高能暂现源 · 每日文献综述

Broadband observations with the Fermi mission reveal that a large fraction of gamma-ray burst (GRB) spectra are dominated by nonthermal emission, while a small fraction are dominated by thermal/quasi-thermal emission, likely indicating the difference in jet composition among GRBs. By selecting two typical long GRBs (080916C and 090902B) and two short GRBs (130603B and 090510), we present a comparative analysis to investigate whether the composition of prompt GRB jets influences the afterglow emission for bursts originating from both massive star collapse and compact binary mergers. Incorporating emission from both primary and cascade electron populations, we fit the multiwavelength afterglow lightcurves of these GRBs with the standard forward shock model and analyze the particle acceleration and radiation physics of the jets. Our results show that the afterglow lightcurve evolution with the characteristic parameters is not related to the composition of the GRB fireball but rather depends on the ambient medium density. The early UV-optical afterglows of the two long GRBs are dominated by synchrotron emission from cascaded e<SUP>±</SUP> pairs produced via the γγ annihilation process, whereas this is not the case for the two short GRBs. These results suggest that the internal energy of the fireball is converted into jet kinetic energy during the prompt phase, and that the fireball composition leaves no detectable footprint on the afterglow jet. Instead, the density of the ambient medium plays an essential role in shaping the afterglow emission.

The Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) produces a large postdetection candidate stream in which genuine astrophysical sources coexist with instrumental artifacts and cosmic-ray events. We present M-EPDet, a three-step postdetection framework for real-time candidate vetting in EP-WXT lobster-eye micropore optics (MPO) data. The framework combines a ResNet-based arm filter, a dual-branch temporal─spectral cosmic-ray filter, and a background-aware Bayesian Blocks module for single-exposure variability screening. Using on-orbit EP-WXT observations, we report decoupled metrics for the cascading system. M-EPDet achieves a real─bogus recall of 98.31% (98.53% × 99.78%) for genuine astrophysical sources, together with rejection rates of 92.99% for instrumental artifacts and 98.18% for cosmic-ray events. In the final step, the Bayesian Blocks module flags 0.75% of the postfiltration observations, corresponding to a 99.25% reduction in candidate volume. The system is deployed in the EP-WXT pipeline as a lightweight real-time service, reducing the manual-inspection burden in candidate vetting.

We report the detection of linear polarization in the radio afterglow of GRB 260310A, representing the first centimeter-wavelength polarization detection of a gamma-ray burst (GRB) afterglow and the first measurement of Faraday rotation in a GRB environment. We detect linearly polarized emission across 11─25 GHz, with a polarization fraction decreasing monotonically from (3.18 ± 0.18)% at 25 GHz to (0.69 ± 0.22)% at 11 GHz. We model the multiwavelength data as emission from a refreshed forward shock (FS) that dominates in the optical and X-rays and a reverse shock (RS) in a structured, relativistic jet that dominates at radio wavelengths. The observed depolarization toward the lower radio frequencies is consistent with suppression by RS synchrotron self-absorption, while the low observed polarization at high frequencies relative to the theoretical maximum suggests a patchy magnetic field in the jet with a coherence scale, θ<SUB>B</SUB> ≍ 10<SUP>−2</SUP> rad. We identify a frequency-dependent rotation of the polarization angle consistent with Faraday rotation, with a rotation measure (RM) of RM = −(8300 ± 90) rad m<SUP>−2</SUP> at the GRB redshift. The magnitude of the RM is consistent with propagation through a dense, magnetized environment, such as a progenitor H II region. These findings demonstrate that GRB afterglows exhibit measurable linear polarization at centimeter wavelengths, and that their polarimetric properties probe both intrinsic jet magnetization and the surrounding medium. Future multifrequency polarimetric monitoring over timescales of days to weeks will enable detailed studies of the evolution of magnetic field structure and provide new constraints on the role of magnetic fields in GRB afterglows.

GRB 250704B/EP250704a, identified as a short gamma-ray burst (sGRB), exhibited prolonged X-ray emission following the prompt phase. The event also showed an unusual optical and infrared (IR) plateau lasting nearly one day, followed by a rapid achromatic decline. This event was extensively monitored by multiple space- and ground-based observatories across the electromagnetic spectrum. We present temporal and spectral analyses of the prompt, extended X-ray, and afterglow emission spanning radio to gamma-ray energies during the first two days after the burst. The observed multi-wavelength properties are consistent with a long-lived accreting millisecond magnetar remnant. In this framework, the extended X-ray emission is interpreted as internal dissipation within a relativistic magnetized outflow powered by the magnetar spin-down luminosity, whereas the optical/IR and radio emission are explained as synchrotron forward-shock radiation with continuous energy injection. The steep late-time decay is explained through temporal evolution of the microphysical parameters during the post-jet-break phase. The X-ray observations can be interpreted as a superposition of internal dissipation and synchrotron forward-shock emission. These results favour the presence of a long-lived magnetar remnant powering the multi-wavelength evolution of GRB 250704B/EP250704a.

Recent high spatial and temporal resolution extreme-ultraviolet (EUV) imaging observations have revealed that quasi-periodic pulsations (QPPs), a ubiquitous signature of impulsive energy release in solar and stellar flares, are also present in much smaller-scale coronal events known as EUV brightenings. Whether QPPs observed across such disparate spatial and energetic scales share a common physical origin remains an open question. Here we analyse 2,146 EUV brightenings observed with Solar Orbiter/EUI and 300 EUV solar flares observed with SDO/AIA, identifying 185 brightenings and 89 flares exhibiting statistically significant damped QPPs. We show that the relationship between damping time and oscillation period follows a common power-law scaling for EUV brightenings and EUV solar flares, consistent with previously reported X-ray QPPs spanning both solar and stellar flares. The persistence of this scaling over a wide range of energies and scales suggests that QPPs are governed by a common underlying physical mechanism.

The Einstein Probe (EP) is dedicated to explore the dynamic X-ray universe and capture transient events in real time with its Wide-field X-ray Telescope (WXT). However, WXT's unprecedentedly large instantaneous field of view, exceeding 3,600 square degrees, simultaneously encompasses numerous known X-ray emitters. Distinguishing genuine novel transients from these persistent sources is a critical observational challenge. To resolve this, EP-WXT incorporates a dedicated reference catalog of known X-ray sources directly into its onboard data processing and triggering system. In this paper, we detail the compilation of this onboard catalog. By merging data from the ROSAT All Sky Survey, the MAXI source list, and a curated stellar flare candidate catalog, we constructed a robust baseline database of 9,000 sources. This catalog provides coordinates, baseline count rates, and spatial veto radii for exceptionally bright emitters. Real-time cross-matching against this database effectively decouples known background sources from the transient alert stream. Recent in-orbit operations validate the high stability and efficiency of this catalog-driven trigger system. Notably, the catalog successfully masked over 6,100 potential triggers from known active stars. This proves its essential role in ensuring EP's rapid and accurate response to genuine astrophysical discoveries.

We compute deviations from observed gravitational-wave signals, where the amplitude of the signal is unchanged. As an example, we consider the detectability of low-lying dynamical tides in binary neutron star or neutron star black hole mergers. Tidal forces can excite oscillatory modes of one or both of the stars in the binary when the orbital frequency of the binary system sweeps through the resonant mode frequency dissipating energy into the vibrational mode. The orbital energy loss to the vibrational mode extracts energy from the orbital motion, advancing the time to merger. The inspiral then continues with an excess phase and a time advance. Both will cause a mismatch when fitting to a system that has not gone through the resonance. To resolve this effect, we compute the mismatch for current and planned detectors using both a quasianalytical approach that relies on the computation of moment integrals and an optimized version of the standard numerical match function. We conclude that detectability can occur for time advances of the order of 1 ms with advanced LIGO-Virgo-KAGRA detectors for an excess energy flux that is a few percent of the gravitational-wave emission. Our results contrast with previous work, which model this effect solely as a phase shift of the waveform or by using the difference in the number of cycles induced by the resonant behavior. We show that tidal resonance effects primarily cause a time advance of the merger, rather than a phase difference, and that the single-frequency approximation commonly used in the literature significantly overestimates the detectability of this effect.

We analysed Nuclear Spectroscopic Telescope Array data of GRS 1915 + 105 (2012─2024) to trace its outburst evolution and clues to the physical processes involved through different phases of intensity, especially those related to the radiation pressure instability. We examined its 1-s binned light curves and observation-long spectra to investigate the short- and long-term variability of GRS 1915 + 105, as an extension of the previous studies, which did not cover the fainter period that started in mid-2018. We assigned a new spectral group of variability, 'states group 2' (SG2), which consists of known classes, <inline-formula><tex-math>$\gamma$</tex-math></inline-formula> and <inline-formula><tex-math>$\omega$</tex-math></inline-formula>, variation of <inline-formula><tex-math>$\phi$</tex-math></inline-formula> (<inline-formula><tex-math>$\phi _1$</tex-math></inline-formula>), and an unclassified feature 'uc'. SG2 is evident when GRS 1915 + 105 entered its most luminous state, when its innermost part of the accretion disc transformed to a slim disc state. Other previously known peculiar classes, <inline-formula><tex-math>$\kappa$</tex-math></inline-formula> and <inline-formula><tex-math>$\rho$</tex-math></inline-formula>, can be considered as the transition class between standard and slim disc, which act as signatures of the starting phase of radiation pressure instability. Only the basic variability classes (<inline-formula><tex-math>$\chi$</tex-math></inline-formula> and <inline-formula><tex-math>$\phi _2$</tex-math></inline-formula>), which represent the standard disc, were commonly found in other black hole X-ray transients (e.g. GX 339─4, MAXI J1820 + 070, and 4U 1543─475). However, a class that represents the slim disc was found in 4U 1543─475, possibly due to both GRS 1915 + 105 and 4U 1543─475 having successfully reached a luminosity of <inline-formula><tex-math>$\ge 0.49\ L_{\rm Edd}$</tex-math></inline-formula>. Our analysis of the fainter period (mid-2018─2024) provides more evidence that GRS 1915 + 105 has not slipped into a quiescent phase.

