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Physics Astrophysics High Energy Astrophysical Phenomena

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Monday 24 August

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM

A General Response Theory for Closure Phases through Visibility Nulls and Image Structure

Shokoufe Faraji and Avery E. Broderick

Closure phase is robust to station based phase errors, yet its connection to image structure is often interpreted only qualitatively and a nonzero closure phase is still interpreted mainly through qualitative symmetry arguments or source specific models. We develop, to our knowledge, the first unified response theory for an arbitrary brightness distribution and an arbitrary zero free observing triangle. Away from visibility zeros, closure phase is naturally a log-visibility observable. This structure yields an exact first order master kernel for image perturbations and a Cartesian moment hierarchy that separates the spatial content of the source change from the sensitivity of the sampled triangle. For a fixed image, the same framework gives a local expansion in Fourier plane displacement, providing a direct description of closure phase evolution along observing tracks. We then identify the boundary of this regular regime: at a true visibility null, the log-visibility expansion fails and the phase behavior is controlled by the local properties of the null, including its order and winding charge, distinguishing removable phase wraps, non-null visibility minima, and nulls for which the visibility phase is multivalued. We validate these expansions using structured ring models. We then apply both branches of the theory to EHT data of M87*, and demonstrate the ability to measure asymmetric image structure associated with higher image moments directly from the evolution of the closure phase. Finally, we show that the same formalism extends naturally to Phase Closure Nulling in optical and infrared interferometry. The resulting framework turns closure phase structure into a quantitative probe of faint and asymmetric source features across interferometric regimes.
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High Energy Astrophysical Phenomena

Signatures of Compact Object Mergers Inside Stars in AGN Disks

Matteo Cantiello, Alexander J. Dittmann, Saavik Ford et al. (+4 more)

Disks of gas accreting onto supermassive black holes, powering active galactic nuclei (AGN), can capture stars from nuclear star clusters or form stars in situ via gravitational instability. The dense, hot disk environment can drive rapid accretion onto embedded stars, dramatically altering their evolution. Models predict that, for sufficiently rapid accretion, fresh gas replenishes hydrogen in stellar cores as quickly as it is burned, and the stars reach a quasi-steady state. Here we study encounters of such massive, long-lived (”immortal”) stars with compact objects in AGN disks. We estimate the encounter rate and the timescale for a single compact remnant to spiral into an AGN star; depending on how strongly feedback regulates the ensuing accretion, the star is either consumed in a collapsar-like, engine-driven transient or converted into a long-lived, quasi-star-like object hosting a central black hole. We then study the merger of a binary black hole (BBH) inside the AGN star, and show that gas drag hardens the binary to merger far faster than gravitational-wave emission alone. The resulting merger is a loud LIGO-Virgo-KAGRA (LVK) source, but the characteristic imprint of the dense environment -a strong suppression and dephasing of the inspiral relative to vacuum- falls in the deci-Hz band rather than the milli-Hz LISA band, and is best resolved by next-generation detectors such as DECIGO. We estimate that this channel could contribute a BBH merger rate of up to $\sim8\,{\rm Gpc^{-3}\,yr^{-1}}$ in favorable scenarios, and discuss the model uncertainties and directions for future work.
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All authors Matteo Cantiello, Alexander J. Dittmann, Saavik Ford, Barry McKernan, Carlos Palenzuela, Rosalba Perna, Taeho Ryu

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

Spin inference with the Black Hole Explorer. I. Fisher information matrix forecast

Joseph R. Farah, Daniel C. M. Palumbo, Michael D. Johnson et al. (+1 more)

General relativity predicts the presence of a thin, bright ring of light superimposed on the image of a black hole (the “photon ring”), whose geometry is sensitive to the spin of the black hole. Detecting this photon ring in observations of nuclear supermassive black holes would yield insight into gravity in the strong-field regime as well as their growth histories. The Black Hole Explorer (BHEX) is a mission being developed to detect the photon ring for the first time, raising the question of how precisely we can constrain spin from its observations. We use the method of Fisher information matrices (FIMs) along with a simple dual-cone semi-analytic emission model to forecast BHEX spin posterior widths for the primary science targets (M87* and Sgr~A*) in a variety of configurations. We find that BHEX can constrain the dimensionless spin of its targets to a precision of $\sigma_{a_*} \ll 0.1$ after 30 orbits, even in the presence of significant systematic errors. We validate our results via numerical checks for stability and robustness, as well as synthetic data cross-validation to assess handling of covariances and prior information in the FIM against a full posterior exploration.
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All authors Joseph R. Farah, Daniel C. M. Palumbo, Michael D. Johnson, Dominic O. Chang

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

More Numerous and Bluer: Companions of the Brightest Little Red Dots Differ from Control Galaxies at $>3\sigma$, Hinting at Synchronized Black Hole Seed Formation

Fabio Pacucci and C. Megan Urry

The Little Red Dots (LRDs) are compact, red sources at $4 \lesssim z \lesssim 9$, likely powered by accreting massive black holes. Multiple studies have detected blue companions in their vicinity: we compare $253$ LRDs, uniformly selected across several JWST deep fields, against $>7000$ matched controls in the same mosaics. We find that $27.7\%$ of the brightest LRD quartile (in F444W) hosts a blue ($\beta<-1$) companion at $0.5-2$ kpc, versus $11.6\%$ of redshift-matched controls: a $\times 2.39$ excess, significant at $3.3\sigma$. Against controls additionally matched in brightness and compactness, the excess ratio is similar ($\times 2.17$), although constrained only at $1.4\sigma$ by the small size of that control pool. This phenomenon is limited to the brightest LRDs, as the full LRD sample pairs at a rate indistinguishable from controls. Moreover, the excess is confined to the close-pair window ($< 2$ kpc), outside which LRD environments are ordinary. Their companions are overwhelmingly ($92\%$) blue and significantly bluer than those of controls ($\beta\approx-2.32$ versus $-1.92$), rejecting a common parent distribution at $3.4\sigma$. The signal is thus directional in brightness, separation, and companion color, as expected for synchronized-pair seed formation. Therefore, we conclude that the association between the brightest LRDs and their close blue companions is physical, i.e., the two phenomena are causally connected: either one drives the other, or both emerge from the same synchronized formation event. A natural explanation is that the radiation from these young, star-forming neighbors enabled the direct collapse of the massive black holes powering the LRDs themselves.
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High Energy Astrophysical Phenomena

Disentangling propagation effects from Fast Radio Burst spectra: An analysis on simulated data

Aishwarya Kumar, Fereshteh Rajabi and Martin Houde

We present a methodology to decouple propagation effects, specifically scattering and dispersion, from the intrinsic spectro-temporal properties of repeating Fast Radio Bursts. Utilizing the Triggered Relativistic Dynamical Model, and assuming superradiance as the emission mechanism, we generate simulated sub-bursts and inject controlled levels of scattering and residual dispersion. For each burst, we measure the sub-burst slope, defined as the trajectory of the centroids in the dynamic spectrum, and the characteristic duration of the burst profile. We then fit a modified sub-burst slope law to the resulting slope-duration measurements to recover the scattering timescale, residual dispersion measure, and other model parameters. Under the thin-screen approximation, the scattering timescale at $1~\mathrm{GHz}$ is precisely recovered, typically to within $\sim 1-2\%$ of the true value. In contrast, the residual dispersion is recovered with comparatively lower precision, with median absolute errors of $\sim 0.3-0.6\ \mathrm{pc \, cm^{-3}}$, reflecting its weaker constraint and degeneracy with an intrinsic parameter. Despite this, the modified sub-burst slope law successfully reproduces the spectro-temporal evolution and accurately constrains the scattering properties even for diverse intrinsic burst populations. These results demonstrate that our framework yields a tractable method for separating propagation-induced distortions from intrinsic emission characteristics to a meaningful degree, enabling more reliable inference of the physical properties of FRB sources.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Updated Upper Limits on the Isotropic Gravitational-Wave Background from LIGO, Virgo, and KAGRA Data through April 2025

The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration: A. G. Abac et al. (+1804 more)

