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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 19 December

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Trails of clouds in binary black holes

Mateja Bošković, Rafael A. Porto and Matthias Koschnitzke

Superradiant instabilities of rotating black holes can give rise to long-lived bosonic clouds, offering natural laboratories to probe ultralight particles across a wide range of parameter space. The presence of a companion can dramatically impact both the cloud's evolution and the binary's orbital dynamics, generating a trail of feedback effects that require detailed modelling. Using a worldline effective field theory approach, we develop a systematic framework for binaries on generic (eccentric and inclined) orbits, capturing both resonant and non-resonant transitions without relying solely on balance laws. We demonstrate the existence of “co-rotating” floating orbits that can deplete the cloud prior to entering the detector's band, triggering eccentricity growth towards a sequence of fixed points. Likewise, we show that “counter-rotating” orbits can also deplete the cloud, driving (unbounded) growth of eccentricity. Furthermore, we uncover novel features tied to orbital inclination. Depending on the mass ratio, equatorial orbits can become unstable, and fixed points may arise not only for aligned or anti-aligned configurations but, strikingly, also at intermediate inclinations. We derive flow equations governing spin-orbit misalignment and eccentricity and identify distinctive signatures that can reveal the presence of boson clouds in the binary's history, as well as key features of possible in-band transitions. These results refine and extend earlier work, yielding a more faithful description of the imprints of ultralight particles in gravitational-wave signals from binary black holes, signatures that are within reach of future detectors such as LISA, Cosmic Explorer, and the Einstein~Telescope.
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Astrophysics of Galaxies

Asymptotic behaviour of galactic small-scale dynamos at modest magnetic Prandtl number

Frederick A. Gent, Mordecai-Mark Mac Low, Maarit J. Korpi-Lagg et al. (+2 more)

Magnetic fields are critical at many scales to galactic dynamics and structure, including multiphase pressure balance, dust processing, and star formation. Dynamo action determines their dynamical structure and strength. Simulations of combined large- and small-scale dynamos have successfully developed mean fields with strength and topology consistent with observations but with turbulent fields much weaker than observed, while simulations of small-scale dynamos with parameters relevant to the interstellar medium yield turbulent fields an order of magnitude below the values observed or expected theoretically. We use the Pencil Code accelerated on GPUs with Astaroth to perform high-resolution simulations of a supernova-driven galactic dynamo including heating and cooling in a periodic domain. Our models show that the strength of the turbulent field produced by the small-scale dynamo approaches an asymptote at only modest magnetic Prandtl numbers. This allows us to use these models to suggest the essential characteristics of this constituent of the magnetic field for inclusion in global galactic models. The asymptotic limit occurs already at magnetic Prandtl number of only a few hundred, many orders of magnitude below physical values in the the interstellar medium and consistent with previous findings for isothermal compressible flows.
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All authors Frederick A. Gent, Mordecai-Mark Mac Low, Maarit J. Korpi-Lagg, Touko Puro, Matthias Reinhardt

Solar and Stellar Astrophysics

On the complex nature of coronal heating

C.A. Breu, D.I. Pontin, E. Priest et al. (+1 more)

A large part of the hot corona consists of magnetically confined, bright plasma loops. These observed loops are in turn structured into bright strands. We investigate the relationship between magnetic field geometry, plasma properties and bright strands with the help of a 3D resistive MHD simulation of a coronal loop rooted in a self-consistent convection zone layer. We find that it is impossible to identify a loop as a simple coherent magnetic flux tube that coincides with plasma of nearly uniform temperature and density. The location of bright structures is determined by a complex interplay between heating, cooling and evaporation timescales. Current sheets form preferentially at the interfaces of magnetic flux from different sources. They may also form within bundles of magnetic field lines since motions within magnetic concentrations drive plasma flows on a range of timescales that provide further substructure and can locally enhance magnetic field gradients and thus facilitate magnetic reconnection. The numerical experiment therefore possesses aspects of both the flux tube tectonics and flux braiding models. While modelling an observed coronal loop as a cylindrical flux tube is useful to understand the physics of specific heating mechanisms in isolation, it does not describe well the structure of a coronal loop rooted in a self-consistently evolving convection zone.
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All authors C.A. Breu, D.I. Pontin, E. Priest, I. De Moortel

Cosmology and Nongalactic Astrophysics

Constraining primordial non-Gaussianity from DESI DR1 quasars and Planck PR4 CMB Lensing

Sofia Chiarenza, Alex Krolewski, Marco Bonici et al. (+54 more)

We present the first measurement of local-type primordial non-Gaussianity from the cross-correlation between $1.2$ million spectroscopically confirmed quasars from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI) and the Planck PR4 CMB lensing reconstructions. The analysis is performed in three tomographic redshift bins covering $0.8 < z < 3.5$, covering a sky fraction of $\sim 20\%$. We adopt a catalog-based pseudo-$C_\ell$ estimator and apply linear imaging weights validated on noiseless mocks. Compared to previous analyses using photometric quasar samples, our results benefit from the high purity of the DESI spectroscopic sample, the reduced noise of PR4 lensing, and the absence of excess large-scale power in the spectroscopic quasar auto-correlation. Fitting simultaneously for the non-Gaussianity parameter $f_{\mathrm{NL}}$ and the linear bias amplitude in each redshift bin, we obtain $f_{\mathrm{NL}} = 2^{+28}_{-34}$ for a response parameter $p=1.6$, and $f_{\mathrm{NL}} = 6^{+20}_{-24}$ for $p=1.0$. These results improve the constraints on $f_{\mathrm{NL}}$ by $\sim 35\%$ compared to the previous analysis based on the Legacy Imaging Survey DR9. Additionally, we derive an optimal weighting scheme to maximize the constraining power. In this case, and assuming $p=1.6$, we obtain $f_\mathrm{NL}=19^{+25}_{-31}$. Our results demonstrate the statistical power of DESI quasars for probing inflationary physics, and highlight the promise of future DESI data releases.
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All authors Sofia Chiarenza, Alex Krolewski, Marco Bonici, Edmond Chaussidon, Roger de Belsunce, Will Percival, Jessica Nicole Aguilar, Steven Ahlen, Anton Baleato Lizancos, Davide Bianchi, David Brooks, Todd Claybaugh, Andrei Cuceu, Kyle Dawson, Axel de la Macorra, Peter Doel, Simone Ferraro, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Hiram K. Herrera-Alcantar, Klaus Honscheid, Dragan Huterer, Mustapha Ishak, Dick Joyce, David Kirkby, Anthony Kremin, Ofer Lahav, Claire Lamman, Martin Landriau, Laurent Le Guillou, Michael Levi, Marc Manera, Paul Martini, Aaron Meisner, Ramon Miquel, Seshadri Nadathur, Jeffrey A. Newman, Gustavo Niz, Nathalie Palanque-Delabrouille, Claire Poppett, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Michael Schubnell, Hee-Jong Seo, Joseph Harry Silber, David Sprayberry, Gregory Tarlé, Benjamin Alan Weaver, Christophe Yèche, Rongpu Zhou, Hu Zou

