Fermi-GBM Observations of the SGR J1935+2154 Burst Forest

Abstract

During 2020 April and May, SGR J1935+2154 emitted hundreds of short bursts and became one of the most prolific transient magnetars. At the onset of the active bursting period, a 130 s burst "forest," which included some bursts with peculiar time profiles, were observed with the Fermi/Gamma-ray Burst Monitor (GBM). In this Letter, we present the results of time-resolved spectral analysis of this burst "forest" episode, which occurred on 2020 April 27. We identify thermal spectral components prevalent during the entire 130 s episode; high-energy maxima appear during the photon flux peaks, which are modulated by the spin period of the source. Moreover, the evolution of the $\nu F_{\nu }$ spectral hardness (represented by $E_{\mathrm{peak}}$ or blackbody temperature) within the lightcurve peaks is anti-correlated with the pulse phases extrapolated from the pulsation observed within the persistent soft X-ray emission of the source six hours later. Throughout the episode, the emitting area of the high-energy (hotter) component is 1-2 orders of magnitude smaller than that for the low-energy component. We interpret this with a geometrical viewing angle scenario, inferring that the high-energy component likely originates from a low-altitude hotspot located within closed toroidal magnetic field lines.

23 pages, 8 figures, 1 table (machine-readable table provided separately), Matches the published version

References in corpus (6)

• INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154
• A Swift gaze into the 2006 March 29th burst forest of SGR 1900+14
• On the Distance of SGR 1935+2154 Associated with FRB 200428 and Hosted in SNR G57.2+0.8
• A radiatively-quiet glitch and anti-glitch in the magnetar 1E 2259+586
• Analytical modeling of pulse-pileup distortion using the true pulse shape; applications to Fermi-GBM
• Simultaneous magnetic polar cap heating during a flaring episode from the magnetar 1RXS J170849.0-400910

Cited by in corpus (14)

• Insight-HXMT dedicated 33-day observation of SGR J1935+2154 II. Burst Spectral Catalog
• Direct Emission of Strong Radio Pulses During Magnetar Flares
• Discovery of the linear energy-dependence of the spectral lag of X-ray bursts from SGR J1935+2154
• Finding the Particularity of the Active Episode of SGR J1935+2154 during Which FRB 20200428 Occurred: Implication from Statistics of Fermi/GBM X-Ray Bursts
• GECAM Observations of the Galactic Magnetar SGR J1935+2154 during the 2021 and 2022 Burst Active Episodes. I. Burst Catalog
• Quasi-Periodic Peak Energy Oscillations in X-ray Bursts from SGR J1935+2154
• Burst phase distribution of SGR J1935+2154 based on Insight-HXMT
• Concise Spectrotemporal Studies of Magnetar SGR J1935+2154 Bursts
• Rotation and dispersion measure evolution of repeating fast radio bursts propagating through a magnetar flare ejecta
• Eclipsed X-ray Bursts from Magnetar SGR J1935+2154 and the Fireball Measurements
• Joint Observation of SGR J1935+2154 with \textit{Insight}-HXMT and KM40m during the active episode of October 2022
• Correlation of Burst Behaviour with Magnetar Age
• Spectral Evidence of Heavy Nuclei from the Neutron Star Crust in Magnetar Bursts
• Investigating the Recursive Short X-ray Burst Behavior of Magnetars Through Crustal Interactions