As the only established primordial gravitational wave observatory in the Northern Hemisphere, the Ali primordial gravitational wave observatory possesses significant potential for optical observations. However, systematic research on high-precision radiative transfer simulation in the optical band remains a gap. This study constructed local monthly mean atmospheric profiles using 20 years (2005–2024) of MERRA-2 model-level data. Utilizing the Combined Atmospheric Radiative Transfer (CART) model, integrated with constraints from a POM-02 sun photometer (providing Aerosol Optical Depth and Precipitable Water Vapor) and a TML-01 Mie-scattering lidar (providing real-time vertical extinction profiles), the slant path atmospheric transmittance (400–1050 nm) was simulated and rigorously validated against DTF-8 sun photometer measurements.We compared two simulation schemes: one based on real-time lidar extinction profiles, and another scaling CART built-in aerosol modes with real-time AOD. The latter was specifically designed to address a practical operational constraint: determining if acceptable simulation accuracy is achievable when real-time vertical extinction profiles are unavailable. The results indicated high consistency with measurements, with overall Pearson correlation coefficients R≥0.97 and RMSE < 0.05. While the lidar-based scheme offered superior precision in visible and near-infrared bands (RMSE 0.005–0.013), the mode-scaling approach proved sufficiently accurate, with RMSE values ranging from 0.028 to 0.044 in these bands, validating its viability as a reliable alternative for operational use. Furthermore, optimal parameter searches revealed that the site is predominantly characterized by ”clean continental” or aerosol-free conditions under clear skies. Given the scarcity of aerosol research at Ali, this conclusion provides a critical reference for local atmospheric characteristics. This study validates the feasibility of using MERRA-2 combined with ground-based observations for high-precision optical band transmittance simulation at the Ali station.

The precise measurement of the cosmic ray composition is a key objective of ground-based cosmic ray experiments. The primary challenge arises due to the significant uncertainties in high-energy hadronic interaction models. These models not only affect the theoretical description of the propagation and evolution of cosmic rays in the atmosphere, but also directly determine the physical interpretation of experimental observations. As one of the principal secondary particles produced in hadronic cascades, muons retain substantial information from the primary interactions owing to their strong penetrating power and small interaction cross-section with matter. This makes them an effective probe for validating hadronic interaction models. In this study, based on the air shower data acquired by Yangbajing hybrid array, a high-statistics measurement of the muon component in cosmic-ray-induced events was performed. Subsequent systematic comparisons between the experimental observations and predictions of major existing hadronic interaction models revealed overall consistency within the "knee" of the cosmic ray energy spectrum, thereby supporting the basic validity of existing models in this range. Additionally, the results of combined spectral and compositional analyses indicated a transition in cosmic ray mass composition around the "knee," shifting from light-nuclei dominance to heavy-nuclei dominance. The findings of our study provide important insights into the applicability of hadronic interaction models in the TeV-PeV energy range and offer observational evidence for understanding not only the physical origin of the "knee" in the cosmic ray energy spectrum but also its compositional evolution mechanisms.

In regions of the Solar System distant from planetary magnetic fields, galactic cosmic rays (GCRs) have generally been assumed to be uniformly distributed over the Earth-Moon distance. However, our analysis of data from the LND (Lunar Lander Neutron and Dosimetry) experiment onboard the Chang'E-4 lander revealed a region of reduced GCR flux in the prenoon sector of the lunar orbit. Further investigation suggests the presence of an energetic particle cavity, formed by Earth's magnetic field acting as an obstacle to GCR propagation. This cavity indicates that the influence of Earth's magnetic field within the space environment extends unexpectedly up to and far beyond the lunar orbit. This finding offers the potential to avoid high radiation levels during future lunar exploration and deep-space missions.

