Lin Lin

The Fermi Gamma-ray Burst Monitor (GBM) has been in operation for over 17 yr, during which it has observed more than 1000 bursts from soft gamma repeaters (SGRs), also known as magnetars. Serving as a laboratory for extreme physics, magnetars are a subfamily of neutron stars characterized by extreme magnetic field strength, observed through a combination of persistent and short transient emission across the electromagnetic spectrum. We present the comprehensive GBM catalog of SGR short bursts, which supersedes the 5 yr catalog of A. C. Collazzi et al. The new catalog contains 1254 SGR short bursts observed over 17 yr, providing the longest uninterrupted, high-sensitivity, all-sky monitoring of magnetar bursts with unprecedented spectral and temporal resolution. Our catalog contains bursts from 17 unique Galactic sources, with major contributions by bursts from SGR J1935+2154 and SGR J1550–5418. We present overall characteristics of these bursts, such as the durations, spectral parameters for various photon models, and fluxes, as well as their comparison with recently published catalogs of other missions and the previous GBM magnetar catalog. The machine-readable catalog, as well as burst spectra and response files, are made publicly available for the community.

Polarization measurements of fast radio bursts (FRBs) probe the magnetized plasma surrounding their central engines. FRB 20240114A is an exceptionally active repeating source, with 17,356 bursts detected between 2024 January 28 and 2025 May 30 by FAST, enabling studies of the temporal evolution of its polarization properties. In this work, we present a polarimetric catalog of 6131 bright bursts (with a signal-to-noise ratio (S/N) ≥ 20, 35.3% of the total sample), including arrival time (MJD _topo ), dispersion measure (DM), burst width ( W _eff ), bandwidth, Faraday rotation measure (RM), linear and circular polarization degrees ( L / I , V / I ), and intrinsic polarization angle (PA ₀ ). We confirm a clear temporal evolution of RM: after an initial stable phase, it decreases linearly by ∼200 rad m ⁻² over 200 days, forming a bimodal distribution, whereas DM remains stable at 529.3 ± 1.2 pc cm ⁻³ . The linear polarization fraction is generally high, with the 3 σ lower bound around 76%, while circular polarization is low, with 1157 of 17,356 bursts (6.67%) having ∣ V ∣/ I ≥ 10%. We perform a power-law fit between ∣ V ∣/ I and ∣RM∣, which yields an index of −2.98 ± 0.80. It is found that the combined 2D distribution of L / I versus V / I remains stable, implying that the emission mechanism is largely invariant. Our PA ₀ measurements show a broad, nonuniform distribution, implying a complex emission geometry. These results suggest that FRB 20240114A resides in a dynamically evolving magneto-ionic environment. This catalog provides a foundation for studies of repeating FRB progenitors and their environments.

The magnetar 1E 1841–045 exhibited a new active episode starting on 2024 August 20, marked by X-ray bursts and enhanced persistent emission. Using data from the Einstein Probe (EP), we report on the timing and spectral results following the onset of this outburst. The pulse profile displays a multipeaked structure, with notable phase shifts in the secondary peak. Energy-resolved pulse profile analysis indicates a transition in the dominant peak of the pulse profile above 5.8 keV. The 0.5–10 keV X-ray spectrum is well modeled by a combined blackbody and power-law (BB+PL) model, showing a ∼20% flux increase following the outburst. Phase-resolved spectroscopy indicates a correlation between BB temperature and pulse profile intensity, along with spectral hardening at a specific pulse phase. The high spatial resolution of EP enables effective separation of the supernova remnant emission, which is crucial for measuring the intrinsic pulse emission of the source. These findings underscore the intricate relationship between magnetar outbursts, pulse profile evolution, and spectral characteristics.

