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

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

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

Accurate estimates of the absorption of X-rays by interstellar gas and dust are of crucial importance for the analysis and interpretation of almost all astronomical soft X-ray observations. However, the present X-ray absorption data extensively used by the community were derived from a reduced interstellar abundance (similar to 70% of solar), while ignoring dust scattering. Therefore, these X-ray absorption data, although highly popular, could have been substantially underestimated. Here, we update the interstellar X-ray absorption and scattering by making use of updated atomic cross sections, updated interstellar abundances, and realistic X-ray dust physics, and appropriately distributing metal elements in gas and dust. The resulting X-ray absorption and scattering data are publicly available on GitHub.

Stars getting close enough to black holes (BHs) can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events (TDEs) have been observed, each involving invariably normal gaseous stars whose debris falls onto the BH, sustaining the flares over years. White dwarfs (WDs), which are the most prevalent compact stars and a million times denser-and therefore tougher-than gaseous stars, can only be disrupted by intermediate-mass black holes (IMBHs) of 102-105 solar masses. WD-TDEs are considered to generate more powerful and short-lived flares, but their evidence has been lacking. Here we report observations of a fast and luminous X-ray transient EP250702a detected by Einstein Probe. Its one-day-long X-ray peak as luminous as 1047-49ergs-1showed strong recurrent flares with hard spectra extending to several tens of MeV gamma-rays, as detected by Fermi/GBM and Konus-Wind, indicating relativistic jet emission. The jet's X-rays dropped sharply from 3×1049ergs-1 to around 1044ergs-1within 20 days (10 days in the source rest frame). These characteristics are inconsistent with any previously known transient phenomena. We suggest that this fast-evolving event over the unprecedentedly short timescale arises likely from disruption of a WD by an IMBH. At late times, a soft component progressively dominates the X-ray spectrum, reaching a luminosity as high as 1044 erg s-1, which is consistent with being extreme super-Eddington emission from an accretion disk expected to form in an IMBH-WD TDE. WD-TDEs open a new window for investigating the elusive IMBHs and their surrounding stellar environments, and they are prime sources of gravitational waves in the band of space-based interferometers.

One of the primary goals of Neutron Star Interior Composition Explorer (NICER)-like X-ray missions is to impose stringent constraints on the neutron star equation of state by precisely measuring their masses and radii. NICER has recently expanded the dataset of inferred mass-radius relations for neutron stars, including four rotation-powered millisecond pulsars PSR J0030+0451, PSR J0740+6620, PSR J0437-4715, and PSR J1231-1411. In this work, the mass-radius relation and X-ray emitting region properties of PSR J1231-1411 are inferred with an independent pulse profile modeling based on the spherical star Schwarzschild-spacetime and Doppler approximation. With one single-temperature elongated hot spot and one single-temperature crescent hot spot, the inferred gravitational mass is $M = 1.12 \pm 0.07 M_{\odot}$ and the inferred equatorial radius is $R_{eq} = 9.91_{-0.86}^{+0.88}$ km (68% credible intervals). It provides an alternative geometry configuration of the X-ray emitting region for PSR J1231-1411 to sufficiently explain the observation data of NICER and XMM-Newton. The inferred radius is smaller than that derived by \citet{salmi2024nicer} ($M = 1.04_{-0.03}^{+0.05} M_{\odot}$, $R_{eq} = 12.6 \pm 0.3$ km), and the inferred mass is slightly higher in this work. The inferred geometry configurations of the X-ray emitting region in both works are non-antipodal, which is not consistent with a centered dipole magnetic field and suggests a complex magnetic field structure.

Based on 6.1  fb^{-1} of e^{+}e^{-} annihilation data collected at center-of-mass energies from 4.600 to 4.843 GeV with the BESIII detector at the BEPCII collider, a partial wave analysis of Λ_{c}^{+}→Λπ^{+}η is performed, and branching fractions and decay asymmetry parameters of intermediate processes are determined. The process Λ_{c}^{+}→Λa_{0}(980)^{+} is observed for the first time, and evidence for the pentaquark candidate Σ(1380)^{+} decaying into Λπ^{+} is found with statistical significance larger than 3σ with mass and width fixed to theoretical predictions. The branching fraction product B[Λ_{c}^{+}→Λa_{0}(980)^{+}]B[a_{0}(980)^{+}→π^{+}η] is determined to be (1.05±0.16_{stat}±0.05_{syst}±0.07_{ext})%, which is larger than theoretical calculations by 1-2 orders of magnitude. Here the third (external) systematic is from B(Λ_{c}^{+}→Λπ^{+}η). Finally, we precisely obtain the absolute branching fraction B(Λ_{c}^{+}→Λπ^{+}η)=(1.94±0.07_{stat}±0.11_{syst})%.

