Scale-invariant Features of X-Ray Bursts from SGR J1935+2154 Detected by Insight-HXMT

Abstract

In this work, we restudy the scale-invariant features of X-ray bursts from the soft gamma repeater (SGR) J1935+2154. To compare with previous studies, we choose 75 bursts from a dedicated 33 days-long observation carried out by Insight-HXMT. We investigate the size difference distributions of net counts, duration, and waiting time. It is found that the cumulative difference distributions of net counts and duration follow the q-Gaussian models with approximately steady q-values, confirming that the scale-invariant features exist in X-ray bursts of SGR J1935+2154. Regarding the varying results of waiting time reported by Sang & Lin and Wei et al, we find that the distributions of waiting time can be well described by the q-Gaussian model. Furthermore, the q-values of waiting time remain relatively stable at the 3σ confidence level, corroborating the scale invariance in the X-ray bursts. Additionally, we note that there is no significant q-value evolution across three Insight-HXMT telescopes. These findings statistically affirm that the X-ray bursts from SGR J1935+2154 can be attributed to an fractal-diffusive self-organized criticality system with a plausible Euclidean spatial dimension S = 3, implying that X-ray bursts from SGR J1935+2154 and associated astrophysical phenomena may share a similar magnetically dominated stochastic process.