NICER Magnetar Burst Catalog

TL;DR

This study presents the largest magnetar burst catalog to date from eight years of NICER observations, identifying 1130 bursts with SGR 1935+2154 contributing the majority. By performing uniform timing and spectral analyses using both blackbody and power-law models in the soft X-ray band ($0.5$–$8$ keV) and applying Bayesian-block burst searches, the work reveals that bursts from SGR 1935+2154 are systematically longer ($\sim$316 ms) than those from other magnetars ($\sim$23 ms) and that higher-flux bursts tend to have harder spectra. The catalog detects two microsecond-scale bursts and shows strong correlations between spectral parameters and flux, while duration–spectral correlations are weak or driven by instrumental selection effects. These results provide a consistent, quantitative dataset to advance physical modeling of magnetar bursts and to compare burst populations across sources. The publicly available catalog will support future investigations into emission mechanisms and magnetic field dynamics in magnetars.

Abstract

In this paper, we present a comprehensive catalog of short bursts from magnetars based on eight years of NICER observations. A total of 1130 bursts were identified, making this the largest magnetar burst catalog to date. The sample is dominated by SGR 1935+2154, which contributes 76% of all detected bursts. We analyzed burst durations, spectral properties, and their correlations across multiple sources. Bursts from SGR 1935+2154 exhibit significantly longer durations, with a mean of 317 ms, compared to a mean of 23 ms for bursts from other magnetars. Two microsecond-scale bursts were detected for the first time, originating from 1E 1048.1-5937 and CXOU J010043.1-721134. Spectral analysis in the 0.5--8 keV range using both blackbody and power-law models shows that bursts with higher fluences have harder spectra. In contrast, correlations between burst duration and spectral parameters are weak or absent. This catalog provides a valuable dataset for studying magnetar short bursts, enabling future modeling efforts and improving our understanding of the diversity and physical mechanisms of magnetar bursts.

Figures (10)

• Figure 1: Distributions of background counts calculated with 0.02 s (left) and 0.2 s (right) time bins. Different colors correspond to the RXTE blank-sky regions identified in the legend. Black dashed lines are the Poisson probability mass function of averaged background counts calculated from Table \ref{['tab:rxte']}.
• Figure 2: The left panel shows the overall duration distribution of the NICER magnetar bursts, and the right panel focuses on bursts with durations longer than 1 ms. In the right panel, the sample is divided into two groups: SGR 1935+2154 and all other magnetars, with each distribution normalised by its respective sample size so that their histogram sums to 1. The red dash-dotted line represents Swift J1555.2$-$5402 (Swift J1555), the yellow dashed line represents Swift J1818.0$-$1607 (Swift J1818), and the green dotted line represents SGR 1830$-$0645 (SGR 1830). The histograms of these three samples are filled for clarity. The blue long-dashed line corresponds to SGR 1935+2154 (SGR 1935), and the black solid histogram represents all bursts. The gray histogram shows all samples except SGR 1935+2154. The blue and the gray curves indicate the log-normal fits to the normalized SGR 1935+2154 and other samples, respectively.
• Figure 3: Light curves of the $\mu$s-scale bursts with 0.3 $\mu$s time bins. The left panel shows the burst with a $T_{90}$ of 0.6 $\mu$s, with the zero point at 2018-11-22T11:58:14.425441 (TDB). The right panel shows the burst with a $T_{90}$ of 5 $\mu$s, with the zero point at 2022-07-24T23:59:07.273212 (TDB). The black vertical dashed lines indicate the Bayesian block boundaries, and the red dotted lines mark the calculated $T_{90}$ intervals.
• Figure 4: Hardness ratio distribution of all bursts. Different histograms represent magnetar groups as defined in Figure \ref{['fig:T90']} and indicated in the legend. The blue curve shows the normal distribution fit to the SGR 1935+2154 sample.
• Figure 5: Blackbody temperature $kT$ (top) and flux $F_{\rm{BB}}$ (bottom) distributions of all bursts. Different histograms represent magnetar groups as defined in Figure \ref{['fig:T90']} and indicated in the legend. For the $kT$ distribution, most Swift J1818.0$-$1607 bursts have fewer than 20 counts, and their $kT$ values were fixed during spectral fitting; therefore, this sample is not plotted separately on the top panel.