We report results from a search for an isotropic stochastic gravitational-wave background using data collected by the LIGO–Virgo–KAGRA Collaboration. The analysis uses data from the first observing run through April 1, 2025, during the fourth observing run. New frequency-domain cuts are implemented to address a class of non-stationary spectral noise features that were not effectively identified and mitigated by existing data-quality checks in past analyses. Consequently, previously analyzed data from the fourth observing run are re-processed with the updated cuts. We find no evidence for a stochastic background signal and place upper limits on the gravitational-wave energy density. In particular, for a background following a power law with spectral index 2/3 as predicted by inspiralling compact binaries, we find $\Omega_\mathrm{GW}(25\,\mathrm{Hz}) \leq 2.0 \times 10^{-9}$, while scale-invariant backgrounds are constrained to $\Omega_\mathrm{GW}(25\,\mathrm{Hz}) \leq 2.8 \times 10^{-9}$, both at the 95% credible level for a log-uniform prior on $\Omega_\mathrm{GW}$. Relative to the constraints from previous data recomputed with the new frequency-domain cuts, these limits improve by a factor of 1.4. We also update bounds on alternative gravity scenarios predicting non-standard polarization modes, and we verify that correlated magnetic noise sources remain below the sensitivity of this search. Combining these observational constraints with population models of compact binary coalescences informed by the latest gravitational-wave transient catalog, GWTC-5.0, we predict the amplitude of the compact binary background to be $\Omega_\mathrm{CBC}(25\,\mathrm{Hz}) = 6.3^{+5.0}_{-2.2} \times 10^{-10}$ at the 90% credible level.
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All authors The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration: A. G. Abac, A. Abe, I. Abouelfettouh, F. Acernese, K. Ackley, A. Adam, C. Adamcewicz, S. Adhicary, D. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I.-L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu, L. Albers, W. Ali, S. Al-Kershi, C. Allene, A. Allocca, S. Al-Shammari, J. A. Alvarez, S. Alvarez-Lopez, W. Amar, O. Amarasinghe, A. Amato, F. Amicucci, C. Amra, A. B. Anand, C. Anand, A. Ananyeva, S. B. Anderson, W. G. Anderson, M. Andia, M. Ando, F. Andrade-Oliveira, M. Andrés-Carcasona, J. L. Andrey, T. Andrić, J. Anglin, J. Anna, J. M. Antelis, S. Antier, T. Aoki, M. Aoumi, E. Z. Appavuravther, E. A. Appelt, S. Appert, S. K. Apple, K. Arai, A. Araya, M. C. Araya, F. Arciprete, J. S. Areeda, N. Aritomi, F. Armato, S. Armstrong, N. Arnaud, M. Arogeti, S. M. Aronson, G. Ashton, Y. Aso, L. Asprea, M. Assiduo, S. Assis de Souza Melo, S. M. Aston, P. Astone, P. S. Aswathi, F. Attadio, F. Aubin, K. AultONeal, G. Avallone, N. Avdeev, E. A. Avila, S. Babak, C. Badger, S. Bae, S. Bagnasco, S. Baimukhametova, L. Baiotti, T. Baka, K. A. Baker, T. Baker, G. Balbi, G. Baldi, N. Baldicchi, M. Ball, G. Ballardin, M. Ballelli, S. W. Ballmer, S. Banagiri, B. Banerjee, D. Bankar, T. M. Baptiste, P. Baral, M. Baratti, J. C. Barayoga, K. Baric, B. C. Barish, D. Barker, N. Barman, F. Barone, B. Barr, M. Barrios, L. Barsotti, M. Barsuglia, D. Barta, M. A. Barton, I. Bartos, A. Basalaev, R. Bassiri, A. Basti, M. Bawaj, J. C. Bayley, A. C. Baylor, P. A. Baynard II, M. Bazzan, V. M. Bedakihale, F. Beirnaert, M. Bejger, A. S. Bell, C. Bellani, D. S. Bellie, D. Beltran-Martinez, E. Benedetti, W. Benoit, I. Bentara, M. Ben Yaala, S. Bera, F. Bergamin, B. K. Berger, M. Beroiz, I. Berry, D. Bersanetti, T. Bertheas, A. Bertolini, J. Betzwieser, D. Beveridge, N. Bevins, J. Bezerra-Sobrinho, R. Bhandare, R. Bhatt, A. Bhattacharjee, D. Bhattacharjee, S. Bhattacharyya, S. Bhaumik, V. Biancalana, F. Bianchi, I. A. Bilenko, M. Bilicki, G. Billingsley, A. Binetti, S. Bini, S. Biot, O. Birnholtz, S. Biscoveanu, A. Bisht, M. Bitossi, M.-A. Bizouard, S. Blaber, J. K. Blackburn, L. A. Blagg, C. D. Blair, D. G. Blair, M. Bloch, N. Bode, N. Boettner, P. Bogdan, G. Boileau, M. Boldrini, G. N. Bolingbroke, L. D. Bonavena, V. A. Bonhomme, E. Bonilla, M. S. Bonilla, A. Bonino, R. Bonnand, A. Borchers, N. Borghi, V. Boschi, S. Bose, V. Bossilkov, Y. Bothra, A. Boudon, T. D. Boybeyi, M. Boyle, A. Bozzi, C. Bradaschia, M. J. Brady, P. R. Brady, A. Branch, M. Branchesi, T. Briant, A. Brillet, M. Brinkmann, P. Brockill, E. Brockmueller, A. F. Brooks, D. D. Brown, M. L. Brozzetti, S. Brunett, G. Bruno, R. Bruntz, J. Bryant, Y. Bu, F. Bucci, A. Buchicchio, A. Buggiani, O. Bulashenko, T. Bulik, H. J. Bulten, A. Buonanno, K. Burtnyk, R. Buscicchio, N. Busdon, D. Buskulic, R. L. Byer, R. Cabrita, V. A. Cáceres-Barbosa, L. Cadonati, G. Cagnoli, C. Cahillane, A. Calafat, J. Calderón Bustillo, J. D. Callaghan, T. A. Callister, E. Calloni, S. R. Callos, K. Cannon, V. Cantory, H. Cao, L. A. Capistran, E. Capocasa, G. Capoccia, E. Capote, C. Capuano, G. Capurri, F. Carbognani, K. J. Cardona-Martínez, M. Carlassara, M. Carpinelli, G. Carrillo, G. Carullo, A. Casallas-Lagos, J. Casanueva Diaz, C. Casentini, S. Caudill, M. Cavaglià, R. Cavalieri, A. Ceja, G. Cella, P. Cerdá-Durán, E. Cesarini, N. Chabbra, W. Chaibi, A. Chakraborty, P. Chakraborty, S. Chakraborty, S. Chalathadka Subrahmanya, C. Chan, J. C. L. Chan, M. Chan, C.-Y. Chang, K. Chang, S. Chao, P. Charlton, E. Chassande-Mottin, C. Chatterjee, Debarati Chatterjee, Deep Chatterjee, M. Chaturvedi, S. Chaty, A. Chen, A. H.-Y. Chen, D. Chen, H. Chen, H. Y. Chen, S. Chen, Yanbei Chen, Yiwen Chen, G. Cheng, H. P. Cheng, P. Chessa, T. Cheunchitra, H. T. Cheung, S. Y. Cheung, F. Chiadini, G. Chiarini, A. Chiba, A. Chincarini, D. Chintala, A. Chiummo, A. Chopra, C. Chou, S. Choudhary, N. Christensen, Y. K. Chu, S. S. Y. Chua, G. Ciani, P. Ciecielag, M. Cieślar, M. Cifaldi, B. Cirok, F. Clara, J. A. Clark, T. A. Clarke, A. Claveus, M. R. Claypool, S. Clesse, F. Cleva, S. M. Clyne, E. Coccia, E. Codazzo, P.-F. Cohadon, D. E. Cohen, E. Colangeli, O. Cole, M. Colleoni, C. G. Collette, J. Collins, S. Colloms, A. Colombo, G. Compère, C. M. Compton, G. Connolly, L. Conti, T. R. Corbitt, I. Cordero-Carrión, S. Corezzi, N. J. Cornish, A. Corsi, S. Cortese, L. A. Corubolo, L. Cotnoir, R. Cottingham, J. A. Cotturone, M. W. Coughlin, P. Couvares, R. Coyne, A. Cozzumbo, J. D. E. Creighton, T. D. Creighton, S. Crook, R. Crouch, J. Csizmazia, K. Csukás, T. J. Cullen, A. Cumming, E. Cuoco, M. Cusinato, R. R. Cuzinatto, L. V. da Conceição, T. Dal Canton, S. Dall'Osso, S. Dal Pra, G. Dálya, Y. Dang, B. D'Angelo, S. Danilishin, O. Danner, S. D'Antonio, K. Danzmann, K. E. Darroch, L. P. Dartez, R. Das, S. Das, A. Dasgupta, V. Dattilo, A. Daumas, I. Dave, A. Davenport, T. F. Davies, D. Davis, M. C. Davis, P. Davis, E. J. Daw, M. Dax, J. De Bolle, E. deBruin, M. Deenadayalan, J. Degallaix, M. De Laurentis, C. J. Delgado Mendez, F. De Lillo, S. Della Torre, W. Del Pozzo, O. M. del Rio, A. Demagny, F. De Marco, G. Demasi, F. De Matteis, C. de Melo, N. Demos, T. Dent, A. Depasse, N. DePergola, R. De Pietri, R. De Rosa, C. De Rossi, E. K. Derrick, M. Desai, D. DeSantis, S. Deshmukh, V. Deshmukh, R. De Simone, S. Determan, S. Dhage, A. Dhani, R. Dhatri, R. Dhurkunde, R. Diab, C. Diaz, M. C. Díaz, F. Diaz Guerra, M. Di Cesare, M. A. Dicorato, T. Dietrich, C. Di Fronzo, M. Di Giovanni, D. Diksha, J. Ding, S. Di Pace, I. Di Palma, D. Di Piero, F. Di Renzo, Divyajyoti, A. Dmitriev, J. P. Docherty, Z. Doctor, N. Doerksen, E. Dohmen, A. Doke, A. Domiciano De Souza, L. D'Onofrio, F. Donovan, K. L. Dooley, S. Doravari, O. Dorosh, F. Dosopoulou, M. Drago, J. C. Driggers, M. Dubois, R. S. Dumbreck, U. Dupletsa, D. D'Urso, P. Dutta Roy, H. Duval, S. Dwivedi, S. E. Dwyer, C. Eassa, M. Eberhardt, M. Ebersold, M. Ebiri, G. Eddolls, A. Effler, J. Eichholz, H. Einsle, M. Eisenmann, M. Emma, K. Endo, R. Enficiaud, V. Ernst, L. Errico, R. Espinosa, M. Esposito, R. C. Essick, H. Estellés, T. Etzel, M. Evans, T. Evstafyeva, J. M. Ezquiaga, F. Fabrizi, V. Fafone, S. Fairhurst, X. Fan, A. M. Farah, B. Farr, W. M. Farr, M. Favata, M. Fays, M. Fazio, J. Feicht, M. M. Fejer, J.