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.

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.

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.

Fast radio bursts (FRBs) are enigmatic cosmic transients of millisecond duration observed in the radio band. The identification of FRB-associated magnetar X-ray bursts (MXBs) from the galactic magnetar SGR J1935+2154 suggests that at least a fraction of FRBs can be produced from magnetar activity. However, the sample size of FRB-associated MXBs is still very small. Here we report a bright and peculiar FRB-associated MXB from SGR J1935+2154 detected by GECAM on November 20, 2022, dubbed MXB 221120. We find that the temporal and spectral properties of MXB 221120 exhibit distinctive features. Its light curve could generally be described by a single FRED function with the superposition of several narrow pulses. Interestingly, we identified a possible quasiperiodic oscillation feature with a center frequency of ∼18 Hz in this MXB. The time-integrated spectrum is best fit by a blackbody model with a temperature (kT) of 18.6 keV, rendering it the first thermal spectrum FRB-associated MXB from SGR J1935+2154. Compared to other MXBs with a single emission episode, MXB 221120 has a longer duration and a higher blackbody temperature, making it an outlier in the burst sample. These results indicate that MXB 221120 may have been produced by a special mechanism with extreme physical conditions.

The Gamma-Ray Monitor (GRM) is a key scientific payload onboard the Space-based Multi-band Variable Object Monitor (SVOM) satellite, designed specifically for the detection and study of gamma-ray bursts (GRBs). Launched into a 625 km low-Earth orbit on 22 June 2024, GRM serves as a large-area, wide-field-of-view instrument capable of observing the hard X-ray and soft gamma-ray emissions in the energy range of 15 keV to 5 MeV. Its primary scientific objectives include: promptly triggering and localizing GRBs (with particular sensitivity to short-hard GRBs), measuring spectral and temporal properties of bursts, monitoring charged particle fluxes in orbit. GRM successfully detected its first GRB (GRB 240627B) on 27 June 2024, and has since maintained a detection rate of more than 100 GRBs per year. Cross-instrument comparisons with detectors such as GECAM and Fermi/GBM have validated the performance and data quality of GRM. This paper provides a comprehensive overview of GRM instrument design, reliability verification through ground testing, in-orbit triggering and localization algorithms, performance calibration, and preliminary in-orbit results, demonstrating its capability as a versatile gamma-ray all-sky monitor.

POLAR-2 is a Sino-European collaborative mission designed to measure the polarization of gamma-ray burst prompt emissions, scheduled for installation on the China Space Station around 2028. To improve the accuracy of GRB polarization measurements and minimize systematic uncertainties, the Broad-band Spectrometer Detector (BSD) was designed to locate GRBs and measure their spectral parameters in the 10-1000 keV energy range with a target energy resolution of similar to 30% at 60 keV. The BSD employs coded-aperture mask imaging technology and primarily consists of a coded-aperture mask plate, 36 detector modular units (each comprising a GAGG crystal array coupled with a SiPM array and front-end electronics), and back-end electronics. For the detector modular unit prototype of BSD, a dedicated test system was designed to verify and evaluate its functionality and performance. The prototype test system includes the front-end electronics, an 8 & times; 8 GAGG scintillator array, a readout system based on a Zynq development board, and a host computer. This paper describes the components of the BSD detector modular unit prototype test system, focusing primarily on the hardware architecture and functionality of the detector's front-end electronics. Performance evaluations of the prototype were carried out under laboratory conditions, and the corresponding results are presented and analyzed. The tests verified the functionality of the system and electronics, evaluated the detector performance with radioactive sources, and investigated the influence of parameter variations on performance metrics. Analysis of the energy spectra identified configuration parameters that meet the design requirements. These parameters were then applied to assess the performance of all 64 detector channels, revealing significant inter-channel variations. Additional tests with different GAGG array dimensions and coupling schemes were performed to study the crosstalk effect of the crystals between channels. The performance study of the prototype not only supports the development and project initiation of the BSD detector but also provides a foundation for further optimization and improvements.

