BEXCO - Room D(109/110)
[GA286] Rapid follow-up observations of gamma-ray bursts with the MAGIC telescopes
Gamma-ray bursts (GRBs) are the most luminous explosions in the Universe, yet many of their basic properties remain poorly understood, particularly for short GRBs with durations less than ~2 sec. Very-high-energy (VHE) gamma rays from GRBs are expected to provide crucial new information on the physical mechanisms of energy dissipation, particle acceleration and radiation in these enigmatic objects. The MAGIC telescopes feature fast repointing capabilities and low energy threshold that are well suited for VHE studies of GRBs. We describe the current status of the MAGIC key observing program for GRBs, including automatic follow-up of the short GRB 160821B that began 24 sec after the burst trigger. Its redshift is z=0.16, to date the nearest GRB observed by MAGIC, and one of the nearest short GRBs ever. We present the results of dedicated analyses of the data up to a few hours after the burst, taken in challenging observing conditions with bright Moon and non-optimal weather. In combination with observations at other wavelengths, we provide possible theoretical interpretations in the framework of GRB afterglow models under different assumptions.