The high altitude detection of astronomical radiation (HADAR) project proposes the use of a refracting telescope composed of four 5.0 m diameter water lenses arranged in a square configuration (100 m & times; 100 m). This configuration features a wide field of view (FoV, up to 0.84 sr) and low-energy threshold characteristics for observing Cherenkov light generated by high-energy cosmic rays in atmospheric air showers. The Fresnel lens exhibits excellent imaging performance, lightweight characteristics, mature manufacturing processes, strong adaptability in high-altitude low-temperature environments, and facilitates array deployment. The lens has been validated through a series of pilot missions in the Joint Exploratory Missions for an Extreme Universe Space Observatory program, leading to the proposal of a telescope unit design that utilizes the Fresnel lens as an alternative to the water lens. This study simulates and examines the effects of parameters such as the radius of curvature, tooth width, and Fresnel lens thickness on the focal length and image spot (r(80)). To this end, five Fresnel lenses with the same focal length as the 5.0 m diameter water lens were designed, the best focusing positions under different incident angles were extracted, and the curved image surface was constructed through fitting. The results indicate that the imaging quality of the Fresnel lens depends on the radius of curvature. With increasing focal length, r(80) decreases gradually until it remains unchanged. The tooth width and thickness of the lens affect the structural complexity of the lens and have little impact on imaging quality. The curved image surface design can effectively suppress the aberrations and changes in the solid angle caused by increased incidence angles, maintaining an acceptance that is approximately consistent across different incidence angles. To meet the scientific objectives (wide FoV and low-energy threshold) consistent with HADAR and consider the engineering constraints (focal length <= 10 m), we select a Fresnel lens with a diameter of 2.0 m and a focal length of 5.3 m (FoV angle 29 degrees, total acceptance 9.81 m2 & centerdot;sr) as the basic lens unit for subsequent array performance simulation. This is based on the premise that the total acceptance is not lower than that of the water lens unit (7.43 m2 & centerdot;sr), the on-axis imaging r(80 )is less than 7.5 cm, and the FoV is as wide as possible.

The Electron-Thermal Neutron Detector Array (ENDA) is located at the Large High Altitude Air Shower Observatory (LHAASO, 4410 m.a.s.l.). It aims to measure the composition-resolved energy spectrum of cosmic rays, particularly in the knee region. Currently, 64 detectors, referred to as ENDA-64, have been deployed and have been operational for over a year. This paper presents the current status of ENDA-64, including the detector’s operational performance, neutron spectrum measurement, and the lateral distributions of secondary particles.

We investigate the intrinsic distributions of key Gamma-Ray Burst (GRB) parameters that are essential to understanding the physics of their central engines, radiation mechanisms, and cosmological evolution. Using our independently developed GodEyes Monte Carlo framework, we generate synthetic long-GRB samples tailored to the Swift/BAT detector and explicitly incorporate instrumental selection effects. In particular, we account for the loss of low-peak-flux events due to the detector's sensitivity threshold, thereby enabling consistent comparisons between theoretical models and observations. Our results constrain the intrinsic distributions of several fundamental properties, including redshift, peak luminosity, isotropic energy, and related quantities. We find that the inferred intrinsic distribution of the spectral index alpha(PL) deviates significantly from that derived from the observed sample. Moreover, we identify an excess of low-luminosity GRBs and show that a triple power-law luminosity function provides a substantially improved description of the data. By establishing a complete forward-modeling and validation pipeline, this work underscores the importance of accounting for observational biases and lays the groundwork for future tests with upcoming detections of faint and optically dark GRBs.

HADAR is an ultra-wide-angle atmospheric Cherenkov telescope that employs a water-lens optical system, offering significant advantages in detecting gamma-ray sources, including bursts, transients, and extended sources. Given its implementation of an innovative transmissive optical technology, the precise pointing accuracy of both the telescope and imaging system is critical, as it directly influences the reconstruction accuracy of gamma-ray events based on Cherenkov light detection. Consequently, rigorous calibration is essential. In this study, we present a calibration method to determine the optical axis orientation of the HADAR imaging system. This method leverages the distinct signal variations observed in the imaging system’s pixel units when bright stars transit through the field of view of the water lens, thereby enabling the precise calibration of the telescope’s geometric properties. Applying this method to the 0.9-meter HADAR prototype system, we analyzed the imaging characteristics induced by bright stars and performed an accurate calibration of the prototype’s imaging system alignment. Our results confirm the effectiveness of this calibration approach. This technique will be further employed for the alignment and calibration of future large-aperture water-lens telescopes in the HADAR experiment.

We develop a self-consistent nonlinear extension of diffusive shock acceleration that incorporates cosmic-ray (CR) backreaction on the shock precursor together with a physically motivated upstream escape mechanism that yields an exponential high-energy cutoff. The CR pressure gradient decelerates the upstream flow ahead of the shock, generating an extended precursor in which higher-rigidity particles sample a larger cumulative velocity gradient and thereby acquire a progressively harder spectrum. Finite-size and escape effects are modeled by a momentum-dependent loss term, which naturally terminates acceleration and steepens the spectrum near the cutoff. The precursor compression ratio is not imposed as a closure condition; instead, it is determined dynamically by enforcing consistency between the injection rate inferred from thermal leakage at the subshock and the injection strength required by the nonlinear shock modification, with CR-driven wave heating providing stabilizing negative feedback. Applying the model to young supernova-remnant-like parameters and standard one-zone Galactic diffusion, we reproduce the main features of the latest DAMPE proton spectrum: gradual hardening from hundreds of GeV to multi-TeV energies, followed by an exponential cutoff at tens of TeV. The resulting spectral evolution follows directly from the competition between precursor-mediated nonlinear feedback and upstream escape.