The SVOM mission is specifically designed to for the detection and localization of Gamma-Ray Bursts (GRBs) and subsequent follow-up observations. Among the four telescopes installed on the SVOM satellite, the Gamma-Ray Monitor (GRM) plays a crucial role in capturing the prompt emission of GRBs due to its wide field of view (FOV) and broad energy range. Accurate determination of the detector's energy response is vital for analyzing GRM data, particularly considering the significant impact of the atmospheric albedo effect on this response. This research focuses on deriving the detector's energy response and establishing a calibration database for the GRM, with particular emphasis on investigating the atmospheric albedo effect. The study shows that the contribution of albedo photons to the detector's effective area depends strongly on the orientation of the GRD line of sight (LoS) relative to Earth and on the incident direction of the GRB. When the GRD LoS is anti-Earth oriented, the albedo effect is minimal, with the highest proportion of albedo effective area accounting for approximately 10

The Space multi-band Variable Object Monitor (SVOM) is an astronomical satellite jointly developed by China and France, primarily focused on the detection of gamma-ray bursts (GRBs) and transient sources. The SVOM satellite was launched on 22nd June, 2024 with four payloads installed onboard. As one of payload, GRM comprises 3 gamma-ray detectors (each detector has an effective area of approximately 200 cm^2) with distinct pointing directions, enabling the temporal and spectral measurements as well as localization of GRBs in the energy range of 15-5000 keV. This article firstly introduces the on-board localization algorithm design for GRM and presents preliminary test results. Then, leveraging abundant ground-based computational resources, a joint fitting method for spectral and localization analysis using Monte Carlo Markov Chain (MCMC) is implemented. In contrast to the on-board localization algorithm, the on-ground MCMC method comprehensively considers the influence of spectral characteristics, thereby mitigating systematic biases. Finally, a systematic analysis based on this method is provided, highlighting the localization and spectral measurement capabilities of GRM. The preliminary localization analysis result for the on-board detected GRB 240629A by both GRM and Fermi/GBM shows that the localization result (error∼4.14^∘) of GRM is consistent with the Fermi/GBM result.

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a collaborative satellite developed by China and France, specifically designed for observing and studying Gamma-Ray Bursts (GRBs) as well as other variable sources. Among its four on-board payloads, the Gamma-Ray Monitor (GRM) is responsible for detecting high-energy photons ranging from 15 keV to 5 MeV, equipped with real-time triggering and localization capabilities. In this paper, we primarily focus on investigating the triggering performance of GRM. Firstly, the energy response matrix of each detector is obtained by using the Geant4 simulation toolkit. Based on the results of background simulations and given samples of GRB, the instrument’s sensitivity and the detection efficiency to GRBs from different directions are estimated. The results demonstrate that GRM exhibits superior sensitivity to GRBs with harder energy spectrum, enabling more than 80% of the GRBs to be triggered within its field of view. By considering satellite orbit and attitude, we conduct a 3-year simulation of GRB observations which reveals that approximately 106 GRBs can be detected annually in the energy range of 50-300 keV by GRM. Moreover, it is observed that optimal triggering energy range correlates with the hardness index values of the GRBs. Finally, we discuss the on-orbit triggering algorithm that has been implemented by GRM along with developing a ground-based multi-timescale search algorithm for identifying potential GRB events. Our work contributes to understanding the on-orbit triggering performance characteristics demonstrated by GRM, while also providing a benchmark for refining ground-based strategies focused on detecting new instances of GRBs, thus amplifying the scientific output obtained from utilizing GRM’s capabilities.

