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

TL;DR

This paper presents a comprehensive catalog of 256 gamma-ray bursts from the magnetar SGR J1935+2154 observed by GECAM during 2021-2022, revealing patterns in burst duration, waiting times, and spectral softness linked to activity episodes and radio bursts.

Contribution

It provides the first extensive burst catalog for SGR J1935+2154 during this period, including detailed statistical analysis and correlation with radio burst activity.

Findings

Burst durations and waiting times follow lognormal distributions.

Burst activity occurs in roughly four episodes over two years.

X-ray burst hardness ratios are softer during active episodes.

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.