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Revisited apparent horizon entropy and GSL in modified gravity

Soma Heydari, Parastoo Askari and Kayoomars Karami

This work presents a universal and revisited formalism for the entropy of the apparent horizon in modified gravity to investigate the validity of the Generalized Second Law (GSL) of thermodynamics. This revisited horizon entropy is constructed directly from the modified Friedmann equations in a Friedmann-Robertson-Walker (FRW) universe. The resulting entropy relation contains, beside the standard Bekenstein-Hawking term, an additional integral contribution that encodes the effective energy density and pressure generated by deviations from general relativity. Using this universal entropy formula, a compact expression for the GSL is derived. This formalism is then applied to some viable $f(T)$ and $f(R)$ gravity models, in order to re-evaluate the validity of the GSL as a function of redshift. The analysis demonstrates that including the integral term in the revisited entropy can relatively improve the late-time validity of the GSL for some of these models while living others unchanged, thereby reinforcing the profound connection between thermodynamics and gravity.
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Astrophysics of Galaxies

Investigating the AGN variability timescale – black hole mass relationship with Gaia, SDSS and ZTF

Adrien Hélias, Sarah C. Gallagher and Pauline Barmby

Active galactic nuclei (AGNs) exhibit variability in their luminosities with timescales that correlate with the mass of the black hole at the centre of the AGN. Presently, the empirical correlation lacks sufficient precision to confidently convert these timescales into black hole masses, especially at the low-mass end. To find more AGNs with timescale measurements, we study a very large catalog of AGNs from the Gaia Data Release 3 called GLEAN (Gaia variabLE AgN; 872228 objects). We identify GLEAN objects with optical spectra from the Sloan Digital Sky Survey DR17 and light curves from the Zwicky Transient Facility (ZTF) DR21. After fitting the light curves with a damped random walk model, we find that the GLEAN light curves have insufficient sampling to extract reliable amplitude and timescale measurements outside the range of 50-100 days. On the other hand, well-sampled ZTF light curves allow more accurate estimations of these parameters. The fractional variability amplitude is an effective, model-independent metric for measuring variability amplitude, but only when derived from high-quality light curves. We provide a catalog of 127 GLEAN AGNs with spectroscopic virial black hole masses, and variability amplitudes and timescales. Though we do not find any low-mass black holes in this AGN sample, we confirm a relationship between the damped random walk timescale and the black hole mass that is consistent with previous studies.
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Instrumentation and Methods for Astrophysics

Searching systematically for coupling of laser and phase-modulation noise in heterodyne interferometry

Kohei Yamamoto, Olaf Hartwig, Lennart Wissel et al. (+3 more)

Heterodyne interferometry for precision science often comes with an optical phase modulation, for example, for intersatellite clock noise transfer for gravitational wave (GW) detectors in space, exemplified by the Laser Interferometer Space Antenna (LISA). The phase modulation potentially causes various noise couplings to the final phase extraction of heterodyne beatnotes by a phasemeter. In this paper, in the format of space-based GW detectors, we establish an analytical framework to systematically search for the coupling of various noises from the heterodyne and modulation frequency bands, which are relatively unexplored so far. In addition to the noise caused by the phase modulation, the high-frequency laser phase noise is also discussed in the same framework. The analytical result is also compared with a numerical experiment to confirm that our framework successfully captures the major noise couplings. We also demonstrate a use case of this study by taking the LISA-like parameters as an example, which enables us to derive requirements on the level of the laser and phase modulation noises in the high frequency regimes.
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All authors Kohei Yamamoto, Olaf Hartwig, Lennart Wissel, Holly Leopardi, Kenji Numata, Ryan Derosa

High Energy Astrophysical Phenomena

Selected topics on: 1) proposal of interpreting the Crab supernova with a GRB 2) progress in identifying the seven GRBs episodes 3) the role of Sagittarius A in identifying the dark matter component (the X fermion)

R. Ruffini, C. Sigismondi, Y. Wang et al. (+10 more)

As the fiftieth anniversary of our common effort in the field of relativistic astrophysics is approaching, we offer a new look to some of our acquired knowledge in a more complete view, which evidence previous unnoticed connections. They are gaining due prominence in reaching a more complete picture evidencing the main results. We outline the history of GRB observations along with a summary of the contributions made by our group to develop the BdHN interpreting model. We show the seven Episodes characterizing the most powerful BdHNe I occurred to date: GRB 190114C and GRB 220101A. New inferences for the explanation of the highest energy radiation in the TeV are presented.
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All authors R. Ruffini, C. Sigismondi, Y. Wang, H. Quevedo, S. Zhang, Y. Aimuratov, P. Chardonnet, C.L. Fryer, T. Mirtorabi, R. Moradi, M. Prakapenia, F. Rastegarnia, S.-S. Xue

High Energy Astrophysical Phenomena

Magnetic field spreading from stellar and galactic dynamos into the exterior

Axel Brandenburg, Oindrila Ghosh, Franco Vazza et al. (+1 more)

