-0.54\pm 0.15}$ in the first $\sim 1300$ s after the trigger and the most energetic photon has an energy $\sim 62$ GeV arriving at $t\sim 520$ s. With reasonable parameters of the 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. The synchrotron self-Compton radiation of the forward shock-accelerated electrons, instead, 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 Cherenkov Telescope Array (CTA) is promising.

ApJL in press

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• Description of atypical bursts seen slightly off-axis
• Origin for the Prompt Spectral Evolution Characteristics and High Energy Emission during the X-Ray Flare in GRB 180720B
• An evolving GeV spectrum from prompt to afterglow: the case of GRB 160509A
• Searching for an additional high-energy component in Fermi-LAT GRB afterglows