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1. Search for Neutrino Emission from Hard X-Ray AGN with IceCube

   https://doi.org/10.3847/1538-4357/ada94b  

   Abbasi, R; Ackermann, M; Adams, J; Agarwalla, S K; Aguilar, J A; Ahlers, M; Alameddine, JM; Amin, N M; Andeen, K; Argüelles, C; et al (March 2025, The Astrophysical Journal)

   Abstract Active galactic nuclei (AGN) are promising candidate sources of high-energy astrophysical neutrinos, since they provide environments rich in matter and photon targets where cosmic-ray interactions may lead to the production of gamma rays and neutrinos. We searched for high-energy neutrino emission from AGN using the Swift-BAT Spectroscopic Survey catalog of hard X-ray sources and 12 yr of IceCube muon track data. First, upon performing a stacked search, no significant emission was found. Second, we searched for neutrinos from a list of 43 candidate sources and found an excess from the direction of two sources, the Seyfert galaxies NGC 1068 and NGC 4151. We observed NGC 1068 at flux ${\varphi }_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}$= $4.02_{-1.52}^{+1.58}\times 10^{-11}$TeV⁻¹cm⁻²s⁻¹normalized at 1 TeV, with a power-law spectral indexγ= 3.10 ${}_{-0.22}^{+0.26}$, consistent with previous IceCube results. The observation of a neutrino excess from the direction of NGC 4151 is at a posttrial significance of 2.9σ. If interpreted as an astrophysical signal, the excess observed from NGC 4151 corresponds to a flux ${\varphi }_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}$= $1.51_{-0.81}^{+0.99}\times 10^{-11}$TeV⁻¹cm⁻²s⁻¹normalized at 1 TeV andγ= 2.83 ${}_{-0.28}^{+0.35}$. 

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2. The half-volume spectrum of a manifold

   https://doi.org/10.1007/s00526-025-02949-z  

   Mazurowski, Liam; Zhou, Xin (May 2025, Calculus of Variations and Partial Differential Equations)

   Abstract We define the half-volume spectrum$$\{{\tilde{\omega }_p\}_{p\in \mathbb {N}}}$$ $\{{\tilde{\omega }}_p{\}}_{p\in N}$of a closed manifold$$(M^{n+1},g)$$ $(M^{n+1},g)$. This is analogous to the usual volume spectrum ofM, except that we restrict top-sweepouts whose slices each enclose half the volume ofM. We prove that the Weyl law continues to hold for the half-volume spectrum. We define an analogous half-volume spectrum$$\tilde{c}(p)$$ $\tilde{c}\left(p\right)$in the phase transition setting. Moreover, for$$3 \le n+1 \le 7$$ $3\le n+1\le 7$, we use the Allen–Cahn min-max theory to show that each$$\tilde{c}(p)$$ $\tilde{c}\left(p\right)$is achieved by a constant mean curvature surface enclosing half the volume ofMplus a (possibly empty) collection of minimal surfaces with even multiplicities. 

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3. HERA Phase I Limits on the Cosmic 21 cm Signal: Constraints on Astrophysics and Cosmology during the Epoch of Reionization

   https://doi.org/10.3847/1538-4357/ac2ffc  

   Abdurashidova, Zara; Aguirre, James E.; Alexander, Paul; Ali, Zaki S.; Balfour, Yanga; Barkana, Rennan; Beardsley, Adam P.; Bernardi, Gianni; Billings, Tashalee S.; Bowman, Judd D.; et al (January 2022, The Astrophysical Journal)

   Abstract Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced the experiment’s first upper limits on the power spectrum of 21 cm fluctuations atz∼ 8 and 10. Here, we use several independent theoretical models to infer constraints on the intergalactic medium (IGM) and galaxies during the epoch of reionization from these limits. We find that the IGM must have been heated above the adiabatic-cooling threshold byz∼ 8, independent of uncertainties about IGM ionization and the radio background. Combining HERA limits with complementary observations constrains the spin temperature of thez∼ 8 neutral IGM to 27 K $〈{\overline{T}}_S〉$630 K (2.3 K $〈{\overline{T}}_S〉$640 K) at 68% (95%) confidence. They therefore also place a lower bound on X-ray heating, a previously unconstrained aspects of early galaxies. For example, if the cosmic microwave background dominates thez∼ 8 radio background, the new HERA limits imply that the first galaxies produced X-rays more efficiently than local ones. Thez∼ 10 limits require even earlier heating if dark-matter interactions cool the hydrogen gas. If an extra radio background is produced by galaxies, we rule out (at 95% confidence) the combination of high radio and low X-ray luminosities ofL_r,ν/SFR > 4 × 10²⁴W Hz⁻¹ $M_{\odot }^{-1}$yr andL_X/SFR < 7.6 × 10³⁹erg s⁻¹ $M_{\odot }^{-1}$yr. The new HERA upper limits neither support nor disfavor a cosmological interpretation of the recent Experiment to Detect the Global EOR Signature (EDGES) measurement. The framework described here provides a foundation for the interpretation of future HERA results. 