-N. Feldhusen, E. Fenyvesi, A. Feo, J. Fernandes, T. Fernandes, G. Fernández Rodríguez, D. Fernando, S. Ferraiuolo, T. A. Ferreira, M. Ferrer-Martinez, F. Fidecaro, P. Figura, I. Fiori, M. Fishbach, R. P. Fisher, S. K. Fitzgerald, V. Fiumara, R. Flaminio, E. Flanagan, S. M. Fleischer, L. S. Fleming, F. Flocco, E. Floden, H. Fong, J. A. Font, F. Fontinele-Nunes, C. Foo, B. Fornal, P. W. F. Forsyth, A. Fragkos, N. Franchini, A. Franco-Ordovas, F. Frappez, F. Frasconi, J. P. Freed, Z. Frei, A. Freise, O. Freitas, R. Frey, W. Frischhertz, P. Fritschel, V. V. Frolov, M. Fuentes-Garcia, R. Fujii, T. Fujimori, Y. Fujiwara, P. Fulda, M. Fyffe, J. R. Gair, S. Galaudage, V. Galdi, M. Galimberti, A. Gamboa, S. Gamoji, A. Ganguly, B. Garaventa, P. García Abia, J. García-Bellido, C. García-Quirós, J. W. Gardner, S. Garg, J. Gargiulo, X. Garrido, A. Garron, F. Garufi, P. A. Garver, C. Gasbarra, F. Gautier, V. Gayathri, T. Gayer, G. Gemme, A. Gennai, V. Gennari, J. George, R. George, O. Gerberding, L. Gergely, A. Ghinassi, Archisman Ghosh, Sayantan Ghosh, Shaon Ghosh, Shrobana Ghosh, Suprovo Ghosh, Tathagata Ghosh, J. A. Giaime, K. D. Giardina, D. R. Gibson, C. Gier, F. Gittins, J. Glanzer, F. Glotin, E. Glowacki, J. Godfrey, R. V. Godley, O. Godwin, A. S. Goettel, E. Goetz, J. Golomb, S. Gomez Lopez, G. González, P. Goodarzi, S. R. Goode, A. Goodwin-Jones, M. Gosselin, S. M. Goss-Grubbs, C. Gostiaux, R. Gouaty, D. W. Gould, D. Goupilliere, K. Govorkova, A. Grado, V. Graham, A. E. Granados, M. Granata, V. Granata, S. Gras, P. Grassia, C. Gray, R. Gray, G. Greco, A. C. Green, L. Green, S. R. Green, A. M. Gretarsson, E. M. Gretarsson, D. Griffith, C. Grimaud, H. Grote, S. Grunewald, A. G. Guerrero, G. M. Guidi, T. Guidry, H. K. Gulati, F. Gulminelli, H. Guo, W. Guo, Y. Guo, A. Gupta, I. Gupta, N. C. Gupta, S. K. Gupta, V. Gupta, N. Gupte, N. Guttman, F. Guzman, M. Haberland, S. Haino, E. D. Hall, E. Z. Hamilton, G. Hammond, W.-B. Han, M. Haney, J. Hanks, C. Hanna, M. D. Hannam, O. A. Hannuksela, H. Hansen, J. Hanson, R. Harada, A. R. Hardison, S. Harikumar, K. Haris, I. Harley-Trochimczyk, J. Harms, G. M. Harry, I. W. Harry, M. T. Hartman, B. Haskell, C.-J. Haster, K. Haughian, H. Hayakawa, K. Hayama, J. Hedberg, A. Heffernan, D. Hegde, M. C. Heintze, J. Heinzel, H. Heitmann, F. Hellman, A. F. Helmling-Cornell, G. Hemming, O. Henderson-Sapir, M. Hendry, I. S. Heng, M. H. Hennig, C. Henshaw, A. Heranval, M. Heurs, A. L. Hewitt, J. Heynen, J. Heyns, S. Hido, S. Hild, M. Hill, S. Hill, Y. Himemoto, C. Hirose, D. Hofman, N. A. Holland, K. Holley-Bockelmann, I. J. Hollows, D. E. Holz, L. Honet, K. M. Hoops, M. E. Hoque, D. J. Horton-Bailey, J. Hough, S. Hourihane, N. T. Howard, E. J. Howell, C. G. Hoy, P. Hsi, H.-Y. Hsieh, C. Hsiung, S.-H. Hsu, W.-F. Hsu, H. Y. Huang, Y. Huang, A. D. Huddart, B. Hughey, D. C. Y. Hui, S. Husa, L. Iampieri, G. A. Iandolo, M. Ianni, Y. Ichinose, K. Ide, R. Iden, A. Ierardi, S. Ikeda, H. Imafuku, K. Imai, Y. Inoue, P. Iosif, J. Irwin, K. Ishida, R. Ishikawa, T. Ishikawa, H. Ishino, M. Isi, K. S. Isleif, Y. Itoh, S. Iwaguchi, M. M. Iwaya, B. R. Iyer, C. Jacquet, T. Jacquot, S. J. Jadhav, S. P. Jadhav, K. Jain, A. L. James, K. Jani, S. Jani, J. Janquart, N. N. Janthalur, S. Jaraba, P. Jaranowski, R. Jaume, W. Javed, M. Jensen, W. Jia, J. Jiang, H.-B. Jin, S.-J. Jin, G. R. Johns, N. A. Johnson, M. C. Johnston, R. Johnston, N. Johny, D. H. Jones, D. I. Jones, R. Jones, P. Joshi, S. K. Joshi, G. Joubert, J. Ju, L. Ju, I. L. Juarez-Reyes, K. Jung, H. B. Kabagoz, B. Kacskovics, T. Kajita, I. Kaku, V. Kalogera, M. Kalomenopoulos, M. Kamiizumi, N. Kanda, S. Kandhasamy, G. Kang, J. B. Kanner, S. J. Kapadia, D. P. Kapasi, A. Karia, A. S. Karia, R. Kashyap, M. Kasprzack, H. Kato, T. Kato, E. Katsavounidis, W. Katzman, R. Kaushik, K. Kawabe, S. Kawamura, D. Keitel, S. A. Kemper, L. J. Kemperman, J. Kennington, R. Kesharwani, J. S. Key, R. Khadela, S. S. Khadkikar, F. Y. Khalili, C. Khamar, F. Khan, M. Khursheed, N. M. Khusid, W. Kiendrebeogo, C. Kim, G. Kim, J. C. Kim, K. Kim, M. H. Kim, S. Kim, Y.-M. Kim, C. Kimball, K. Kimes, M. Kinnear, J. S. Kissel, S. Klimenko, A. M. Knee, N. Knust, K. Kobayashi, S. M. Koehlenbeck, K. Kohri, K. Kokeyama, S. Koley, P. Kolitsidou, A. E. Koloniari, K. Komori, K. Kompanets, A. K. H. Kong, A. Kontos, K. Kopczuk, L. M. Koponen, M. Korobko, X. Kou, N. Kouvatsos, T. Koyama, D. B. Kozak, E. Kraja, S. L. Kranzhoff, V. Kringel, N. V. Krishnendu, S. Kroker, A. Królak, K. Kruska, J. Kubisz, K. Kubota, G. Kuehn, D. Kukla, A. Kulur Ramamohan, Achal Kumar, Anil Kumar, Dhruv Kumar, Praveen Kumar, Prayush Kumar, Rahul Kumar, Rakesh Kumar, Ravi Kumar, J. Kume, K. Kuns, N. Kuntimaddi, S. Kuroyanagi, K. Kwak, K. Kwan, S. Kwon, G. Lacaille, D. Laghi, A. H. Laity, N. Lajili, A. Lakhal, E. Lalande, M. Lalleman, S. Lalvani, M. Landry, R. N. Lang, A. Lange, J. A. Lange, R. Langgin, B. Lantz, I. La Rosa, O. Laske, P. D. Lasky, L. Lavezzi, J. Lawrence, M. Laxen, A. Lazzarini, C. Lazzaro, P. Leaci, L. Leali, Y. K. Lecoeuche, H. W. Lee, J. Lee, K. Lee, R.-K. Lee, R. Lee, Sungho Lee, Sunjae Lee, W. Lee, Y. Lee, F. Legger, I. N. Legred, J. Lehmann, L. Lehner, M. Le Jean, A. Lemaître, R. Lemrani Alaoui, M. Lenti, M. Leonardi, M. Lequime, M. Lesovsky, N. Letendre, M. Lethuillier, Y. Levin, S. Lexmond, K. Leyde, A. K. Y. Li, K. L. Li, T. G. F. Li, X. Li, Y. Li, Z. Li, Q. Liang, C-Y. Lin, E. T. Lin, F. Lin, L. C.-C. Lin, Y.-C. Lin, C. Lindsay, S. D. Linker, A. Liu, F. Liu, G. C. Liu, Jian Liu, S. Liu, F. Llamas Villarreal, J. Llobera-Querol, R. K. L. Lo, J.-P. Locquet, S. C. G. Loggins, L. T. London, A. Longo, M. Lopez Portilla, A. Lorenzo-Medina, V. Loriette, M. Lormand, M. Lorusso, G. Losurdo, T. P. Lott IV, J. D. Lough, H. A. Loughlin, C. O. Lousto, N. K. Y. Low, N. Lu, H. Lück, O. Lukina, D. Lumaca, A. P. Lundgren, L. Lunghini, A. W. Lussier, L.-T. Ma, X. Ma, M. Ma'arif, S. MacBride, K. Machida, D. M. Macleod, I. A. O. MacMillan, A. Macquet, S. S. Madekar, S. Maenaut, S. S. Magare, R. M. Magee, E. Maggio, M. Magnozzi, P. Mahapatra, M. Mahesh, S. Majhi, E. Majorana, C. N. Makarem, E. Makelele, N. Malagon, D. Malakar, J. A. Malaquias-Reis, U. Mali, S. Maliakal, A. Malik, L. Mallick, A.-K. Malz, N. Man, M. Mancarella, V. Mandic, V. Mangano, Z. Mangi, B. Mannix, G. L. Mansell, M. Manske, M. Mantovani, M. Mapelli, S. Marchetti, F. Marion, J. Mark, A. S. Markosyan, J. Markus, E. Maros, S. Marsat, F. Martelli, I. W. Martin, R. M. Martin, B. B. Martinez, M. Martinez, V. Martinez, A. Martini, Juan Carlos Martins, Julio C. Martins, D. V. Martynov, E. J. Marx, L. Massaro, A. Masserot, M. Masso-Reid, T. Masters, S. Mastrogiovanni, G. Mastropasqua, M. Matiushechkina, A. Matte-Landry, L. Maurin, N. Mavalvala, N. Maxwell, A. McCann, G. McCarrol, R. McCarthy, D. E. McClelland, S. McCormick, L. McCuller, L. I. McDermott, C. McElhenny, G. I. McGhee, K. B. M. McGowan, J. McIver, A. McLeod, I. McMahon, T. McRae, R. McTeague, K. McWhirter, D. Meacher, B. N. Meagher, R. Mechum, L. G. Medeiros, R. M. Mehta, A. Melatos, C. S. Menoni, R. A. Mercer, L. Mereni, K. Merfeld, E. L. Merilh, J. R. Mérou, C. Messick, M. Meyer-Conde, F. Meylahn, H. Miao, C. Michel, Y. Michimura, H. Middleton, D. P. Mihaylov, S. J. Miller, M. Millhouse, E. Milotti, V. Milotti, E. Minakaki, Y. Minenkov, Ll. M. Mir, L. Mirasola, C.-A. Miritescu, A. Mishra, C. Mishra, T. Mishra, A. Mitchell, J. G. Mitchell, O. Mitchem, S. Mitra, V. P. Mitrofanov, K. Mitsuhashi, R. Mittleman, O. Miyakawa, S. Miyoki, G. Mo, L. Mobilia, S. R. P. Mohapatra, M. Molina-Ruiz, M. Mondin, M. Montani, G. Montefusco, C. J. Moore, D. Moraru, A. More, S. More, C. Moreno, E. A. Moreno, G. Moreno, A. Moreso Serra, C. Morgan, S. Morisaki, S. Moriwaki, Y. Moriwaki, G. Morras, A. Moscatello, M. Mould, B. Mours, C. M. Mow-Lowry, L. Muccillo, F. Muciaccia, Arunava Mukherjee, D. Mukherjee, Samanwaya Mukherjee, Soma Mukherjee, Subroto Mukherjee, Suvodip Mukherjee, N. Mukund, A. Mullavey, C. L. Mungioli, Y. Murakami, M. Murakoshi, P. G. Murray, D. Nabari, S. Nadji, A. Nagar, N. Nagarajan, K. Nakagaki, A. Nakamura, K. Nakamura, H. Nakano, M. Nakano, D. Nanadoumgar-Lacroze, D. Nandi, V. Napolano, S. U. Naqvi, P. Narayan, A. Nardecchia, I. Nardecchia, T. Narikawa, H. Narola, L. Naticchioni, R. K. Nayak, J. Neeson, L. Negri, A. Nela, C. Nelle, A. Nelson, T. J. N. Nelson, A. Nemmani, A. Neunzert, M. Newell, S. Ng, T. C. K. Ng, L.