In theory, burst activity of the magnetar can lead to the formation of fireballs trapped by the magnetic field and corotating with the star. However, smoking-gun observational evidence of the fireball is elusive. We envisage that the fireball emission should occasionally be eclipsed by the magnetar, especially when the burst duration is comparable to the magnetar's spin period. In this work, we first discover a peculiar type of burst whose light curve has a plateau-like feature among the long bursts of the magnetar SGR J1935+2154 detected by GECAM and Fermi/Gamma-ray Burst Monitor. Then, based on these bursts, we identified four burst candidates with eclipse-like characteristics. By fitting their light curves with the eclipse fireball model, the viewing angle of the magnetar relative to its spin axis is estimated to be 17 degrees +/- 10 degrees, and the distances from the fireballs to the magnetar are found to be more than 5 times the magnetar's radius, indicating that the fireballs are suspended in the magnetosphere rather than adhering to the magnetar surface. Furthermore, we find that this configuration is well consistent with the implication of the cyclotron resonance scattering feature we found in their spectra. Our results suggest that some intermediate X-ray bursts may originate from magnetic reconnection within the magnetosphere rather than the starquake.

We present a comprehensive multiwavelength analysis of the long-duration gamma-ray burst (GRB) 250424A. Our dataset spans from the prompt gamma-ray emission to late-time optical monitoring, including spectra obtained with the Keck 10\,m telescope. We find that the afterglow light curves display a prominent, simultaneous shallow decay phase in both X-ray and optical bands, followed by an achromatic transition to a standard decay regime. The broadband spectral energy distributions are well-modeled by a single power-law function, indicating a common synchrotron origin for the emission across frequencies. We interpret the afterglow evolution within the framework of a relativistic forward shock refreshed by continuous energy injection. This scenario successfully reproduces the observed temporal and spectral behavior, yielding an isotropic equivalent kinetic energy of $E_{\rm K,iso} \approx 5.5 \times 10^{52}$ erg and an injection index of $q\approx 0.34$ in a constant-density circumburst environment. The shallow decay phase is consistent with sustained energy injection lasting $\sim$ 9 ks. Despite the relatively low redshift, late-time optical observations reveal no distinct supernova component; however, our derived upper limits do not strictly rule out the presence of a typical GRB-associated supernova.

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.

PSR J2021+4026 is a remarkable gamma-ray pulsar exhibiting repeated transitions between high gamma-ray flux (HGF) and low gamma-ray flux (LGF) states. With 17 yr Fermi Large Area Telescope monitoring, we reveal persistent secular evolution and enhanced spin-down rate variability within individual emission states-beneath the quasiperiodic state transitions. After removing discrete jumps, the jump-corrected flux delta F gamma shows a three-phase evolution: rise ( +2.02-0.15+0.17%yr-1 ), decline ( -3.72-0.47+0.34%yr-1 ), and rapid rise ( +14.9-4.4+6.4%yr-1 ), with all rates quoted relative to the long-term mean flux < F gamma > = 7.8 x 10-10 erg cm-2 s-1. Moreover, the flux of the LGF state is gradually approaching the stable HGF level at a rate of +0.72% +/- 0.11% yr-1. These results demonstrate that secular flux evolution in PSR J2021+4026 operates largely independently of discrete state transitions, yet jointly with them drives the system toward a stable high-flux equilibrium.

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.

CATCH-1 is the first pathfinder within the Chasing All Transients Constellation Hunters (CATCH) space mission. Its payloads include the Silicon Drift Detector (SDD) system and light-weight X-ray optics. The main goal of CATCH-1 is to validate key technologies of the timing satellites in the constellation, such as the electronics of the SDD detector system, Micro-Pore Optics (MPO), and the deployable mast. The SDD detector system is required to operate with high energy resolution and dead time to detect various transients. This paper presents the design and performance of the SDD electronics system of CATCH-1. The electronics system comprises frontend electronics (FEE) and a data acquisition system (DAQ). Test results demonstrate that the energy resolution of all four detector channels are better than 150 eV at 5.9 keV, with the energy band ranging from 0.5 to 8 keV, and the dead time is better than 10 mu s, meeting the design specifications.

