Constraints on the very high energy gamma-ray emission from short GRBs with HAWC

TL;DR

This study used HAWC data from 2014 to 2020 to search for very-high-energy gamma-ray emission from 47 short GRBs, finding no evidence but setting limits that constrain theoretical models and interstellar medium densities.

Contribution

First comprehensive search for VHE gamma-ray emission from short GRBs using HAWC data, providing upper limits that inform models of GRB emission and environment.

Findings

No VHE emission detected from the 47 short GRBs.

Upper limits constrain the synchrotron self-Compton model.

Low interstellar densities challenge VHE observability.

Abstract

Many gamma-ray bursts (GRBs) have been observed from radio wavelengths, and a few at very-high energies (VHEs, > 100GeV). The HAWC gamma-ray observatory is well suited to study transient phenomena at VHEs due to its large field of view and duty cycle. These features allow for searches of VHE emission and can probe different model assumptions of duration and spectra. In this paper, we use data collected by HAWC between December 2014 and May 2020 to search for emission in the energy range from 80 to 800 GeV coming from a sample 47 short GRBs that triggered the Fermi, Swift and Konus satellites during this period. This analysis is optimized to search for delayed and extended VHE emission within the first 20 s of each burst. We find no evidence of VHE emission, either simultaneous or delayed, with respect to the prompt emission. Upper limits (90% confidence level) derived on the GRB fluence are used to constrain the synchrotron self-Compton forward-shock model. Constraints for the interstellar density as low as $10^{-2}$ cm$^{-3}$ are obtained when assuming z=0.3 for bursts with the highest keV-fluences such as GRB 170206A and GRB 181222841. Such a low density makes observing VHE emission mainly from the fast cooling regime challenging.