This study investigates the morphological classification and drifting rate measurement of the repeating fast radio burst (FRB) source FRB 20240114A using the Five-hundred-meter Aperture Spherical Telescope. Detected on 2024 January 14, FRB 20240114A exhibited an exceptionally high burst rate, revealing unique properties. Through observational campaigns over several months, we selected a data set comprising 3203 bursts (2109 burst clusters) during a continuous monitoring session (15,780 s) on 2024 March 12. Improving upon previous work, we clarify the definitions of sub-bursts, bursts, and burst clusters. Using an average dispersion measures of 529.2 pc cm ⁻³ , we classified the burst clusters into Downward Drifting, Upward Drifting, No Drifting, No Evidence for Drifting, Not-Clear, and Complex burst clusters. Among the 978 burst clusters that exhibit drifting behavior, 233 (23.82%) show upward drifting. Additionally, if 142 upward-drifting single-component burst clusters are excluded, upward-drifting double- and multicomponent burst clusters still account for 10.89% of the 836 burst clusters exhibiting drifting behavior, equating to 91 burst clusters. Furthermore, if only upward-drifting burst clusters with consecutive time intervals (or upward-drifting bursts) are considered, only nine bursts remain. Drifting rate comparisons with other physical quantities reveal that the drifting rate increases with peak frequency for single-component burst clusters with drifting behavior. Moreover, in single-component burst clusters, those with upward drifting exhibit smaller effective widths, bandwidths, and fluxes than their downward-drifting counterparts. A Kolmogorov–Smirnov test further indicates that upward-drifting burst clusters possess longer consecutive time intervals than downward-drifting ones, suggesting distinct underlying physical mechanisms.

The recent launches of the Einstein Probe and the Space Variable Objects Monitor mission have led to the detection of a growing number of long gamma-ray bursts (GRBs) with significant, early soft X-ray flux during their gamma-ray emission, prompting the question of whether their multiband prompt emission shares a common origin in region and mechanism. To address this, we utilize the 20-year Swift archival data, which provides a substantial sample of joint soft X-ray and gamma-ray observations, enabling a systematic joint spectral study. We resolve 110 temporal pulses from 46 GRBs and find that a single power-law model with a low-energy break or cutoff adequately describes the prompt spectra from 150 keV down to 0.5 keV. More than half of the sample pulses require a break around a few keV, with average spectral indices 〈 α ₁ 〉 = −0.88 and 〈 α ₂ 〉 = −1.46 consistent with synchrotron radiation in a marginally fast-cooling regime. The observed spectral evolution and the distribution of indices support a single-emission-region origin, where the varying spectral shapes are largely governed by the evolution of the synchrotron cooling frequency ν _c and the effect of finite emission width. The observed differences in the temporal behavior between X-ray and gamma-ray light curves can be naturally explained by this spectral evolution across the broad band.

A magnetar X-ray burst (MXB) is usually composed of a single pulse or multiple pulses with rapid rise and brief duration mostly observed in the hard X-ray (soft gamma-ray) band. Previous work studied the temporal behavior of some magnetar bursts and employed the fast rise exponential decay (FRED) model to fit pulses of MXB. However, whether there is another kind of pulse shape has not been explored. In this study, we systematically examined the light curve of MXBs from SGR J1935+2154 detected by the Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor between 2021 and 2022. We find that there are different light-curve morphologies. Especially, we discover a peculiar and new pattern, exponential rise and cutoff decay (ERCOD), which is significantly different from FRED and could be well described by a mathematical function we proposed. We find that MXBs with ERCOD shape are generally longer in duration, brighter in the peak flux, and harder in spectrum than those with FRED. We note that the ERCOD shape is not unique to SGR J1935+2154 but also present in other magnetars. This new light-curve pattern may imply a special burst and radiation mechanism of magnetar.

SGR J1935+2154 is an extremely active magnetar and the source of the first fast radio burst in the Milky Way, characterized as a magnetar X-ray burst, but whether the temporal features of this magnetar are specific or not is not well known. Based on data from the Fermi Gamma-ray Burst Monitor (GBM), Gravitational Wave High-energy Electromagnetic Counterpart All-Sky Monitor (GECAM), and Hard X-ray Modulation Telescope (HXMT), we investigate the temporal properties of pulses and bursts, covering parameters such as the minimum variability timescale (MVT), duration, rise/decay/waiting times, skewness, peakedness, pulse width, and number of pulses. Except for the number of pulses, all parameters follow the log-Gaussian distribution. In the GBM and GECAM data, MVT and duration exhibit a negative correlation, while the number of pulses and duration (or MVT) exhibit a positive (or negative) correlation. Universal power-law relationships exist among parameters, for example, rise time is positively correlated with decay time, while decay/rise time (or width) and peakedness show a negative correlation. We did not find a significant difference compared with another magnetar, SGR J0501+4516. Finally, the parameters observed by GBM and GECAM show no significant differences, but some parameters observed by HXMT differ from both, suggesting that they may originate from a different physical mechanism.

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 ∼3σ. 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.

Magnetars are neutron stars with ultrahigh magnetic fields (~10¹⁴–10¹⁵ 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. The 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 2021 January to 2022 December, 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 are detected 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 ± 20 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.