Abstract
Abstract Magnetar hyperflares are the most plausible explanation for fast radio bursts (FRBs)—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 an 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. 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 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.
Highlights
Soft gamma-ray repeaters (SGR) and anomalous Xray pulsars (AXPs) are associated with highly magnetized neutron stars or magnetars
We conclude that no significant very high energy (VHE) gamma-ray emission has been detected by H.E.S.S. during the follow-up observations of SGR 1935+2154
The HXMT burst associated with the fast radio bursts (FRB) is dominated by a power law and is primarily nonthermal in nature according to Li et al (2021), which is very rare for SGRs (6% of SGR bursts as per Li et al (2021))
Summary
Soft gamma-ray repeaters (SGR) and anomalous Xray pulsars (AXPs) are associated with highly magnetized neutron stars or magnetars. They generate bursts of emission at irregular time intervals. The crust of the neutron star is thought to break owing to the intense shifts of the ultrastrong magnetic field causing the emission of hard X-rays and gamma rays. During these short (∼0.1 s) bursts, the brightness of these objects can increase by a factor of 1000 or more.
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