-A. T. Nguyen, T. T. Nguyen, L. Nguyen Quynh, A. B. Nielsen, Y. Nishino, A. Nishizawa, S. Nissanke, W. Niu, F. Nocera, J. Noller, M. Norman, C. North, J. Novak, G. Nurbek, L. K. Nuttall, K. Obayashi, J. Oberling, C. E. Ochoa, C. O'Connor, J. O'Dell, E. Oelker, M. Oertel, G. Oganesyan, J. J. Oh, T. O'Hanlon, M. Ohashi, F. Ohme, Y. Okabe, I. Oke, R. Oliveira, R. Omer, N. O'Neill, M. Onishi, K. Oohara, P. Ophardt, R. J. Oram, B. O'Reilly, R. O'Shaughnessy, S. Oshino, J. Ostrovska, A. Osumi, I. Ota, G. Othman, M. Otsuka, D. J. Ottaway, A. Ouzriat, H. Overmier, B. J. Owen, A. E. Pace, M. A. Page, A. Pai, S. Pal, M. A. Palaia, M. Pálfi, C. Palomba, H. Pan, J. Pan, K.-C. Pan, P. K. Panda, Shiksha Pandey, Swadha Pandey, P. T. H. Pang, F. Pannarale, B. C. Pant, F. H. Panther, M. Panzeri, F. Paoletti, A. Paoli, A. Paolone, A. Papadopoulos, E. E. Papalexakis, L. Papalini, G. Papigkiotis, A. Paquis, A. Parisi, B.-J. Park, Jihwan Park, Junegyu Park, W. Parker, G. Pascale, D. Pascucci, A. Pasqualetti, L. Passenger, D. Passuello, O. Patane, A. V. Patel, L. Pathak, A. Patra, B. Patricelli, B. G. Patterson, K. Paul, S. Paul, E. Payne, T. Pearce, M. Pedraza, A. Pele, F. E. Peña Arellano, X. Peng, Y. Peng, S. Penn, A. Perreca, J. Perret, D. Pesios, S. Petracca, C. Petrillo, H. P. Pfeiffer, H. Pham, K. A. Pham, K. S. Phukon, H. Phurailatpam, L. Piccari, O. J. Piccinni, M. Pichot, A. Pied, M. Piendibene, F. Piergiovanni, L. Pierini, G. Pierra, V. Pierro, M. Pillas, B. Pillon, L. Pinard, I. M. Pinto, M. Pinto, B. J. Piotrzkowski, M. Pirello, A. Pisarski, M. D. Pitkin, E. Placidi, M. L. Planas, C. Plunkett, R. Poggiani, E. Polini, M. Polo, J. Pomper, L. Pompili, J. Poon, E. Porcelli, A. S. Porter, E. K. Porter, C. Posnansky, J. Powell, G. S. Prabhu, M. Pracchia, A. K. Prajapati, K. Prasai, R. Prasanna, P. Prasia, G. Pratten, G. Principe, G. A. Prodi, P. Prosperi, P. Prosposito, A. Puecher, J. Pullin, M. Punturo, P. Puppo, M. Pürrer, H. Qi, M. Qiao, J. Qin, G. Quéméner, V. Quetschke, P. J. Quinonez, R. Rading, I. Rainho, S. Raja, C. Rajan, B. Rajbhandari, M. R. Raj Sah, K. E. Ramirez, F. A. Ramis Vidal, M. Ramos Arevalo, A. Ramos-Buades, S. Ranjan, M. Ranjbar, K. Ransom, R. Rao, P. Rapagnani, B. Ratto, A. Ravichandran, A. Ray, V. Raymond, M. Razzano, J. Read, J. Redepenning, J. Regan, T. Regimbau, T. Reichardt, S. Reid, C. Reissel, D. H. Reitze, A. I. Renzini, B. Revenu, A. Revilla-Peña, F. Ricci, M. Ricci, A. Ricciardone, J. Rice, J. W. Richardson, M. L. Richardson, K. Riles, H. K. Riley, A. Riminucci, F. Robinet, M. Robinson, A. Rocchi, J. Rodriguez, R. Rodriguez Lopez, L. Rolland, J. G. Rollins, A. E. Romano, R. Romano, A. Romero-Rodríguez, I. M. Romero-Shaw, J. H. Romie, S. Ronchini, T. J. Roocke, T. J. Rosauer, C. A. Rose, D. Rosińska, M. P. Ross, M. Rossello-Sastre, S. Rowan, K. Rowlands, S. K. Roy, S. Roy, T. RoyChowdhury, D. Rozza, P. Ruggi, G. H. Ruiz, E. Ruiz Morales, K. Ruiz-Rocha, V. Russ, S. M. S, S. Sachdev, T. Sadecki, F. Safai Tehrani, P. Saffarieh, S. Safi-Harb, S. Saha, T. Sainrat, S. Sajith Menon, K. Sakai, Y. Sakai, M. Sakellariadou, S. Sakon, F. Salces-Carcoba, L. Salconi, M. Saleem, F. Salemi, M. Sallé, M. Salomé, S. U. Salunkhe, S. Salvador, A. Salvarese, A. Samajdar, P. M. Samir, A. Sanchez, E. J. Sanchez, J. Sanchez, D. Sanchez-Cid, N. Sanchis-Gual, J. R. Sanders, E. M. Sänger, F. Santoliquido, E. Sapkin, F. Sarandrea, T. R. Saravanan, P. Sarkar, A. Sasli, P. Sassi, B. Sassolas, O. Sauter, R. L. Savage, T. Savicheva, T. Sawada, H. L. Sawant, D. Schaetzl, M. Scheel, A. Schiebelbein, M. G. Schiworski, K. Schluterman, P. Schmidt, R. Schnabel, M. Schneewind, R. M. S. Schofield, M. Schoor, K. Schouteden, B. W. Schulte, M. Schulz, B. F. Schutz, E. Schwartz, M. Scialpi, J. Scott, S. M. Scott, R. M. Sedas, T. C. Seetharamu, M. Seglar-Arroyo, Y. Sekiguchi, D. Sellers, N. Sembo, E. G. Seo, J. W. Seo, G. Seong, V. Sequino, M. Serra, C. K. Sethi, A. Sevrin, T. Shaffer, U. S. Shah, M. A. Shaikh, L. Shao, J. Sharkey, A. K. Sharma, Preeti Sharma, Priyanka Sharma, Sushant Sharma-Chaudhary, P. Shawhan, T. Shen, Z.-H. Shi, K. Shimode, H. Shinkai, S. Shirke, D. H. Shoemaker, D. M. Shoemaker, R. W. Short, S. ShyamSundar, H. Siegel, V. Sierra, D. Sigg, L. Silenzi, P. J. S. Silva, L. Silvestri, M. Simmonds, L. P. Singer, A. Singh, D. Singh, M. K. Singh, N. Singh, S. Singh, M. R. Sinha, A. M. Sintes, V. Skliris, B. J. J. Slagmolen, T. J. Slaven-Blair, J. Smetana, D. A. Smith, J. R. Smith, J. Smith, L. Smith, W. J. Smith, S. Soares de Albuquerque Filho, M. Soares-Santos, K. Somiya, I. Song, S. Soni, V. Sordini, F. Sorrentino, H. Sotani, N. E. Sovitzky, F. Spada, V. Spagnuolo, A. P. Spencer, M. Spera, P. Spinicelli, A. K. Srivastava, F. Stachurski, V. V. Stanford, A. Stanton, D. A. Steer, N. Steinle, J. Steinlechner, S. Steinlechner, C. Stephens, N. Stergioulas, M. StPierre, J. Stremiz, M. D. Strong, A. Strunk, M. Suchenek, S. Sudhagar, R. Sugimoto, L. Suleiman, K. D. Sullivan, J. Sun, L. Sun, S. Sunil, J. Suresh, P. J. Sutton, K. Suzuki, M. Suzuki, A. Svizzeretto, B. L. Swinkels, A. Syx, M. J. Szczepańczyk, M. Tacca, M. Tagliazucchi, H. Tagoshi, S. C. Tait, H. Takaba, K. Takada, H. Takahashi, R. Takahashi, A. Takamori, S. Takano, H. Takeda, I. Takimoto Schmiegelow, C. Talbot, M. Tamaki, N. Tamanini, D. Tanabe, K. Tanaka, S. J. Tanaka, S. Tanioka, D. B. Tanner, W. Tanner, L. Tao, R. D. Tapia, E. N. Tapia San Martín, A. Taruya, J. D. Tasson, J. G. Tau, A. Tejera, J. G. Temple, Y. Teng, H. Themann, A. Theodoropoulos, M. P. Thirugnanasambandam, L. M. Thomas, M. Thomas, P. Thomas, J. E. Thompson, S. R. Thondapu, E. Thrane, J. Tissino, A. Tiwari, Pawan Tiwari, Praveer Tiwari, S. Tiwari, V. Tiwari, M. R. Todd, E. Tofani, M. Toffano, A. M. Toivonen, K. Toland, T. Tomaru, V. Tommasini, H. Tong, C. I. Torrie, I. Tosta e Melo, E. Tournefier, A. Trapananti, R. Travaglini, F. Travasso, G. Traylor, L. Traylor, M. Trevor, M. C. Tringali, A. Tripathee, G. Troian, A. Trovato, L. Trozzo, R. J. Trudeau, T. Tsang, S. Tsuchida, K. Tsuji, L. Tsukada, A. Tuci, M. Turconi, C. Turski, H. Ubach, A. S. Ubhi, N. Uchikata, T. Uchiyama, R. P. Udall, T. Uehara, V. Undheim, V. Upadhyaya, L. E. Uronen, T. Ushiba, M. Vacatello, H. Vahlbruch, G. Vajente, J. Valencia, M. Valentini, E. Vallejo-Pagès, S. A. Vallejo-Peña, S. Vallero, M. van Dael, E. Van den Bossche, J. F. J. van den Brand, C. Van Den Broeck, M. van der Kolk, M. van der Sluys, A. Van de Walle, J. van Dongen, K. Vandra, M. VanDyke, H. van Haevermaet, J. V. van Heijningen, P. Van Hove, J. Vanier, J. Vanosky, N. van Remortel, M. Vardaro, A. F. Vargas, V. Varma, A. Vecchio, G. Vedovato, J. Veitch, P. J. Veitch, S. Venikoudis, P. Verdier, M. Vereecken, D. Verkindt, B. Verma, S. Verma, Y. Verma, S. M. Vermeulen, F. Vetrano, A. Veutro, A. Viceré, S. Vidyant, A. D. Viets, A. Vijaykumar, A. Vilkha, N. Villanueva Espinosa, E. T. Vincent, J.-Y. Vinet, S. Viret, S. Vitale, A. Vives, L. Vizmeg, B. Vizzone, H. Vocca, D. Voigt, E. R. G. von Reis, J. S. A. von Wrangel, W. E. Vossius, L. Vujeva, S. P. Vyatchanin, J. Wack, L. E. Wade, M. Wade, K. J. Wagner, L. Wallace, R.-Z. Wan, H. Wang, P. Wang, W. H. Wang, Y. F. Wang, Z. Wang, R. L. Ward, J. Warner, M. Was, T. Washimi, N. Y. Washington, D. Watarai, B. Weaver, S. A. Webster, N. L. Weickhardt, M. Weinert, A. J. Weinstein, R. Weiss, L. Wen, K. Wette, C. Wheeler, J. T. Whelan, B. F. Whiting, E. G. Wickens, D. Wilken, B. M. Williams, D. Williams, M. J. Williams, N. S. Williams, J. L. Willis, B. Willke, M. Wils, L. Wimmer, C. W. Winborn, A. Wingfield, J. Winterflood, C. C. Wipf, G. Woan, N. E. Wolfe, H. T. Wong, I. C. F. Wong, T. Wouters, J. L. Wright, M. Wright, B. Wu, C. Wu, D. S. Wu, H. Wu, K. Wu, Z. Wu, E. Wuchner, D. M. Wysocki, V. A. Xu, Y. Xu, N. Yadav, H. Yamamoto, K. Yamamoto, T. S. Yamamoto, T. Yamamoto, R. Yamazaki, T. Yan, H. Yang, K. Z. Yang, Y. Yang, Z. Yarbrough, J. Yébana Carrilero, A. B. Yelikar, X. Yin, J. Yokoyama, T. Yokozawa, M. Yoshihara, S. Yuan, H. Yuzurihara, M. Zanatta, M. Zanolin, M. Zeeshan, T. Zelenova, J.-P. Zendri, M. Zeoli, M. Zerrad, M. Zevin, H. Zhang, J. Zhang, L. Zhang, N. Zhang, R. Zhang, T. Zhang, C. Zhao, J. Zhao, Yue Zhao, Yuhang Zhao, L.-M. Zheng, Y. Zheng, L. Zhizhong, H. Zhong, H. Zhou, H. O. Zhu, X.-J. Zhu, Z.-H. Zhu, Z. Zhu, D. Z. Zieba, A. B. Zimmerman, L. Zimmermann, M. E. Zucker

