MAGIC detection of GRB 201216C at $z=1.1$

TL;DR

This paper reports the detection of the distant GRB 201216C at z=1.1 by MAGIC telescopes, modeling its high-energy emission with SSC, and suggesting a wind-like medium, marking a significant advancement in very-high-energy GRB observations.

Contribution

First detection of a GRB at z=1.1 at very-high-energy, with detailed modeling favoring a wind-like environment, expanding understanding of GRB afterglows.

Findings

GRB 201216C detected at z=1.1, the farthest at VHE.

SSC model explains broadband emission from optical to VHE.

A wind-like medium is favored for this GRB.

Abstract

Gamma-ray bursts (GRBs) are explosive transient events occurring at cosmological distances, releasing a large amount of energy as electromagnetic radiation over several energy bands. We report the detection of the long GRB~201216C by the MAGIC telescopes. The source is located at $z=1.1$ and thus it is the farthest one detected at very high energies. The emission above \SI{70}{\GeV} of GRB~201216C is modelled together with multi-wavelength data within a synchrotron and synchrotron-self Compton (SSC) scenario. We find that SSC can explain the broadband data well from the optical to the very-high-energy band. For the late-time radio data, a different component is needed to account for the observed emission. Differently from previous GRBs detected in the very-high-energy range, the model for GRB~201216C strongly favors a wind-like medium. The model parameters have values similar to those found in past studies of the afterglows of GRBs detected up to GeV energies.