The exteriors of stellar and galactic dynamos are usually modeled as current-free potential fields. A more realistic description might instead be that of a force-free magnetic field. Here, we suggest that, in the absence of outflows, neither of these reflect the actual behavior when the magnetic field spreads diffusively into a more poorly conducting turbulent exterior outside dynamo. In particular, we explain why the usual ordering, in which the dipole magnetic field is the most slowly decaying one, is altered, and why the quadrupole can develop a toroidal component that decays even more slowly with radial distance. This is a robust feature that persists even for spatially nonuniform magnetic diffusivities. It is most clearly seen for spherical dynamo volumes and becomes more complicated for oblate ones. In either case, however, these fields are confined within a magnetosphere, beyond which the field strength drops exponentially. We demonstrate that the Faraday displacement current, which plays a role in a vacuum, can safely be neglected in all cases. The superposition of magnetic fields from galaxies in the outskirts of voids between galaxy clusters therefore cannot explain the magnetization of the intergalactic medium in voids, reinforcing the conventional expectation that these fields are of primordial origin. For quadrupolar configurations, the synchrotron emission from the magnetosphere is found to be constant along concentric rings. The dipolar and quadrupolar configurations display large-scale radial trends that are potentially distinguishable with existing radio telescopes.
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All authors Axel Brandenburg, Oindrila Ghosh, Franco Vazza, Andrii Neronov

High Energy Astrophysical Phenomena

Constraining the Prompt Atmospheric Neutrino Flux Combining IceCube's Cascade and Track Samples