The process e^+e^-→K_S^0K_S^0ψ (3686) is studied by analyzing e+e− collision data samples collected at eight center-of-mass energies ranging from 4.682 to 4.951 GeV with the BESIII detector operating at the BEPCII collider, corresponding to an integrated luminosity of 4.1 fb−1. Observation of the e^+e^-→K_S^0K_S^0ψ (3686) process is found for the first time with a statistical significance of 6.3σ, and the cross sections at each center-of-mass energy are measured. The ratio of cross sections of e^+e^-→K_S^0K_S^0ψ (3686) relative to e+e− → K+K−ψ(3686) is determined to be σ(e^+e^-→K_S^0K_S^0ψ (3686))/σ(e^+e^-→K^+K^-ψ (3686))=0.45± 0.25 , which is consistent with the prediction based on isospin symmetry. The uncertainty includes both statistical and systematic contributions. Additionally, the K_S^0ψ (3686) invariant mass distribution is found to be consistent with three-body phase space. The significance of a contribution beyond three-body phase space is only 0.8σ.

Using 7.9fb−1 of e+e− collision data collected at s=3.773 GeV with the BESIII detector at the BEPCII collider, we search for the massless dark photon with the flavor-changing neutral current processes D0→ωγ′ and D0→γγ′ for the first time. No significant signals are observed, and the upper limits at the 90% confidence level on the massless dark photon branching fraction are set to be 1.1×10−5 and 2.0×10−6 for D0→ωγ′ and D0→γγ′, respectively. These results provide the most stringent constraint on the new physics energy scale associated with cuγ′ coupling in the world, with the new physics energy scale related parameter |C|2+|C5|2<8.2×10−17 GeV−2 at the 90% confidence level. Published by the American Physical Society 2025

Based on a sample of (2712.4 ± 14.3) × 106 ψ(3686) events collected with the BESIII detector, a partial wave analysis of the decay ψ (3686)→ΛΣ^0π^0 + c.c. is performed to investigate Λ* and Σ* resonances in the π^0Σ^0 and π0Λ invariant mass distributions. Significant contributions are found from the Λ(1405), Λ(1520), Λ(1600), Λ(1670), Λ(1690), Λ(1800), Λ(1890), Λ(2325), Σ(1385), Σ(1660), Σ(1670), Σ(1750), and Σ(1910). The masses, widths, and production branching fractions for each component are determined. In addition, the branching fraction of ψ (3686)→ΛΣ^0π^0 + c.c. is measured to be (1.544 ± 0.013 ± 0.071) × 10−4 for the first time, where the first uncertainty is statistical and the second systematic.

A bstract Based on 7.33 fb − 1 of e + e − collision data collected by the BESIII detector operating at the BEPCII collider at center-of-mass energies from 4.128 to 4.226 GeV, a search for the Majorana neutrino ν m is conducted in the lepton-number-violating decays of $$ {D}_{\textrm{s}}^{+} $$ D s + → h − h 0 e + e + . Here, h − represents a K − or π − , and h 0 represents a π 0 , $$ {K}_S^0 $$ K S 0 or ϕ . No significant signal is observed, and the upper limits of their branching fractions at the 90% confidence level are determined to be $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → ϕπ − e + e + ) < 6 . 9 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → ϕK − e + e + ) < 9 . 9 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → $$ {K}_S^0 $$ K S 0 π − e + e + ) < 1 . 3 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → $$ {K}_S^0 $$ K S 0 K − e + e + ) < 2 . 9 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → π − π 0 e + e + ) < 2 . 9 × 10 − 5 and $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → K − π 0 e + e + ) < 3 . 4 × 10 − 5 . The Majorana neutrino is searched for with different mass assumptions within the range [0 . 20 , 0 . 80] GeV /c 2 in the decay of $$ {D}_{\textrm{s}}^{+} $$ D s + → ϕe + ν m with ν m → π − e + , and the upper limits of the branching fractions at the 90% confidence level are at the level of 10 − 5 –10 − 2 , depending on the mass of the Majorana neutrino.

