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The Pierre Auger Observatory (Auger) and the Telescope Array (TA) are the world's two largest ultra-high-energy cosmic ray (UHECR) observatories. They operate in the Southern and Northern hemispheres, respectively, at similar latitudes but with distinct surface detector (SD) designs. A significant challenge in studying UHECR physics across the full sky is the apparent discrepancy in flux measurements between the two experiments. This discrepancy could arise from astrophysical differences and/or systematic effects related to their detector designs and sensitivities to extensive air shower components. To address this, the Auger@TA working group aims to cross-calibrate the two observatories with a self-triggering micro-Auger array within the TA array. This micro-array consists of eight Auger Surface Detector (SD) stations equipped with Water Cherenkov Detectors (WCDs) and AugerPrime Surface Scintillator Detectors. Seven SD stations, configured with a centered-1-PMT design, are arranged in a hexagonal pattern with one station in the center, with 1.5 km spacing, mirroring the Auger layout. The eighth station, which features a standard 3-PMT Auger station, is located in conjunction with a TA detector at the center of the hexagon, forming a triplet for high-statistics and low-uncertainty cross-calibration. A custom communication system that uses readily available components enables seamless communication between stations and remote access to each station through a central computer. The micro-array is now fully deployed, and initial data-taking is about to start. This presentation will detail the instrumentation, communication systems, central data acquisition system, expected performance of the micro-array, and preliminary results as appropriate. 

With dramatic advancements in biological data generation, genetic rescue and reproductive technologies, and inter-institutional coordination of care across entire animal populations, zoos, aquariums, and their collaborators are uniquely positioned to lead population-wide research benefiting animal wellbeing and species survival. However, procedural and inter-institutional barriers make it exceedingly difficult to access existing zoological biospecimens and data at scale. To address this, the Zoonomics Working Group, representing diverse roles across three zoological associations (AZA, EAZA, WAZA), proposes a biodiversity biobank alliance that develops and delivers shared resources to support the collection, storage, and sharing of biological samples and associated data across the zoological and conservation community. By biobank alliance, we mean a community-guided effort that develops shared resources, standards, ethos, and practices for collecting, storing, and sharing biological samples and associated data voluntarily through transparent processes, consistent with professional accreditation standards and international best practices. While initially focused on addressing the needs and regulatory landscape of U.S. institutions, the alliance is designed to create frameworks that are adaptable and adoptable for international expansion. Such a framework would help the zoological community navigate the ethical, legal, and practical challenges of managing biospecimen collections, making access more efficient, reliable, and robust. Achieving this vision requires collective agreement on ethical principles such as reciprocity, transparency, and data stewardship, ensuring that research is both feasible and proactively supported. Such coordination will drive advances in fundamental biology and accelerate progress in animal health, welfare, management, and biodiversity conservation. 

Abstract Axion-like particles (ALPs) are hypothetical particles and compelling candidates for cold dark matter. Their existence could be probed through their conversions into photons in the presence of magnetic fields. In this work, we explore the effect of these photon-ALP conversions by searching for an attenuation in the observed gamma ray spectra of galactic sources that emit at energies of hundreds of TeV. We analyze data from the High-Altitude Water Cherenkov (HAWC) Observatory for the source 3HWC J1908+063. No evidence of photon-ALP conversions was found, and we set constraints on the ALP parameter space. Specifically, we derive exclusion limits for ALPs with masses in the range 10^-8 eV ≤m_a≤ 10^-6 eV and photon-ALP couplings in the range 10^-12 GeV^-1≤g_aγ≤ 10^-10 GeV^-1, based on HAWC observations. 

Abstract We present a new study on the MeV–TeVγ-ray origin of HESS J1857+026 using data collected from the Fermi–LAT, VERITAS, and HAWC observatories. A spatial and spectral study of HESS J1857+026 including radiative modeling of the MeV–TeV spectrum determines the likely dominantγ-ray origin as a pulsar wind nebula (PWN) powered by the energetic pulsar PSR J1856+0245. The MeV–TeV spectrum is further characterized through basic evolutionary radiative modeling assuming a PWN origin to constrain the physical properties of the system such as the magnetic field strength and PWN age. The results of the PWN evolutionary model are consistent with the observational constraints of the system, finding an age of the system betweenτ = [16, 21] kyr and a magnetic field strength betweenB = [0.4, 1.6]μG. These estimates support an evolved PWN scenario where the observedγ-ray emission is generated by the relativistic electrons' inverse Compton (IC) scattering off local photon fields; however, the low-energy (E < 10 GeV) spectral component could be dominated by hadronic emission originating from a supernova remnant (SNR). For a PWN component above 10 GeV, we measure the conditions for particle diffusion, finding that the local diffusion (D(50 TeV) ∼ 10²⁸cm⁻²s⁻¹) is suppressed compared to the interstellar medium (ISM) value, in agreement with similar TeV PWNe. By measuring the radial surface brightness profiles of theγ-ray source across multiple instruments, we demonstrate that the combined MeV–TeV spatial information is a powerful tool to constrain particle diffusion properties. 