R. Abbasi, M. Ackermann, J. Adams et al. (+428 more)

The IceCube Neutrino Observatory has observed a diffuse flux of high-energy astrophysical neutrinos for more than a decade. A relevant background to the astrophysical flux is prompt atmospheric neutrinos, originating from the decay of charmed mesons produced in cosmic-ray-induced air showers. The production rate of charmed mesons in the very forward phase space of hadronic interactions, and consequently, the prompt neutrino flux, remains uncertain and has not yet been observed by neutrino detectors. An accurate measurement of this flux would enhance our understanding of fundamental particle physics such as hadronic interactions in high-energy cosmic-ray-induced air showers and the nucleon structure. Furthermore, an experimental characterization of this background flux will improve the precision of astrophysical neutrino flux spectral measurements. In this work, we perform a combined fit of cascade-like and track-like neutrino events in IceCube to constrain the prompt atmospheric neutrino flux. Given that the prompt flux is a sub-dominant contribution, treating systematic uncertainties arising from the potential mis-modeling of the conventional and astrophysical neutrino fluxes is critical for its measurement. Our analysis yields a non-zero best-fit result, which is, however, consistent with the null hypothesis of no prompt flux within one standard deviation. Consequently, we establish an upper bound on the flux at $4\times 10^{-16}$ (GeV m$^2$ s sr)$^{-1}$ at 10 TeV.
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All authors R. Abbasi, M. Ackermann, J. Adams, S. K. Agarwalla, J. A. Aguilar, M. Ahlers, J.M. Alameddine, S. Ali, N. M. Amin, K. Andeen, C. Argüelles, Y. Ashida, S. Athanasiadou, S. N. Axani, R. Babu, X. Bai, J. Baines-Holmes, A. Balagopal V., S. W. Barwick, S. Bash, V. Basu, R. Bay, J. J. Beatty, J. Becker Tjus, P. Behrens, J. Beise, C. Bellenghi, S. Benkel, S. BenZvi, D. Berley, E. Bernardini, D. Z. Besson, E. Blaufuss, L. Bloom, S. Blot, I. Bodo, F. Bontempo, J. Y. Book Motzkin, C. Boscolo Meneguolo, S. Böser, O. Botner, J. Böttcher, J. Braun, B. Brinson, Z. Brisson-Tsavoussis, R. T. Burley, D. Butterfield, M. A. Campana, K. Carloni, J. Carpio, S. Chattopadhyay, N. Chau, Z. Chen, D. Chirkin, S. Choi, B. A. Clark, P. Coleman, G. H. Collin, D. A. Coloma Borja, A. Connolly, J. M. Conrad, D. F. Cowen, C. De Clercq, J. J. DeLaunay, D. Delgado, T. Delmeulle, S. Deng, P. Desiati, K. D. de Vries, G. de Wasseige, T. DeYoung, J. C. Díaz-Vélez, S. DiKerby, T. Ding, M. Dittmer, A. Domi, L. Draper, L. Dueser, D. Durnford, K. Dutta, M. A. DuVernois, T. Ehrhardt, L. Eidenschink, A. Eimer, C. Eldridge, P. Eller, E. Ellinger, D. Elsässer, R. Engel, H. Erpenbeck, W. Esmail, S. Eulig, J. Evans, P. A. Evenson, K. L. Fan, K. Fang, K. Farrag, A. R. Fazely, A. Fedynitch, N. Feigl, C. Finley, L. Fischer, D. Fox, A. Franckowiak, S. Fukami, P. Fürst, J. Gallagher, E. Ganster, A. Garcia, M. Garcia, G. Garg, E. Genton, L. Gerhardt, A. Ghadimi, C. Glaser, T. Glüsenkamp, J. G. Gonzalez, S. Goswami, A. Granados, D. Grant, S. J. Gray, S. Griffin, S. Griswold, K. M. Groth, D. Guevel, C. Günther, P. Gutjahr, C. Ha, C. Haack, A. Hallgren, L. Halve, F. Halzen, L. Hamacher, M. Ha Minh, M. Handt, K. Hanson, J. Hardin, A. A. Harnisch, P. Hatch, A. Haungs, J. Häußler, K. Helbing, J. Hellrung, B. Henke, L. Hennig, F. Henningsen, L. Heuermann, R. Hewett, N. Heyer, S. Hickford, A. Hidvegi, C. Hill, G. C. Hill, R. Hmaid, K. D. Hoffman, D. Hooper, S. Hori, K. Hoshina, M. Hostert, W. Hou, M. Hrywniak, T. Huber, K. Hultqvist, K. Hymon, A. Ishihara, W. Iwakiri, M. Jacquart, S. Jain, O. Janik, M. Jansson, M. Jeong, M. Jin, N. Kamp, D. Kang, W. Kang, A. Kappes, L. Kardum, T. Karg, M. Karl, A. Karle, A. Katil, M. Kauer, J. L. Kelley, M. Khanal, A. Khatee Zathul, A. Kheirandish, H. Kimku, J. Kiryluk, C. Klein, S. R. Klein, Y. Kobayashi, A. Kochocki, R. Koirala, H. Kolanoski, T. Kontrimas, L. Köpke, C. Kopper, D. J. Koskinen, P. Koundal, M. Kowalski, T. Kozynets, A. Kravka, N. Krieger, J. Krishnamoorthi, T. Krishnan, K. Kruiswijk, E. Krupczak, A. Kumar, E. Kun, N. Kurahashi, N. Lad, C. Lagunas Gualda, L. Lallement Arnaud, M. J. Larson, F. Lauber, J. P. Lazar, K. Leonard DeHolton, A. Leszczyńska, C. Li, J. Liao, C. Lin, Q. R. Liu, Y. T. Liu, M. Liubarska, C. Love, L. Lu, F. Lucarelli, W. Luszczak, Y. Lyu, M. Macdonald, J. Madsen, E. Magnus, Y. Makino, E. Manao, S. Mancina, A. Mand, I. C. Mariş, S. Marka, Z. Marka, L. Marten, I. Martinez-Soler, R. Maruyama, J. Mauro, F. Mayhew, F. McNally, K. Meagher, S. Mechbal, A. Medina, M. Meier, Y. Merckx, L. Merten, J. Mitchell, L. Molchany, S. Mondal, T. Montaruli, R. W. Moore, Y. Morii, A. Mosbrugger, M. Moulai, D. Mousadi, E. Moyaux, T. Mukherjee, R. Naab, M. Nakos, U. Naumann, J. Necker, L. Neste, M. Neumann, H. Niederhausen, M. U. Nisa, K. Noda, A. Noell, A. Novikov, A. Obertacke, V. O'Dell, A. Olivas, R. Orsoe, J. Osborn, E. O'Sullivan, V. Palusova, H. Pandya, A. Parenti, N. Park, V. Parrish, E. N. Paudel, L. Paul, C. Pérez de los Heros, T. Pernice, T. C. Petersen, J. Peterson, M. Plum, A. Pontén, V. Poojyam, Y. Popovych, M. Prado Rodriguez, B. Pries, R. Procter-Murphy, G. T. Przybylski, L. Pyras, C. Raab, J. Rack-Helleis, N. Rad, M. Ravn, K. Rawlins, Z. Rechav, A. Rehman, I. Reistroffer, E. Resconi, S. Reusch, C. D. Rho, W. Rhode, L. Ricca, B. Riedel, A. Rifaie, E. J. Roberts, M. Rongen, A. Rosted, C. Rott, T. Ruhe, L. Ruohan, D. Ryckbosch, J. Saffer, D. Salazar-Gallegos, P. Sampathkumar, A. Sandrock, G. Sanger-Johnson, M. Santander, S. Sarkar, M. Scarnera, P. Schaile, M. Schaufel, H. Schieler, S. Schindler, L. Schlickmann, B. Schlüter, F. Schlüter, N. Schmeisser, T. Schmidt, F. G. Schröder, L. Schumacher, S. Schwirn, S. Sclafani, D. Seckel, L. Seen, M. Seikh, S. Seunarine, P. A. Sevle Myhr, R. Shah, S. Shah, S. Shefali, N. Shimizu, B. Skrzypek, R. Snihur, J. Soedingrekso, D. Soldin, P. Soldin, G. Sommani, C. Spannfellner, G. M. Spiczak, C. Spiering, J. Stachurska, M. Stamatikos, T. Stanev, T. Stezelberger, T. Stürwald, T. Stuttard, G. W. Sullivan, I. Taboada, S. Ter-Antonyan, A. Terliuk, A. Thakuri, M. Thiesmeyer, W. G. Thompson, J. Thwaites, S. Tilav, K. Tollefson, S. Toscano, D. Tosi, A. Trettin, A. K. Upadhyay, K. Upshaw, A. Vaidyanathan, N. Valtonen-Mattila, J. Valverde, J. Vandenbroucke, T. Van Eeden, N. van Eijndhoven, L. Van Rootselaar, J. van Santen, J. Vara, F. Varsi, M. Venugopal, M. Vereecken, S. Vergara Carrasco, S. Verpoest, D. Veske, A. Vijai, J. Villarreal, C. Walck, A. Wang, E. H. S. Warrick, C. Weaver, P. Weigel, A. Weindl, J. Weldert, A. Y. Wen, C. Wendt, J. Werthebach, M. Weyrauch, N. Whitehorn, C. H. Wiebusch, D. R. Williams, L. Witthaus, M. Wolf, G. Wrede, X. W. Xu, J. P. Yanez, Y. Yao, E. Yildizci, S. Yoshida, R. Young, F. Yu, S. Yu, T. Yuan, S. Yun-Cárcamo, A. Zander Jurowitzki, A. Zegarelli, S. Zhang, Z. Zhang, P. Zhelnin, P. Zilberman

Cosmology and Nongalactic Astrophysics

Implicit Likelihood Inference of the Neutrino Mass Hierarchy from Cosmological Data

Ke Wang and Jia-Yi Feng

In this paper, we turn to the Learning the Universe Implicit Likelihood Inference (LtU-ILI) pipeline to perform a multi-round ILI of the neutrino mass hierarchy from cosmological data, including $TT$, $TE$, $EE$ power spectra of Planck 2018 and distance ratios of DESI DR2. More precisely, we first embed the CMB power spectra simulator $\mathtt{CLASS}$ into the LtU-ILI pipeline. And then, opting for Sequential Neural Likelihood Estimation (SNLE), we sequentially train neural networks using $6$ rounds of $10000$ simulations to target a “black box” likelihood of our forward model with one additional neutrino mass hierarchy parameter $\tilde{\Delta}$ and six base cosmological parameters. We find $\tilde{\Delta}=0.12^{+0.21}_{-0.23}~(68\%{\rm CL})$.
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Astrophysics of Galaxies

