Tidal disruption events (TDEs), in which stars are disrupted by supermassive black holes, have been proposed as potential sources of high-energy neutrinos through hadronic interactions. X-ray-bright TDEs provide dense photon fields conducive to neutrino production via proton-photon (p gamma) processes. We conducted a time-dependent unbinned likelihood analysis of ten years ( 2008-2018 ) of IceCube muon-track data, focusing on ten TDEs with confirmed X-ray detections during this period. We report a neutrino flare candidate spatially and temporally coincident with the TDE ATLAS17jrp, occurring 19 d after the onset of its X-ray activity and lasting for 56 d, with a post-trial p-value of 0.01. This significance is modest, representing a hint of an association. We illustrate the neutrino emission using a simple lepto-hadronic model, where X-ray photons serve as target fields. While this model can account for the neutrino data around 100 TeV, the low-energy neutrinos may imply contributions from an additional component. Although constrained by the sample size of X-ray-detected TDEs, these results underscore the need for high-cadence X-ray monitoring and future neutrino observatories to further explore the connection between TDEs and high-energy neutrinos.

We present multiwavelength afterglow fitting results for three events that exhibit late afterglow rebrightening behavior: EP240414a ( z = 0.401), GRB 240529A ( z = 2.695), and GRB 240218A ( z = 6.782), which span a broad range of redshifts, from the local to the high-redshift Universe. We prove that the peculiar afterglow light curves of the three bursts can be well fitted by structured jets propagated in the free-to-shocked-stellar-wind environment of stellar-wind-blown bubbles. This scenario offers a self-consistent explanation for the observed subclass of afterglows that exhibit rebrightening that is characterized by steep rises and rapid decays. It also provides a unified solution for such events and offers pathways for studying both the jet generation mechanism and the propagation processes of jets through the envelope of the progenitor. This study reveals that the structured jets produced by such events exhibit a narrow jet core and a steep angle-dependent energy decay index, suggesting highly magnetized jets. The derived transition radii from free stellar winds to shocked stellar winds for all three events are smaller than 0.5 pc, with statistical analysis of similar events indicating a median value of 0.1 pc, which conflicts with numerical simulation results. We anticipate that future observations by the Einstein Probe and SVOM missions will enhance the understanding of analogous events and further reveal information about progenitors and their circum-environments.

We present a comprehensive temporal and spectral analysis of the long-duration gamma-ray burst GRB 110801A, utilizing multiband data from the Neil Gehrels Swift Observatory and ground-based telescopes. The gamma-ray emission exhibits a distinct two-episode ("double-burst") structure. Rapid follow-up observations in the optical and X-ray bands provide full coverage of the second burst. The optical light curve begins to rise approximately 135 s after the trigger, significantly preceding the second emission episode observed in X-rays and gamma rays at similar to 320 s. This chromatic behavior suggests different physical origins for the optical and high-energy emissions. Joint broadband spectral fitting (optical to gamma rays) during the second episode reveals that a two-component model, consisting of a power law plus a Band function, provides a superior fit compared to single-component models. We interpret the power-law component as the afterglow of the first burst (dominating the optical band), while the Band component is attributed to the prompt emission of the second burst (dominating the high-energy bands). A physical synchrotron model is also found to be a viable candidate to explain the high-energy emission. Regarding the afterglow, the early optical light curve displays a sharp transition from a rise of similar to t2.5 to similar to t6.5, which is well-explained by a scenario involving both reverse shock and forward shock components. We constrain the key physical parameters of the burst, deriving an initial Lorentz factor Gamma 0 similar to 60, a jet half-opening angle theta j similar to 0.09, and an isotropic kinetic energy Ek,iso similar to 1054.8 erg.

The gravitational wave (GW) event S250206dm, as the first well-localized neutron star (NS) merger candidate potentially located in the mass gap, presented a unique opportunity to probe the electromagnetic signatures from such a system. Here we report a deep, multiband search with the new 2.5 m Wide Field Survey Telescope (WFST), covering similar to 64% of the localization region up to a 5 sigma limiting magnitude of 23 mag. In total, 12 potential candidates have been identified, but none of them are likely related to S250206dm. This nondetection provides the most stringent constraint to date on any associated kilonova. Crucially, an AT 2017gfo-like event at 269 Mpc can be excluded only by WFST observations. Based on ejecta mass limits, a NS-black hole with a large mass ratio (Q greater than or similar to 3.2) is disfavored. This optically derived constraint on the mass ratio reaches, for the first time, a precision comparable to that inferred from the GW signal. This work presents the best observation of this type of event until now, and demonstrates the power of rapid, deep follow-up observations to constrain the properties of compact binary progenitors, offering key insights into the constituents of the mass gap.

