Speaker
Description
We first discuss an off-axis jet model for the short gamma-ray burst (sGRB) 170817A associated with the gravitational wave event GW170817. We show that the origin of the off-axis emission arises from an off-center region of the jet, neither the jet core around the primary axis nor the line of sight at the viewing angle. This off-center location is generally created by the product of the rapidly declining (with angle) jet energy and the increasing beaming term, and can solve spectral puzzles. Then we apply the model to very-high-energy emission from an off-axis GRB. We show that different energy photons (MeV and TeV photons in particular) arrive from different emission zones for off-axis observers even if the emission radius is the same. This off-axis zone-shift effect does not justify the usual one-zone approximation and also produces a time-delay of VHE photons comparable to the GRB duration, which is crucial for future VHE observations, such as by the Cherenkov Telescope Array. If time allows, we will also touch upon cocoon emission from sGRBs and emphasize the difference from that from collapsars.
