Rotation-powered pulsars exhibit stable emission characteristics most of the time. However, their radiative state can vary with the sudden changes of rotational state such as glitches. To date, pulsed radiation changes associated with glitches have only been detected in the radio band. Since the emission regions of radio and γ-ray may differ, searching and investigating whether glitches can induce changes in high-energy radiation would further deepen our understanding of how glitches affect the magnetosphere of pulsars. We report successive variations in the γ-ray pulsed radiation of PSR J0205+6449 following the glitch at MJD 54904 observed by the Fermi/LAT. The amplitude ratio of the two peaks showed a hint of an increase during MJD 54905–54940 initially, followed by a recovery to the mean level and a significant (>5 σ) decrease in the separation between the two peaks over MJD 54940–55000. The amplitude ratio of the two peaks increased (∼3 σ) again in MJD 55000–55160, accompanied by a marginal flux variation. Finally, the pulsed radiation reverted to its normal state. This is the first significant detection of pulsed radiation variation associated with a glitch in γ-ray pulsars. We attribute this to magnetospheric reconfiguration triggered by localized crustal breaking and associated elastic displacement near the polar cap following the glitch.

With the growing number of gamma-ray monitors in operation, several research teams have adopted a strategy of joint operation and scientific duty to improve efficiency. A successful example is the GECAM–HXMT–SVOM (GHS) constellation collaboration, which sets a precedent for other gamma-ray monitor constellations. However, joint duty also presents challenges to burst advocates (BAs), including an increased number of triggers and, more importantly, frequent switching between various systems due to incompatibilities among different missions, which complicates the situation. To address the current requirements of multiwavelength and multimessenger astronomy, we developed a customized framework for unified trigger processing within the GHS joint duty, named “BAs’ Rapid Evaluation and Analysis Kit for Formulating Alerts and Summary Tools” ( BREAKFAST ). This framework incorporates a series of automated, semiautomated, and manual pipelines designed to rapidly process triggers of prompt emissions in the gamma-ray band from different instruments, while maintaining flexible compatibility for future missions. The pursuit of BREAKFAST goes beyond merely providing trigger processing for BAs. BREAKFAST also aims to identify high-value targets through rapid analysis and to guide follow-up telescopes by providing timely reports, thereby serving as an important bridge between prompt-emission observations and afterglow observations. To this end, a suite of comprehensive analysis modules is included in BREAKFAST , particularly the specially designed module that predicts X-ray afterglow brightness based on prompt-emission properties. The framework’s effectiveness has already been demonstrated in recent observational campaigns, and it is expected to play a significant role in the discovery and observation of peculiar transients in the future.

Abstract Following the orbit insertion of the Einstein Probe satellite, we conducted the first five-month test monitoring campaign of 1E 2259+586, 4U 0142+61, and 1E 1048.1−5937 using the Follow-up X-ray Telescope. No significant bursting activity was detected from any of the three sources during this interval. Timing analysis reveals that the spin peri- ods of 1E 2259+586 and 4U 0142+61 remained stable, with measured frequencies of 0.143279150(2) Hz and 0.115001270(2) Hz, respectively. In contrast, 1E 1048.1−5937 ex- hibited a measurable spin-frequency derivative of −20(3) × 10−15, with a spin frequency of 0.154749612(5) Hz. Spectral analysis indicates that the soft X-ray emission is well described by either an absorbed double blackbody model or a blackbody plus power-law model. Under the blackbody plus power-law model, the best-fit parameters are: for 1E 2259+586, Γ ∼ 3.61, kT ∼ 0.42 keV, and an unabsorbed flux of 1.613 × 10−10 erg cm−2 s−1, for 4U 0142+61, Γ ∼ 3.31, kT ∼ 0.37 keV, and an unabsorbed flux of 1.937 × 10−10 erg cm−2 s−1, and for 1E 1048.1−5937, Γ ∼ 3.21, kT ∼ 0.66 keV, and an unabsorbed flux of 4.52 × 10−10 erg cm−2 s−1. The blackbody temperatures (kT ≈ 0.3 − 0.7 keV) are consistent with thermal emission from the hot neutron star surface. The power-law component exhibits a pho- ton index of Γ ≈ 3 − 4, indicating a soft spectrum that is likely produced by magnetospheric radiative processes. By leveraging the high spatial resolution and superior imaging capabil- ities of EP-FXT, this study presents a comprehensive diagnostic of the timing and spectral properties of these magnetars, demonstrating the unique value of EP-FXT for characterizing dynamic celestial sources.