Abstract Based on a data sample of (10087 ± 44) × 106 J/ψ events taken with the BESIII detector, we search for the flavor-changing neutral current charmonium decay J/ψ → D 0 μ + μ − + c.c. . No significant signal above the background is observed, and the upper limit on its branching fraction is set to be ℬ(J/ψ → D 0 μ + μ − + c.c.) < 1.1 × 10 −7 at the 90% confidence level. This marks the first search for a flavor-changing neutral current charmonium decay involving muons in the final state.

In this paper we present the current status of the enhanced X-ray Timing and Polarimetry mission, which has been fully approved for launch in 2030. eXTP is a space science mission designed to study fundamental physics under extreme conditions of matter density, gravity, and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring the effects of quantum electro-dynamics, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, the eXTP mission is poised to become a leading observatory for time-domain and multi-messenger astronomy in the 2030's, as well as providing observations of unprecedented quality on a variety of galactic and extragalactic objects. After briefly introducing the history and a summary of the scientific objectives of the eXTP mission, this paper presents a comprehensive overview of: 1) the cutting-edge technology, technical specifications, and anticipated performance of the mission's scientific instruments; 2) the full mission profile, encompassing spacecraft design, operational capabilities, and ground segment infrastructure.

A bstract By analyzing e + e − collision data with an integrated luminosity of 7.9 fb − 1 collected with the BESIII detector at the center-of-mass energy of 3.773 GeV, the branching fraction of D + → τ + ν τ is determined as $$ \mathcal{B} $$ B = (9.9 ± 1.1 stat ± 0.5 syst ) × 10 − 4 . Using the most precise result $$ \mathcal{B} $$ B ( D + → μ + ν μ ) = (3.981 ± 0.079 stat ± 0.040 syst ) × 10 − 4 [1], we determine R τ/μ = Γ( D + → τ + ν τ )/Γ( D + → μ + ν μ ) = 2.49 ± 0.31, achieving a factor of two improvement in precision compared to the previous BESIII result. This measurement is in agreement with the standard model prediction of lepton flavor universality within one standard deviation.

Based on (2712.4 ± 14.3) × 106 ψ(3686) events collected at the BESIII detector operating at the BEPCII collider, we present the first observation of the decay ψ (3686)→K^-Λ (1520)Ξ^+ + c.c.. The product branching fraction ℬ[ψ (3686)→K^-Λ (1520)Ξ^++c.c.]×ℬ[Λ (1520)→ pK^-] is measured to be (9.47 ± 0.75 ± 0.97) × 10−7, where the first uncertainty is statistical and the second systematic.

Massive stars end their lives as core-collapse supernovae, among which some extremes are broad-lined type Ic supernovae from Wolf-Rayet stars associated with long-duration gamma-ray bursts (LGRBs) with powerful relativistic jets. Their less-extreme brethren make unsuccessful jets that are choked inside the stars, appearing as X-ray flashes or low-luminosity GRBs. However, there exists a population of extragalactic fast X-ray transients with timescales ranging from seconds to thousands of seconds, whose origins remain obscure. Here we report the discovery of the bright X-ray transient EP240414a detected by the Einstein Probe, which is associated with the type Ic supernova SN 2024gsa at a redshift of 0.401. The X-ray emission evolution is characterized by a very soft energy spectrum peaking at <1.3 keV, which makes it different from known LGRBs, X-ray flashes or low-luminosity GRBs. Follow-up observations at optical and radio bands revealed the existence of a weak relativistic jet that interacts with an extended shell surrounding the progenitor star. Located on the outskirts of a massive galaxy, this event reveals a population of explosions of Wolf-Rayet stars characterized by a less powerful engine that drives a successful but weak jet, possibly owing to a progenitor star with a smaller core angular momentum than in traditional LGRB progenitors.