We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from theGaiaspace mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 (~77%) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 are sdOBs (~21%), 32 are sdOs (~11%), and 30 are He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in theGaiacolour-magnitude diagram. The remaining sources in the sample include cataclysmic variables, blue horizontal branch stars, hot white dwarfs, and MS stars. We derived the mid-plane densityρ₀and scale height h_zfor the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech²). The best-fit values areρ₀= 5.17 ± 0.33 × 10⁻⁷stars pc⁻³and h_z= 281 ± 62 pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases toρ₀= 6.15_−0.53^+1.16× 10⁻⁷stars pc⁻³. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates. 

Abstract We present the monitoring of the TeV-emitting radio galaxies M87, NGC 1275, 3C 264, and IC 310 with the High-Altitude Water Cherenkov Observatory (HAWC) over a period of approximately 7.5 yr. The analysis includes light curves at daily, weekly, and monthly timescales for the four sources. We report the detection of gamma-ray emission from M87 with a significance exceeding 5σ, providing the integrated TeV spectrum from the longest temporal coverage to date. The source is well described as a point-like source modeled by a power-law spectrum with spectral index Γ = 2.53 ± 0.29 and a flux of (7.09 ± 1.24) × 10⁻¹³cm⁻²s⁻¹TeV⁻¹at 1 TeV. The maximum energy of the detected emission in M87, at 1σconfidence level, reaches 26.5 TeV. HAWC’s observation of M87 reveals a low flux spectrum for the longest observation to date of this radio galaxy. 3C 264 is marginally detected with a significance slightly below 4σ, while NGC 1275 and IC 310 are not detected. The weekly light curves show an increased number of fluxes above 2σfor M87 starting in 2019 and for 3C 264 starting in 2018, which can be interpreted as the moments at which these sources start to exhibit an enhanced steady TeV emission. Cumulative significance analysis reveals quantitative evidence for long-term variability. M87 shows enhanced emission from 2019, while 3C 264 exhibits increased activity from 2018, resembling variable sources like Markarian 421 rather than steady sources like the Crab. This supports the importance of monitoring radio galaxies to identify periods of higher activity and flares, enabling further multimessenger studies. 

Abstract Gamma-ray binaries are luminous in gamma rays, composed of a compact object orbiting a massive companion star. The interaction between these two objects can drive relativistic outflows, either jets or winds, in which particles can be accelerated to energies reaching hundreds of teraelectronvolts (TeV). However, it is still debated where and under which physical conditions particles are accelerated in these objects and ultimately whether protons can be accelerated up to PeV energies. Among the well-known gamma-ray binaries, LS 5039 is a high-mass X-ray binary with an orbital period of 3.9 days that has been observed up to TeV energies by the High Energy Stereoscopic System. We present new observations of LS 5039 obtained with the High Altitude Water Cherenkov (HAWC) observatory. Our data reveal that the gamma-ray spectrum of LS 5039 extends up to 200 TeV with no apparent spectral cutoff. Furthermore, we confirm, with a confidence level of 4.7σ, that the emission between 2 and 118 TeV is modulated by the orbital motion of the system, and find a 2.2σhint of variability above 100 TeV. This indicates that these photons are likely produced within or near the binary orbit, where they can undergo absorption by the stellar photons. In a leptonic scenario, the highest energy photons detected by HAWC can be emitted by ∼200 TeV electrons inverse Compton scattering stellar photons, which would require an extremely efficient acceleration mechanism operating within LS 5039. Alternatively, a hadronic scenario could explain the data through proton–proton or proton–gamma collisions of protons accelerated to petaelectronvolt energies.