Long gamma-ray bursts (GRBs) frequently exhibit complex prompt-emission morphology, including a bright main-emission (ME) episode followed by a weaker extended-emission (EE) component. Whether these subcomponents are produced by the same central engine under different physical conditions remains unclear. Here, we present a systematic, pulse-resolved analysis of 24 Swift Burst Alert Telescope (BAT) long-duration GRBs that exhibit a well-separated ME episode (G<SUB>1</SUB>) followed by a fainter EE episode (G<SUB>2</SUB>) after a background-consistent quiescent interval. For each episode, we measure the episode-only duration (T<SUB>90</SUB>), count-based hardness ratio, minimum variability timescale (MVT), and spectral lag using the same Swift-BAT analysis pipeline adopted in Paper I. We find that the EE is typically softer and smoother than the ME: HR<SUB>EE</SUB> &lt; HR<SUB>ME</SUB> in 20 of 24 events, and MVT<SUB>EE</SUB> &gt; MVT<SUB>ME</SUB> in 19 of 24 events. The EE also shows a broader lag distribution, including both large positive and negative lags, although the sample-wide median lag offset is not statistically significant. Both episodes remain in the long-GRB track in the duration─hardness and duration─MVT planes. These results suggest that the EE in long GRBs may represent a physically distinct regime of the central engine, characterized by a lower luminosity, longer emission timescales, and softer spectral properties, rather than a simple continuation of the main burst. The observed trends are consistent with late-time central engine activity, such as fallback accretion onto a black hole or protomagnetar spin-down.

We present a time-dependent magnetar-binary weather framework for hyperactive repeating fast radio bursts (FRBs). The burst engine is treated phenomenologically as a magnetar, while a companion-supplied magnetized plasma environment regulates Faraday rotation, polarization transport, transparency, visibility, and apparent activity. We distinguish orbital climate, the deterministic phase-connected contribution of a wind, disk, or shocked sheath, from weather, the stochastic contribution of sectors, filaments, streamers, and eruptive magnetized structures. We test three nested models: M0, a smooth or isolated local environment; M1, deterministic binary climate; and M2, climate plus localized weather. The comparison uses a joint multi-observable likelihood for rotation measure (RM), dispersion measure (DM), linear and circular polarization, width, bandwidth, activity diagnostics or exposure-corrected rates where available, and transparency constraints, with model preferences summarized using the Bayesian information criterion (BIC). FRB 20220529 provides the strongest eruptive-weather test: its RM reached <mml:math><mml:mrow><mml:mn>1977</mml:mn><mml:mo>±</mml:mo><mml:mn>84</mml:mn><mml:mspace></mml:mspace><mml:mrow><mml:mrow><mml:mi>r</mml:mi></mml:mrow><mml:mi>a</mml:mi><mml:mi>d</mml:mi><mml:mspace></mml:mspace><mml:msup><mml:mi>m</mml:mi><mml:mrow><mml:mo>−</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mrow></mml:math> and recovered in about two weeks, with M2 favored over M1 by <mml:math><mml:mrow><mml:mstyle><mml:mi>∆</mml:mi></mml:mstyle><mml:mrow><mml:mrow><mml:mi>B</mml:mi></mml:mrow><mml:mi>I</mml:mi><mml:mi>C</mml:mi></mml:mrow><mml:mo>=</mml:mo><mml:mn>596.8</mml:mn></mml:mrow></mml:math>. FRB 20240114A is best described as a slow structured-sector crossing, with M2 favored by <mml:math><mml:mrow><mml:mstyle><mml:mi>∆</mml:mi></mml:mstyle><mml:mrow><mml:mrow><mml:mi>B</mml:mi></mml:mrow><mml:mi>I</mml:mi><mml:mi>C</mml:mi></mml:mrow><mml:mo>=</mml:mo><mml:mn>138.3</mml:mn></mml:mrow></mml:math>; its detected counts are retained only as catalog activity diagnostics because complete observing-window metadata are unavailable. FRB 20201124A is climate-compatible but not weather-required in the daily products; the reported 26.24 ± 0.02 day RM periodicity provides independent support for an orbital-climate interpretation. For FRB 20220529, the weak DM response gives a conservative lower limit of order 0.8 mG on the coherent line-of-sight field. The framework unifies RM drift, RM flares, and RM periodicity as dynamical limits of a binary-controlled plasma environment.

Motivated by the confirmed multimessenger event GW170817/GRB 170817A, we carry out an archival search for temporal and spatial associations between gamma-ray bursts (GRBs) and both significant and subthreshold gravitational wave (GW) candidates reported in the public search products of GWTC-2.1, GWTC-3, and GWTC-4.0. GRB trigger times and sky positions are taken from the GRBweb compilation of Swift-BAT and Fermi-GBM. GW candidates from the search pipelines are correlated with GRBs using time windows from 1 s to 10<SUP>3</SUP> s and spatial consistency tests based on the released sky-localization maps. We find no statistically significant GW─GRB associations on short timescales comparable to that of GW170817/GRB 170817A. The closest temporal connection is found between GRB 231126A and the GW candidate 231126_010928, with a delay of ∆t = 164.692 s, and with the GRB localization overlapping a high-probability region of the GW skymap. From the associated three-dimensional BAYESTAR localization, we infer a luminosity distance of <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>D</mml:mi></mml:mrow><mml:mrow><mml:mi>L</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>395</mml:mn><mml:msubsup><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>1970</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>2497</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula> Mpc (90% credible interval). For this candidate, we additionally performed Bayesian parameter estimation using Bilby with Markov Chain Monte Carlo sampling to obtain posterior parameters.

Type I X-ray bursts are one of the most frequent and energetic phenomena observed in the Galaxy. Numerical studies of accreting neutron stars undergoing type I X-ray bursts provide a tool to understand steady burning on the surface of neutron stars and calculate the properties of regular bursts, as well as rare and energetic bursts at low accretion rates. We model type I X-ray bursts for different physical model parameters, using the MESA (Modules of Experiments in Stellar Astrophysics) code. We determine how mass, metallicity, base luminosity and mass-accretion rate affect the observed recurrence time of bursts. We also look at the accretion rates associated with the transition between stable H and He burning, He ignition with mixed H/He burning, He ignition in a H-depleted layer, shallow H ignition with He accumulation and deep H ignition followed by He ignition. Depending on the accretion rate, the observed recurrence time shows a different correlation with increasing metallicity. For the first time, we identify the igniting fuel numerically, by monitoring the CNO and triple-alpha reaction fluxes during the burst, instead of the conventional timescale of H depletion through CNO burning. From the CNO and triple-alpha reaction fluxes we find a unique pattern for each case, which we use to distinguish between each bursting regime.

The pristine underdense patches of the Universe, cosmic voids, are powerful cosmological laboratories, uniquely sensitive to dark energy, modified gravity, and neutrino masses, yet their baryonic content remains uncharacterized. We present the first constraint on baryon underdensity in voids, exploiting the dispersion measures (DMs) of fast radio bursts (FRBs) as tracers of the electron column. By stacking 3455 sight lines from CHIME/FRB with ∼15' localizations on 1228 Sloan Digital Sky Survey (SDSS) BOSS voids over redshifts 0.2 &lt; z &lt; 0.7, we measure a DM deficit toward void centers at 3.2σ significance, indicating that diffuse baryons inhabit the emptiest corners of the cosmic web at a suppressed level. The measured signal amplitude is consistent with an effective Universe model built directly from the observed galaxy underdensity in these voids, and a baryonic model calibrated to the FRB DM─redshift relation (α<SUB>v</SUB> = 1.80 ± 0.87). A uniform-density void model yields an electron density contrast of δ<SUB>e,v</SUB> = −0.58 ± 0.30, implying a tentative ∼60% ± 30% underdensity of baryons in void interiors relative to the cosmic mean. Jointly interpreting our FRB measurement with existing stacks of the thermal Sunyaev─Zel'dovich effect on voids further constrains the mean gas temperature to T<SUB>e</SUB> ≲ (1.1 ± 0.7) × 10<SUP>6</SUP> K, pointing to a warm-hot diffuse phase, consistent with hydrodynamical simulations. With forthcoming FRB and galaxy surveys, this approach opens a new window onto baryon mapping, with direct implications for feedback models governing gas expulsion into low-density environments, and for the use of cosmic voids to extract cosmological constraints.

We present soft X-ray spectroscopy of the black-hole X-ray binary V4641 Sgr with the XMM-Newton Reflection Grating Spectrometer (RGS). The RGS spectrum shows narrow emission features from N VI─VII and O VII─VIII superimposed on a partially covered disc blackbody continuum. A blind Gaussian search confirms the presence of significant lines at the expected rest wavelengths. He-like triplet ratios (high G, low R) and full photoionization modelling both indicate a dense, photoionized plasma. Small redshifted velocities of <inline-formula><tex-math>$\sim 540$</tex-math></inline-formula>─<inline-formula><tex-math>$720\, \mathrm{km\ s^{-1}}$</tex-math></inline-formula> are suggested, which are consistent with quasi-static or slowly flowing gas away from the observer after accounting for systematics. Photoionization modelling requires two XSTAR components with an intermediate ionization parameter (<inline-formula><tex-math>$\log \xi \simeq 3.1$</tex-math></inline-formula>) and a low ionization parameter (<inline-formula><tex-math>$\log \xi \simeq 0.36$</tex-math></inline-formula>), respectively. The simultaneous European Photon Imaging Camera pn (EPIC-pn) spectrum suggests highly ionized Fe emission structures, hinting at an additional, more highly ionized component. These results imply the existence of a radially extended, multiphase, and dense disc atmosphere in the source. We compare the source with other X-ray binaries showing similar emission lines. V4641 Sgr shares a similarly high inclination with other sources; however, the presence of low ionization emission lines distinguishes it from the rest.