GW170817 remains the only binary neutron star merger detected through multimessenger emission. Its afterglow has been monitored for nearly a decade, offering an unprecedented opportunity to probe the properties of the outflow. The shallow decay of the very late-time afterglow challenges the prediction of a collimated structured jet. Motivated by recent general-relativistic magnetohydrodynamic simulations, we propose that the GW170817 afterglow is powered by a wobbling jet that drags a ring on the sky. This structure predicts a post-break decay rate shallower than that of a collimated jet, as observers will see a progressively longer emitting arc after the break. A misaligned ring-shaped jet can therefore self-consistently explain the multimessenger data without invoking any extra component. Through a Bayesian analysis of the multimessenger data, we find a ring-shaped jet is favored over a collimated jet at a significance level of 4.8σ. Our results imply a wobbling angle of ∼ 27^∘. Such a large angle points to a significant disk tilt, potentially arising from disk-infalling gas interaction or asymmetric angular momentum ejection. Similar shallow decays have also been found in other GRB afterglows, raising the possibility that wobbling jets are common among GRBs.

Using deep near-infrared and optical JWST and Hubble Space Telescope imaging, we identify a new host-galaxy candidate for the short GRB 061201 at an angular offset of ∼2″ from the optical afterglow, with a best-fit photometric redshift of z ∼ 1.2. We compare it with the prior putative host candidate at z = 0.111. The new candidate has a chance-coincidence probability of P _cc = 0.18, above the classical 0.1 threshold but consistent with a physical association given the depth of the JWST imaging. In contrast, the lower P _cc = 0.11 of the z = 0.111 galaxy is driven primarily by bright-tail statistics. A high-redshift origin is favored by three lines of evidence. First, although both scenarios satisfy the Amati ( E _p,i – E _iso ) relation, the beaming-corrected energy at z = 0.111 makes GRB 061201 an outlier in the Ghirlanda ( E _p,i – E _γ ) relation. Second, near-infrared data disfavor an AT2017gfo-like kilonova at z = 0.111. Third, afterglow modeling favors the high-redshift scenario, with the Akaike information criterion (AIC) for the z = 1.2 model lower than that for z = 0.111 by ΔAIC = 16.35. Adopting the z ∼ 1.2 candidate as the host gives a physical offset of 16.4–16.9 kpc (substantially reduced from ∼42 kpc implied under the low-redshift scenario) and a stellar age of ∼2 Gyr, consistent with the general population of short gamma-ray bursts (sGRBs). Furthermore, a low-redshift origin implies a binary neutron-star merger rate of ∼1400 Gpc ^−3 yr ^−1 , in tension with gravitational-wave constraints. We conclude that a moderately high-redshift host provides a more self-consistent physical framework for GRB 061201, demonstrating the capability of deep JWST imaging for historically hostless sGRBs.

We report the first detection of GeV γ -ray flaring activity from the compact symmetric object (CSO)–like source 4C 76.03, based on 17 yr of Fermi-Large Area Telescope (LAT) observations. Its long-term, time-averaged γ -ray properties are consistent with the 4FGL-DR4 catalog. However, a time-resolved analysis with 100 day binning reveals two prominent flares occurring on timescales of approximately 30 and 20 days, separated by ∼2.5 yr, with nearly identical fluxes, test statistic (TS) values, and photon indices. The short-timescale variability indicates localized and transient energy dissipation in the nuclear region, likely associated with newly injected jet components. Although the γ -ray emission does not directly trace the long-term jet power responsible for building the observed radio structure, it demonstrates that the central engine remains active. In the context of CSO evolution, 4C 76.03 may represent a rare transitional case, where repeated energy injections allow the source to exceed the canonical ∼500 pc scale of most CSOs, providing key insight into the early stages of radio jet evolution.