High Energy Astrophysical Phenomena

Binary Neutron Star Merger Simulations with Microphysical Equation of State using Spritz

Fatemeh Hossein Nouri, Jay V. Kalinani, Bruno Giacomazzo et al. (+2 more)

We present the first binary neutron star merger simulations performed with the general-relativistic magnetohydrodynamics (GRMHD) Spritz code employing a finite-temperature tabulated equation of state. Two magnetized binaries with the LS220 equation of state and a GW170817-like chirp mass, differing only in their mass ratios ($q=1$ and $q=0.7$), are evolved from the late inspiral through merger, hypermassive neutron-star (HMNS) formation, and delayed collapse to a black hole (BH). We investigate how the binary mass ratio influences the postmerger evolution, jet-launching conditions, and matter ejection. We find that the equal-mass binary forms a slightly longer-lived HMNS, allowing more efficient magnetic-field amplification during the post-merger evolution. As a result, it accumulates larger magnetic fluxes, develops a magnetically dominated funnel, and launches a collimated magnetically driven polar outflow. In contrast, the unequal-mass binary ejects approximately 50% more mass but exhibits weaker magnetic-field amplification, with the polar region remaining turbulent and baryon loaded throughout our simulation, suggesting that the development of a magnetically dominated funnel is likely delayed.
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All authors Fatemeh Hossein Nouri, Jay V. Kalinani, Bruno Giacomazzo, Riccardo Ciolfi, Albino Perego

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM

AI-Assisted Extraction of Follow-up Observations from GCN Circulars in Astro-COLIBRI

Fabian Schüssler, S. Bisero, M. Cellier et al. (+6 more)

We present a new Astro-COLIBRI component that converts free-text GCN Circulars into structured, event-linked follow-up records and combines them with structured reports submitted directly by the community. A continuously running Circular listener associates new reports with transient events, applies deterministic pre-analysis, and invokes a schema-constrained large language model extraction step for photometry, contacts, redshifts, and other reported results and metadata. The resulting records are submitted to the Astro-COLIBRI API, normalized into a common event-level follow-up database, and exposed through the web and mobile interfaces as report summaries, contact tools, optical-afterglow context figures, and downloadable CSV or VOTable products. After tuning, all 1,775 Circulars of an operational evaluation corpus covering the first half of 2026 completed the workflow without failures. An internal human audit of 210 Circulars confirmed 25,827 of 25,880 definite field-level decisions (99.80%), with the remaining errors confined to observation timing and facility attribution in eight of 231 assessed reports. Extracted redshifts agree with the independent GRBweb compilation for 228 of the 249 events the two share, and every disagreement traces to a limit, a candidate-host estimate, or a value later refined rather than to a misread Circular. The final pipeline was applied to the full GCN archive since 2016, yielding 68,393 individual observations from 26,811 reports across 5,787 transient events, and is now running in real time on new Circulars. The reusable parsing and normalization pipeline is released as the open-source Python package astro-colibri-circular-parser. This paper describes the scientific motivation, architecture, extraction schema, quality-control safeguards, user-facing products, and current use-cases of the system.
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All authors Fabian Schüssler, S. Bisero, M. Cellier, A. Ciric, B. Cornejo, I. Jaroschewski, A. Kaan Alkan, W. Kiendrébéogo, A. Saint-Paul

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Complex frequency evolution of direct waves from binary black hole mergers

Ling Sun, Sizheng Ma, Patrick P. Chen et al. (+3 more)

While no signal originating at a black hole's event horizon can reach future null infinity, information about the horizon and its immediate vicinity can be encoded in asymptotic properties of waves emitted by matter or field perturbations falling toward a growing/forming horizon. Within a response-filtered framework, "direct wave" denotes source-sensitive plunge and remnant-formation information revealed by filtering the black-hole response. Unlike a stationary damped sinusoid with a fixed complex frequency, the direct wave follows the evolving source and has an evolving instantaneous complex frequency tied at late times to the remnant horizon angular velocity $\Omega_H$ and surface gravity $\kappa_H$. Using rational filters, we remove quasinormal modes from numerical-relativity waveforms to study this evolution. Before numerical contamination, trajectories depend on remnant spin: the real frequency evolves toward $2\Omega_H$ from above for lower spins ($\chi_f\lesssim0.7$) and from below for higher spins ($\chi_f\gtrsim0.7$), while the instantaneous decay rate increases, with best-resolved cases approaching the expected value of $3\kappa_H$. As in particle-plunge results, the horizon-controlled value is approached only at late times, as frame dragging controls near-horizon motion. For $\chi_f\sim0.7$ remnants of non-precessing, comparable-mass binaries, the early-time real frequency is close to $2\Omega_H$ because the binary orbital frequency transitions smoothly to the remnant horizon frequency. Finite-time deviations therefore carry information about merger/collapse dynamics rather than undermining the horizon connection. Full direct-wave evolution requires numerical-relativity calibration. We further show that approximate pole-zero pairing in the Kerr response motivates a minimal filter set that suppresses quasinormal-mode features while revealing source-trajectory information.
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All authors Ling Sun, Sizheng Ma, Patrick P. Chen, Andrew Laeuger, Neil Lu, Yanbei Chen

High Energy Astrophysical Phenomena

Neutron star masses from electron-capture supernovae under equation-of-state uncertainties

Vishal Parmar, Domenico Scordino and Ignazio Bombaci

Electron-capture supernovae (ECSNe) are a promising formation channel for low-mass neutron stars, but the minimum gravitational mass of the neutron stars they produce depends on both the progenitor core structure and the neutron-star matter equation of state (EOS). We compute the electron-capture (EC) threshold gravitational mass ($M^\star_{WD}$) of cold white-dwarf-like O–Ne–Mg cores with representative compositions and map the baryon number onto cold neutron-star configurations constructed from a Bayesian ensemble of unified crust–core EOSs. Although the EC threshold density is sensitive to the concentrations of the O–Ne–Mg mixture, the threshold baryon number of the O–Ne–Mg core varies only weakly, producing a narrow remnant-mass window. In the baseline case with no baryonic mass loss during the transition from the EC threshold mass O–Ne–Mg core to the remnant neutron star, standard ECSNe yield remnant neutron stars with gravitational masses of $1.24$–$1.265\, M_\odot$, with only a small EOS-induced spread. Small baryonic mass losses of $0.01$–$0.02\, M_\odot$ shift this range modestly downward, but the $1.174\, M_\odot$ companion of PSR J0453+1559 would require an extreme mass loss close to $0.10\, M_\odot$, which is not favored by current ECSN simulations. We find that the residual EOS dependence of the remnant mass is controlled mainly by the pressure around nuclear saturation density, while the corresponding tidal deformability remains sensitive to the remnant radius and compactness. Thus, low-mass double neutron star systems can in principle connect ECSN-like formation channels with gravitational-wave constraints on the EOS. Our results show that ECSNe naturally form low-mass neutron stars, but within a restricted mass range; the lightest observed neutron stars likely require low-mass iron-core collapse, ultra-stripped supernovae, or other nonstandard channels.
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High Energy Astrophysical Phenomena

Reconstructing the Auger UHECR Dipole: A Hybrid Analysis of 4LAC AGNs and Nearby Starburst Galaxies