The prompt emission of gamma-ray bursts (GRBs) could be composed of different spectral components, such as a dominant nonthermal Band component in the keV–MeV range, a subdominant quasi-thermal component, and an additional hard nonthermal component extending into the GeV range. The existence and evolutionary behaviors of these components could provide essential constraints on physical models, such as ejecta composition and dissipation processes. Although numerous GRBs have been found to exhibit one or two spectral components, reports of GRBs containing all three components remain rare. In this Letter, based on the joint observations of GRB 240825A from multiple gamma-ray telescopes, we conduct a comprehensive temporal and spectral analysis to identify the presence and evolution of all three components. The bulk Lorentz factor of this bright and relatively short-duration burst is independently obtained from the thermal and hard nonthermal components, supporting a jet penetration scenario. The multisegment broken power-law feature observed in the flux lightcurves suggests the presence of an early afterglow in the keV–MeV band and hints at a possible two-jet structure. Furthermore, the observed transition from positive to negative on the spectral lag can be interpreted as misalignment in the cross-correlation function analysis of pulses, which is caused by evolution of the soft and hard components.

The Space-based multiband astronomical Variable Objects Monitor (SVOM) detected its first short gamma-ray burst (GRB), GRB 240715A, in flight, which was jointly observed by Fermi. Based on observational data of SVOM/GRM and Fermi/GBM, we perform a comprehensive temporal and spectral analysis of individual pulses in the prompt emission of this burst, and novel characteristics are revealed. First, opposite evolutions of spectral lag are found in the first and third pulse of this burst. Second, the large negative lag of the first pulse is an outlier in the short GRB sample, especially when the pulse duration is considered. Spectral analysis shows that the negative lag of the first pulse is caused by the evolution of the spectrum index and is irrelevant to E _peak , which is inconsistent with the previous study. The intrinsic mechanism is probably attributed to electron cooling in the decaying magnetic field, which leads to the continuous hardening of the spectrum index and results in negative lag. Furthermore, spectral analysis also shows that the third pulse is more likely to be described by a quasi-thermal spectrum, indicating the existence of photospheric emission. It is difficult to explain how the synchrotron radiation appears before photospheric emission in a single GRB, and some assumptions are discussed.

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 the increased number of triggers and, more importantly, the frequent switching between various systems due to incompatibilities among different missions, which complicates the situation. To address the current requirements of multi-wavelength and multi-messenger astronomy, we developed a customized framework for unified trigger processing within the GHS joint duty, named "BA's Rapid Evaluation and Analysis Kit for Formulating Alerts and Summary Tools" (BREAKFAST). This framework incorporates a series of automated, semi-automated, 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 filtering high-value targets and guiding follow-up telescopes through rapid analysis and reporting, thus 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.

Type I gamma-ray bursts (GRBs) are believed to originate from compact binary mergers usually with a duration of main emission less than 2 s. However, recent observations of GRB 211211A and GRB 230307A indicate that some merger-origin GRBs could last much longer. Since they show strikingly similar properties (indicating a common mechanism), which are different from the classic “long”-short burst (e.g., GRB 060614), we find they form an interesting subclass of type I GRBs, and we suggest to name them as type IL GRB. We find that the prompt emission of type IL GRB is composed of three episodes: (1) a precursor followed by a short quiescent (or weak emission) period, (2) a long-duration main emission, and (3) an extended emission. With this burst pattern, a good candidate, GRB 170228A, was found in the Fermi/Gamma-ray Burst Monitor archive data. Temporal and spectral analyses indeed show that GRB 170228A falls in the same group with GRB 211211A and GRB 230307A in many diagnostic figures. Thus, this burst pattern could be a good reference for rapidly identifying type IL GRBs and very helpful for conducting low-latency follow-up observation. We estimated the occurrence rate and discussed the physical origins and implications for the three emission episodes of type IL GRBs. Our analysis suggests the premerger precursor model, especially the magnetar super flare model, is more favored for type IL GRBs. More observations in multiwavelength and multimessenger are required to deepen our understanding of this subclass of GRB.

