Probing VHE gamma-ray emission from GW events with H.E.S.S

TL;DR

H.E.S.S. has actively followed up on gravitational wave events, especially neutron star mergers, to search for very high energy gamma-ray emission, setting new constraints and preparing for future observations in O4.

Contribution

This paper presents the first constraints on VHE gamma-ray emission from GW events using H.E.S.S. data and discusses strategies for upcoming O4 observations.

Findings

H.E.S.S. observed GW170817 and set limits on VHE emission.

Constraints on magnetic fields in merger remnants were established.

Prepared observation strategies for the upcoming O4 GW run.

Abstract

Gravitational wave (GW) events, particularly those connected to the merger of compact objects such as neutron stars, are believed to be the primary source of short gamma-ray bursts. To explore the very high energy (VHE) component of the emission from these events, the H.E.S.S. collaboration has dedicated a substantial effort and observing time to follow up on these events. During the second and third GW observing runs, H.E.S.S. was the first ground-based instrument to observe the GW170817 binary neutron star merger. In addition, H.E.S.S. followed four binary black hole mergers. The data acquired by H.E.S.S. was used to constrain the VHE emission from these events for the first time. H.E.S.S. also monitored the GW170817 source for approximately 50 hours and obtained limits that constrained the magnetic field in the merger remnant to $> 24 \mu G$. As the fourth GW observing run (O4) approaches, the H.E.S.S. collaboration has allocated significant observation time to the follow-up of GW events. This contribution provides an overview of the science results derived from the H.E.S.S. follow-up of GW events, a technical overview of the GW follow-up strategies for O4, and an update on H.E.S.S. activities during O4.