Interpreting the strong clustering of ultra-diffuse galaxies by halo spin bias

Qinglin Ma, Cheng Li, Yangyao Chen et al. (+1 more)

We use the IllustrisTNG300-ODM simulation to investigate the spin bias of low-mass halos and its connection to the strong clustering of ultra-diffuse galaxies (UDGs) reported by Zhang et al. (2025). By comparing two halo spin definitions-one using only bound particles ($\lambda_{\rm b}$) and another including unbound particles ($\lambda_{\rm a}$)-we demonstrate that the spin bias of low-mass halos critically depends on the definition. While $\lambda_{\rm a}$ yields stronger clustering for higher-spin halos at all masses, $\lambda_{\rm b}$ produces an inverted trend below $M_{\rm h}\sim 10^{11} \rm M_{\odot}/h$. This discrepancy is driven by a subset of halos in high-density environments that have large $\lambda_{\rm a}$ but small $\lambda_{\rm b}$. Using an empirical model implemented in SDSS-like mocks, we link the stellar surface-mass-density ($\Sigma_\ast$) of a galaxy to $\lambda_{\rm a}$ of its host halo and find an anti-correlation that more diffuse dwarfs tend to reside in higher-spin halos. The model naturally reproduces the observed strong clustering of UDGs within the standard $\Lambda$CDM framework without invoking exotic assumptions such as self-interacting dark matter. The high fraction of unbound particles in UDG hosts likely originates from tidal fields in dense regions, an effect particularly significant for low-mass halos. We discuss how the angular momentum of a halo represented by $\lambda_{\rm a}$ may be transferred to the gas to affect size and surface density of the galaxy that forms in the halo.
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All authors Qinglin Ma, Cheng Li, Yangyao Chen, Houjun Mo

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Boiling away asymmetries: low-scale phase transitions, gravitational waves and leptogenesis

Leonardo Grimaldi, Michele Lucente and Silvia Pascoli

Leptogenesis is one of the most popular mechanisms to account for the observed baryon asymmetry of the Universe. A generic feature of leptogenesis is a large separation of scales between the epoch of baryon asymmetry production (sphaleron freeze-out at temperature $T \sim 130$ GeV) and the one where it affects the big bang nucleosynthesis processes (BBN at $T \sim 1$ MeV). Any entropy release between these two epochs would lead to a dilution of previously produced relics, such as the baryons. Motivated by the recent evidence of a stochastic gravitational waves background (SGWB) in the nHz frequency range, we consider the case of supercooled first-order phase transition and we study the impact of the induced entropy dilution on the leptogenesis parameter space. We employ the Type-I seesaw with 2 right-handed neutrinos as benchmark scenario, and demonstrate that the viable leptogenesis parameter space is significantly reduced. Interestingly, the values of dilution predicted by the SGWB best fit points in several first order phase transition scenarios would completely exclude the leptogenesis parameter space testable by future experiments, thus establishing a phenomenological interconnection between leptogenesis, SGWB, first order phase transition and neutrino mass generation. Our analysis can be generalised to different leptogenesis models and entropy dilution mechanisms.
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Solar and Stellar Astrophysics

Pre-supernova O-C shell mergers could produce more $^{44}\mathrm{Ti}$ than the explosion

Joshua Issa and Falk Herwig

The formation of $^{44}\mathrm{Ti}$ in massive stars is thought to occur during explosive nucleosynthesis, however recent studies have shown it can be produced during O-C shell mergers prior to core collapse. We investigate how mixing according to 3D macro physics derived from hydrodynamic simulations impacts pre-supernova O-C shell merger nucleosynthesis and if it can dominate explosive supernova production of $^{44}\mathrm{Ti}$ and other radioactive isotopes. We compare a range of observations and models of explosive $^{44}\mathrm{Ti}$ yields to pre-explosive multi-zone mixing-burning nucleosynthesis simulations of an O-C shell merger in a $15~\mathrm{M_\odot}$ $Z=0.02$ stellar model with mixing conditions corresponding to different 3D hydro mixing scenarios. Radioactive species produced in the $\mathrm{O}$ shell have a multi-dex spread in pre-explosive yield predictions across different 3D mixing scenarios of $1.54~\mathrm{dex}$ and $2.14~\mathrm{dex}$ on average depending on mass cut. $^{44}\mathrm{Ti}$ has the largest spread of $4.78~\mathrm{dex}$ and $4.81~\mathrm{dex}$ depending on mass cut. Further, we show that the pre-explosive production of $^{44}\mathrm{Ti}$ can be larger than the explosive production of models and can match observations. Our results also show that 3D mixing physics enhances $^{44}\mathrm{Ti}$ in 1D models without modifying $^{56}\mathrm{Ni}$ yields. We conclude that quantitative predictions of $^{44}\mathrm{Ti}$ and other radioactive species more broadly require an understanding of the 3D hydrodynamic mixing conditions present during the O-C shell merger.
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Solar and Stellar Astrophysics

A VLA search for compact radio sources in the explosive molecular outflows DR 21 and G5.89

Vanessa Yanza, Sergio A. Dzib, Aina Palau et al. (+3 more)