As an interesting subclass of gamma-ray bursts (GRBs), Type IL GRBs (such as GRB 211211A and GRB 230307A) features a long-duration prompt emission but originating from a compact binary merger. The “long duration” emission of Type IL GRBs are dominantly composed of the main burst, rather than the extended emission, differentiating them from the traditional “long-short” GRB (e.g., GRB 060614). A previous study has reported several Type IL GRBs by visual inspection of their light curves. In this work, we established a detailed criterion to identify Type IL GRBs by light curve and then systematically searched the archival Fermi/Gamma-ray Burst Monitor data with this criterion, resulting in a sample of five type IL GRBs from 2014 January 1 to 2024 January 1, i.e., GRB 230307A, GRB 211211A, GRB 200914A, GRB 200311A, and GRB 170228A. Apart from the light-curve pattern, we find that the temporal and spectral properties of these five GRBs also support this classification. Interestingly, we find that the energy ratio between extended emission and main emission is almost constant (∼0.7, with small scattering) for these GRBs, which have strong implications on the mechanism of Type IL burst. We discuss theoretical models to interpret the progenitor, central engine, and extended emission of these Type IL bursts.

The 100 m long X-ray test facility (100XF for clarity) in Institute of High Energy Physics of CAS has been playing an increasingly important role in the X-ray astronomy field in China. 100XF has been contributing to the missions under development, such as the Einstein Probe mission. The facility has also been providing support to R&D of focusing X-ray optics in China that will enable future X-ray telescopes to be realized, such as the enhanced X-ray Timing and Polarization (eXTP) mission. A pnCCD-based camera has been employed at 100XF to rapidly measure the performance of the X-ray optics. In this work, we study the performance of the camera and its spectral and imaging applications at 100XF. The camera system can provide a high frame readout rate, with a low readout noise <3 e−. It is sensitive to X-ray photons in the 3–10 keV energy band with a high quantum efficiency exceeding 90%. Actually, the low threshold of detection energy range can reach down to 0.2 keV. The energy resolution can reach 145.2 eV for single events and 154.8 eV for all valid events (including single events and split events) at 6.4 keV. The camera also exhibits excellent imaging capability in both the full frame mode and the windowing mode, with a readout rate of up to 1000 Hz. Finally, a prototype of a focusing X-ray mirror shell of eXTP was smoothly measured with this camera. The obtained on-axis point-spread function and half-power diameter are consistent with expectations. It is proven that the camera can improve the capability of 100XF in characterizing the X-ray optics. This camera will be very useful for performing on-ground calibrations for future X-ray telescope missions.

It has been more than half a century since the serendipitous discovery of gamma-ray bursts (GRBs, a kind of extreme violent emission of short-duration flashes of gamma-rays occurring randomly over time and in space at cosmological distances), made by the Vela satellites. So far, the observed samples of GRBs have been greatly improved, and the theoretical studies have also made remarkable achievements. However, there are still many unanswered questions about GRBs, such as their classification and origin(s), the composition of the relativistic jet in which the gamma-rays are generated, the radiation mechanism and the magnetic field configuration, etc. Among the questions, a variety of theoretical models have been proposed for interpreting the radiation mechanism of GRBs, and different models predict different polarization properties of the gamma-rays generated during prompt emissions. Accordingly, the polarization measurements can be used to study the mechanism of GRBs and to understand the physical properties such as the structure of the extreme relativistic jet that generates gamma-rays and the configuration of its magnetic field. However, technically it has been quite challenging to measure the polarizations of GRBs during their prompt emissions. Fortunately, some newly developed polarimeters in recent years have overcome major technical difficulties on polarization measurements in space, openning a new window for space hard X-ray/gamma-ray polarimetry. The gamma-ray burst polarimeter POLAR, which was launched onboard the China's space lab "Tiangong-2" on 15th September 2016, is a space mission dedicated for the polarization measurements of GRB prompt emissions in the 50-500 keV energy range, under the collaboration between Chinese and European scientists. During the about 6 months of space observation, POLAR detected 55 confirmed GRBs jointly with other missions and some possible individual GRBs by itself. The first detailed polarization measurements with high precision for 5 GRBs detected by POLAR have been published in 2019, and finally a catalog of 14 GRBs polarization measurement results in total was published, which is the best GRB polarization measurement results so far thanks to the high sensitivity and large field of view of the instrument, as well as the precisely calibrated systematic errors for polarization measurements. The results show that the detected GRBs are at most modestly polarized. Another new finding of the evolution of the intrapulse polarization angle provides us with a new insight into the GRB physics. POLAR results raised large interests as well as several critical scientific questions regarding GRB physics. Furthermore, the scientific potentials of POLAR have been extended during the flight by optimizing the working parameters which enabled the instrument to detect the Crab pulsar for navigation test studies, as well as several solar flares. The POLAR-2 mission, which is the successor of POLAR, aims to answer some key questions raised by POLAR with the launching date around 2025. In this paper, we first give a brief introduction to POLAR, then present the polarization measurement results of detected GRBs and the progress of the navigation test using the observed pulsar signals. In addition, a brief introduction is given to POLAR-2, and its preliminary scientific capabilities are prospected.