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4. Detection of Molecular Clouds in the PeVatron Candidate Source LHAASO J0341+5258 by the Nobeyama 45-m Radio Telescope

   https://doi.org/10.3847/1538-4357/adb7df  

   Tsuji, Naomi; Takekawa, Shunya; Mori, Kaya; Mitchell, Alison; Zhang, Shuo; Bangale, Priyadarshini; DiKerby, Stephen; Ergin, Tülün; Woo, Jooyun; Safi-Harb, Samar; et al (April 2025, The Astrophysical Journal)

   Abstract We report a new CO observation survey of LHAASO J0341+5258, using the Nobeyama Radio Observatory 45-m telescope. LHAASO J0341+5258 is one of the unidentified ultra-high-energy (UHE;E> 100 TeV) gamma-ray sources detected by LHAASO. Our CO observations were conducted in 2024 February and March, with a total observation time of 36 hr, covering the LHAASO source (∼0 $\stackrel{\text{°}}{.}$3–0 $\stackrel{\text{°}}{.}$5 in radius) and its surrounding area (1° × 1 $\stackrel{\text{°}}{.}$5). Within the LHAASO source extent, we identified five compact (<2 pc) molecular clouds at nearby distances (<1–4 kpc). These clouds can serve as proton–proton collision targets, producing hadronic gamma rays via neutral pion decays. Based on the hydrogen densities (700–5000 cm⁻³) estimated from our CO observations and archived Hidata from the Dominion Radio Astrophysical Observatory survey, we derive the total proton energy ofW_p(E> 1 TeV) ∼ 10⁴⁵erg to account for the gamma-ray flux. One of the molecular clouds appears to be likely associated with an asymptotic giant branch (AGB) star with an extended CO tail, which may indicate some particle acceleration activities. However, the estimated maximum particle energy below 100 TeV makes the AGB-like star unlikely to be a PeVatron site. We conclude that the UHE emission observed in LHAASO J0341+5258 could be due to hadronic interactions between the newly discovered molecular clouds and TeV–PeV protons originating from a distant SNR or due to leptonic emission from a pulsar wind nebula candidate, which is reported in our companion X-ray observation paper. 

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5. Multiwavelength Observation of a Candidate Pulsar Halo LHAASO J0621+3755 and the First X-Ray Detection of PSR J0622+3749

   https://doi.org/10.3847/1538-4357/adc92b  

   Adams, C B; Archer, A; Bangale, P; Bartkoske, J T; Benbow, W; Buckley, J H; Chen, Y; Christiansen, J L; Chromey, A J; Duerr, A; et al (May 2025, The Astrophysical Journal)

   Abstract Pulsar halos are regions around middle-aged pulsars extending out to tens of parsecs. The large extent of the halos and well-defined central cosmic-ray accelerators make this new class of Galactic sources an ideal laboratory for studying cosmic-ray transport. LHAASO J0621+3755 is a candidate pulsar halo associated with the middle-aged gamma-ray pulsar PSR J0622+3749. We observed LHAASO J0621+3755 with VERITAS and XMM-Newton in the TeV and X-ray bands, respectively. For this work, we developed a novel background estimation technique for imaging atmospheric Cherenkov telescope observations of such extended sources. No halo emission was detected with VERITAS (0.3–10 TeV) or XMM-Newton (2–7 keV) within 1^∘and $10^{\prime }$around PSR J0622+3749, respectively. Combined with the LHAASO Kilometer Square Array (KM2A) and Fermi-LAT data, VERITAS flux upper limits establish a spectral break at  ∼1–10 TeV, a unique feature compared with Geminga, the most studied pulsar halo. We model the gamma-ray spectrum and LHAASO-KM2A surface brightness as inverse Compton emission and find suppressed diffusion around the pulsar, similar to Geminga. A smaller diffusion suppression zone and harder electron injection spectrum than Geminga are necessary to reproduce the spectral cutoff. A magnetic field ≤1μG is required by our XMM-Newton observation and synchrotron spectral modeling, consistent with Geminga. Our findings support slower diffusion and lower magnetic field around pulsar halos than the Galactic averages, hinting at magnetohydrodynamic turbulence around pulsars. Additionally, we report the detection of an X-ray point source spatially coincident with PSR J0622+3749, whose periodicity is consistent with the gamma-ray spin period of 333.2 ms. The soft spectrum of this source suggests a thermal origin. 

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