Swaraj Pratim Sarmah, Umananda Dev Goswami and Sovan Chakraborty

The large-scale dipole anisotropy observed by the Pierre Auger Observatory above $8$~EeV provides important clues about the origin of ultra-high-energy cosmic rays (UHECRs). In this work, we investigate whether gamma-ray active galactic nuclei (AGNs) from the Fermi-LAT Fourth AGN Catalog (4LAC) can explain the observed dipole and examine the contribution of nearby starburst galaxies (SBGs). Incorporating source fluxes, redshift distributions, GZK attenuation, and a mixed-composition framework, we demonstrate that single-source populations of AGNs and SBGs alone fail to reproduce the observed Auger dipole. To resolve this, we construct a hybrid AGN+SBG model. The best-fit solution for the $8$–$16$~EeV interval requires a $23$% AGN contribution and $45$% SBG contribution, which gives a dipole amplitude of $5.03$% while maintaining the dipole direction of ($104.1^\circ$, $-25.1^\circ$) with angular separation of $7.10^\circ$. In the other energy intervals also, we find that the nearby SBGs increasingly dominate the anisotropic component while AGNs provide a subdominant contribution alongside a quasi-isotropic background.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM

When a neural surrogate cannot accelerate a solver: runtime share, closed-loop drift, and the economics of uncertainty gating in a stiff coupled simulation

L. Thümmler and T. Kuroda

Learned surrogates for expensive inner solver blocks are a widely pursued route to faster multiphysics simulation. We report a controlled, end-to-end negative result and identify three structural barriers, none of them a deficiency of the network we trained. The testbed is the implicit Newton solve coupling energy-dependent neutrino radiation to matter in a general-relativistic radiation-hydrodynamics code, its most expensive physics routine per call. First, per-call cost and share of runtime are different quantities, and only the second bounds acceleration. An exclusive self-time profile puts the target block at 16.9% of critical-rank wall clock, capping any surrogate at ~1.2x by Amdahl's law. A surrogate 5.8x cheaper per call merely ties the solver, and the configuration stable enough to run without fallback reaches only parity. Second, offline accuracy cannot rank surrogates for deployment: across fourteen networks the pooled Spearman error-versus-survival correlation (rho = +0.73) is a between-family confound that vanishes under control (rho = -0.04). Third, a correct out-of-distribution gate cannot accelerate a loop that leaves its training distribution. We give the break-even deferral fraction in closed form: because the visited states sit 73x off the data manifold, the gate defers 96.8 to 99.7% of cells, almost invariant to surrogate quality. Including its own cost, the gated loop is a 0.94 to 0.96x slowdown. We further separate stability from fidelity: a never-crashing gated run accumulates a linear -19.9% density bias over 6000 steps. The error is a directed, ballistically accumulating bias, not the variance-driven divergence the autoregressive literature targets.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Signed Sound-Speed Deformations of BSk24-Anchored Barotropes: Neutron-Star Response

Ioannis Papathanasiou

Background: Localized structure in the equilibrium squared sound speed can affect neutron-star observables, but modifying $dP/d\epsilon$ requires thermodynamically consistent reconstruction and assessment over the complete declared domain. Purpose: We quantify the response to positive and negative localized sound-speed changes around a unified BSk24 baseline while keeping the deformation geometry, admission criteria, reconstruction, and fixed-mass comparison protocol fixed. Method: A Gaussian profile with quintic smootherstep activation is added to $c_{\rm s}^2$. Proposals violating $P>0$ or $0<c_{\rm s}^2\leq1$ anywhere in the retained domain are rejected before reconstruction. Passing cases are reconstructed as effective cold one-fluid barotropes and evolved with the Tolman-Oppenheimer-Volkoff and tidal equations. Results: The $A=0$ case reproduces the undeformed control exactly. A localized change produces a persistent pressure offset, relocates the fixed-mass central state, and yields a mass-dependent, nonlinear, sign-asymmetric response. For $A=-0.8$ and $+0.8$, respectively, $\Delta\Lambda/\Lambda_0=(-46.02\%,+35.33\%)$ at $1.4\,M_\odot$ and $(-63.52\%,+87.17\%)$ at $2.0\,M_\odot$. The reached stiffened feature remains core connected at the reporting endpoints, whereas the softened feature becomes an off-center shell at high mass. Conclusions: These phenomenological BSk24-anchored effective barotropes illustrate how a local sound-speed intervention propagates through thermodynamic reconstruction and stellar structure. They are not BSk24 predictions or evidence for a microscopic composition or phase transition.
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High Energy Astrophysical Phenomena

Extensive Air Showers Parameters Estimation Using Machine Learning Techniques with Simulations of the FAST Telescope

Jiří Kvita, Monika Machalová, Radek Přívara et al. (+2 more)

We present the capabilities of the Fluorescence detector Array of Single-pixel Telescopes (FAST) observatory in the single telescope configuration as an important step towards the possible future large-field observatory for detecting ultra-high-energy cosmic rays. Reconstruction of main shower physics parameters are explored on noise-free simulated events using machine learning techniques in the challenging domain of a low-intensity transient signal. We find a very good correlation between the true and reconstructed energy of the shower even with the information from just the four photomultipliers of the single FAST telescope, and a reduced performance for the maximum of the shower development Xmax, using various architectures of artificial deep and convolutional neural networks, with a comparison to a benchmark gradient boost regression model. The resolution in the energy is found at the sub-percent level, while in Xmax it is~$5\%$. The relative difference between predicted and true values is under one percent for energy, while for Xmax it ranges from $-8\%$ to $+17\%$, which can be attributed to the limited information from the single FAST telescope configuration. The results constitute an important capabilities verification and a lesson learned with implications for established FAST prototypes as well as for more complex configurations of the FAST observatory under construction.
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All authors Jiří Kvita, Monika Machalová, Radek Přívara, Rostislav Vodák, Jan Tomeček

High Energy Astrophysical Phenomena

A Two-month, Galaxy-targeted NIR Follow-up of the Sub-solar-mass Gravitational Wave Candidate S251112cm: Probing Electromagnetic Counterpart Scenarios

Gregory S. H. Paek, Felipe Olivares E. and Willem B. Hoogendam

S251112cm is a nearby ($93 \pm 27$~Mpc) compact-binary merger candidate with a high inferred probability that at least one component is below $1\,M_\odot$. This event provides a rare test case for electromagnetic follow-up of a theoretically predicted but unconfirmed sub-solar-mass merger candidate. Motivated by scenarios predicting NIR-bright emission over weeks to months, we carried out a deep, galaxy-targeted UKIRT $J$-band campaign over approximately two months, prioritizing host candidates by a ranking that combines the three-dimensional localization probability with WISE W1 luminosity as a stellar-mass proxy. Of $\sim9000$ candidate hosts, we monitored 59, corresponding to 7.7% of the cumulative weighted host prior. Difference imaging reveals no convincing transient down to typical depths of $J\sim22$–23~mag (AB). At this distance, both a Type~Ic-BL supernova template and an AT\,2017gfo-like KN template—including time-shifted variants up to $\Delta t \sim 60$~days—would have remained above our median depth for multiple epochs within the monitored hosts. Comparison with a canonical KN model grid, summarized through conditional weighted consistent-fraction maps, shows that bright configurations with high dynamical and wind-ejecta masses are strongly disfavored, while less luminous configurations remain largely permissible. While these constraints are host-limited and do not constitute an event-wide exclusion, this campaign provides the first empirical case study of long-baseline, deep NIR follow-up for a sub-solar-mass merger GW class and demonstrates a host-weighted framework applicable to future galaxy-targeted campaigns.
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High Energy Astrophysical Phenomena

Timing, Polarization, and Single-Pulse Properties of Long-Period FAST Pulsars

Habtamu Menberu Tedila, Shijun Dang, Di Li et al. (+5 more)

We present phase-connected timing and polarization measurements for two long-period FAST-CRAFTS pulsars, PSRs J0000+6252 and J2131+3642, and extend single-pulse emission-state analysis to a five-source sample including PSRs J1903+1407, J1502+4653, and J2112+4058. FAST L-band timing baselines span 414 to 511 days; the two pulsars have spin periods of 1.11 to 1.55 s, period derivatives of $(3.99$ to $4.06)\times10^{-15}~{\rm s~s^{-1}}$, characteristic ages of 4.34 to 6.16 Myr, surface magnetic fields of $(2.15$ to $2.52)\times10^{12}$ G, and spin-down luminosities of $(4.21\times10^{31}$ to $1.16\times10^{32})~{\rm erg~s^{-1}}$. Their rotation measures are $70.2\pm26.7$ and $-44.6\pm7.6~{\rm rad~m^{-2}}$, with linear polarization fractions of 17.6% to 27.2%. PSR J2131+3642 shows a short monotonic PA segment permitting a formal rotating-vector-model fit, though limited longitude coverage leaves the geometric parameters poorly constrained; PSR J0000+6252 has too few PA points for such a fit. Gaussian mixture modeling (GMM) of single-pulse energy distributions identifies null, weak, and burst components in PSRs J0000+6252, J1903+1407, J1502+4653, and J2112+4058, while J2131+3642 shows only weak and burst states. We also identify bright single pulses (peak intensity $\geq10\times$ the integrated average profile): 42 in J0000+6252, four each in J1903+1407 and J2112+4058, and none in J2131+3642 or J1502+4653. These bright pulses occur within the main emission window with no evidence of periodic recurrence, consistent with sporadic enhancements of the normal radio-emission beam. For J2112+4058, we measure a scattering timescale $\tau_{\rm sc}=5.84\pm0.18$ ms at $\nu_{\rm ref}=1.25$ GHz. Together, these results highlight the diversity of magnetospheric variability among slowly rotating neutron stars.
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All authors Habtamu Menberu Tedila, Shijun Dang, Di Li, Pei Wang, Jianping Yuan, Rai Yuen, Na Wang, Shakhboz Khasanov

High Energy Astrophysical Phenomena

Tidal disruption of stellar binaries as a pathway to exotic transients

Mauricio González-Servín, Emilio Tejeda, Susana Lizano et al. (+2 more)