Cloud radiative forcing (CRF) exerts a profound influence on the global radiation budget and climate change, yet retrieval methods, accuracy, and regional applicability remain in urgent need of improvement, and highresolution gridded data products are still lacking. In this study, we developed a physics-machine learning (ML) hybrid retrieval approach for CRF by combining an atmospheric radiative transfer model with ML techniques. Regional validation demonstrates that the optimal method achieved monthly mean R2 values of 0.88 for both the top of the atmosphere (TOA) and the bottom of the atmosphere (BOA) shortwave CRF (SWCRF), with corresponding RMSE values of 11.79 and 13.82 W & sdot;m- 2. Ground-based station validation further shows that the optimal method yields a daily mean R2 of 0.83 for BOA SWCRF, underscoring its high accuracy and robustness across diverse spatial and temporal scales. Applying this method, we generated a 2002-2022 SWCRF dataset over the Qinghai-Xizang Plateau, with mean values of -54.3, -63, and 8.7 W & sdot;m- 2 for TOA, BOA, and atmospheric (ATM) forcing, respectively. TOA and BOA exhibit gradually intensifying cooling effects, while ATM shows a rapidly weakening warming effect. Cloud fraction, cloud optical thickness, and water vapor are identified as the dominant factors influencing SWCRF. This work substantially enhances the precision and resolution of CRF retrievals and provides an important reference for climate change impact studies.

Short gamma-ray bursts (sGRBs) are widely believed to originate from mergers of compact binaries, including binary neutron stars and neutron star–black hole systems. However, the observed sGRB population is strongly shaped by selection effects associated with detector sensitivity, triggering criteria, and jet orientation, which bias the inferred luminosity, redshift, and spectral distributions. We develop a forward-modeling framework to constrain the intrinsic properties and cosmic formation rate of sGRBs by simulating their detection with two independent instruments operating in different energy bands: the Fermi Gamma-ray Burst Monitor (GBM) and the Swift Burst Alert Telescope (BAT). At the level of the raw observations, the two samples exhibit apparent differences in their brightness and spectral distributions. We generate synthetic sGRB populations using parameterized luminosity functions, spectral models, and redshift evolution tied to the cosmic star formation history convolved with a power-law delay-time distribution. Each burst is passed through realistic, instrument-specific detector responses, background conditions, and onboard trigger algorithms, and is then spectrally fit to recover observable quantities. We find that a single intrinsic population model nevertheless provides a statistically consistent description of both datasets, reproducing the observed distributions of low-energy spectral index, peak energy, and fluence. The analysis reveals strong selection biases that favor low-redshift detections and truncate the observed distributions of peak energy, fluence, and duration, while only weakly affecting the low-energy spectral index. Correcting for jet beaming, we infer local sGRB formation rates of ∼258 and 562 yr ^−1 Gpc ^−3 from Swift/BAT and Fermi/GBM, broadly consistent with binary neutron-star merger rates inferred from gravitational-wave observations.

Investigating the intrinsic distributions of gamma-ray bursts (GRBs) is essential for understanding their physical origins, as these properties are closely tied to the central engine, radiation mechanisms, and cosmological evolution. In this study, we examine the intrinsic parameters of GRBs using synthetic populations calibrated to Fermi Gamma-ray Burst Monitor (Fermi-GBM) observations. We generated a large GRB population through Monte Carlo-based population modeling, simulated the Fermi-GBM detector response, and performed spectral fitting for simulated detected bursts. By comparing the simulation output with actual Fermi-GBM data, we find that the observed properties of the simulated bursts show good agreement with real observations, demonstrating the reliability of our simulation pipeline and spectral-fitting procedures. We also identify a noticeable deviation in the beta parameter between the intrinsic distribution (before detector response) and the observed distribution (after detector response), which is likely driven by statistical uncertainties under low signal-to-noise conditions. Based on the validated simulations, we derive the intrinsic distributions of key long-GRB properties-including luminosity, isotropic energy, and redshift-and estimate a local GRB rate of 1.41 +/- 0.22 Gpc-3 yr-1.

