Searching for TeV Gamma-Ray Emission from SGR 1935+2154 during Its 2020 X-Ray and Radio Bursting Phase

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.

An updated view and perspectives on high-energy gamma-ray emission from SGR J1935+2154 and its environment

“…This is because the flux calculation in previous work is associated with the upper limits of the gamma integral measured by H.E.S.S. [52], which was updated in [45].…”

“…SGR 1935+2154 is associated with the middle-aged galactic SNR G57.2+0.8 at a distance of about 6.6 kpc (see [37,51] and references therein). Assuming this distance, [45] derive a luminosity upper limit L(E > 600 GeV) < 1.3 × 10 34 erg/s. This places constraints on persistent VHE emission from SGR 1935+2154 during the H.E.S.S.…”

“…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 were derived [see 45, for details].…”

“…where L 0 is the initial spin-down power of the SGR, η = 1.0 is the efficiency factor, τ 0 = 3.37 yr is the pulsar time scale defined as the ratio of the initial rotational energy to the initial spin-down luminosity [see 54] and L is the gamma-rays luminosity of the burst state from H.E.S.S. upper limits [45]. The initial spin-down power is calculated using the current JCAP10(2022)041…”

“…The main goal of the present paper is to extend our previous study where we have investigated particle acceleration models for SNR G57.2+0.8 hosting SGR J1935+2154 [see 37, for details] motivated by H.E.S.S., Fermi-GBM and INTEGRAL VHE gamma-ray observations [see 44,45]. Here, we have used GALPROP propagation code [46][47][48] in its enhanced version [49] performing 3D diffusion/re-acceleration model simulations.…”