GECAM Observations of the Galactic Magnetar SGR J1935+2154 during the 2021 and 2022 Burst Active Episodes. I. Burst Catalog

TL;DR

This study presents a targeted, sub-threshold search of GECAM-B/C data for bursts from the magnetar SGR J1935+2154 during 2021–2022, yielding 159 and 97 bursts respectively and noting 14 joint detections including the FRB-associated event on 2022-10-14. By employing LR-based detection with a 10 ms time-bin and five spectral templates (SoftBand, CPL, OTTB, Blackbody, Powerlaw), the authors map burst locations and characterize a rich burst catalog. The analysis reveals that burst durations and waiting times follow lognormal distributions, identifies a quasi-periodic activity cycle with a period of $P=134.63$ days and an $80\%$ duty cycle, and shows a progressive softening of the burst spectra over the two-year span. The results, including the four active episodes and the FRB association, enhance understanding of magnetar burst behavior and provide essential context for the forthcoming Paper II spectral study and FRB-magnetar connection models.

Abstract

Magnetar is a neutron star with an ultrahigh magnetic field ($\sim 10^{14}-10^{15}$ G). The magnetar SGR J1935+2154 is not only one of the most active magnetars detected so far, but also the unique confirmed source of fast radio bursts (FRBs). Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is dedicated to monitor gamma-ray transients all over the sky, including magnetar short bursts. Here we report the GECAM observations of the burst activity of SGR J1935+2154 from January 2021 to December 2022, which results in a unique and valuable data set for this important magnetar. With a targeted search of GECAM data, 159 bursts from SGR J1935+2154 are detected by GECAM-B while 97 bursts by GECAM-C, including the X-ray burst associated with a bright radio burst. We find that both the burst duration and the waiting time between two successive bursts follow lognormal distributions. The period of burst activity is $134\pm20$ days, thus the burst activity could be generally divided into four active episodes over these two years. Interestingly, the hardness ratio of X-ray bursts tends to be softer during these two years, especially during the active episode with radio bursts detected.

Figures (11)

• Figure 1: The targeted search location (TL) of bursts. The red star marks the accurate position of SGR J1935+2154 (R.A. = 293.73°, Decl. = 21.90°).
• Figure 2: The angle separation between the targeted search location (TL) of burst and true position of SGR J1935+2154.
• Figure 3: The significance of burst v.s angle separation between the targeted search location (TL) and true position of SGR J1935+2154.
• Figure 4: Representative examples of GECAM-detected bursts of SGR J1935+2154. For each burst, light curves are shown for high gain (HG, 6–300 keV). The background of each burst is shown by the red dotted line. The green vertical dotted line and blue dotted line are assessed by the Bayesian block (BB) algorithm.
• Figure 5: The burst history of SGR J1935+2154 observed by GECAM-B/C.