Tidal disruption event (TDE) progenitors are commonly modelled as single stars on parabolic orbits around a supermassive black hole (SMBH), yet observations reveal a richer diversity of dynamical pathways. We show that tidal separation of stellar binaries by a $10^6\,M_\odot$ SMBH provides a natural mechanism for producing eccentric TDEs. Using restricted three-body and SPH simulations, we model a solar-like star (SLS)–white dwarf (WD) binary on a parabolic orbit. The binary orbital phase governs the outcome: one component is captured onto a tightly bound orbit while the other is ejected as a hypervelocity object, naturally producing TDEs with eccentricities $e \neq 1$. We classify these into Elliptical TDEs (eTDEs) and Hyperbolic TDEs (hTDEs), occurring with equal probability. For $\sim 88\%$ of orientations the disruption is clean, with no mass accreted by the WD. The remaining $\sim 12\%$, in two narrow phase windows, leaves the WD with a captured debris envelope (WDDE). About a third of that, $\sim 4\%$ of orientations, involves a direct WD–SLS collision near pericenter, with fallback peaking up to five times earlier and twenty times higher than for a single star; for the innermost $\sim 1.5\%$ the total WDDE mass exceeds $1.4\,M_\odot$, though the degenerate core does not, since the captured material forms a non-degenerate envelope, suggesting outcomes ranging from nova-like events to peculiar red giant-like objects. Depending on the phase, the mechanism may also produce repeating partial TDEs (rTDEs) and quasi-periodic eruptions (QPEs). Binary–SMBH encounters provide a robust channel for generating diverse TDEs with distinct observational signatures.
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All authors Mauricio González-Servín, Emilio Tejeda, Susana Lizano, Luis A. Manzaneda, Raúl Cano-Villegas

High Energy Astrophysical Phenomena

Probing AU-Scale Magnetic-Field Reversals in the Interstellar Medium with Pulsar Scintillation

Jacob Yen, Daniel Baker, Dongzi Li et al. (+1 more)

AU-scale structures in the interstellar medium have become relevant across several areas of astrophysics, from ISM microphysics to pulsar timing arrays and cosmic-ray (CR) propagation. Current sheets formed at magnetic-field reversals have drawn particular attention because they can deflect the dominant GeV CR population through large angles. Pulsar scintillation, an outstanding probe of plasma density, resolves these structures—but not their magnetic configuration. Conventional Faraday rotation measures (RM) are only marginally sensitive at AU scales and are further compromised by ionospheric systematics. We propose a method that isolates birefringence-induced polarization—the signature of magnetic reversal—by applying phase retrieval to polarized data. Pulsar scintillation further resolves ray paths separated by $\sim 1\,\rm{AU}$, enabling differential RM measurements that suppress the ionospheric common mode while preserving the AU-scale magnetic signal. We demonstrate the method on an archival observation of PSR B0834+06. Phase retrieval resolves the 1-ms scattering feature into two branches in Doppler-delay space. Under the corrugated current-sheet interpretation, these branches correspond to ray paths sampling opposite sides of an AU-scale current sheet. We measure a branch-to-branch RM difference of $(-9.3\pm3.2)\times 10^{-3}\text{ rad m}^{-2}$ at 2.9$\sigma$ across a 10-MHz band. The signal is consistent with a field reversal of $|\Delta\langle B_\parallel \rangle| \simeq4.4\pm2.1\,\mu\rm G$, sufficient to sustain a long-lived sheet. With only six independent subbands, we present this as a proof of concept rather than a definitive detection. If it proves scalable, its full implementation could constrain cosmic-ray transport and inform models of propagation-induced noise in pulsar timing arrays.
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All authors Jacob Yen, Daniel Baker, Dongzi Li, Ue-Li Pen

Sunday 23 August

High Energy Astrophysical Phenomena

Galactic Microquasar and Supernova Remnants Imprinting on Diffuse Neutrino and Gamma-Ray Sky

Shiqi Yu and Bing Theodore Zhang

Recent detections of Galactic diffuse neutrinos by IceCube and $\gamma$-rays by LHAASO offer direct probes into the origin of Galactic cosmic rays. Conventional diffuse templates typically assume a single cosmic-ray injection spectrum across a wide energy range, without accounting for independent contributions from distinct accelerator populations. Here, we present a numerical framework that models Galactic diffuse neutrino and $\gamma$-ray emission that incorporates contributions from both microquasar and supernova remnant populations. By anchoring CR injection to local observations and utilizing high-resolution 3D target gas distributions, our model suggests multi-population contributions to the diffuse sky: escaped cosmic rays from supernova remnants dominate below $\sim10\text{ TeV}$, while those from microquasars become the primary driver at higher energies. Our predicted neutrino flux agrees well with the recent 12-year IceCube measurements, establishing a physically motivated baseline for the diffuse hadronic background while leaving room for unresolved point-like sources. This flexible framework provides testable predictions for current and future multi-messenger observatories, accommodating diverse accelerator populations and updated observational constraints.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Extreme mass-ratio inspirals around rotating accelerating black holes

Xin-Dong Du, Tao Zhou, Wei Xiong et al. (+2 more)

Extreme mass-ratio inspirals (EMRIs) can magnify small departures from Kerr dynamics into appreciable gravitational-wave phase shifts accumulated over many orbital cycles. We exploit this sensitivity to investigate the imprint of a rotating black hole's acceleration on an EMRI waveform. The spinning C metric poses two obstacles to the standard Kerr flux framework: the spacetime is not asymptotically flat, and the acceleration breaks the reflection symmetry that supports exactly equatorial circular timelike orbits. For sufficiently small acceleration $AM$, we therefore formulate the calculation in an intermediate Kerr-like wave zone satisfying $M/r\ll1$ and $Ar\ll1$, and construct a near-equatorial circular orbit by examining its coupled radial–polar stability. We derive the separated point-particle source for the spin$-2$ radial Teukolsky equation, construct a regular normalized angular solution, solve the radial equation using the Sasaki–Nakamura transformation and the Green function method, and couple the resulting horizon and far-zone fluxes to the adiabatic evolution of stable near-equatorial circular orbits. The framework recovers the Kerr limit and reproduces the dominant $l=2$ Kerr fluxes with relative errors of order $10^{-7}$. Acceleration modifies both radiation reaction and the orbital frequency, producing a characteristic nonmonotonic accumulated dephasing. For $M=10^6M_\odot$, $m_s/M=10^{-5}$, $a/M=0.7$, and $AM=3\times10^{-7}$, the dominant-mode dephasing slightly exceeds $1$ rad over one year. Thus even weak acceleration can generate an order-radian secular phase imprint on long-duration EMRIs within the controlled regime of the present approximation.
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All authors Xin-Dong Du, Tao Zhou, Wei Xiong, Tieguang Zi, Peng-Cheng Li

Saturday 22 August

High Energy Astrophysical Phenomena

The imprint of individual neutron star spins on ejecta, $r$-process nucleosynthesis, and kilonovae in binary neutron star mergers

Beyhan Karakas, Rahime Matur, David Radice et al. (+2 more)

To leading order, the gravitational-wave (GW) signal from binary neutron stars depends on the individual spins, $\chi_1$ and $\chi_2$, only through the effective spin parameter $\chi_{\rm eff}$. We present the first systematic investigation of individual-spin effects on ejecta, $r$-process nucleosynthesis, and kilonova emission, including comparisons at fixed total mass, mass ratio and $\chi_{\rm eff}$. We use numerical relativity ejecta from three total mass regimes with the finite-temperature, composition-dependent SFHo equation of state and neutrino emission and absorption. For $M_{\rm tot}=2.55\,M_\odot$ at fixed $\chi_{\rm eff}=0$, individual spins change the dynamical ejecta mass by a factor of ${\sim}45$, while the absolute $A\geq140$ yield spans more than two orders of magnitude and the lanthanide to light $r$-process mass ratio increases from ${\sim}2$ to ${\sim}70$. Prompt-collapse $4.10\,M_\odot$ models show heavy-element yield differences exceeding four orders of magnitude at $\chi_{\rm eff}=0$. The kilonova retains the individual-spin imprint, with peak brightness differences reaching ${\sim}0.9$ mag. At $40\,{\rm Mpc}$, all three fixed $\chi_{\rm eff}=0$ pairs remain above adopted depths at common epochs for all viewing angles, with same-epoch colour differences reaching ${\sim}1.5$ mag. The colour imprint persists when the simulation-derived secular ejecta are replaced by the same parametric disc outflow, indicating that disc mass differences are not the primary driver and that dynamical ejecta make an important contribution. Neutrino absorption systematically brightens the kilonova and shifts peak-associated colours blueward. These EM signatures can break the degeneracy between individual spins in the GW signal.
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All authors Beyhan Karakas, Rahime Matur, David Radice, Roland Haas, Maximilian Ruffert

High Energy Astrophysical Phenomena

Particle acceleration and non-thermal broadband spectrum of extended shocked outflows in black hole binary V4641 Sgr - a galactic pevatron

Andrei Bykov, Sergei Osipov, Vadim Romansky et al. (+2 more)

Stellar mass black holes accreting at a super-Eddington rate produce strong outflows and non-thermal radiation up to PeV energy. Recently, very high energy (VHE) emission was discovered from the environment of the galactic microquasar V4641 Sgr, which is known to experience super-Eddington outbursts. We present MHD simulations supplemented with a nonlinear kinetic Monte Carlo model that reproduces the observed radio, X-ray, and gamma-ray emission from the region over tens of parsecs surrounding V4641 Sgr. The reported multi-wavelength non-thermal emission can be explained as produced by PeV electrons accelerated by a system of strong shock waves created by the interaction between a narrow trans-relativistic polar jet and a quasi-spherical accretion-disk wind. The shock positions are associated with bright spots of the gamma-ray and X-ray radiation, whose spatial profiles can be tested with dedicated observations. The model predicts that a sizable fraction of the jet's kinetic energy is channeled into TeV-PeV protons, suggesting that such systems might be powerful sources of PeV-range cosmic rays during the accelerator activity cycle. In this model, the bow-tie shape structure discovered by MeerKAT in V4641 Sgr is associated with the radio emission from the termination surface of the quasi-spherical accretion-disk wind. The newly presented (from the SRG/eROSITA all-sky survey) and archival (INTEGRAL and Swift BAT) X-ray data are quantitatively consistent with the model, and simultaneously reproduce VHE measurements with H.E.S.S., HAWC, and LHAASO. Deeper X-ray observations will provide a test of the intermittent operation of the accelerator, in contrast with more persistent sources such as SS433/W50.
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All authors Andrei Bykov, Sergei Osipov, Vadim Romansky, Eugene Churazov, Ildar Khabibullin

High Energy Astrophysical Phenomena

Correlation of gamma-ray and optical variability of BL~Lacertae during the period of high blazar activity