Abstract High-energy cosmic-ray monitoring in low Earth orbit (LEO) is important for space science and exploration, yet it is usually limited to the dedicated cosmic-ray detectors. Here we show that GECAM, although designed as a gamma-ray all-sky monitor, can monitor high-energy cosmic rays through its novel design of simultaneous-event (STE). We first combine multi-component incident-particle models with \textsc{Geant4} simulations to calibrate the particle component--energy--multiplicity response of STE, and then apply to the GECAM observation data during geomagnetic storms. The simulations show that STE signals are dominated by GeV--TeV protons, whereas the highest-fold channels, especially STE(21--25), contain a significant contribution from $\sim 10$--$20$ GeV electrons. Thus, STE(5--20) mainly trace rigidity-dependent variations of primary protons, while STE(21--25) provides an electron-sensitive diagnostic. By analyzing the GECAM observation data during geomagnetic storms, we find a STE multiplicity-dependent response which is consistent with rigidity-dependent Forbush modulation and time-dependent geomagnetic transmissivity near cutoff and penumbral regions. These results demonstrate that GECAM can monitor high-energy cosmic-ray variations in LEO as a Micro Cosmic-Ray Observatory (MICRO), complementing those dedicated cosmic-ray instruments.

The spectral evolution characteristics of the prompt emission in gamma-ray bursts (GRBs) have been extensively studied, but detailed investigations of the spectral evolution in a GRB flare remain lacking. In this work, we present the first analysis of spectral parameter evolution in a GRB flare through high-time-resolved spectral fitting of the brightest flare in GRB 221009A. We find that the alpha-flux, Ep-flux, and Ep-alpha relationships during both the overall phase and the rising phase of the flare can be well described by a simple power-law model, showing positive correlations. Therefore, we conclude that the brightest flare exhibits "double-tracking" behavior. Since values of alpha do not exceed the synchrotron "death line" (-2/3), we explain this phenomenon using the magnetic dissipation synchrotron radiation model. In the decay phase of the flare, the Ep-flux and Ep-alpha correlations become notably flatter, with their power-law indices decreasing significantly compared to those in the rising phase. This may be due to the fact that the next flare begins to erupt before the brightest flare has completely ended, resulting in the combined effects of both two flares. Our study of the spectral parameter relations of the brightest flare provides new insights into the radiation mechanisms of both the GRB prompt emission and flares.

Silicon photomultiplier (SiPM) has been increasingly used in detectors of space telescopes. As a critical parameter of SiPM, dark current could be affected by many factors, such as temperature, overvoltage, and radiation damage. However, how the dark current of SiPM evolves in long-term under different space environments has not been systematically studied yet. SiPM is utilized in a series of GECAM instruments operating in different orbits and conditions, which provides a great opportunity to study this problem. Here, we present the first results on the SiPM dark current long-term (up to 5 yr) evolution of GECAM instruments, including GECAM-A, GECAM-B, and GECAM-C. We find that, while the short-term variation of SiPM dark current is primarily caused by the temperature fluctuation, the long-term evolution is predominantly determined by the accumulated radiation dose. Based on the GECAM design, we developed a model to describe the long-term evolution of the SiPM dark current, and all the long-term dark current evolution of GECAM-A/B/C could be well fitted by our model. Based on the comparison between GECAM instruments, it is evident that the SiPM dark current growth rate is independent of the working status of the SiPM but dependent on the radiation level, which is closely related to the altitude of orbit (500-600 km). We also find that the growth of the dark current can explain the decrease in energy gain of the detector. These results provide important guidelines for the performance study and prediction of GECAM instruments as well as the design of SiPM-based detectors of future missions.