The Living Swift-XRT Point Source Catalogue (LSXPS) enables near real-time searches for X-ray transients. Many detected candidates are faint, often near the XRT detection limit, and are classed as 'low significance', as it is often unclear whether their apparent brightening reflects a genuine transient or a statistical fluctuation. Some of these sources are affected by Eddington bias, a statistical effect that inflates measured fluxes near the detection threshold. We present a simulation-based Bayesian framework that corrects for this bias and provides more accurate probabilities for each source being truly transient, i.e. that its true intensity exceeds the historical 3<inline-formula><tex-math>$\sigma$</tex-math></inline-formula> upper limit. Applied to LSXPS data, this method yields more reliable classifications, recovering over 500 transients above this threshold ─ more than an eight-fold increase over the original confirmed sample. Using extensive simulations based on real Swift-XRT images, we validate the robustness of this approach, showing that it remains stable across varying exposure times and background conditions. These results demonstrate that the LSXPS transient probabilities, corrected for Eddington bias, provide a reliable and internally consistent framework for real-time X-ray transient identification.

We investigate solar flare size and waiting-time correlations within individual active regions (ARs) - where by size we mean soft X-ray peak flux - using a recent convolutional neural network (CNN)-based flare catalog. We examine 1,089 events during 18-27 March 2024, when four ARs (13614, 13615, 13617, and 13619) transited the disk. A probabilistic framework is developed to associate the CNN-detected events with their AR of origin, using extreme ultraviolet images. The ARs are observed to flare at different mean rates, ranging from (0.33 ± 0.05) hr<SUP>-1</SUP> in AR 13617 and AR 13619 to (2.83 ± 0.11) hr<SUP>-1</SUP> in AR 13615. The background-subtracted peak-flux distributions in the individual ARs follow power laws above a lower threshold with indices in the range 1.6-1.9. Size-waiting-time correlations are evaluated using time symmetry tests (i.e., tests of the statistical equivalence of waiting times before and after a flare), the Spearman rank correlation, and the Efron-Petrosian test for truncated data. No statistically significant correlations between flare sizes and waiting times are detected in most studied ARs at most times, although we identify specific instances of correlations in AR 13615. We discuss the implications for models of solar flare recurrence.

We present the discovery and multiwavelength follow-up of gamma-ray bursts (GRB) 250818B, detected by the Space Variable Objects Monitor (SVOM) and localized by the Gravitational-wave Optical Transient Observer. We compile X-ray, optical/near-infrared, and radio data into broad-band light curves and spectral energy distributions. Despite being initially reported as short, the public prompt light-curve figure suggests a duration of <inline-formula><tex-math>$\sim 5$</tex-math></inline-formula> s, arguing against a secure short-duration classification. The afterglow is unusually bright relative to short-GRB samples: in X-rays and optical it is broadly consistent with the long-GRB population, while in the radio it is among the most luminous events in the short-GRB comparison sample and remains within the long-GRB range. MeerKAT detects the source at 3.1 GHz, while the Atacama Large Millimetre/submillimetre Array provides deep higher-frequency limits. Keck/LRIS spectroscopy shows continuum and metal absorption (Fe II, Mg II, Mg I), giving <inline-formula><tex-math>$z=1.216$</tex-math></inline-formula>. Synchrotron forward-shock modelling favours a constant-density medium and refreshed (energy-injection) emission, well described by a two-component jet with core isotropic-equivalent kinetic energy <inline-formula><tex-math>$E_{0}\sim 8\times 10^{52}$</tex-math></inline-formula> erg, ambient number density <inline-formula><tex-math>$n_0\sim 12\, \mathrm{cm^{-3}}$</tex-math></inline-formula>, jet half-opening angle <inline-formula><tex-math>$\theta _j\simeq 0.13$</tex-math></inline-formula> rad (<inline-formula><tex-math>$\sim 7.4^\circ$</tex-math></inline-formula>), and electron index <inline-formula><tex-math>$p\simeq 1.67$</tex-math></inline-formula>. We do not identify a host conclusively: the data admit either a faint LS DR10 galaxy at <inline-formula><tex-math>$\sim 4\, {\rm arcsec}$</tex-math></inline-formula> (<inline-formula><tex-math>$\sim 34$</tex-math></inline-formula> kpc) as an offset candidate, or a fainter, near-coincident uncatalogued host. GRB 250818B highlights the power of rapid counterpart identification in the SVOM era, while uncertain prompt classification and inconclusive host association still limit progenitor interpretation.

The detection of GW231123, a gravitational-wave (GW) event with exceptionally massive and rapidly spinning black holes, suggests the possible formation within an active galactic nucleus (AGN) disk, which provides a favorable environment for potentially generating an observable electromagnetic (EM) counterpart. We conduct a search for such a counterpart by crossmatching the GW localization with a comprehensive catalog of AGN flares from the Zwicky Transient Facility. Our analysis yields six plausible optical flare candidates that are spatially and temporally coincident with GW231123 and exhibit significant deviations from their AGN baseline flux. These candidates provide a well-defined starting point for evaluating a possible EM counterpart of GW231123. To facilitate future verification, we present a set of observational diagnostics that can be used to confirm or rule out their association, enabling a more systematic exploration of the AGN formation channel in upcoming multimessenger searches.

Pulse profile modelling via relativistic ray-tracing can constrain the system parameters of neutron stars, notably their mass and radius. Among these objects, accreting millisecond pulsars (AMPs) are promising targets, because they are bright in X-rays and their potentially polarized radiation can lead to complementary constraints on the emission geometry. We perform combined analysis of NICER and IXPE observations of the recently discovered the 448-Hz pulsar SRGA J144459.2-604207, with IXPE providing X-ray polarization information. NICER and IXPE jointly favour a large mass and radius for our best-fitting model, for which the neutron star has two independent hotspots. The primary hotspot is centered near the northern rotational pole, the secondary in the southern hemisphere, and the observer inclination is in the range 50-75 degrees. The primary hotspot is large (up to half the surface area) and contributes the majority of the non-pulsed X-rays, while the secondary is hotter and the major contributor to the overall pulse profile shape. However, many parameters are inferred to be near the prior bounds, which could indicate that the model does not adequately account for important physics. Furthermore, we tested several different methodologies for joint analysis of the two data sets: the results are sensitive to the method used, something that merits further study with synthetic data. In the future, we expect simultaneously recorded data will lead to improved parameter constraints, especially when multi-band and polarized data are combined.

The estimate of the bolometric luminosity and the radiative efficiency are two key aspects for understanding the properties of the accretion flow around a supermassive black hole (BH). In this paper, we focus on the estimate of the bolometric luminosity and the radiative efficiency of the early super-Eddington accretion flow in tidal disruption events (TDEs). Specifically, we first perform radiation hydrodynamic simulations of super-Eddington accretion flow in TDE environment, and then calculate the corresponding emergent spectra with the method of post processing for the simulation data. Based on the emergent spectra, we calculate the isotropic-equivalent X-ray bolometric correction factor k<SUB>bol</SUB> and the radiative efficiency η of the super-Eddington accretion flow. We find that both k<SUB>bol</SUB> and η are BH mass and viewing-angle dependent. k<SUB>bol</SUB> is in the range of about a few tens to a few thousands, and η is in the range of ~10<SUP>-3</SUP> - 10<SUP>-1</SUP> for BH mass in the range of 10<SUP>6 - 7</SUP>M<SUB>⊙</SUB> and the viewing angle in the range of 0<SUP>o</SUP> - 90<SUP>o</SUP>. Finally, we apply the derived k<SUB>bol</SUB> and η to some specific TDEs to estimate the accreted mass during an event, which can significantly alleviate the so-called missing energy problem in TDEs.

Radio emission during X-ray binary outbursts is dominated by synchrotron radiation from relativistic jets, but is usually studied through total-intensity diagnostics such as flux density, spectra, variability, and proper motion. Radio spectropolarimetry provides a complementary probe of the magneto-ionic plasma through Faraday rotation and depolarisation. When the Faraday rotating material is local to the source, these effects can constrain the jet plasma composition and mass content, but this approach is rarely applied to transient jetted sources. We present MeerKAT L-band spectropolarimetry of the black hole X-ray binary Swift J1727 during its 2023 outburst, focusing on the brightest radio flaring interval, when relativistic jets were being launched intermittently. Using multiple spectropolarimetric techniques, we identify transient Faraday-complex structure coincident with the major radio flares. The close temporal association with the flaring activity, together with the stability of the foreground Faraday screen, favours an origin local to the jet rather than in the ISM or in a separate local screen external to the emitting plasma. Since internal Faraday rotation is suppressed in a pure electron-positron plasma, the data favour a dominant electron-proton component. Interpreting the characteristic Faraday thickness as internal rotation, and anchoring the magnetic-field and size scales with synchrotron self-absorption arguments, we infer a characteristic Faraday-rotating mass of order M<SUB>rot</SUB> ~ 10<SUP>21</SUP> g, corresponding to only a small fraction, f<SUB>rot</SUB> ~ 10<SUP>-3</SUP>, of the accreted mass available during the flare. These results show that time-domain spectropolarimetry can turn transient Faraday complexity into a diagnostic of jet composition, mass loading, and plasma evolution in X-ray binary outbursts, and potentially other transient jetted sources.

Tidal disruption event (TDE) light curves are increasingly used to infer the masses of quiescent supermassive black holes (M<SUB>BH</SUB>), offering a powerful probe of low-mass black hole demographics independent of host-galaxy scaling relations. However, most semi-analytic TDE models invoke assumptions aligned with a full stellar disruption, despite theoretical expectations that partial disruptions dominate the TDE population. In this work we test the robustness of current TDE models using three repeating partial TDEs (rpTDEs), in which the multiple flares produced by the same surviving stellar core must yield consistent black hole masses. We present spectroscopic observations establishing AT 2023adr as a rpTDE, making it the third such spectroscopically confirmed event. We independently model the flares of the three rpTDEs; 2020vdq, 2022dbl, and 2023adr, applying fallback-accretion fits, stream-stream collision scaling relations, luminosity-based empirical relations, accretion disc models, and cooling-envelope fits. After accounting for statistical and model-specific systematics, we find that all TDE models generally return self-consistent M<SUB>BH</SUB> values between flares, and are broadly consistent with host-galaxy M<SUB>BH</SUB> proxies, recovering M<SUB>BH</SUB> to within 0.3-0.5 dex. However, the convergence of fallback models towards unphysical stellar masses and impact parameters reveals limitations in existing fallback model grids. We also show that light curve coverage, particularly in the near-ultraviolet, is critical for constraining model parameters. This has direct implications for interpreting the thousands of TDE light curves expected from upcoming surveys such as the Rubin Observatory's Legacy Survey of Space and Time, where from MOSFiT simulations, we find that M<SUB>BH</SUB> may be underestimated on average by 0.1 - 0.5 dex depending on peak light curve coverage and the availability of follow-up data.

