External Inverse-Compton Emission Associated with Extended and Plateau Emission of Short Gamma-Ray Bursts: Application to GRB 160821B

The recent detection of TeV photons from two gamma-ray bursts (GRBs), GRB 190114C and GRB 180720B, has opened a new window for multimessenger and multiwavelength astrophysics of high-energy transients. We study the origin of very high energy (VHE) gamma-rays from the short GRB 160821B, for which the MAGIC Collaboration reported a similar to 3 sigma statistical significance. Short GRBs are often accompanied by extended and plateau emission, which is attributed to internal dissipation resulting from activities of a long-lasting central engine, and Murase et al. (2018) recently suggested the external inverse-Compton (EIC) scenario for VHE counterparts of short GRBs and neutron star mergers. Applying this scenario to GRB 160821B, we show that the EIC flux can reach similar to 10(-12) erg cm(-2) s(-1) within a time period of similar to 10(3)-10(4) s, which is consistent with the MAGIC observations. EIC gamma-rays expected during the extended and plateau emission will be detectable with greater significance by future detectors such as the Cerenkov Telescope Array. The resulting light curve has a distinguishable feature, where the VHE emission is predicted to reach the peak around the end of the seed photon emission.

Automated summary

The study investigates the origin of very high energy gamma-rays from the short GRB 160821B, suggesting the external inverse-Compton scenario for VHE counterparts. By applying this scenario, it is found that the EIC flux is consistent with MAGIC observations, and future detectors like the Cerenkov Telescope Array will enable the detection of EIC gamma-rays with greater significance.