Discovery of Evolution of the Temporal Features of X-Ray Bursts from SGR J1935+2154

Abstract SGR J1935+2154 has undergone eight active episodes since its discovery in 2014. In this study, our focus is on the evolution of the temporal characteristics including burst duration, minimum variation timescale (MVT), and waiting time across these active episodes observed by Fermi/Gamma-ray Burst Monitor (GBM). We find a linear increase in the logarithmic mean of burst duration over time, with a deviation during the fourth and eighth active episodes containing X-ray burst (XRB)−Fast Radio Burst (FRB) 200428 and XRB−radio burst 221021 association events. We also find a possible increasing burst frequency, with the fourth active episode exhibiting an exceptionally high burst rate. Therefore, XRB−FRB 200428 is potentially triggered by energetic events such as a large crust, magnetic reconnection, or glitches. The MVT analysis reveals deviations in the sixth and seventh active episodes with ∼3 σ . These results may suggest evolving magnetospheric field geometry, neutron star crust, and energy release mechanisms of SGR J1935+2154. Finally, our findings predict that longer XRB durations indicate the highly likely occurrence of XRB and radio burst association events, warranting focused multiwavelength observations during such episodes, which will also be further confirmed or disproved by future observations.