Solar flares are efficient particle accelerators, with a substantial fraction of the energy released manifesting as nonthermal particles. While the role that nonthermal electrons play in transporting flare energy is well studied, the properties and importance of nonthermal protons are rather less well understood. This is in large part due to the paucity of diagnostics, particularly at the lower-energy (deka-keV) range of nonthermal proton distributions in flares. One means to identify the presence of deka-keV protons is by an effect originally described by Orrall &amp; Zirker. In the Orrall─Zirker effect, nonthermal protons interact with ambient neutral hydrogen, and via charge exchange produce a population of energetic neutral atoms (ENAs) in the chromosphere. These ENAs subsequently produce an extremely redshifted photon in the red wings of hydrogen spectral lines. We revisit predictions of the strength of this effect using modern interaction cross sections, and numerical models capable of self-consistently simulating the flaring nonequilibrium ionization stratification, and the nonthermal proton distribution (and, crucially, their feedback on each other). We synthesize both the thermal and nonthermal emission from Ly α and Ly β, the most promising lines that may exhibit a detectable signal. These new predictions are weaker and more transient than prior estimates, but the effects should be detectable in fortuitous circumstances. We degrade the Ly β emission to the resolution of the Spectral Imaging of the Coronal Environment (SPICE) instrument on board Solar Orbiter, demonstrating that though likely difficult, it should be possible to detect the presence of nonthermal protons in flares observed by SPICE.

A hyperaccreting stellar-mass black hole (BH) has been proposed as the candidate central engine of gamma-ray bursts (GRBs). Comparing the predictions from the central engine models with the temporal behavior of GRBs is of great interest. In this paper, using the open-source GRMHD HARM-COOL code, we evolve several 2D magnetized hyperaccreting BH models with realistic equation of state in a fixed curved space-time background. We extend the code to include the calculation of neutrino annihilation power. We then study the time evolution of BH central engine parameters, i.e., the neutrino annihilation power, the Blandford-Znajke (BZ) power, and the initial magnetization σ<SUB>0</SUB>. We find that the neutrino power is generally consistent with previous analytical results. Usually, the neutrino annihilation process tends to launch a thermal "fireball", while the BZ jet is Poynting-flux-dominated. Our results, especially the evolution characteristics of σ<SUB>0</SUB> may help to understand the complex GRB spectral behavior.

We investigate how the gamma-ray burst (GRB) jet─ejecta interaction in neutron star mergers affects the early r-process-powered kilonova emission (t ≤ 1 day), using the detailed atomic opacities developed in S. Banerjee et al. (2020, 2024), appropriate for epochs as early as t ∼ 1 hr after the merger. Exploring jets with different powers and opening angles, we find that the interaction shifts the spectral peak to longer wavelengths, most strongly for lines of sight near the polar (jet) axis. This is caused by the jet's cocoon, which, after breaking out of the ejecta, forms a low-density outer layer. In this layer, the opacity can reach as high as <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>κ</mml:mi></mml:mrow><mml:mrow><mml:mi>exp</mml:mi></mml:mrow></mml:msub><mml:mo>∼</mml:mo><mml:mn>200</mml:mn><mml:mspace></mml:mspace><mml:msup><mml:mrow><mml:mi>cm</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup><mml:mspace></mml:mspace><mml:msup><mml:mrow><mml:mi>g</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:math> </inline-formula>, forcing photons to escape from cooler, faster-moving material rather than from the hot inner ejecta. Similarly, the bolometric light curves are also modified, showing suppressed early time luminosity toward polar viewing angles compared to the equatorial direction, since the photosphere resides in this outer layer where radioactive heating is weaker than in the bulk ejecta. These signatures are also evident in multicolor light curves, particularly in the ultraviolet and u bands. The strongest observational signatures are expected in the UVEX NUV and Swift UVW2 and UVM2 bands, and remain detectable out to viewing angles of ∼60° for t ≲ 1 day. For example, in the UVEX NUV band at 100 Mpc, the jet can suppress the emission by up to ∼2.7 mag in the polar direction. A rapid follow-up with future ultraviolet facilities such as ULTRASAT and UVEX will provide valuable constraints on GRB jets through early time kilonova observations.

The explosion of a star is first marked by the shock wave breaking out of the stellar surface, producing a burst of ultraviolet and X-ray radiation. These events are observationally rare, despite likely accompanying the majority of supernovae (SNe). Here, we report on our multiwavelength observing campaign of the closest Einstein Probe fast X-ray transient (FXT) EP260321a at z = 0.0344. The thermal (kT = 130 eV) X-ray emission with peak luminosity of 1.0 × 10<SUP>45</SUP> erg s<SUP>−1</SUP> points to a shock breakout origin. We demonstrate that EP260321a is accompanied by a broad-lined Type Ic supernova, SN 2026gzf. The supernova (SN) properties, including its spectral evolution, lightcurve evolution, and expansion velocities, are all typical of the energetic stripped-envelope SNe associated with gamma-ray bursts (GRBs). However, deep X-ray upper limits obtained with the Chandra X-ray Observatory do not detect an X-ray afterglow, and instead exclude the afterglow of known GRBs or FXTs. If the stellar explosion launched a successful relativistic jet, we require that it had both a low Lorentz factor of Γ<SUB>0</SUB> &lt; 30 and a kinetic energy of E<SUB>kin</SUB> &lt; 10<SUP>49</SUP> erg for a stellar wind density of A<SUB>*</SUB> ≳ 1. We propose that EP260321a originated from a mildly relativistic, weak outflow that was choked by the progenitor star. This scenario is capable of naturally explaining its low X-ray luminosity and lack of prompt gamma-ray emission. EP260321a bridges the gap between SN 2008D and low-luminosity GRBs, suggesting a greater diversity in the physical parameters of stripped stars as they undergo terminal collapse.

We study the persistent black hole X-ray binary Cyg X-1, recently observed by XRISM Resolve and simultaneously by NICER and NuSTAR in its hard spectral state. We confirm the result of Draghis et al. that fits of the Resolve data alone with the simplest available relativistic reflection model, relxill, yield a black hole spin parameter close to the maximum, a<SUB>*</SUB> ≍ 0.99. However, fitting with an improved, Comptonization-based model, relxillCp, yields a low a<SUB>*</SUB> = 0. 0<SUP>+0.17</SUP>. A similarly low range is obtained with another Comptonization-based model, reflkerrD. Then fits to the combined data require two Comptonization model components but are consistent with any spin value. We conclude that the spin value of Cyg X-1 is strongly model dependent. However, low spin values are consistent with the constraints from gravitational waves. All of the models constrain the inner disk radius to be ≲10 gravitational radii, which is consistent with a recent finding of the weakness of thermal reverberation in Cyg X-1. The suggested source geometry is that of an outflowing disk corona, which was also proposed to explain the X-ray polarization observed from this source.

Recent long-term radio monitoring of tidal disruption events (TDEs) suggests that radio afterglows are common. Most studies argue that these afterglows may arise from forward shocks (FS) produced by the interaction between the TDE outflow and the hot, diffuse circumnuclear medium (CNM). Current theoretical models do not model the evolution of relativistic electrons in space, which introduces uncertainties. Here, we conducted hydrodynamic simulations to study the spatial evolution of relativistic electrons, and calculated the synchrotron spectra via radiative transfer. We focus on the FS scenario with non-relativistic outflows, and various parameters of the outflow and CNM are explored. A moderate outflow with kinetic energy of several 10<SUP>50</SUP> erg in a Galactic center─like CNM can produce mJy-level radio afterglows at a distance of 100 Mpc. The self-absorption frequency exhibits a slow decline at early times and a rapid decrease at late times. We derived the temporal evolution of the high-frequency radio flux, revealing its characteristic rise and decline pattern. We also find that (1) the radio spectra for narrow outflows are clearly anisotropic along different sight lines; (2) the FS parameters inferred from radio spectra using conventional analytical formulas deviate significantly from those in simulations, in which the inferred shock radii are half of those from simulations, and the inferred energies are an order of magnitude lower.

We demonstrate that magnetospheric interactions between merging neutron stars (NSs) generate dual-jetted current outflows, analogous to the Alfvén wings observed during planetary interactions in the solar system. Using three-dimensional relativistic MHD simulations, we model the interaction as a conducting sphere moving through a highly magnetized plasma of the companion's magnetosphere. Unusually, the interaction operates in a regime that is relativistic yet sub-Alfvénic. Electromagnetic draping amplifies magnetic fields in a narrow layer near the stellar surface, leading to the generation of electric currents along the local magnetic field. The generation of beamed outflows enhances the instantaneous power of the pulsar-like radio and high-energy emission, produces spin/orbital modulations, and is likely to lead to observable precursor emission preceding the main gravitational wave event.

