Searching for GRBs at VHE with MAGIC: the status before CTA

TL;DR

This paper reviews MAGIC's efforts in detecting VHE gamma-ray emission from GRBs, highlighting upgrades, results, and implications for future CTA observations, with only one firm detection to date.

Contribution

It presents the status and results of MAGIC's GRB follow-up program from 2013 to 2018, including upper limits and methodological improvements, as a precursor to CTA.

Findings

Only GRB 190114C was firmly detected in VHE.

MAGIC's follow-up procedure is effective and well-tested.

Upper limits provide insights into GRB emission mechanisms.

Abstract

Gamma-Ray Bursts (GRBs) are one of the main targets for current and next generation Imaging Atmospheric Cherenkov Telescopes (IACTs). Given their transient behavior, especially in the case of their prompt emission phase, performing fast follow-up observations is challenging for IACTs, which have a narrow field of view and limited duty cycle. Despite this, MAGIC plays a major role in the search for Very High Energy (VHE, E>100 GeV) gamma-ray emission from GRBs: this is possible thanks to its fast repositioning speed, low energy threshold and high sensitivity at the lowest energies. In 2013 the MAGIC GRB automatic procedure was upgraded, increasing the number of GRBs followed in the prompt and early afterglow phases and decreasing dramatically hardware failures during fast repositioning. Currently, only GRB 190114C was firmly detected in the VHE band, while for other GRBs no significant detection was achieved. In such a case, upper limits (ULs) can give insight into the physics driving such eluding sources, especially on their emission mechanisms. In this contribution we report on the status of the GRB follow-up with MAGIC and focus on the ULs and results obtained from a sample of GRBs observed between 2013 and 2018. This GRB catalog is the result of the MAGIC well-designed and tested follow-up procedure, and it serves as a precursor of GRBs observation with the next generation IACT system, the Cherenkov Telescope Array (CTA).