We present high-angular-resolution ($\sim0\rlap{.}''1$) VLA Ku-band (12–18 GHz) observations of two explosive molecular outflows (EMOs), DR 21 and G5.89, in a search for runaway stars related to these explosive events. In DR 21, we identified 13 compact radio sources (CRS), 9 located in the DR 21 core and near the CO streamer ejection region. The radio properties of the CRSs show that three are nonthermal radio emitters, likely magnetically active stars, while the nature of the remaining CRSs cannot be conclusively identified. All detected CRSs are good candidates for follow-up proper motion studies to confirm whether they are runaway stars. We also identify multiple ionized arc-shaped structures that can be fitted with parabolas whose symmetry axes converge to a position coincident with CRSs #11, raising the possibility that this source is the main ionizing star. A re-analysis of the 18 molecular outflow streamers refines the center of the explosive event, which aligns closely with the position indicated by the arcs convergence point, supporting a common stellar origin for the EMOs and the HII-region. In G5.89, the observations reveal a shell with a square-like morphology. The strong extended emission from this HII region prevents the detection of weak compact radio sources inside the shell; only two were identified well beyond the shell, and a single parabolic arc was fitted within this region. Overall, arc structures in ionized regions seem to be good tracers of the origin of the ionizing sources.
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All authors Vanessa Yanza, Sergio A. Dzib, Aina Palau, William J. Henney, Luis F. Rodríguez, Luis A. Zapata

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Baryogenesis and EDMs in the 2HDM with a Complex Singlet

Björn Garbrecht and Edward Wang

We perform the first joint analysis of baryogenesis from initial Higgs charges (also called Higgsogenesis) and electric dipole moments (EDMs) in a model with two Higgs doublets, a complex scalar, and a Majorana fermion. In our proposed scenario, baryogenesis happens in three steps: (1) The decay of the scalar produces an asymmetry between the two Higgs doublets which is partly transferred to fermions via Standard Model processes. (2) This asymmetry is converted into a $B-L$ charge via interactions mediated by the Majorana fermion. (3) The weak sphaleron processes partially convert the resulting $B-L$ charge into a $B$ asymmetry. We perform a numerical analysis of baryogenesis and the EDM contributions and find that, due to resonant enhancement, baryogenesis is possible with singlet masses as low as $10^5$ GeV. We also find that for some parameters, the model can give large contributions to the electron and neutron EDM while also producing baryogenesis. The present scenario offers a new perspective on interpreting observational bounds in terms of cosmology: Because it relies on out-of-equilibrium decays, the questions of baryogenesis and $CP$ violation in the Higgs sector may be linked with EDM signals without the additional assumption of a first order electroweak phase transition.
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Instrumentation and Methods for Astrophysics

The MeerKLASS L-band On-the-Fly Continuum Survey: Data Release 1

Sarvesh Mangla, Joseph J. Mohr, Kristof Rozgonyi et al. (+8 more)

The MeerKAT Large Area Synoptic Survey (MeerKLASS) collaboration has acquired multiple passes of L-band (856-1712 MHz) scanning observations over a 268 deg$^2$ sky region. This scanning enables efficient, large-area sky surveys by continuously scanning the MeerKAT array back and forth at fixed elevation while recording data at 2 sec intervals, progressively covering the survey region as the Earth rotates. We employ a novel on-the-fly (OTF) interferometric imaging technique to construct continuum images and catalogs from 16 hours of scan data. These data products, constituting the first MeerKLASS L-band data release (DR1), consist of high-fidelity radio continuum images and a catalogue of 34,874 radio sources detected with a SNR$>$9. The resulting Stokes I images achieve a median noise level of 33 $\mu$Jy\,beam$^{-1}$ and a median angular resolution of approximately $25.5''\times 7.8''$. Cross-comparisons with previous surveys confirm the consistency of our flux density scale within 5% and astrometric precision within $1.5''$. Additionally, flux densities measured across the seven sub-bands enable in-band spectral-index estimates for the detected sources, providing insights into their physical properties and the broader source population. We compute the differential source counts, finding good agreement with existing measurements and validating our end-to-end processing. This data release demonstrates the effectiveness of scanning surveys when combined with OTF interferometric imaging. Commensal intensity mapping and interferometric imaging offers a dramatic enhancement of survey science per invested hour of observations and could therefore be an appealing option for next generation facilities like SKA-Mid.
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All authors Sarvesh Mangla, Joseph J. Mohr, Kristof Rozgonyi, Suman Chatterjee, Keith Grainge, Sourabh Paul, Mario G. Santos, Yvette Perrott, Oleg M. Smirnov, Cyril Tasse, Laura Wolz

Cosmology and Nongalactic Astrophysics

Evolving and interacting dark energy: photometric and spectroscopic synergy with DES Y3 and DESI DR2

M. Tsedrik and B. Bose

We investigate the Dark Scattering (DS) interacting dark energy scenario, characterised by pure momentum exchange between dark matter and dark energy, combined with a time-dependent equation-of-state for dark energy described by the Chevallier-Polarski-Linder (CPL) parametrisation. This class of models is weakly constrained by CMB observations and can exhibit distinctive late-time suppression of structure growth. We derive constraints on cosmological, DS, and CPL parameters using three two-point correlation functions from the Dark Energy Survey Year 3 data, combined with baryon acoustic oscillation measurements from DESI, Type Ia supernovae from DES Year 5, and CMB data from Planck. We find the dark-sector interaction parameter $A_\mathrm{ds}$ to be consistent with zero for all data combinations, and that CPL provides a statistically preferred fit over DS for the selected probes. From the full data combination we obtain $w_0=-0.76 \pm 0.06, \, w_a=-0.77^{+0.23}_{-0.20}$ for CPL, and $w_0=-0.79^{+0.05}_{-0.06}, \, w_a=-0.56^{+0.24}_{-0.15}, \, (A_\mathrm{ds}=9.8^{+2.8}_{-9.5} \, \mathrm{bn/GeV})$ for DS. The inclusion of DES photometric information improves the Figure-of-Merit on $(w_0,w_a)$ by $\sim$12% for CPL and $\sim$25% for DS relative to DESI+SN+CMB alone. We find no evidence for an $S_8$ discrepancy between the low-$z$ and high-$z$ measurements in either model. These results provide the most stringent pre-Euclid constraints on DS from a combined photometric and spectroscopic analysis.
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High Energy Astrophysical Phenomena

Validating the performance of the Radio Neutrino Observatory in Greenland using cosmic-ray air showers