We report on NICER and MAXI observations of a long-duration thermonuclear X-ray burst and a subsequent outburst-like X-ray flare from the neutron star low-mass X-ray binary MAXI J0911─655. Prior to the burst, the source was in a persistent low/hard state with a power-law-dominated spectrum (Γ ∼ 1.7) and a mass accretion rate of ∼1% of the Eddington limit. The long burst, detected by MAXI on 2020 May 22 (MJD 58991.7101), was rapidly followed up by NICER. From time-resolved spectroscopy of the cooling tail, we estimate an exponential decay time of ≍43 minutes, the ignition column depth of ≍0.1 × 10<SUP>12</SUP> g cm<SUP>−2</SUP>, the burst fluence of ≍1.1 × 10<SUP>−4</SUP> erg cm<SUP>−2</SUP>, and the total energy release of ≍1.2 × 10<SUP>42</SUP> erg. Approximately 1 day after the burst onset, the 0.5─10 keV light curve unexpectedly rebrightened, initiating an outburst-like flare. During the peak of this flare, the persistent power-law flux increased from its preburst level of ∼0.27 × 10<SUP>−9</SUP>─1.4 × 10<SUP>−9</SUP> erg cm<SUP>−2</SUP> s<SUP>−1</SUP>. This flux enhancement was accompanied by significant spectral softening, with the photon index increasing to Γ ∼ 2.2. Subsequently, the flux decayed and the source returned to its baseline low/hard state. The observed timescales and energetics suggest that intense irradiation from the long burst amplified the ongoing thermal─viscous accretion process. This heating drove an inside-out heating front that temporarily enhanced the mass accretion rate, providing compelling observational evidence of a thermonuclear burst directly modulating the accretion dynamics of its surrounding disk.

The evolution of neutron stars (NSs) embedded within massive stellar envelopes is a critical phase in binary stellar evolution, potentially leading to the formation of Thorne-Żytkow Objects (TŻOs) or catastrophic collapse. We present the first fully coupled general relativistic hydrodynamics simulations of hypercritical accretion onto NSs that simultaneously incorporate gray two-moment (M1) neutrino transport and an <inline-formula><mml:math><mml:mi>α</mml:mi></mml:math></inline-formula>-chain nuclear reaction network. By investigating four distinct progenitor evolutionary stages, we resolve the complex interplay between intense neutrino cooling, multidimensional fluid dynamics, and nuclear feedback. Our results show that, while vigorous convection is triggered in the postshock region, the global energy budget is primarily governed by neutrino cooling, which effectively balances the accretion power. Crucially, even though our M1 transport scheme captures neutrino absorption and localized heating, the efficient cooling sink and high ram pressure of the infalling envelope prevent the formation of any core-collapse supernovalike explosion. We find that all nucleosynthetically processed material (<inline-formula><mml:math><mml:mi>T</mml:mi><mml:mo>&gt;</mml:mo><mml:mn>5</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>GK</mml:mi></mml:math></inline-formula>) remains strictly gravitationally bound, challenging the assumption that these systems contribute significantly to galactic nucleosynthetic yields via convective dredge-up. The lack of sustained outflows and the persistent hypercritical accretion rates suggest that embedded NSs will rapidly exceed the Tolman-Oppenheimer-Volkoff mass limit on timescales of minutes to hours. We conclude that these systems are not stable TŻOs but are rather transient precursors to catastrophic black hole formation and potential central engines for high-energy transients.

Reducing the gaps in the X-Ray afterglow light curve (LC) of Gamma-ray bursts (GRBs) proves to be of immense value as their potential to be used as cosmological probes. Accurate reconstruction tightens the two-dimensional Dainotti (<mml:math><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi>a</mml:mi></mml:msub><mml:mspace></mml:mspace><mml:mo>−</mml:mo><mml:mspace></mml:mspace><mml:msub><mml:mi>L</mml:mi><mml:mi>a</mml:mi></mml:msub></mml:mrow></mml:math>) relation among the rest-frame plateau end time T<SUB>a</SUB>, its corresponding luminosity L<SUB>a</SUB>, and consequently its extension to the fundamental plane -approaching the ideal scenario of a perfect satellite that provides complete, gap-free LC coverage. This study expands on previous GRB reconstruction work on 521 GRBs by introducing five distinct models: Kernel Ridge Regression (KRR), Cubic Smoothing Spline (CSS), Gaussian Process via ANN (GP via ANN), Artificial Neural Networks (ANN), and Symbolic Regression (SR). Our research reveals that the CSS model achieves the highest uncertainty reduction for all three parameters, outperforming all previous machine learning and statistical models. Additionally, CSS, KRR, and ANN models achieve a perfect 0% outlier rate for the Good GRBs subclass. The CSS model performs best as it balances flexibility to capture intricate LC structures with stability to avoid overfitting noisy, sparse data. These progressions are crucial for utilizing GRBs as theoretical model discriminators through their LC parameters and as standard candles in cosmology, and forecasting GRB redshifts with the latest advanced machine-learning techniques.

A particle detected at the South Pole was born in a galaxy that churned out stars when the Universe was young.

Radio flares have been postulated as being associated with the production of astrophysical neutrinos. For example, TXS 0506+056 exhibits a 2─3 yr delay between the 2017 IceCube-170922A/γ-ray flare and a GHz radio maximum. We quantitatively test if the delayed radio flare originates from the same compact region where neutrinos and γ rays are produced as it expands downstream and synchrotron self-absorption is reduced. Starting from the 2017 flare blob parameters, we model the expanding production region and its evolving radio emission with LeHaMoC in a fully time-dependent framework, and compare our 1.2─22 GHz light curves to RATAN-600 data. We study different scenarios with increasing levels of sophistication, including continuous injection and energy redissipation on parsec scales. While a simple expanding-blob scenario fails to reproduce the radio data, a downstream dissipation episode of particles in the optically thin regime, followed by jet deceleration, successfully describes the radio evolution. The radio flare is powered by leptonic synchrotron emission and is largely insensitive to the proton population relevant for neutrino production, implying that the delayed radio flare mainly probes downstream dissipation and beaming in certain jet configurations, instead of being a direct radiative counterpart of the compact neutrino-production zone.

We present new James Webb Space Telescope (<inline-formula><tex-math>$JWST$</tex-math></inline-formula>) NIRSpec and MIRI integral-field spectroscopy of the remarkable system SN 2010da/NGC 300 ULX-1, the only known ultraluminous X-ray source powered by a neutron star with a supergiant donor. Our new data, taken in 2024 November, reveal that the optical and near-infrared counterpart has dramatically faded since 2018 and no longer exhibits molecular absorption features characteristic of a red supergiant. Instead, the spectral energy distribution (SED) shows the donor has returned to its pre-outburst appearance, and is dominated by infrared continuum consistent with an optically thick warm (<inline-formula><tex-math>$\approx$</tex-math></inline-formula>900 K) dust shell. The bolometric luminosity indicates the presence of a surviving luminous source with <inline-formula><tex-math>$\log (L/\mathrm{ L}_\odot)$</tex-math></inline-formula> = 4.11<inline-formula><tex-math>$\pm$</tex-math></inline-formula>0.02. Radiative transfer modelling of the mid-infrared SED reveals a broad emission feature peaking near <inline-formula><tex-math>$\sim$</tex-math></inline-formula>11 μm, best reproduced by silicon carbide (SiC) dust grains, a composition typically associated with carbon-rich evolved stars. We rule out a failed supernova scenario, which would predict a large drop in luminosity and continued fading. Given the association of SiC dust with asymptotic giant branch (AGB) stars, we suggest the donor star may be an AGB star that has survived and is now heavily enshrouded ─ having returned to a dust-obscured state following a transient post-outburst phase in which the system appeared as a red supergiant. We propose a revised evolutionary timeline in which the 2010 outburst initiated sustained super-Eddington accretion and temporarily altered the circumstellar environment. These observations provide rare insight into eruptive mass-loss, dust formation, and binary interaction in a unique system.

A widely accepted picture of an accretion flow in the luminous soft spectral state of X-ray binary systems is a geometrically thin disc structure much like the classic analytic solution of Shakura &amp; Sunyaev. Although the analytic models are troubled by instabilities and miss important aspects of physics, such as magnetic fields, they are successfully used as a framework for interpreting observational data. Here, we compare the results of general relativistic radiative magnetohydrodynamic (GRRMHD) simulations of optically thick, mildly sub-Eddington accretion on a stellar-mass black hole (the puffy disc) with established analytic and semi-analytic accretion models in the same regime. From the simulations, we find that the accretion flow is stabilised by the magnetic field, with a puffed-up, optically thick region resembling a warm corona surrounding a denser and cooler disc core. However, the stratified vertical structure of the disc significantly influences the observational picture of such a system. We analyse the inner disc structure, flow properties, effective viscosity, and inner edge position, and compare them to the predictions of standard models. We find that the simulated discs share some similarities with the models; however, they differ in several important aspects, most notably: the photosphere is geometrically thick, the inner edge is located closer to the central black hole than the analytic models assume, the surface density is significantly lower than analytically predicted, and the effective viscosity parameter is not constant but rises steeply in the innermost region.

Context. Spectral signatures are crucial in the era of large X-ray surveys, as effective methods for source identification and classification are needed due to the scale of the data they yield. Automatic machine learning methods have proven useful for such tasks, but so far they have not been applied to large spectral datasets, such as the Chandra Source Catalog. Aims. Our aim was to develop a compact and physically meaningful representation of Chandra X-ray spectra using deep learning. To verify that the learned representation captures relevant information, we evaluated it through classification, regression, and interpretability analyses, and we measured the mutual information between spectral and time-domain properties of these sources to aid in future identification of transient events. Methods. We used a transformer-based autoencoder to compress X-ray spectra into representations in an eight-dimensional latent space. Astrophysical source types and physical summary statistics were compiled from external catalogs. We evaluated the learned representation in terms of spectral reconstruction accuracy, clustering performance regarding eight known astrophysical source classes, and correlation with physical quantities such as hardness ratios and hydrogen column densities (N<SUB>H</SUB>). Results. Upon reconstruction, clustering in the latent space yielded a balanced classification accuracy of ~40% across the eight source classes, increasing to ~69% when restricted to Active Galactic Nuclei and stellar-mass compact objects exclusively. Moreover, latent features correlate with spectral and temporal properties, suggesting that the compressed representation captures physically relevant information. Conclusions. Features learned directly from X-ray spectra capture relevant physical information as effectively as human-extracted features that require additional computations. They can be used for both classification and regression in large surveys, and they also share mutual information with time-domain properties. The methodology presented in this paper can be adapted to existing and upcoming X-ray catalogs.

