Searching for TeV gamma-ray emission from SGR\,1935+2154 during its 2020 X-ray and radio bursting phase

TL;DR

This study reports on H.E.S.S. observations of SGR 1935+2154 during its 2020 bursting phase, aiming to detect TeV gamma-ray emission associated with magnetar flares and fast radio bursts, but finds no significant signals.

Contribution

First simultaneous VHE gamma-ray observations of a magnetar during a flaring state coinciding with X-ray bursts, setting upper limits on gamma-ray emission.

Findings

No significant TeV gamma-ray emission detected.

Upper limits established for persistent and transient gamma-ray flux.

Results inform future VHE follow-up strategies for magnetar activity.

Abstract

Magnetar hyperflares are the most plausible explanation for fast radio bursts (FRB) -- enigmatic powerful radio pulses with durations of several milliseconds and high brightness temperatures. The first observational evidence for this scenario was obtained in 2020 April when a FRB was detected from the direction of the Galactic magnetar and soft gamma-ray repeater SGR\,1935+2154. The FRB was preceded by two gamma-ray outburst alerts by the BAT instrument aboard the Swift satellite, which triggered follow-up observations by the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. has observed SGR\,1935+2154 for 2 hr on 2020 April 28. The observations are coincident with X-ray bursts from the magnetar detected by INTEGRAL and Fermi-GBM, thus providing the first very high energy (VHE) gamma-ray observations of a magnetar in a flaring state. High-quality data acquired during these follow-up observations allow us to perform a search for short-time transients. No significant signal at energies $E>0.6$~TeV is found and upper limits on the persistent and transient emission are derived. We here present the analysis of these observations and discuss the obtained results and prospects of the H.E.S.S. follow-up program for soft gamma-ray repeaters.