The characteristic structure of cosmic-ray anisotropy around 200 GeV provides a key opportunity to study the origin and propagation of cosmic rays. With an anisotropy amplitude of only 10^-4 at this energy, this regime is particularly well suited for testing anisotropy models. Existing space- and ground-based experiments have not yet achieved sufficiently accurate measurements of this structure. The High Altitude Detection of Astronomical Radiation (HADAR) experiment may be particularly well suited to address this issue. This paper presents the expected HADAR observations of large-scale cosmic-ray anisotropy in the 0.1–10 TeV range. The analysis indicates that HADAR should achieve the statistical precision required to resolve anisotropy amplitudes of approximately 0.01

Introduction:Electron-Neutron Detector Array (ENDA) is designed to measure thermal neutrons produced by hadronic interactions between cosmic ray extensive air showers (EAS) and the surrounding environment as well as electrons around the cores of EAS. ENDA is located within Large High Altitude Air Shower Observatory (LHAASO). ENDA was expanded from an initial 16 detectors to 64 detectors in April 2023, so called ENDA-64, and has been running alongside LHAASO. The stability and consistency of neutron detection are crucial for laying a solid foundation for subsequent data analysis and physical results. Methods:We obtain the stability by studying variations of event rate and thermal neutron rate in each cluster and the consistency by comparing distribution of number of thermal neutrons between clusters. Additionally, we investigate the specific influences of the rainy and dry seasons, as well as the presence or absence of sand cubes under the detectors, to examine the environmental factors affecting neutron measurement performance. Results:The calibration results indicate good consistency in thermal neutron detection across the clusters, with the maximum inconsistency of 6.85%. The maximum instability of event rate and thermal neutron rate over time are 4.68% and 11.0% respectively. The maximum inconsistency between the clusters without the sand cubes is 18%. The use of sand cubes is effective in protecting the target material from rainwater, and the sand cubes help the cluster to increase collection of neutrons generated by EAS events.

This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024, during which extensive construction modified the original landscape. The study focuses on the impacts of meteorological factors and building obstructions. The results reveal a progressive degradation in seeing as the monitoring setup passively changed: the median values were 0.'' 76 (the original location), 0.'' 83 during the Terrace, and 0 .'' 99 at the new Dome (temporarily considered the permanent monitoring location). Once the instruments are fully deployed, wind speed and wind direction critically affect seeing quality, with optimal conditions occurring when the wind speed is 2-6 m s(-1) and the wind direction is between 180 degrees and 270 degrees. However, in 2023 and 2024, the wind speeds decreased, and the prevailing wind direction shifted from southwest to northwest, correlating with poorer seeing. Computational Fluid Dynamics simulations reveal that the construction of the Wide Field Survey Telescope altered the local wind field, increasing turbulence around the Dome, especially when the winds blow from 225 degrees to 255 degrees. In contrast, Platform A, located in a higher and more open area, consistently maintained better seeing, particularly after midnight, likely due to fewer obstructions and lower nocturnal heat release.

Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), γ-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by γ-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energies. However, discerning the dominant acceleration mechanisms (leptonic versus hadronic), the relative contributions of specific source classes, and the role of particle transport in shaping their observed emission are central goals of modern UHE astrophysics. Here we report the discovery of a giant UHE γ-ray emitter at -17.5° off the Galactic plane - a region where UHE γ-ray sources are rarely found. The emitter exhibits a distinctive asymmetric shape, resembling a giant "Peanut" spanning 0.45° \times 4.6°, indicative of anisotropic particle distribution over a large area. A highly aged millisecond pulsar (MSP) J0218+4232 is the sole candidate accelerator positionally coincident with the Peanut region. Its association with UHE γ-rays extending to 0.7 PeV, if confirmed, would provide the first evidence of a millisecond pulsar powering PeV particles. Such a finding challenges prevailing models, which posit that millisecond pulsars cannot sustain acceleration to PeV energies. The detection reveals fundamental gaps in understanding particle acceleration, cosmic-ray transport, and interstellar magnetic field effects, potentially revealing new PeV accelerator (PeVatron) classes.

Studying the afterglow of gamma-ray bursts (GRBs) is essential for refining theoretical models, uncovering their underlying physical processes, and exploring potential new physics. Multiwavelength investigations have emerged as a fundamental approach for deciphering the complex nature of GRBs, harnessing the complementary observational capabilities of advanced spaceborne observatories and sophisticated ground-based facilities. The High Altitude Detection of Astronomical Radiation (HADAR) experiment utilizes a novel wide-angle atmospheric Cherenkov detection technology, offering the advantages of a wide field of view and a low energy threshold. It is capable of not only observing the very-high-energy (VHE) gamma radiation from GRBs but also conducting observational studies on the optical afterglow of GRBs. In this work, we simulated the expected observations of HADAR for the optical and VHE gamma radiation afterglow of GRB 190114C. The results indicate that HADAR can effectively observe both bands of this GRB, particularly demonstrating excellent sensitivity in the optical band and providing good imaging of its radiation process. This demonstrates that HADAR is capable of conducting effective observations and research on the optical radiation of similar GRBs. Its contributions can refine relevant theoretical research and may enable attempts to observe gravitational-wave counterparts.