The discovery of the gravitational-wave event GW170817 from a binary neutron star merger, together with its multi-wavelength electromagnetic counterparts, marks the beginning of the era of multi-messenger gravitational-wave astronomy. Observations of gravitational-wave signals from compact binary mergers enable an independent measurement of the luminosity distance to the source. This implies that gravitational-wave sources can serve as "standard sirens" to probe the expansion history of the Universe, providing a new approach to constrain cosmological parameters. In this paper, we review the basic principles of using gravitational-wave standard sirens to constrain cosmology. We discuss various methods for determining the source distance and redshift, as well as the capabilities of second- and third-generation ground-based detectors and space-based detectors in constraining cosmological parameters, especially the Hubble constant and dark energy parameters. By examining three types of standard sirens—binary neutron star mergers with electromagnetic counterparts as bright sirens, stellar-mass binary black hole mergers as dark sirens, and the dark lensed sirens—we illustrate the methodology, challenges, and future prospects of the standard siren approach.

We present the multiwavelength variability of the BL Lac object PKS 0735+178, associated with the high-energy neutrino event IC211208A. The light curves cover the radio (1─230 GHz), optical, and Fermi-LAT <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray bands over a <inline-formula><tex-math>$\sim$</tex-math></inline-formula>30 yr time-scale. The light curves are correlated, with delays from 0 to 1200 d increasing towards lower frequencies, consistent with emission from an opacity-stratified jet. The bright flare after the IC211208A event indicates emission from a compact, optically thick region with enhanced activity and more efficient particle acceleration. Short optical and <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray bursts have been detected very close to the neutrino event, within a few days. The <inline-formula><tex-math>$\sim$</tex-math></inline-formula>12-d lag between the <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray and optical emissions is detected for the first time, suggesting that the emission regions are not co-spatial. A characteristic variability time-scale of <inline-formula><tex-math>$\sim$</tex-math></inline-formula>10─11 yr is robustly detected in the radio─mm bands (<inline-formula><tex-math>${\ge} 3\sigma$</tex-math></inline-formula>), while the optical and <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray data show weaker, shorter period signals. The independent constraints from the VLBI core-shift measurements and radio time delays yield consistent estimates of the jet geometry and disturbance propagation, supporting variability governed by jet propagation effects. The long-term modulation is consistent with a slow variation in energy release at the jet base, while individual flares arise from shocks propagating downstream. Jet precession may contribute to the long-term modulation; however, the required viewing angles are inconsistent with the VLBI constraints, indicating that precession alone cannot explain the observed variability.

We present a new analysis of the James Webb Space Telescope infrared (IR) spectra of GRB 230307A(AT 2023vfi), a long gamma-ray burst (GRB) with an IR excess and spectral lines suggestive of significant heavy r-process production. The spectra, taken 29 and 61 d after the GRB trigger, have blackbody-like continua with <inline-formula><tex-math>$T_{\rm eff} \approx 550$</tex-math></inline-formula> K and an emission line near 2.1 μm, previously attributed to [Te 3]. This line identification has been used as evidence for an r-process-powered kilonova (KN), despite no KN model producing a blackbody-like spectrum at late times. Such an IR continuum could be emitted by newly formed dust, and we model the thermal emission to infer dust properties, including composition and mass. We find that the emission requires at least 3─<inline-formula><tex-math>$6 \times 10^{-3}$</tex-math></inline-formula> M<inline-formula><tex-math>$_{\odot }$</tex-math></inline-formula> of carbon or silicate dust, which is inconsistent with r-process yields expected from a neutron-star merger. Alternatively, the continuum could be from <inline-formula><tex-math>$2\times 10^{-3}$</tex-math></inline-formula> M<inline-formula><tex-math>$_{\odot }$</tex-math></inline-formula> of metallic iron dust, which is mildly consistent (at 3<inline-formula><tex-math>$\sigma$</tex-math></inline-formula>) with KN models, but such dust is unlikely to form in the expanding ejecta. GRB 230307A's low late-time luminosity also constrains the amount of radioactive <inline-formula><tex-math>$^{56}$</tex-math></inline-formula>Ni produced to &lt;<inline-formula><tex-math>$6.3 \times 10^{-2}$</tex-math></inline-formula> M<inline-formula><tex-math>$_{\odot }$</tex-math></inline-formula> (3<inline-formula><tex-math>$\sigma$</tex-math></inline-formula>). No KN model can simultaneously form the necessary dust for the IR continuum and heavy elements for the [Te 3] line. We conclude that the blackbody continuum is not due to dust emission, or GRB 230307A did not originate from a binary compact-object merger.

We introduce accelerated sequential posterior inference via reuse (ASPIRE), a broadly applicable framework that transforms existing posterior samples and Bayesian evidence estimates into unbiased results under alternative models without rerunning the original analysis. ASPIRE combines normalizing flows with a generalized sequential Monte Carlo (SMC) scheme, enabling efficient updates of existing results and reducing total likelihood evaluations and wall times by factors of up to 5.8 and 5.5, respectively, with larger gains per posterior sample. This addresses a growing problem in gravitational-wave astronomy, where events must be repeatedly reanalyzed under different models or physical hypotheses. We show that ASPIRE reproduces full Bayesian results when switching waveform models or adding physical effects such as spin precession and orbital eccentricity. With this statistical robustness, ASPIRE turns repeated reanalyses into fast, reliable updates—paving the way for systematic studies of waveform systematics, scalable reanalyses across large event catalogs, and broadly applicable Bayesian reanalysis across other scientific domains.

Persistent, low-luminosity low-mass X-ray binaries offer a unique opportunity to study accretion in this poorly understood regime as well as to unveil new members of the ultracompact X-ray binary (UCXB) family, which are characterised by orbital periods (P<SUB>orb</SUB>) shorter than ∼80 min. We report on a NuSTAR archival observation that, for the first time above 10 keV, spatially resolves the Galactic Centre pair SLX 1744−299 and SLX 1744−300. We find SLX 1744−300 to be slightly brighter, with a flux ratio of ∼1.15, increasing to ∼1.3 when extrapolated to 0.5─10 keV. Both the timing (root-mean-square variability) and spectral properties (well described in both cases by a thermal Comptonisation model) indicate that the systems were in the hard state. The two sources, however, display markedly different behaviour throughout the observation. SLX 1744−299 shows a gradual flux decline consistent with a decrease in the mass-accretion rate, whereas SLX 1744−300 remains steady but exhibits two short-recurrence Type-I X-ray bursts indicative of mixed H and He burning. Combining our results with previously reported upper limits on the distance, we derived low persistent X-ray luminosities of L<SUB>X</SUB> ≲ 1.1 × 10<SUP>36</SUP> erg s<SUP>−1</SUP> and L<SUB>X</SUB> ≲ 2.6 × 10<SUP>36</SUP> erg s<SUP>−1</SUP> (3─78 keV) for SLX 1744−299 and SLX 1744−300, respectively. The corresponding mass-accretion rates, when compared with the critical values from the disc instability model, favour P<SUB>orb</SUB> ≲ 90 min and P<SUB>orb</SUB> ≲ 105─155 min. Although both limits are formally compatible with the UCXB regime, the case of SLX 1744−299 appears significantly more compelling, also considering the previously reported intermediate-duration burst.

We searched for transient and variable X-ray sources in the elliptical galaxy NGC 4552 using the Chandra and XMM-Newton observations from 2001-2012. We detected 14 transient and variable X-ray sources within the 4R<SUB>e</SUB> region of the galaxy, which exhibited peak state and undetected flux behaviour in the Chandra observations. Among them, two sources (T1 and T14) exceed the X-ray luminosity <inline-formula><tex-math id="TM0001" notation="LaTeX">$10^{39}\rm ~erg~s^{-1}$</tex-math></inline-formula> in the detected observations and have the peak state and undetected luminosity ratio of ≥14.3 and ≥8.7, respectively, which we classified as transient and variable ultra-luminous X-ray sources (ULXs). For the third relatively bright transient source, the flux varies by a factor of 3 across the detected observations, and the hardness ratio analysis suggests a normal X-ray binary system. The remaining sources have luminosities in the <inline-formula><tex-math id="TM0002" notation="LaTeX">$10^{37}-10^{38} \rm ~erg~s^{-1}$</tex-math></inline-formula> range, and the spectral analysis indicates that the sources may belong to neutron star or black hole X-ray binary systems, either in the hard or thermal-dominated state. The identified transient and variable ULXs exhibited high variability and soft spectral characteristics, which are consistent with ULXs accreting at super-Eddington rates. The near-infrared (NIR) counterpart search using JWST observations identified potential NIR counterparts for three mildly variable sources, and their magnitudes in different NIR bands suggest a red supergiant companion for each source. Deep X-ray monitoring observations can shed further light on the new transient and variable ULXs.

Gravitational-wave events from compact binary coalescences (CBCs) can be used as standard sirens: they encode the luminosity distance to their sources, which yields a measurement of the Hubble constant ($H_0$) if the source's redshift is known. In the absence of an electromagnetic counterpart, $H_0$ can still be inferred statistically from the cataloged galaxies within the event's sky localization volume via the dark siren, or galaxy catalog method. In this work we examine how the depth of a volume-limited galaxy catalog affects this inference and identify the most efficient spectroscopic strategy for an unbiased measurement of $H_0$ at a median precision of $0.98\%$. The strategy is to carry out spectroscopic surveys to a depth of $r \sim 19$ for the ten best-localized events observed in one year by the LIGO Hanford, LIGO Livingston, and LIGO-India network at A$^\#$ sensitivity. Such a campaign requires a minimum of one night of electromagnetic follow-up observations, or five nights under the most conservative assumptions. For the Hanford, Livingston, and Virgo network at A$+$ sensitivity, the same ten-event strategy yields a median precision of $2.63\%$.