ABSTRACT The X/gamma-ray polarimetry of the Crab pulsar/nebula is believed to hold crucial information on their emission models. In the past, several missions have shown evidence of polarized emission from the Crab. The significance of these measurements remains, however, limited. New measurements are therefore required. POLAR is a wide Field of View Compton-scattering polarimeter (sensitive in 50–500 keV) onboard the Chinese spacelab Tiangong-2 that took data from 2016 September to 2017 April. Although not designed to perform polarization measurements of pulsars, we present here a novel method, which can be applied to POLAR as well as that of other wide Field of View polarimeters. The novel polarimetric joint-fitting method for the Crab pulsar observations with POLAR, allows us to obtain constraining measurements of the pulsar component. The best-fitting values and corresponding 1σ deviations for the averaged phase interval: (PD = $14\substack{+15 \\-10}$ per cent, PA = $108\substack{+33 \\-54} ^{\circ }$), for Peak 1: (PD = $17\substack{+18 \\-12}$ per cent, PA = $174\substack{+39 \\-36} ^{\circ }$) and for Peak 2: (PD = $16\substack{+16 \\-11}$ per cent, PA = $78\substack{+39 \\-30} ^{\circ }$). Furthermore, the 3σ upper limits on the polarization degree are for the averaged phase interval (55 per cent), Peak 1 (66 per cent) and Peak 2 (57 per cent). Finally, to illustrate the capabilities of this method in the future, we simulated 2 yr observation to the Crab pulsar with POLAR-2. The results show that POLAR-2 is able to confirm the emission to be polarized with 5σ and 4σ confidence level if the Crab pulsar is polarized at $20{{\,\rm per\,cent}}$ and $10{{\,\rm per\,cent}}$, respectively.

伽马射线监视器是SVOM卫星上的大面积、大视场、高探测效率的探测器载荷,主要完成硬X射线、软伽马射线的能谱观测和伽马暴触发.数据管理系统是其重要的组成部分,负责载荷的遥测和遥控,进行探测器科学数据星上的预处理和管理,在轨实时产生伽马暴触发、光变曲线等信息进行快速下传,对伽马暴联合观测和精确定位分析具有重要的意义.文章介绍了伽马射线监视器数据管理系统的物理需求,以现场可编程门阵列和单片机为核心的系统设计方案,以及数据预处理和管理的软件实现方法.各项测试结果表明,伽马射线监视器数据管理系统运行稳定,功能和性能都达到了预期的设计指标.

为了满足向SVOM卫星GRM载荷输出不同能谱和时间间隔分布的γ射线脉冲信号序列需求,设计了一种GRM探头模拟器,它可以根据已知的脉冲序列文件,模拟输出每个探头的脉冲信号.经过测试.该模拟器运行良好,为GEB软件功能测试以及性能验证提供了可靠的数据源.