As one of the primary scientific payloads on board the Fermi Gamma-ray Space Telescope, the Gamma-ray Burst Monitor (GBM) is designed to detect and study gamma-ray bursts as well as other high-energy transient events, including solar flares, magnetar bursts, and terrestrial gamma-ray flashes. A major challenge in GBM observations is the highly complex and variable background radiation, which can obscure astrophysical events and degrade subsequent analysis. Reliable background modeling is therefore crucial for reliable signal extraction and for enhancing the overall scientific performance of the instrument. We present a deep neural network approach for background spectral modeling of the GBM detector. Built on the transformer framework, our model uses intragroup multilayer perceptron encoding and intergroup multihead self-attention to capture complex dependencies among diverse physical variables. A learnable gating mechanism adaptively fuses the global context with feature-group information, enabling the model to simultaneously exploit global context and local physical correlations and thereby improve background estimation. Experimental results show that the model predicts light curves comparable to and in some cases better than those from orbit-level revisit analyses. For spectral reconstruction, the model predicts across 118 energy channels every 4.096 s, with more than 98% of channels showing standardized residuals lying within the +/- 3 sigma range.

Massive stars die as core-collapse supernovae, whose optical light emerges days after the implosion. Theory predicts that the initial collapse-driven shock, upon breaking through the star and dense circumstellar medium, emits a brief thermal flash of soft X-rays and ultraviolet. Yet these elusive first signals have remained largely undetected, owing to limited wide-field soft X-ray monitoring. Here we report the discovery of a soft X-ray flash, EP260321a, followed days later by a broad-lined supernova from an envelope-stripped progenitor. Its X-ray spectrum, best modeled with blackbody, establishes it as the long-sought archetypal shock breakout. The burst's duration and energetics place the breakout at a radius of 300 solar radii, tracing a dense surrounding shell and revealing abrupt mass ejection within the final month before collapse.

Flares are usually observed during the afterglow phases of Gamma-ray bursts (GRBs) in the soft-X-ray, optical, and radio bands—but rarely in the gamma-ray band. Despite its extraordinary brightness, GECAM-C has accurately measured both the bright prompt emission and flare emission of GRB 221009A without instrumental effects, offering a good opportunity to study the relation between them. In this work, we present a comprehensive analysis of the flare emission of GRB 221009A, which is composed of a series of flares. Among them, we identify an exceptionally bright flare with a record-breaking isotropic energy E _iso = 1.82 × 10 ^53 erg for GRB flares. It exhibits the highest peak energy ever detected in GRB flares, E _peak ∼ 300 keV, making it a genuine gamma-ray flare. It also shows rapid rise and decay timescales, significantly shorter than those of typical X-ray flares observed in the soft-X-ray or optical bands but comparable to those observed in prompt emissions. Despite these exceptional properties, the flare shares several common properties with typical GRB flares. We note that this is the first observation of a GRB flare in the keV–MeV band with sufficiently high temporal resolution and high statistics, bridging the last gap between the prompt emission and flare.

POLAR-2, the successor of the POLAR experiment aboard China’s Tiangong-2 space lab, is set to be deployed on the China Space Station. The POLAR-2 mission aims to conducting high-precision polarization measurements of high-energy transients with a primary focus on Gamma-Ray Bursts (GRBs), following POLAR’s pioneering accurate polarization measurements of GRB prompt emission. One of the key advancements in POLAR-2 is the inclusion of a dedicated Broad-band Spectrometer Detector (BSD) instrument, designed to provide precise measurements of GRB location and spectral parameters, which are critical inputs for accurate polarization analysis of POLAR-2’s dedicated High-energy Polarimetry Detector (HPD), which is made of plastic scintillator bars array. BSD employs a coded-aperture mask imaging technique and pixelated GAGG scintillation crystals, offering a wide half-coded field of view of ∼ 132^∘× 125^∘ and an operational energy range of 10–1000 keV. Simulation results indicate that the instrument can achieve a localization accuracy of approximately 1.5^∘ for faint GRBs similar to GRB 170817A, satisfying the core requirements of GRB polarimetry with HPD. BSD also has moderate capability for GRB polarimetry, particularly at several hundred keV energy. This paper outlines the preliminary design of BSD and presents an overall evaluation of its expected scientific performance, based on extensive Monte Carlo simulations and preliminary ground-based calibration tests.

