Individual and Averaged Power Density Spectra of X-ray bursts from SGR J1935+2154: Quasiperiodic Oscillation Search and Slopes

TL;DR

This study searches for quasi-periodic oscillations in X-ray bursts from SGR J1935+2154 using Bayesian methods, analyzes the power density spectra, and finds no definitive QPOs but identifies possible signals around 40 Hz, providing insights into magnetar emission physics.

Contribution

The paper applies a Bayesian approach to search for QPOs in hundreds of X-ray bursts from SGR J1935+2154 and analyzes the PDS continuum properties, revealing new statistical distributions and correlations.

Findings

No significant QPOs detected in individual or averaged bursts.

Possible QPO at ~40 Hz consistent with previous reports.

PDS slope peaks around 2.5, higher than in gamma-ray bursts.

Abstract

The study of quasi-periodic oscillations (QPOs) and power density spectra (PDS) continuum properties can help shed light on the still illusive emission physics of magnetars and as a window into the interiors of neutron stars using asteroseismology. In this work, we employ a Bayesian method to search for the QPOs in the hundreds of X-ray bursts from SGR J1935+2154 observed by {\it Insight}-HXMT, GECAM and Fermi/GBM from July 2014 to January 2022. Although no definitive QPO signal (significance $>3\sigma$) is detected in individual bursts or the averaged periodogram of the bursts grouped by duration, we identify several bursts exhibiting possible QPO at $\sim$ 40 Hz, which is consistent with that reported in the X-ray burst associated with FRB 200428. We investigate the PDS continuum properties and find that the distribution of the PDS slope in the simple power-law model peaks $\sim$ 2.5, which is consistent with other magnetars but higher than 5/3 commonly seen in gamma-ray bursts. Besides, the distribution of the break frequency in the broken power-law model peaks at $\sim$ 60 Hz. Finally, we report that the power-law index of PDS has an anti-correlation and power-law dependence on the burst duration as well as the minimum variation timescale.