We report the first detection of GeV gamma-ray flaring activity from the compact symmetric object (CSO)-like source 4C 76.03, based on 17 years of Fermi-LAT observations. Its long-term, time-averaged gamma-ray properties are consistent with the 4FGL-DR4 catalog. However, a time-resolved analysis with 100-day binning reveals two prominent flares occurring on timescales of approximately 30 days and 20 days, separated by about 2.5 years, with nearly identical fluxes, test statistic (TS) values, and photon indices. The short-timescale variability indicates localized and transient energy dissipation in the nuclear region, likely associated with newly injected jet components. Although the gamma-ray emission does not directly trace the long-term jet power responsible for building the observed radio structure, it demonstrates that the central engine remains active. In the context of CSO evolution, 4C 76.03 may represent a rare transitional case, where repeated energy injections allow the source to exceed the canonical 500 pc scale of most CSOs, providing key insight into the early stages of radio jet evolution.

We report the first detection of gamma-ray emission from the young radio galaxy JVAS J1311+1658, classified as a compact symmetric object (CSO). This detection is characterized by a recent GeV gamma-ray flare identified in Fermi-Large Area Telescope data during MJD 60032.6-60132.6, with a gamma-ray source detected at a significance level of similar to 6.2 sigma. The average 0.1-300 GeV flux is measured to be (1.6 +/- 0.6) & times; 10-8 ph cm-2 s-1, with a photon spectral index of Gamma = 2.15 +/- 0.185. We find that a radiative model of the radio lobes significantly underestimates the observed gamma-ray emission. The strong flux and short-term variability over similar to 100 days suggest that the emission likely originates from newly launched subkiloparsec-scale jets at the core. This detection provides a unique window into the extreme environments and early-stage jet activity of young radio galaxies, offering insights into their initial evolution and the formation of relativistic jets in the earliest phases of galaxy growth.

Using deep near-infrared and optical images from JWST and HST, we identify a new host galaxy candidate for GRB 061201. It lies 2" from the optical afterglow position. Photometric redshift fitting yields z 1.2. We compare the previously proposed host at z=0.111 with the new candidate. The chance-coincidence probability is P_cc=0.18, above the classical threshold of 0.1 but consistent with a physical association given the extreme depth of JWST imaging. In contrast, evaluated with corresponding JWST observations, the previously claimed host has a lower P_cc=0.11, which is driven primarily by bright-tail statistics rather than a more plausible association. A high-z origin is favored by three independent lines of evidence. First, for the z=0.111 scenario, the beaming-corrected energy shows GRB 061201 is an outlier of the Ghirlanda (E_p,i-E_γ) relation for short GRBs, while for the z=1.2 scenario, it is well consistent with the Amati relation. Second, deep near-infrared observations rule out a kilonova similar to AT2017gfo at z=0.111. Third, afterglow modeling yields an AIC criterion of ΔAIC=16.35, providing strong evidence for the high-redshift scenario. Assuming the host candidate is the actual host galaxy of GRB 061201, the physical offset is 16.4-16.9 kpc (substantially reduced from 42 kpc) and the host stellar age is 2 Gyr, which are consistent with the host population of short GRBs. A low-redshift origin would lead to a very high binary neutron star merger rate of 1400 Gpc^-3 yr^-1, which is contradictory to the gravitational-wave constraint. We suggest that GRB 061201 originates from a moderately high-redshift (z 1.2) host, significantly alleviating this apparent merger rate discrepancy. This case demonstrates the power of deep JWST exposures in revealing the host galaxies of historically hostless GRBs.

EP241217a is an X-ray transient detected by the Einstein Probe lasting for about 100 s and without accompanying γ -ray detection. The optical spectroscopy reveals the redshift of EP241217a is 4.59. By combining the γ -ray upper limit provided by GECAM-C, there is a considerable possibility that EP241217a is a typical type II gamma-ray burst, but it is fainter than the detection threshold of any available γ -ray monitors (i.e., E _γ _,iso ≲ 10 ^53 erg). The X-ray light curve exhibits a plateau lasting for ∼5 × 10 ^4 s. However, the joint analysis with optical data suggests the presence of an achromatic bump peaking at ∼3 × 10 ^4 s after the trigger, indicating the actual duration of the X-ray plateau may be significantly shorter than it appears. To interpret the achromatic bump, we adopt the scenario of a mildly relativistic jet coasting in a wind-like medium and encountering a rapid density enhancement of the circumburst medium, which is likely induced by the interaction of the progenitor’s stellar wind and the interstellar medium. However, this model cannot fully explain observed data, and some issues do exist, e.g., the observed spectrum is harder than the model prediction. Consequently, we conclude that the scenario of a mildly relativistic jet coasting in the wind-like medium cannot explain all observed features of EP241217a. In addition, some alternative models commonly invoked to explain X-ray plateaus are discussed, but there are more or less issues when they were applied to EP241217a. Therefore, further theoretical modeling is encouraged to explore the origin of EP241217a.