Context. Be/X-ray binary pulsars exhibit transient outbursts and complex timing behaviour, including millihertz quasi-periodic oscillations (QPOs), whose physical origin and energy dependence remain poorly understood. The bright outbursts of 1A 0535+262 in November 2020 provide an ideal laboratory to investigate these properties. Aims. We aim to characterise the temporal evolution and energy-dependent properties of the millihertz QPO during its 2020 giant outburst, with a focus on trying to detect this feature at lower energies. Methods. We used the multi-Lorentzian fitting framework that was recently introduced to jointly model the power spectra and the real and imaginary parts of the cross-spectrum. Our analysis incorporates simultaneous broadband X-ray observations from the Neutron Star Interior Composition Explorer (NICER) and Insight-HXMT, spanning the 0.2–120 keV energy range. Results. We report the first detection of weak, but significant, millihertz QPOs at low X-ray energies (< 27 keV), extending their detection to a new energy regime. The centroid frequency evolves from 41 to 93 mHz, with the peak root-mean-square amplitude detected in the 50–65 keV range. Throughout the outburst, the QPOs generally exhibit a hard lag between 0.12π rad and 0.9π rad. However, at the outburst peak, the higher-energy bands (> 35 keV) display a soft lag of up to ∼ − 0.93π rad. We propose that interactions between soft seed photons and an extended outflow located outside the magnetosphere can account for the observed hard lags, although the physical origin of the transient soft lags remains uncertain. Furthermore, we detect a double-peaked millihertz QPO only at high energies (E > 35 keV) near peak luminosity. The two peaks maintain an approximately constant separation of 2νspin and exhibit anti-correlated phase evolution. The combination of this constant frequency separation and opposite phase trends is difficult to reconcile within existing theoretical models. Conclusions. Our results indicate that the millihertz QPOs in the Be/X-ray binary 1A 0535+262 are closely linked to the coupled evolution of a soft-photon source and a Comptonising outflow or corona. The joint cross-spectral framework provides a complementary probe of millihertz QPOs beyond traditional power-spectral analyses.

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.

We have conducted a detailed spectral analysis of Swift J0243.6+6124 in its sub-Eddington regime, as observed by Insight-HXMT and NICER during a series of outbursts including the giant one in 2018, and discovered a new transition at L _t ∼ 4.5 × 10 ^37 erg s ^−1 accompanied by the evolution of the spectral parameters, in particular a significant turnover of the blackbody normalization. L _t in the sub-Eddington regime represents the fifth transition luminosity identified so far, further increasing the complexity of Swift J0243.6+6124, and it may be explained by introducing a multipolar magnetic field configuration, where weak (∼2.8 × 10 ^12 G) and strong (∼1.6 × 10 ^13 G) magnetic poles govern the emission at different accretion rates. Such a magnetic field configuration is equivalent to a relatively weak pure dipole magnetic field of ∼6.6 × 10 ^12 G on the scale of the magnetospheric radius, and allows the local magnetic field of the neutron star to exceed 10 ^13 G.

We conduct an in-depth study of the quasi-periodic oscillation (QPO) properties of RE J1034+396 by constructing QPO phase-folded light curves from 10 XMM-Newton observations during 2020–2021. Our analysis reveals that the QPO in the source exhibits two mutually convertible lag-energy modes: “hard lag” and “soft lag.” Despite different lag characteristics, the energy dependencies of the rms amplitude of the QPO under both modes are consistent, suggesting the two types of QPO originate from the same physical mechanism. By performing a spectral analysis, we further find a correlation between time-lag modes and spectral states: the soft lag mode typically corresponds to harder X-ray spectra and higher blackbody temperatures. Through comprehensive comparison of multiple theoretical models, we propose that the relativistic precession model of the corona provides a plausible qualitative explanation for the observed complex phenomena, including time-lag mode transitions, and variations of spectral hardness and QPO signal strength.

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.

We present a multiwavelength analysis of the nearby millisecond pulsar PSR J0437-4715, combining Hubble Space Telescope (HST) far-ultraviolet, ROSAT soft X-ray, and XMM-Newton X-ray data, to model its broadband emission and energy-resolved pulse profiles and infer key stellar parameters via Bayesian inference. The broadband emission includes cold thermal, hot thermal, and nonthermal components: cold bulk surface emission is modeled with a nonmagnetized partially ionized hydrogen atmosphere; hot-spot emission adopts the pulse profile modeling technique with a nonmagnetized fully ionized hydrogen atmosphere model; and nonthermal emission is included as a phase-invariant power-law component. By adopting an informative prior on the hot-spot geometry informed by radio polarization position angle measurements, the joint multi-instrument analysis yields a statistically viable and radio-consistent solution with a gravitational mass of 1.38 +/- 0.03 M circle dot and an equatorial circumferential radius of 13.25 -0.35+0.34 km (68% confidence intervals). The hot-spot geometry consists of two spherical caps with uniform temperature distributions: the primary hot spot is situated at a colatitude of approximate to 130 degrees, and the secondary hot spot lies at a colatitude of approximate to 9 degrees, close to the north pole. It yields tighter radius constraints than HST+ROSAT fits and shifts the radius posterior distribution to larger values relative to NICER-only fits. This work demonstrates the importance of multiwavelength data in refining neutron star mass-radius measurements and resolving geometric degeneracies.

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.