As of 2023 December, the high-energy telescope (HE) of Insight-HXMT has detected 72 short-duration gamma-ray bursts (sGRBs), which may be related to binary compact star mergers. In this work, we locate these sGRBs by adopting an enhanced time-delay localization method based on the Li modified cross-correlation function (Li-CCF), jointly with Insight-HXMT/HE, Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor, Fermi/Gamma-ray Burst Monitor (GBM), INTEGRAL/SPI-ACS, and Konus-Wind. The results indicate that joint localization improves accuracy (3 σ ) by an average of 59% compared to results with GBM alone, and the participation of HXMT improves the joint localization accuracy (3 σ ) by an average of 47%. The median and minimum of the joint localization area are 229 and 0.2 square degrees, respectively. We also propose a method to effectively locate those bursts (e.g., GRB 200415A) for which HE suffered from data saturation. In addition, we investigate whether the multiple annuli are independent when there is overlapping data through simulations. The results show that as long as the data from both satellites used have not been overlapped at the same time, the localization results (annuli) are independent. Finally, we verify the robustness of the results by comparing the precise localization bursts observed by Swift/Burst Alert Telescope, as well as publishing the high-time-resolution light curves, orbits and localization probability sky maps in Hierarchical Equal Area Isolatitude Pixelization format files on the website https://ihepbox.ihep.ac.cn/ihepbox/index.php/s/LO1eRZ0SBIEiBIg .

As China’s first X-ray astronomy satellite, the hard X-ray modulation telescope (Insight-HXMT) carries three sets of X-ray telescopes. The high energy X-ray telescope (Insight-HXMT/HE) could serve as an all-sky gamma-ray monitor with a detection area of up to 5000 cm2 and energy range from about 200 keV to 3 MeV. These characteristics, together with the high orbital inclination angle (43°) of the satellite, make the HE very suitable for detecting terrestrial gamma-ray flashes (TGFs). In this work, we implemented a dedicated TGF search algorithm for Insight-HXMT/HE, and identified 282 bright TGFs in its first four years of operation. We made a systematic study on the properties of these TGFs, including trigger time, duration, intensity, as well as the lightning association. We found that TGFs detected in mid-latitude regions (30° to 43°) are rare and they do not exhibit significantly different properties compared with TGFs in low-latitude (within 30°). Interestingly, the hardness ratio of TGF measured by Insight-HXMT/HE seems to be independent of the TGF duration, which differs from previous studies. These results show that, despite the dedicated design for astronomical observation, Insight-HXMT/HE is a versatile instrument to study energetic radiation phenomena from the Earth.

The Einstein Probe mission is an astronomical satellite developed in China, focusing on time-domain astronomy in the soft X-ray energy band. A key payload of this mission is the follow-up X-ray telescope (FXT), which is the result of international collaboration between China and Europe. The FXT features gold-coated nickel Wolter-I-type focusing mirrors and utilizes PNCCD detectors for imaging and spectroscopy in the focal plane. We reviewed the seven-year development history of the FXT. Initially, the configuration of the FXT consisted of a single telescope unit in 2017, but it later evolved into a dual-unit setup. Building on the successful design of eROSITA, the FXT team has innovatively introduced new operational modes for the PNCCD. FXT team also developed an ultra-compact helium pulse tube refrigerator, which cools the PNCCD down to -90 ^∘ C. Additionally, various passive shielding measures have been implemented to protect against high-energy charged particles and enhance radiation resistance. These advancements have significantly improved the overall performance and reliability of the FXT. The ground calibrations and tests of the FXT demonstrate that its primary performance meets the established design goals. The FXT has exhibited outstanding performance in orbit, establishing itself as one of the space X-ray telescopes with considerable international influence.

Abstract The process e + e − → K S 0 K S 0 ψ 3686 $$ {e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686) $$ is studied by analyzing e + e − collision data samples collected at eight center-of-mass energies ranging from 4.682 to 4.951 GeV with the BESIII detector operating at the BEPCII collider, corresponding to an integrated luminosity of 4.1 fb −1. Observation of the e + e − → K S 0 K S 0 ψ 3686 $$ {e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686) $$ process is found for the first time with a statistical significance of 6.3σ, and the cross sections at each center-of-mass energy are measured. The ratio of cross sections of e + e − → K S 0 K S 0 ψ 3686 $$ {e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686) $$ relative to e + e − → K + K − ψ(3686) is determined to be σ e + e − → K S 0 K S 0 ψ 3686 σ e + e − → K + K − ψ 3686 = 0.45 ± 0.25 $$ \frac{\sigma \left({e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686)\right)}{\sigma \left({e}^{+}{e}^{-}\to {K}^{+}{K}^{-}\psi (3686)\right)}=0.45\pm 0.25 $$ , which is consistent with the prediction based on isospin symmetry. The uncertainty includes both statistical and systematic contributions. Additionally, the K S 0 ψ 3686 $$ {K}_S^0\psi (3686) $$ invariant mass distribution is found to be consistent with three-body phase space. The significance of a contribution beyond three-body phase space is only 0.8σ.