Short and long-short gamma-ray bursts (GRBs) are widely believed to be powered by neutron star mergers. In this work, we calculate local rate of such GRBs and find a relatively high value of ∼ 786-2468 Gpc^-3 yr^-1 when including the very narrow collimation event GRB 061201. Considering that its redshift is not very reliable, after excluding this event, the rate is ∼ 195-666 Gpc^-3 yr^-1. We also calculate the electromagnetically (EM) bright neutron star merger rate inferred from the LIGO/Virgo/KAGRA observations up to the end of the first epoch of the O4 run, and derive a rate of ∼ 66-347 Gpc^-3 yr^-1. This rate is somewhat lower than the value obtained from the GRBs, even after excluding GRB 061201. The non-detection of any viable EM bright merger in the O4b and O4c observing runs favors an even lower rate, which starts to challenge the neutron star merger origin of the short and long-short GRBs and may suggest additional contribution from the mergers of other compact object (like the neutron star-white dwarf) binaries, as speculated initially by King et al. (2007) in interpreting the long-short event GRB 060614.

Precise direct cosmic-ray (CR) measurements provide an important probe to study the energetic particle sources in our Galaxy, and the interstellar environment through which these particles propagate. Uncertainties on hadronic models, ion-nucleon cross sections in particular, are currently the limiting factor toward obtaining more accurate CR ion flux measurements with calorimetric space-based experiments. We present an energy-dependent measurement of the inelastic cross section of protons and helium-4 nuclei (alpha particles) on a Bi4Ge3O12 target, using 88 months of data collected by the DAMPE space mission. The kinetic energy range per nucleon of the measurement points ranges from 18 GeV to 9 TeV for protons, and from 5 GeV/n to 3 TeV/n for helium-4 nuclei. Our results lead to a significant improvement of the CR flux normalization. In the case of helium-4, these results correspond to the first cross section measurements on a heavy target material at energies above 10 GeV/n. Published by the American Physical Society 2025

In this paper, we report the detection of the very-high-energy (VHE, 100 GeV < E < 100 TeV) and ultra-high-energy (UHE, E > 100 TeV) γ-ray emissions from the direction of the young star-forming region W43, observed by the Large High Altitude Air Shower Observation (LHAASO). The extended γ-ray source was detected with a significance of ∼16 σ by KM2A and ∼17 σ by WCDA, respectively. The angular extension of this γ-ray source is about 0.5 degrees, corresponding to a physical size of about 50 pc. We discuss the origin of the γ-ray emission and possible cosmic ray acceleration in the W43 region using multi-wavelength data. Our findings suggest that W43 is likely another young star cluster capable of accelerating cosmic rays (CRs) to at least several hundred TeV.

The operation of upcoming ultra-high-energy cosmic-ray, gamma-ray, and neutrino radio-detection experiments, like the Giant Radio Array for Neutrino Detection (GRAND), poses significant computational challenges involving the production of numerous simulations of particle showers and their detection, and a high data throughput. GRANDlib is an open-source software tool designed to meet these challenges. Its primary goal is to perform end-to-end simulations of the detector operation, from the interaction of ultra-high-energy particles, through -- by interfacing with external air-shower simulations -- the ensuing particle shower development and its radio emission, to its detection by antenna arrays and its processing by data-acquisition systems. Additionally, GRANDlib manages the visualization, storage, and retrieval of experimental and simulated data. We present an overview of GRANDlib to serve as the basis of future GRAND analyses.

Secondary cosmic ray fluxes are important probes of the propagation and interaction of high-energy particles in the Galaxy. Recent measurements of primary and secondary cosmic ray nuclei have revealed unexpected spectral features that demand a deeper understanding. In this work we report the direct measurement of the cosmic ray boron spectrum from 10  GeV/n to 8  TeV/n with eight years of data collected by the Dark Matter Particle Explorer (DAMPE) mission. The measured spectrum shows a hardening at 182±24  GeV/n with a spectral index of γ_{1}=3.02±0.01 before the break and an index change of Δγ=0.31±0.05 after the break. A simple power law model is disfavored at a confidence level of 8σ. Compared with the hardenings measured in the DAMPE proton and helium spectra, the secondary boron spectrum hardens roughly twice as much as these primaries, which is consistent with a propagation related mechanism to interpret the spectral hardenings of cosmic rays observed at hundreds of GeV/n.

Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early Universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5–4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a, whose bright peak was also detected by the Swift Burst Alert Telescope and Konus-Wind through off-line analyses. At a redshift of z = 4.859, EP240315a showed a much longer and more complicated light curve in the soft-X-ray band than in gamma rays. Benefiting from a large field of view ( 3,600°2) and a high sensitivity, EP-WXT captured the earlier engine activation and extended late engine activity through a continuous detection. With a peak X-ray flux at the faint end of previously known high-z GRBs, the detection of EP240315a demonstrates the great potential for EP to study the early universe via GRBs. The death of massive stars has traditionally been discovered by explosive events in the gamma-ray band. Liu et al. show that the sensitive wide-field monitor on board Einstein Probe can reveal a weak soft-X-ray signal much earlier than gamma rays.

The Giant Radio Array for Neutrino Detection (GRAND) is an envisioned observatory of ultra-high-energy particles of cosmic origin, with energies in excess of 100 PeV. GRAND uses large surface arrays of antennas to look for the radio emission from extensive air showers that are triggered by the interaction of ultra-high-energy cosmic rays, gamma rays, and neutrinos in the atmosphere or underground. In particular, for ultra-high-energy neutrinos, the future final phase of GRAND aims to be sensitive enough to detect them in spite of their plausibly tiny flux. Three prototype GRAND radio arrays have been in operation since 2023: GRANDProto300, in China, GRAND@Auger, in Argentina, and GRAND@Nançay, in France. Their goals are to field-test the GRAND detection units, understand the radio background to which they are exposed, and develop tools for diagnostic, data gathering, and data analysis. This list of contributions to the 39th International Cosmic Ray Conference (ICRC 2025) presents an overview of GRAND, in its present and future incarnations, and a first look at data collected by GRANDProto300 and GRAND@Auger, including the first cosmic-ray candidates detected by them.

Following its launch on 2024 January 9, the Einstein Probe (EP) telescope has detected hundreds of fast X-ray transients (FXTs), yet their physical origins remain elusive. Understanding their luminosity function and formation rate is crucial for elucidating their nature. Recently, the EP team has provided the latest catalog of EP-detected FXTs. Based on this catalog, we present a model-independent nonparametric approach to derive the luminosity function and formation rate of FXTs. Our analysis reveals significant cosmological luminosity evolution, characterized by a scaling relationship of (1 + z ) 3.58 . After accounting for this evolution, we establish that the local luminosity function is best represented by a broken power law, with a break luminosity of (4.17 ± 0.34) × 10 46 erg s −1 . The formation rate exhibits a broken power law as ρ ( z ) ∝ (1 + z ) −4.25 at z ⪅ 0.9 and ρ ( z ) ∝ (1 + z ) −0.26 at z ⪆ 0.9, yielding a local rate of approximately 153 . 8 − 95.1 + 249.4 Gpc −3 yr −1 . This rate is higher than that of long gamma-ray bursts (LGRBs). Our findings indicate that a component of FXTs is associated with LGRBs.

The blazars are one of the leading candidate sources of high-energy neutrinos. Recently, two blazars have been found to be temporally and spatially correlated with some IceCube high-energy neutrino events. The two blazars, GB6 J2113+1121 and NVSS J171822+423948, are flat spectrum radio quasars (FSRQs) with redshifts greater than unity. In particular, NVSS J171822+423948 has a redshift of 2.7, which provides an important probe for studying the radiation processes of jets from active galactic nuclei in the early Universe. To better understand the physical origin of the IceCube neutrinos, we adopt the one-zone leptohadronic model to fit the multimessenger emission of GB6 J2113+1121 and NVSS J171822+423948 during their γ -ray flaring periods and then calculate the high-energy neutrino detection probability. The chance of detecting a single muon neutrino from these two sources is found to be ∼2% and 0.8%, respectively. Although such detection rates are not high mainly because of their high redshifts, our investigation strongly suggests that these sources are efficient PeV neutrino emitters. Our results also indicate that electromagnetic cascades produced by hadronic processes contribute significantly to X-ray and γ -ray emissions. However, high-energy γ -rays can be severely absorbed by the soft photon field from the broad-line region, which weakens the correlation between γ -rays and neutrinos, while suggesting a stronger connection between X-rays and neutrinos. We predict that IceCube will continue to detect neutrinos from FSRQs with redshifts greater than 1 in the future.