S. Agarwal, J. A. Aguilar, N. Alden et al. (+79 more)

The Radio Neutrino Observatory in Greenland (RNO-G) is currently under construction with the aim to detect neutrinos with energies beyond $\sim 10\,\mathrm{PeV}$. A critical part of early detector commissioning is the study of detector characteristics and potential backgrounds, for which cosmic rays play a crucial role. In this article, we report that the number of cosmic rays detected with RNO-G's shallow antennas is consistent with expectations. We further verified the agreement in the observed cosmic-ray signal shape with expectations from simulations after careful treatment of the detector systematics. Finally, we find that the reconstructed arrival direction, energy, and polarization of the cosmic-ray candidates agrees with expectations. Throughout this study, we identified detector shortcomings that are mitigated going forward. Overall, the analysis presented here is an essential first step towards validating the detector and high-fidelity neutrino detection with RNO-G in the future.
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All authors S. Agarwal, J. A. Aguilar, N. Alden, S. Ali, P. Allison, M. Betts, D. Besson, A. Bishop, O. Botner, S. Bouma, S. Buitink, R. Camphyn, J. Chan, S. Chiche, B. A. Clark, A. Coleman, K. Couberly, S. de Kockere, K. D. de Vries, C. Deaconu, P. Giri, C. Glaser, T. Glüsenkamp, H. Gui, A. Hallgren, S. Hallmann, J. C. Hanson, K. Helbing, B. Hendricks, J. Henrichs, N. Heyer, C. Hornhuber, E. Huesca Santiago, K. Hughes, A. Jaitly, T. Karg, A. Karle, J. L. Kelley, C. Kopper, M. Korntheuer, M. Kowalski, I. Kravchenko, R. Krebs, M. Kugelmeier, D. Kullgren, R. Lahmann, C.-H. Liu, Y. Liu, M. J. Marsee, K. Mulrey, M. Muzio, A. Nelles, A. Novikov, A. Nozdrina, E. Oberla, B. Oeyen, N. Punsuebsay, L. Pyras, M. Ravn, A. Rifaie, D. Ryckbosch, F. Schlüter, O. Scholten, D. Seckel, M. F. H. Seikh, Z. S. Selcuk, J. Stachurska, J. Stoffels, S. Toscano, D. Tosi, J. Tutt, D. J. Van Den Broeck, N. van Eijndhoven, A. G. Vieregg, A. Vijai, D. Washington, C. Welling, D. R. Williams, P. Windischhofer, S. Wissel, R. Young, A. Zink

Astrophysics of Galaxies

The contribution of the color space in LSST-like photometry for the selection of extragalactic globular cluster candidates

Nicholas Schweder-Souza, Ana L. Chies-Santos, Rafael S. de Souza et al. (+16 more)

Globular clusters (GCs) are excellent tracers of their host galaxies' evolutionary histories. Traditional methods for identifying GCs in galaxies rely on cuts over photometric catalogs and can yield source lists with high levels of contamination from compact background galaxies and foreground stars. In an era when large-scale sky surveys produce photometry for millions of sources, it is essential to employ flexible and scalable tools to reliably identify GCs in external galaxies. To prepare for surveys like Rubin/LSST, we need to explore practical methodological improvements and quantify the limitations inherent in the datasets. This paper investigates the selection of point-like extragalactic GCs exclusively in the $ugrizY$ color space. We use archival data to assemble an LSST-like photometric catalog for the Fornax Cluster containing labeled confirmed GCs, galaxies, and stars. From this catalog, using principal component analysis and non-linear auto-encoders (AEs), we construct inputs to random forest and multi-layer perceptron classifiers. We show that selecting GCs using all the 15 available colors can lead to a minimum contamination rate of ~30%, whereas the use of color-color diagrams may double such rate. If only the first 4 principal components of the colors are used instead, the same minimum contamination rate is achieved without increasing incompleteness. The AEs did not improve GC identification. To further reduce contamination and extract the full potential of LSST for star cluster studies, we argue for the need to augment photometric information with ancillary data (morphology from space-based missions and near-infrared photometry) before attempting to leverage more complex models.
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All authors Nicholas Schweder-Souza, Ana L. Chies-Santos, Rafael S. de Souza, Kristen C. Dage, Charles J. Bonatto, Juan P. Caso, Michele Cantiello, Pedro dos Santos-Lopes, Pedro Floriano, Thayse A. Pacheco, Katherine L. Rhode, Pauline Barmby, Jennifer Sobeck, Ana I. Ennis, Yasna Ordenes-Briceño, Teymoor Saifollahi, Julia Gschwend, Niranjana P., Rubens E. G. Machado

Astrophysics of Galaxies

Across the Universe: GW231123 as a magnified and diffracted black hole merger

Srashti Goyal, Hector Villarrubia-Rojo and Miguel Zumalacarregui

GW231123 appears as the most massive binary black hole (BBH) ever observed by the LIGO interferometers with total mass $190-265 M_\odot$. A high observed mass can be explained by the combination of cosmological redshift and gravitational magnification if the source is aligned with a gravitational lens, such as a galaxy. Small-scale objects such as stars and remnants diffract the signal, distorting the wavefront and providing additional lensing signatures. Here we present an analysis of GW231123 combining for the first time the effects of diffraction by a small-scale lens and gravitational magnification by an external potential, modelled as an embedded point-mass lens (PL), finding an intriguing case for the lensing hypothesis. Lensing is favoured by the data, with a false alarm probability of the observed Bayes factors bounded below $<1\%$, or $\sim 2.6 \sigma$ confidence level. Including lensing lowers the total source mass of GW231123 to $100-180 M_\odot$, closer to BBHs reported so far, and also removes discrepancies between different waveform approximants and the need for high component spins. We reconstruct all source and lens properties, including the microlens mass $190-850 M_\odot$, its offset, the magnitude of the external gravitational potential and its orientation. The embedded PL analysis leads to a lighter microlens compared to the isolated PL. Within our assumptions, the reconstruction is complete up to an ambiguity between the distance and projected density (mass-sheet degeneracy). Assuming a single galaxy as the macroscopic lens allows us to infer the total amplification of the signal, placing the event at redshift $0.7-2$, and predict the probability $~55\%$ of forming an additional detectable image due to strong lensing by the macrolens. We discuss the implications of our findings on the source and nature of the microlens, including a possible dark matter origin.
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Earth and Planetary Astrophysics