X-ray flaring activity from active galactic nuclei (AGNs) may mimic the expected emission from tidal disruption events (TDEs), thus contaminating TDE searches. To compare X-ray emission properties between TDEs and AGNs, we crossmatch publicly available XMM-Newton and Swift-XRT point-source catalogs with the Million Quasars Catalog and optically selected TDEs. We find that AGNs tend to become softer with a similar hardness ratio (HR) value to TDEs during their flaring events. The soft HRs during flaring events in these AGNs are driven by the emergence of a blackbody-like component below ∼2 keV, likely associated with the soft X-ray excess, as well as the continuum emission becoming steeper with the increase of accretion rate. We find that 2.5% of AGNs in XMM-Newton (23 out of 920) and 4.4% of AGNs in Swift-XRT (179 out of 4089) display flares with peak count rate &gt;2σ from the median count rate and peak HR &lt; −0.75. The rate of such flares in XMM-Newton and Swift-XRT is (1.1─2.5) × 10<SUP>−3</SUP> galaxy<SUP>−1</SUP> yr<SUP>−1</SUP> and (0.9─2.0) × 10<SUP>−3</SUP> galaxy<SUP>−1</SUP> yr<SUP>−1</SUP>, respectively. We also estimate the rate of flares with a maximum flux change (peak/min) of &gt;20× over on a rest-frame timescale of 2 yr or more with an HR &lt; −0.75 at peak to be (4.7─11.0) × 10<SUP>−5</SUP> galaxy<SUP>−1</SUP> yr<SUP>−1</SUP> and (3.1─7.1) × 10<SUP>−5</SUP> galaxy<SUP>−1</SUP> yr<SUP>−1</SUP> in XMM-Newton and Swift-XRT, respectively. Finding an optical or infrared counterpart may help to identify these flaring AGNs. We confirm 61% and 79% of flaring sources from XMM-Newton and Swift-XRT, respectively, as AGNs through variability in Zwicky Transient Facility light curves or a Wide-field Infrared Survey Explorer W1 − W2 &gt; 0.8 mag color cut.

Metallicity can play a significant role in massive binary evolution through its impact on the opacity within stellar interiors and wind-driven mass loss. In this work, we investigate how the double neutron star (DNS) delay time distribution (DTD) is shaped by the metallicity-dependent evolution of the helium star−NS progenitor system. Drawing from insights rooted in single and binary star physics, we argue that at a given metallicity, the stellar radius during the helium main sequence sets a lower limit on the size of the DNS orbit at birth. We then perform population synthesis with the detailed binary evolution code POSYDON to illustrate the resulting DTD across a range of metallicities. Our results indicate that, independent of the common envelope efficiency and reasonable natal kicks, the majority of DNS mergers across metallicities typically occur no earlier than ≃40 Myr after star formation and peak strongly between 80 and 250 Myr. Roughly 15% of DNSs merge within 80 Myr, which may explain r-process enrichment in environments with brief star formation histories, while ≳20% merge on delay times &gt;1 Gyr, providing an explanation for short gamma-ray bursts in old, metal-poor galaxies. The shape of the DTD can be complex, with a metallicity-dependent split in the dominant formation channel imprinting a characteristic double-peaked structure. Although ideally oriented natal kicks can produce very short merging DNS, we find that the required kick magnitudes are inconsistent with observations. Our work has implications for assessing the contribution of DNS mergers to r-process enrichment and gamma-ray bursts/kilonovae transients across cosmic time.

Measuring the mass distribution of supermassive black holes (SMBHs) over cosmic time remains particularly challenging for the low-mass (M<SUB>∙</SUB> ≲ 10<SUP>8</SUP> M<SUB>⊙</SUB>) population at z &gt; 1. This population is also the most sensitive to SMBH seeding and early growth models. In this work, we construct a semiempirical model for the redshift evolution of the tidal disruption event (TDE) rate under multiple SMBH mass function prescriptions, and show that the observed redshift-dependent rate of TDEs is very sensitive to the SMBH mass function and its evolution with redshift. We further incorporate galaxy-scale processes that evolve with redshift—namely, increasing galaxy nuclear stellar densities, enhanced galaxy─galaxy merger rates, dust obscuration, and a possible top-heavy initial mass function at early cosmic times—and quantify their combined impact on the TDE rate. We find that including these effects generally results in a volumetric TDE rate that increases with redshift until a maximum near cosmic noon, before declining at higher redshift, where SMBHs that can disrupt stars become increasingly scarce. We forecast TDE rates in the Rubin Legacy Survey of Space and Time (LSST) and the Roman High Latitude Time Domain Survey, alongside expectations for serendipitous TDE rates in the JWST COSMOS-Web survey. Finally, we provide a methodology for using a flux-limited survey of TDEs in LSST to directly constrain the redshift evolution of the SMBH mass function.

FRB 20240114A is extraordinarily active, and therefore presents an opportunity to search for the periodicity predicted by magnetar models of Fast Radio Bursts (FRB). Zhang, et al. (2025) observed 11,553 bursts, including 3196 on MJD 60381 (March 12, 2024). We find no significant peak in the periodogram of those bursts, which occur within 15628 s. This interval is short enough that even with a characteristic slowing age of 1 year a periodicity ≥0.1s would not significantly dephase within the observation. Introducing modulation artificially shows that an amplitude of 0.15 would have been detected robustly.

The origins of merging compact binaries observed by the LIGO─Virgo─KAGRA gravitational-wave detectors remain uncertain, with multiple astrophysical channels possibly contributing to the merger rate. Formation processes can imprint nontrivial correlations in the underlying distribution of source properties, but current understanding of the overall population relies heavily on simplified and uncorrelated parametric models. In this work, we use PIXELPOP—a high-resolution Bayesian nonparametric model with minimal assumptions—to analyze multidimensional correlations in the astrophysical distribution of masses, spins, and redshifts of black-hole mergers from mock gravitational-wave catalogs constructed using population-synthesis simulations. With full parameter estimation on 400 detections at current sensitivities, we show explicitly that neglecting population-level correlations biases inference. In contrast, modeling all significant correlations with PIXELPOP allows us to correctly measure the astrophysical merger rate across all source parameters. We then propose a nonparametric method to distinguish between different formation channels by comparing the PIXELPOP results back to astrophysical simulations. For our simulated catalog, we find that only formation channels with significantly different physical processes are distinguishable, whereas channels that share evolutionary stages are not. Given the substantial uncertainties in source formation, our results highlight the necessity of multidimensional astrophysics-agnostic models like PIXELPOP for robust interpretation of gravitational-wave catalogs.

Flare ribbons form as a result of energy deposition associated with particles accelerated in low layers of the solar atmosphere. The fine-scale structures of flare ribbons, also called ribbon kernels, offer a potentially powerful diagnostic of the flare reconnection process, however, to date the dynamic evolution of ribbon kernels has not been fully characterized in statistical studies. Here, we checked the state-of-the-art observations (cadence ≤2.5 s) of solar flares in the ultraviolet from space by Interface Region Imaging Spectrograph over the past 12 yr. Our results showed the first statistical study of multiple spatially resolved flare kernel quasiperiodic pulsation events for 31 flares, with the period of 6─24 s. The ribbon kernels have a spatial scale of 480─1200 km and some kernels exhibit an unprecedented fast "winking" process, i.e., quasiperiodic pulsation-like flashing of individual kernels. The shortest heating time reaches about 2─3 s, implying that the energy is deposited only in a small localized region within flare ribbons, persisting for only a few seconds. Meanwhile, some ribbon kernels were observed to slip along the ribbon at speeds of 20─1800 km s<SUP>−1</SUP>. These observations strongly imply a joint picture for the dynamics and the bursty nature of ribbon kernels as being due to coupled effects of plasmoid formation and three-dimensional magnetic reconnection in the overlaying coronal current sheet. We suggest that the observed flare behaviors provide strong observational evidences of 3D bursty reconnection.

In the 2021 outburst of RS Ophiuchi, the gamma-ray and the X-ray flux were measured quasi-simultaneously from day 1 after the optical peak, offering the first comprehensive view of shocks in a nova occurring in a symbiotic system. We present a previously unpublished observation done with NuSTAR in the 3─79 keV range, 9 days after maximum, and we review the complex history of the evidence of shocks in the previous outbursts of this nova in light of the intensive X-ray monitoring of 2021. We find evidence that the shock causing the particle acceleration measured with the Cherenkov telescopes also produced the thermal flux detected in the 0.2─30 keV X-ray range, while the large gamma-ray flux observed with Fermi after about a day is not consistent with the X-ray observations. We conclude that an initial, strong shock, with a particle─particle loss timescale shorter than the timescale of particle acceleration at energy higher than a few GeV, occurred close to the red giant atmosphere, where either the X-rays' emitting volume was reduced by turbulence, or—perhaps less likely—the X-rays were completely absorbed by large column density near the giant and by the accretion wake along the line of sight. We compare RS Oph with other novae in long-period systems with evolved companions, discussing how the shocks' phenomenology is a powerful tool to derive other physical parameters. Finally, we discuss predictions that in T CrB, expected to have a new nova outburst within the next few years, the shocks may not be as energetic as in RS Oph.

Superluminous supernovae (SLSNe) are rare transients that are ∼10─100 times more luminous than ordinary stellar explosions, reaching peak optical luminosities ∼10<SUP>44</SUP>─10<SUP>45</SUP> erg s<SUP>−1</SUP>. The energy source powering SLSNe remains uncertain. In this work, we explore the multiwavelength and multimessenger signatures of the scenario in which SLSNe are powered by a newly born millisecond magnetar. We model the dynamical evolution and emission from the coupled system comprised of the magnetar, wind, nebula, and supernova ejecta, consistently evaluating the pair multiplicity of the wind and nebula regions, and the bulk wind Lorentz factor governing the e<SUP>+</SUP> − e<SUP>−</SUP>injection spectra in the nebula. We compute the thermal and nonthermal electromagnetic signatures, neutrino signatures, and investigate their detection prospects. For SN 2017egm, the nearest observed SLSNe, our prediction for high-energy gamma rays matches the recent detection by the Fermi Large Area Telescope. For neutrinos, using SN 2017egm a canonical SLSNe, we find that in the era of the Vera C. Rubin Observatory, a stacking analysis with upcoming neutrino observatories can lead to 3σ detection significance of neutrino events from a population of SLSNe within a decade of operation.