Marina S. Butuzova and Mark A. Gorbachev

Investigating the correlation of flux variability in blazars across multiple spectral bands provides a key tool for constraining emission mechanisms and jet physical parameters. We study the gamma-ray and optical variability correlation of BL Lacertae on timescales of about 1 day during September 2022, when the source was within the TESS field of view, and over a longer period (April 2022 - September 2023) encompassing its gamma-ray flare, which finishes the series of flares during the high-activity phase. Our analysis confirms the Synchrotron Self-Compton mechanism as the origin of the gamma-ray emission, characterized by a zero time lag. For the longer interval, the Discrete Correlation Function (DCF) reveals a second statistically significant peak at the time lag of about 12 days. We demonstrate that this peak arises due to the presence of an additional flare in one of the bands, which accompanies a gamma-ray and optical flares correlated at zero time lag. We interpret the orphan flare origin in terms of the propagation of an injected blob of high-energy electrons along a jet with a decaying magnetic field, accounting for electron radiative cooling.
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High Energy Astrophysical Phenomena

Pair Discharges and Radio Emission from Millisecond-Pulsar and White-Dwarf Magnetospheres

Tuomo Salmi and Joonas Nättilä

Coherent radio emission is observed from compact astrophysical objects with relatively weak magnetic fields, including millisecond pulsars and white dwarfs, the latter being proposed as possible sources of long-period radio transients. In such environments, the standard pair discharge mechanism—driven by curvature radiation and one-photon pair production—can fail because the low magnetic field strength suppresses photon conversion. We analyze a discharge mechanism that operates efficiently in weak-field magnetospheres, including two-vertex quantum electrodynamic processes: inverse Compton up-scattering of background photons followed by either two-photon or one-photon pair creation depending on the seed photon temperature. Using first-principles radiative particle-in-cell simulations incorporating exact QED cross sections, we demonstrate that these mechanisms robustly generate pair cascades in millisecond-pulsar magnetospheres and in hot white-dwarf environments. The resulting system exhibits limit-cycle behavior and generates electromagnetic field fluctuations capable of producing coherent radio emission, providing a natural explanation for radio activity in low-field compact objects.
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High Energy Astrophysical Phenomena

Finite-Solid-Angle Boltzmann Radiation Transport on Dynamical Spacetimes in AthenaK

Hengrui Zhu, Alexander J. Dittmann, Lizhong Zhang et al. (+3 more)

We extend the finite-solid-angle general relativistic radiation transport method of C. J. White et al. (2023) to time-dependent spacetimes represented in ADM form. This Valencia-type solver retains the angular transport and local implicit matter coupling of the original HARM-type solver, but replaces its time-independent Kerr–Schild tetrad and conserved-variable normalization with an Eulerian formulation. A Cholesky-gauge spatial tetrad makes the frame and its derivatives algebraic functions of the ADM variables, providing smooth, metric-compatible angular transport. The resulting transport system couples directly to an evolving spacetime, agnostic to the gauge evolution equations. Our test suite, including flat and curved beams, radiation–fluid coupling, and time-dependent geometries, establishes the accuracy and robustness of this approach. We further apply the Valencia-type solver to a radiative circumbinary disk, illustrating its potential for multi-messenger studies of dynamical strongly gravitating systems.
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All authors Hengrui Zhu, Alexander J. Dittmann, Lizhong Zhang, James M. Stone, Eduardo Mario Gutierrez, David Radice

High Energy Astrophysical Phenomena

Discovery of an Extremely Luminous Sporadic Radio Pulsar

Fengqiu Adam Dong, Robert Main, Jackson D. Taylor et al. (+25 more)

We have discovered PSR J2108+5055, an extremely luminous but sporadic mode-changing rotating radio transient (RRAT), with a period of 0.495 s using the Canadian Hydrogen Intensity Mapping Experiment/Fast Radio Burst instrument (CHIME/FRB). We show that the brightest pulse from PSR J2108+5055 has a flux density of 3.1+/-1.0 kJy, corresponding to a spectral luminosity of (7.5+/-2.3)x10^23 erg s^-1 Hz^-1, assuming a dispersion-measure-derived distance of 1.6+/-0.3 kpc. We place an upper limit on the duty cycle of PSR J2108+5055 at 0.002% and measure a surface magnetic field of 5.8x10^11 G, a characteristic age of 1.2x10^7 yr, and a spindown luminosity of 2.2x10^32 erg s^-1. Using a simple model based on the Green Bank North Celestial Cap (GBNCC) survey, we place an upper limit on the number of PSR J2108+5055-like sources with similar peak flux densities in the GBNCC survey area of ~80 RRATs. We show that if PSR J2108+5055 were placed at the edge of the Local Group of galaxies, the Five-Hundred-Meter Aperture Spherical Telescope (FAST) would detect its brightest pulse. The second brightest pulse has a peak flux density of 1.5+/-0.7 kJy, and FAST would detect such a pulse out to ~1 Mpc, covering the inner Local Group, including Andromeda.
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All authors Fengqiu Adam Dong, Robert Main, Jackson D. Taylor, Shion Andrew, Alyssa Cassity, Shami Chatterjee, Alice P. Curtin, Emmanuel Fonseca, B. M. Gaensler, Jason Hessels, Victoria Kaspi, Afrokk Khan, Lars Künkel, Mattias Lazda, Calvin Leung, Kiyoshi W. Masui, Ryan Mckinven, Mason Ng, Ayush Pandhi, Aaron B. Pearlman, Ziggy Pleunis, Alexander W. Pollak, Sachin Pradeep E. T., Scott M. Ransom, Paul Scholz, Kaitlyn Shin, Kendrick Smith, Ingrid Stairs

High Energy Astrophysical Phenomena

Pair Discharges and Radio Emission from Pulsar Magnetospheres

Joonas Nättilä and Tuomo Salmi

Radio pulsars can power their coherent radio emission through intermittent plasma discharges in magnetospheric gaps. The nonlinear coupling between particle acceleration, quantum electrodynamic (QED) processes, and electric field screening remains difficult to model self-consistently. We present an analytical concurrency model and first-principles particle-in-cell (PIC) simulations of polar cap discharges. The model predicts limit-cycle behavior where the electric field and plasma density oscillate with a frequency set by the local plasma frequency, modified by the plasma inertia. One-dimensional simulations with exact QED rates and realistic plasma parameters validate these predictions. The discharges generate pair multiplicities up to $M_\pm \sim 10^4$ and excite electric field oscillations with spectra consistent with pulsar radio microstructure. These results provide a theoretical framework connecting microphysical gap dynamics to macroscopic observables.
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Friday 21 August

High Energy Astrophysical Phenomena

Galactic Electron-Positron Annihilation Emission from X-Ray Binaries with Transient and Persistent Jets

Argen Gian Detoito and Henric Krawczynski

The Galactic Center exhibits a persistent 0.511 MeV emission characteristic of electron-positron annihilation. Various astrophysical sources may be responsible for supplying the positrons, yet their contributions with respect to the total annihilation rate is uncertain. X-ray binaries have historically been a primary candidate, possibly contributing a significant fraction of the Galactic positrons. X-ray binaries can produce positrons through the Blandford-Znajek mechanism, two-photon pair production in the corona, and/or one-photon pair production for strongly-magnetized compact objects. These positrons may then be channeled into the Interstellar Medium through jets or winds. In this work, we argue that X-ray binaries cannot contribute to the electron-positron annihilation flux alone. We present 0.511 MeV line fluxes and all-sky maps produced by X-ray binaries and stellar flares from the Galactic stellar population, along with the gamma-ray continuum from positrons produced by X-ray binaries. To do so, we solve the particle transfer equation using Green's functions. The total morphology is slightly asymmetric towards negative longitudes and positive latitudes. We find five 0.511 MeV flux hotspots in the generated all sky maps and scrutinize the contribution of individual sources to these hotspots. Observations of these hotspots can reveal the contribution of X-ray binaries to the Galactic positrons. The upcoming Compton Spectrometer and Imager (COSI) mission could image a hotspot near Cygnus X-1. The detection of the other hotspots requires a telescope with improved arcminute angular resolution.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Kerr-Newman and genuine Kerr black holes in the Bertotti-Robinson magnetic field

Hryhorii Ovcharenko and Jiri Podolsky

We present a spacetime that describes a rotating and charged black hole immersed in an external magnetic field. This exact solution to the Einstein-Maxwell equations has a surprisingly simple form which reduces to standard Kerr-Newman metric, and to the uniform Bertotti-Robinson magnetic universe. We show that the Kerr-BR solution presented in [Phys. Rev. Lett. 135, 181401 (2025)] has a special charge, and we identify a genuine Kerr black hole without any charge, in the magnetic field. In the weak-field limit it gives the Wald solution. We analyze main physical properties of the new family, namely singularities, horizons, regularity of axes, charges, entropy and temperature.
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High Energy Astrophysical Phenomena

When the stars don't align: Investigating inconsistencies in binary black hole formation across population synthesis codes

Alexandra G. Guerrero, Michael Zevin, Duncan B. Maclean et al. (+4 more)

Binary population synthesis (BPS) codes are valuable tools for investigating the end-to-end lives of binary stars as well as a myriad of observed astrophysical phenomena. Many “rapid" BPS codes rely on semi-analytical single-star evolutionary tracks and disjointed prescriptions for binary physics. Updated “hybrid" or “detailed" BPS codes incorporate improved methodologies, but at a steeper computational cost that may limit broad exploration of physical uncertainties. Given the widespread use of BPS in modern astrophysical research, it is imperative to systematically compare BPS codes across the spectrum of computational efficiency, flexibility, and physical realism to gauge their consistency and robustness. In this work, we perform BPS on three single-metallicity populations of identical initial binaries using three modern codes — the rapid code $\texttt{COSMIC}$, the hybrid code $\texttt{METISSE}$ integrated into $\texttt{COSMIC}$, and the detailed code $\texttt{POSYDON}$ — ensuring consistent physical parameterizations where possible. We find stark differences in the properties, formation pathways, and progenitors of binary black hole (BBH) merger populations across the three codes. In a population of one million binaries at $0.01 Z_\odot$, each code results in $\sim 5,000\mbox{--}9,000$ BBHs that merge within a Hubble time. However, $\lesssim 14\%$ of progenitors overlap between two codes, and only $\textit{one}$ initial binary becomes a BBH merger across all three codes. Identical progenitors often follow different evolutionary pathways in each code and result in inconsistent BBH properties. Our results highlight the need for a deeper understanding of physical and computational differences between BPS codes and caution against over-interpreting results from any individual BPS code.
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All authors Alexandra G. Guerrero, Michael Zevin, Duncan B. Maclean, Katelyn Breivik, Carl L. Rodriguez, Max M. Briel, Daniel E. Holz