Flares are usually observed during the afterglow phase of Gamma-Ray Bursts (GRBs) in soft X-ray, optical and radio bands, but rarely in gamma-ray band. Despite the extraordinary brightness, GECAM-C has accurately measured both the bright prompt emission and flare emission of GRB 221009A without instrumental effects, offering a good opportunity to study the relation between them. In this work, we present a comprehensive analysis of flare emission of GRB 221009A, which is composed of a series of flares. Among them, we identify an exceptionally bright flare with a record-breaking isotropic energy E_ iso = 1.82 × 10^53 erg of GRB flares. It exhibits the highest peak energy ever detected in GRB flares, E_ peak∼ 300 keV, making it a genuine gamma-ray flare. It also shows rapid rise and decay timescales, significantly shorter than those of typical X-ray flares observed in soft X-ray or optical band, but comparable to those observed in prompt emissions. Despite these exceptional properties, the flare shares several common properties with typical GRB flares. We note that this is the first observation of a GRB flare in the keV-MeV band with sufficiently high temporal resolution and high statistics, which bridges the last gap between prompt emission and flare.

GECAM is a constellation of all-sky monitors in hard X-ray and gamma-ray band primarily aimed at high energy transients such as gamma-ray bursts, soft gamma-ray repeaters, solar flares and terrestrial gamma-ray flashes. As GECAM has the highest temporal resolution (0.1 μs) among instruments of its kind, it can identify the so-called simultaneous events (STE) that deposit signals in multiple detectors nearly at the same time (with a 0.3 μs window). However, the properties and origin of STE have not yet been explored. In this work, we implemented, for the first time, a comprehensive analysis of the STE detected by GECAM, including their morphology, energy deposition, and the dependence on the geomagnetic coordinates. We find that these STE probably result from direct interactions between high-energy charged cosmic rays and satellite. These results demonstrate that GECAM can detect, identify, and characterize high-energy cosmic rays, making it a Micro Cosmic-Ray Observatory (MICRO) in low Earth orbit.

We regret that this statement “This work was supported by China’s Space Origins Exploration Program.” was omitted in the beginning of the Acknowledgements.

The Gamma-Ray Monitor (GRM) is a key payload of the Space-based multiband astronomical Variable Objects Monitor (SVOM) mission, which is designed to detect gamma ray bursts (GRBs) within the energy range of 15 keV to 5 MeV. The GRM Instrument Center (GRM_IC) features real-time data processing through the X-band, enabling rapid response of high-energy GRB events. The system employs an event-driven architecture and distributed design, achieving efficient processing and real-time monitoring of massive observational data. Through comprehensive data production processes and scientific data product management, the system achieves efficient production of scientific data products of the L1B / C level through the submission of jobs to the task scheduling system. Through modular architecture design and automated processing workflow, the GRM data processing system realizes precise conversion and scientific analysis of GRB detection data, providing robust technical support for future system upgrades and cross-platform collaboration.

We presented a comprehensive multi-epoch timing and multiwavelength analysis of the accreting millisecond X-ray pulsar MAXI J1957+032, covering two major outbursts in 2022 and 2025. By reanalyzing the 2022 outburst data from the Neutron Star Interior Composition Explorer (NICER), we found the spin frequency and orbital parameters from the observations in 0.3-5 keV. For the 2025 outburst, we reported the detection of pulsations with the Einstein Probe (EP). Based on the similar to 3-year baseline between these two outbursts, we measured a significant long-term spin-down rate of nu(center dot) = (-5.73 +/- 0.28) x 10(-14) Hz s(-1). Assuming that the quiescent spin-down is driven by magnetic dipole radiation, we inferred a spin-down luminosity of L approximate to 1.1 x 10(36) erg s(-1) and a surface dipolar magnetic field of B approximate to (7.3 - 10.4)x10(8) G. Furthermore, we conducted a deep radio pulsation search with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during the X-ray quiescent state in 2024, resulting in a non-detection with a 7 sigma flux density upper limit of 12.3 mu Jy. This corresponds to a radio efficiency upper limit of xi < 2.8 x 10(-10), which is significantly lower than that of typical millisecond pulsars with a similar spin-down power. This profound radio pulsation faintness can be explained by two primary scenarios: either a geometric effect, wherein the pulsar's radio beam is directed away from our line of sight, or a physical suppression of the emission mechanism, potentially caused by a persistent low-level accretion flow during the X-ray quiescent state.

Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a constellation of all-sky monitors in hard X-ray and gamma-ray bands, primarily observing high-energy transients such as gamma-ray bursts, soft gamma-ray repeaters, solar flares, and terrestrial gamma-ray flashes. As GECAM has the highest temporal resolution (0.1 μs) among instruments of its kind, it can identify the so-called simultaneous events (STEs) that deposit signals in multiple detectors nearly at the same time (with a time window of 0.3 μs). However, the properties and origin of STEs have not yet been explored. In particular, STEs may impact the observation of high-energy transients. In this work, we present the first systematic study of the properties of STEs detected by GECAM, including the morphology, energy deposition, and the dependence on the geomagnetic latitude. Based on their properties, we suggest that these STEs probably result from direct interactions between high-energy charged cosmic rays and the satellite. GEANT4 Monte Carlo simulations using the GECAM spacecraft mass model were carried out to provide additional support for this interpretation. Our result indicates that GECAM could potentially detect and characterize the high-energy cosmic rays through STEs, thereby extending its scientific capability.

Fast radio burst (FRB) is mysterious phenomenon with millisecond-duration radio pulses observed mostly from cosmological distance. The association between FRB 200428 and a magnetar X-ray burst (MXB) from SGR J1935 + 2154 has significantly advanced the understanding of FRB and magnetar bursts. However, it is uncertain whether this association between MXB and FRB (i.e. MXB/FRB 200428) is genuine or just coincidental only based on this single event. Here we report the discovery of a bright (similar to 7.6 x 10(-7) erg . cm(-2) in 1-250 keV) magnetar X-ray burst detected by Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) on 2022 October 14 (dubbed as MXB 221014) from SGR J1935 + 2154, which is associated with an FRB detected by Canadian Hydrogen Intensity Mapping Experiment and Green Bank Telescope. We conducted a detailed temporal and spectral analysis of MXB 221014 with GECAM data and find that it is a bright and typical (T-90 similar to 250 ms) X-ray burst from this magnetar. Interestingly, we find two narrow X-ray pulses in the MXB, one of which temporally aligns with the main pulse of the FRB 221014 similar to 5.70 ms latter than the peak time of FRB 221014), resembling the feature found in MXB/FRB 200428. Furthermore, we did comprehensive comparison between MXB/FRB 221014 and MXB/FRB 200428, and find that while the two events share several common features, they also exhibit distinct differences, highlighting the variety of the MXB-FRB association morphology. This finding not only confirms the association between MXB and FRB but also provides new insights into the mechanism of and the relationship between FRB and MXB.

The Pathfinder of the Type-A satellites in the Chasing All Transients Constellation Hunters (CATCH) space mission is equipped with Micro-Pore Optics (MPOs) and four single-pixel Silicon Drift Detectors (SDDs). Due to the lack of position resolution in an individual SDD, we propose a new method based on the cross-arms in the point spread function (PSF) of MPOs to enhance the satellite’s capability in identifying contaminating sources and locating target sources. By placing one detector on each of the horizontal and vertical cross-arms on the focal plane, we can use the changes in the relative counts on the cross-arms detectors to deduce the location of the source. Simulated observations demonstrate that, for a target source with a flux of 1 Crab and an exposure time of 200 s, the cross-arms detectors can identify contaminating source with the same flux level at an off-axis angle larger than 8' , and improve positioning accuracy to 6' . Furthermore, we extend the simulation study to CATCH Type-A, which plans to use an SDD array. In situations where sources exhibit the same flux of 1 Crab and the exposure time is merely 1 s, a 16 × 16 SDD array is capable of identifying contaminating source with an off-axis angle greater than 2.4' and can achieve a positioning precision of 1.8' .

The spectral evolution characteristics of the prompt emission in gamma-ray bursts (GRBs) have been extensively studied, but detailed investigations of spectral evolution in a GRB flare remain lacking. In this work, we present the first analysis of spectral parameter evolution in a GRB flare through high time-resolved spectral fitting of the Brightest Flare in GRB 221009A. We find that the α-Flux, E_p-Flux, and E_p-α relationships during both the overall phase and the rise phase of flare can be well described by simple power-law model, showing positive correlations. Therefore, we conclude that Brightest Flare exhibits "Double-tracking" behavior. Since values of α do not exceed the synchrotron "death line" (-2/3), we explain this phenomenon using a magnetic dissipation synchrotron radiation model. In the decay phase of flare, the E_p-Flux and E_p-α correlations become notably flatter, with their power-law indices decreasing significantly compared to those in the rise phase. This may be due to the fact that the next flare begins to erupt before the Brightest Flare has completely ended, resulting in the combined effects of both two flares. Our study of spectral parameter relations of the Brightest Flare provides new insights into the radiation mechanisms of both GRB prompt emission and flares.