The wide-field X-ray telescope (WXT) is the primary payload of the Einstein Probe (EP) mission. Utilizing innovative lobster-eye micro-pore optics (MPO), it achieves an unprecedented combination of a large instantaneous field-of-view (FoV) and high detection sensitivity. Precise scientific data analysis relies fundamentally on a standardized and robust calibration database (CALDB). In this paper, we present the design and implementation of the WXT CALDB. The database is designed to manage calibration data for 12 independent WXT modules and 48 CMOS sensors, incorporating both extensive on-ground calibration results and dynamic in-orbit updates. We detail the directory hierarchy, naming conventions, functionality, and the specific formats of key calibration products. The WXT CALDB is seamlessly integrated into the WXT data analysis pipeline, ensuring high data integrity and maximizing the scientific return of the mission.

The exceptionally bright gamma-ray burst GRB 221009A, detected up to multi-TeV energies by the LHAASO observatory, provides a unique opportunity to probe possible deviations from standard photon propagation at extreme energies. In particular, it allows to test quadratic subluminal Lorentz Invariance Violation (LIV) scenarios through a potential enhancement of the observed flux at the highest energies. We argue that excesses in the GRB 221009A data currently classified as non-detections at energies E ≳ 30 TeV warrant further investigation, as they may indicate a recovery of the observable spectrum consistent with the LIV-induced suppression of <mml:math><mml:mrow><mml:mi>γ</mml:mi><mml:mi>γ</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mi>e</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math> interactions during propagation. The absence of such a signature would allow one to exclude previously unexplored regions of the parameter space associated with the energy scale of new physics.

Relativistic Doppler boosting significantly affects the observed emission of astrophysical jets resulting in observational biases. In this work, we investigate the observational biases and modelling opportunities which arise due to relativistic boosting using two X-ray binary case studies. Using the one-sided jet ejecta from MAXI J1535−571, we demonstrate that incorporating non-detections of the receding jet ejecta into kinematic modelling can significantly improve parameter estimation, reducing posterior uncertainties by over <inline-formula><tex-math>$40{{\ \rm per\ cent}}$</tex-math></inline-formula>. For the bipolar jets of MAXI J1820+070, we recover the intrinsic jet rest-frame emission of both approaching and receding jet components, demonstrating that they follow a common power-law evolution. Using this rest-frame emission profile as a base model, we show that current observational strategies strongly bias against detecting ejecta with high initial Lorentz factors <inline-formula><tex-math>${\gtrsim} 5$</tex-math></inline-formula> and receding ejecta components across a broad region of parameter space. These results highlight the importance of observational strategy selection, particularly early-time and late-time observations, and leveraging non-detections in the modelling of relativistic jets. More generally, quantifying observational biases and maximizing modelling capabilities by incorporating the non-detection of receding jets can be employed to enhance interpretation of future gravitational-wave/optically triggered observations of off-axis, extragalactic jetted transients.

The origins of fast radio bursts (FRBs) remain uncertain, although magnetars are a leading progenitor candidate. Because magnetars are thought to form primarily through core-collapse supernovae in young stellar populations, the discovery of FRB 20200120E in a globular cluster (GC) in the nearby galaxy M81 was unexpected given the ancient stellar populations of GCs. Expanding the sample of FRBs localized to nearby galaxies is therefore essential for testing FRB formation channels in old stellar environments. M49 (NGC 4472) is a nearby (<inline-formula><tex-math>$\approx 17$</tex-math></inline-formula> Mpc), radio-quiet giant elliptical galaxy in the Virgo cluster hosting an extensive GC system (<inline-formula><tex-math>$\approx 7000$</tex-math></inline-formula> GCs), making it an ideal target for GC FRB searches. We conducted a 9-h SnapShotCal observation of M49 using the Five-hundred-meter Aperture Spherical Telescope (FAST) 19-beam receiver, covering approximately 4230 GCs (<inline-formula><tex-math>$T_{\rm eff}={2.1}$</tex-math></inline-formula> h per GC), and performed a comprehensive single-pulse search with TRANSIENTX over a dispersion-measure range of 0─<inline-formula><tex-math>$5000\, \mathrm{pc\, cm^{-3}}$</tex-math></inline-formula>. No unambiguous astrophysical FRBs were detected. The most significant trigger reached a post-processed signal-to-noise ratio of <inline-formula><tex-math>$8.6\, \sigma$</tex-math></inline-formula> at a dispersion measure of <inline-formula><tex-math>$412.2\, \mathrm{pc\, cm^{-3}}$</tex-math></inline-formula>, but is statistically consistent with thermal noise after accounting for the false-alarm rate. Using the radiometer equation, we derive a beam-averaged peak flux-density sensitivity of <inline-formula><tex-math>$\approx 16.5$</tex-math></inline-formula> mJy (corresponding to a fluence limit of <inline-formula><tex-math>$\approx 16.5\, \mathrm{mJy\, ms}$</tex-math></inline-formula> for a 1 ms burst) and place an upper limit on the FRB occurrence rate of <inline-formula><tex-math>${4.7}\times 10^{-4}\, \mathrm{FRB\, GC^{-1}\, h^{-1}}$</tex-math></inline-formula>. Our non-detection implies that no bright bursts were observed above this fluence threshold during the observing window. The derived rate limit is therefore sensitivity-limited and applies only to bursts above <inline-formula><tex-math>$\approx 16.5\, \mathrm{mJy\, ms}$</tex-math></inline-formula> (for a 1 ms burst), constraining only the detectable (high-fluence) portion of the GC FRB population.

Fast radio bursts (FRBs) are luminous, millisecond-duration extragalactic radio transients that have emerged as a powerful, complementary cosmological probe for investigating the late-time cosmic evolution, offering unique advantages over conventional probes such as Type Ia supernovae, baryon acoustic oscillations, and cosmic microwave background radiation. This review systematically summarizes the cosmological applications of FRBs, focusing on their critical roles in measuring the Hubble constant (H<SUB>0</SUB>) and constraining dark energy properties. Benefiting from the precise dispersion measure—redshift relation of localized FRBs, the integrated electron density of the intergalactic medium (IGM) along the line of sight can be tightly modeled, enabling independent and low-redshift measurements of the cosmic expansion rate. Current FRB samples consisting of localized and non-localized events provide competitive H<SUB>0</SUB> constraints, offering an independent method to measure H<SUB>0</SUB>. FRBs also serve as effective tracers to constrain dark energy equation-of-state parameters. We comprehensively discuss key limiting factors for FRB cosmological precision, including uncertainties in Galactic and host galaxy electron density models, and IGM inhomogeneities. With the rapid growth of high-precision FRB surveys and localized FRB samples, FRBs are promising to provide stringent constraints on late-time cosmic acceleration, dark energy evolution and cosmic baryons.

We conduct a cross-correlation analysis between large-scale structures traced by the Two Micron All Sky Survey (2MASS) galaxy catalog and the cosmic dispersion measures of 133 localized fast radio bursts (FRBs). The cross-correlation signal is measured as a function of the comoving separation R between 2MASS galaxies and background FRB sightlines, making full use of the available redshift information for both datasets. Our measurements are consistent with a null detection over the range <inline-formula><tex-math id="TM0001" notation="LaTeX">$0.01 \lt R\, [h^{-1}\, \mathrm{Mpc}] \lt 1$</tex-math></inline-formula>. Using a halo-based model in which free-electron density profiles are drawn from the hydrodynamical simulation IllustrisTNG-300 (TNG300), we show that the null signal at <inline-formula><tex-math id="TM0002" notation="LaTeX">$R \sim 0.01\, h^{-1}\, \mathrm{Mpc}$</tex-math></inline-formula> is inconsistent with the TNG300 prediction. This discrepancy indicates that the hot-gas mass fraction in halos with masses of <inline-formula><tex-math id="TM0003" notation="LaTeX">$10^{12-13}\, M_\odot$</tex-math></inline-formula> hosting 2MASS galaxies must be lower than that predicted by TNG300. A simple phenomenological modification of the TNG300 model suggests that the hot-gas mass fraction in halos of <inline-formula><tex-math id="TM0004" notation="LaTeX">$10^{12-13}\, M_\odot$</tex-math></inline-formula> should be below <inline-formula><tex-math id="TM0005" notation="LaTeX">${\sim }10\%$</tex-math></inline-formula> of the global baryon fraction in the nearby universe, implying the need for stronger feedback in this mass range. Our constraints are consistent with those inferred from X-ray emission and Sunyaev-Zel'dovich measurements in galaxies, while providing a direct estimate of the hot-gas mass fraction that does not rely on electron-temperature measurements. These results demonstrate that galaxy-FRB cross correlations offer a powerful probe of feedback processes in galaxy formation.

We report large day-timescale variations in the orientation of the southeast─northwest jet in the prototype microquasar GRS 1915+105. These results are based on three-epoch East Asia VLBI Network (EAVN) observations at 6.7 GHz, obtained during giant radio flares in 2025 detected by the RATAN-600 monitoring program. Our observations reveal the smallest position angle (PA) of 118<SUP>∘</SUP> ± 7<SUP>∘</SUP>ever measured for the jet in GRS 1915+105, which increases to 152<SUP>∘</SUP> ± 2<SUP>∘</SUP>within 37 days. Based on the literature results, we further suggest that the jet orientation has exhibited significant variations over a PA range of 118<SUP>∘</SUP>─188<SUP>∘</SUP> since 2023. This unusual jet orientation behavior in GRS 1915+105 during its current X-ray-obscured state may arise from a warped, precessing inner accretion disk, as implied by recent X-ray spectroscopy. Notably, one image reveals a peculiar morphology in GRS 1915+105, which likely indicates lateral spreading of the approaching southeast jet. Future observations are essential to clarify the issues raised in this work.