# MAGICal GRB 190114C: Implications of cutoff in the spectrum at sub-$GeV$ energies

## TL;DR

This paper analyzes the spectral cutoff in GRB 190114C at sub-GeV energies, revealing insights into the emission mechanisms, intrinsic opacity, and the transition from prompt to afterglow phases, with implications for understanding high-energy gamma-ray bursts.

## Contribution

It provides the first detailed spectral analysis of GRB 190114C's cutoff at sub-GeV energies and constrains the emission site and Lorentz factor, highlighting multiple emission regions.

## Key findings

- Detection of a sub-GeV spectral cutoff in GRB 190114C.
- Evidence for multiple emission sites contributing to the observed spectrum.
- Constraints on the prompt emission site and Lorentz factor.

## Abstract

GRB 190114C is an unusual gamma-ray burst (GRB) due to its detection at sub-$TeV$ energies by MAGIC, seen at redshift z = 0.42. This burst is one of the brightest GRB detected by \fermi. A joint GBM-LAT analysis of the prompt emission reveals the presence of sub-$GeV$ spectral cutoff when the LAT \emph{low-energy events} (LLE) data is also examined. A similar high-energy cutoff was likewise reported in GRB 160509A and GRB 100724B earlier, as well as handful of other sources. The cutoff can be explained by the intrinsic opacity due to pair production within the emitting region. GRB 190114C shows a transition from non-thermal to a quasi-thermal-like spectrum and a radiation component that can be attributed to afterglow. Based on spectral analysis, we constrain the site of the prompt emission and $Lorentz$ factor. Knowing that sub-$TeV$ photons are detected in MAGIC, we perceive that the observed spectrum is indeed an overlap from two emission sites, where the emission observed in \fermi is more consistent with prompt emission produced via photospheric dissipation along with a concurrent component from the external shock.