The dominant radiation mechanism that powers the prompt gamma-ray emission in gamma-ray bursts (GRBs) remains poorly understood. High quality, time- and energy-resolved linear polarization measurements of prompt gamma-ray photons can distinguish between synchrotron and inverse-Compton processes and provide crucial constraints on the outflow properties. This will be achieved by POLAR-2 that is proposed as a dedicated GRB polarimeter and successor to POLAR. The High-energy Polarimetry Detector (HPD) is one of the three instruments of POLAR-2 that features significantly improved sensitivity in the 40-1000) keV energy range and a detection area four times larger than that of POLAR. Here we demonstrate the capabilities of the HPD to constrain key physical model parameters by creating and fitting to synthetic sources using a time-resolved spectro-polarimetric theoretical model of prompt GRB emission. The time-resolved spectral and polarization fits are performed using a novel technique featuring maximum likelihood over an unbinned (in time and energy) list of detected events. The constrained model parameters directly relate to the underlying source physics that would reveal an accelerating, coasting or decelerating emission region. For a pulse fluence of F=10(-5)F(-5)ergcm(-2) and higher we can constrain the time-integrated polarization degree to an absolute accuracy (1 sigma) of about 2.2F(-5)(-1/2) per cent, as long as source photons dominate over the background. In bright GRBs, such unprecedented accuracy at these energies will allow to distinguish between different models for the prompt GRB emission mechanism and constrain the magnetic field geometry, jet angular structure and outflow composition.

We present a detailed polarimetric analysis of Cen X-3 using IXPE observations during its high state, revealing a complex, energy-dependent polarization behavior. While phase-averaged polarization shows marginal energy dependence, phase-resolved analysis reveals that the energy dependence of the polarization angle is strongly phase-dependent, with dramatic variations visible in a few specific phase intervals. We modeled this behavior using a two-component polarization framework consisting of a pulsed component governed by the rotating vector model (RVM) and an additional phase-dependent component. By allowing the additional component’s polarized flux to vary with pulse phase while fixing its PA, the observed complex behavior can be reconciled with a single set of RVM parameters across all energies. Spectroscopic analysis using IXPE, NICER, and NuSTAR during the high state reveals phase-modulated intrinsic hydrogen column density and covering fraction, suggesting that the wind properties are modulated with pulse phase. Our findings indicate that phase-dependent scattering in the disk wind may significantly alter the observed polarization properties of X-ray pulsars.

The polarization signatures of Gamma-ray Burst (GRB) afterglows serve as a powerful diagnostic tool for studying their environments and jet physics. This work systematically investigates the X-ray (2–8 keV) polarization properties of standard GRB afterglows and assesses their detectability with the Polarimetry Focusing Array aboard the enhanced X-ray Timing and Polarimetry (eXTP) satellite. A Morris global sensitivity analysis is first conducted to identify the dominant parameters, which are then assigned observationally motivated probability distributions. In particular, the isotropic energy, half-opening angle, and initial Lorentz factor are sampled jointly via a Gaussian copula to reproduce the empirical Ghirlanda and Liang correlations. Monte Carlo simulations of 10^3 afterglows are performed and validated against the observed 10 keV flux distributions of a selected Fermi–Swift sample (K–S p = 0.29 at 10^3 s and p = 0.18 at 10^4 s). The simulations yield an overall polarization event rate of ≲ 1.5% for standard GRB X-ray afterglows with eXTP/PFA, reflecting the intrinsically low polarization produced by a random magnetic field confined to the shock plane. The optimal detection window occurs near the jet break at late times, when the PD peaks. For exceptionally luminous events such as GRB 221009A, however, the PD remains above the MDP over the full interval 10^3–10^6 s, demonstrating that eXTP/PFA can capture nearly the entire polarization evolution for such rare, bright bursts.

Gamma-ray bursts (GRBs) are the most energetic explosive events in the Universe, yet the physical mechanism of their prompt emission remains a mystery. Especially, it is unclear whether the energy dissipation mechanism in the GRB jet is dominated by kinetic energy or magnetic energy. Here, we studied the pulses in the prompt emission of the second brightest GRB to date, GRB 230307A, which was accurately measured by the Gravitational wave high-energy electromagnetic counterpart all-sky monitor (GECAM), with focus on the cumulative distributions of peak counts and duration of pulses as well as the waiting time between pulses. We find that these cumulative distributions show scale-invariant behavior, well consistent with the prediction of the self-organized criticality (SOC) theory. This is the first robust evidence of an SOC feature in the prompt emission of a single GRB. Moreover, the statistical properties of pulses in the prompt emission of GRB 230307A are very similar to those of solar flares. Our findings suggest that the prompt emission of GRB is powered by the dissipation of magnetic energy in the ultra-relativistic jet, supporting the Poynting-flux-dominated prompt models.