Surrogate-Accelerated Bayesian Inversion for Exoplanet Interior Characterization

Tijn De Wringer, Caroline Dorn, Emily O. Garvin et al. (+1 more)

Characterizing the interior structure of exoplanets is an inverse problem often solved using Bayesian inference, but this approach is hampered by the high computational cost of planetary structure models. To overcome this barrier, we present a robust framework that accelerates inference by replacing the computationally expensive physics-based forward model with a fast polynomial chaos-Kriging (PCK) surrogate directly within a Markov chain Monte Carlo (MCMC) sampling loop. We rigorously validate our approach using a suite of tests, including a direct comparison against a benchmark MCMC inference using the full forward model, and a large-scale coverage study with 1000 synthetic test cases to demonstrate the statistical reliability of our inferred credible intervals. Our surrogate-assisted framework achieves a computational speedup of over 2 orders of magnitude (factor of $\sim$320), reducing single-CPU inference times from days to minutes. This efficiency is achieved with a surrogate that requires only a few hundred forward model evaluations for training \rev{for a single planet}. This data efficiency provides significant flexibility for model developments and a clear advantage over common machine learning approaches, which typically demand vast training sets ($>10^6$ model runs) and intensive pre-computation. The PCK surrogate maintains high fidelity with $R^2 > 0.99$ for most scenarios, and root-mean-square errors typically an order of magnitude smaller than observational uncertainties. This efficiency enables large scale population studies while preserving statistical robustness, which is computationally impractical with traditional methods.
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All authors Tijn De Wringer, Caroline Dorn, Emily O. Garvin, Stefano Marelli

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Quantum state of interacting primordial inhomogeneities: de-squeezing and decoherence

Amaury Micheli, Yuto Oshima and Tomo Takahashi

We investigate how interactions affect the quantum state of scalar perturbations during inflation and the quantum correlations they may exhibit. Focusing on the case of scalar perturbations in single-field inflation, we model interactions using a Lindblad equation with a non-unitary contribution quadratic in the scalar perturbations, and of parametrisable amplitude and time dependence. We compute the quantum state of these interacting perturbations, which is fully described by its purity and squeezing parameters. First, we show that, in most of the parameter space, not only the purity but also the squeezing parameter is significantly reduced by interactions. Second, we show that this de-squeezing induced by the interactions, on top of the purity loss, causes a further suppression of quantum correlations. We thus emphasise that the quantum or classical character of the correlations exhibited by the perturbations cannot be correctly determined by computing the effect of interactions on the purity alone. Since the phenomenological framework adopted in this paper encompasses a wide class of possible interactions, our results provide general insights into the nature of decoherence processes in primordial fluctuations.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Slowly rotating Black Holes in DHOST Theories

Hugo Candan, Karim Noui and David Langlois

We study slowly rotating black hole solutions within Degenerate Higher Order Scalar Tensor (DHOST) theories. Starting from a static, spherically symmetric metric solution of a DHOST theory, we employ the Hartle-Thorne ansatz to model a slowly rotating spacetime. We show that the differential equation governing the frame-dragging function $\omega$ (which is supposed to depend on the radial coordinate only) is integrable for any DHOST theory allowing us to obtain its explicit form. We also consider angular dependence in $\omega$ and show that regularity at the horizon and at infinity forbids it, as in General Relativity. As an illustration of the formalism introduced here, we study the slowly-rotating version of black hole solutions with primary hair obtained recently, examining the influence of the rotation on the Innermost Stable Circular Orbit (ISCO) and on the circular light trajectories in the equatorial plane.
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Astrophysics of Galaxies

Observations of AGN-driven feedback: dynamics and ionization of the filaments in M87

Camille Poitras, Marie-Lou Gendron-Marsolais, Valeria Olivares et al. (+9 more)

We present a comprehensive kinematic and ionization analysis of the warm ionized filaments ($10^4$ K) in M87, the central galaxy of the Virgo cluster, using new integral field spectroscopy from MEGARA (GTC) and SITELLE (CFHT). MEGARA targets the southeastern (SE) filaments (3 kpc from the nucleus), coincident with the only known molecular gas clump, and the far eastern (FE) filament (15 kpc), spatially isolated within an old radio lobe. SITELLE fully maps the filaments, offering the first complete views of their kinematics and excitation. Combined with archival ALMA, MUSE and Chandra data, these observations offer a multi-phase view of gas dynamics. The filaments display complex motions inconsistent with simple rotation. Velocity structure functions (VSFs) of the warm and cold gas in the central and SE filaments show consistent steep slopes (2/3) and flattening on small scales of a few hundred parsecs, possibly suggesting energy injection from Type Ia supernovae, though interpretation is method-limited. The FE filament shows a lower VSF amplitude, suggesting less active driving. ALMA CO emission is co-spatial and kinematically aligned with the ionized gas, the latter showing broader velocity dispersions. Ionization diagnostics indicate AGN-related processes (e.g., shocks) dominate, with higher-energy excitation near the radio lobes and lower-energy fossil feedback signatures in the FE filament. Finally, the filaments follow the same strong H$\alpha$-X-ray surface brightness correlation seen in other clusters, supporting local thermal coupling between phases. However, the FE filament deviates from this trend, possibly due to uplift from past AGN outbursts or limitations in the analysis method.
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All authors Camille Poitras, Marie-Lou Gendron-Marsolais, Valeria Olivares, Yuan Li, Adrien Picquenot, Aurora Simionescu, Matteo Fossati, Alessandro Boselli, Laura Hermosa Muñoz, Sara Cazzoli, Julie Hlavacek-Larrondo, Annabelle Richard-Laferrière

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

GW231123: Overlapping Gravitational Wave Signals?

Qian Hu, Harsh Narola, Jef Heynen et al. (+4 more)

The recently discovered gravitational wave event GW231123 was interpreted as the merger of two black holes with a total mass of 190-265 $M_\odot$, making it the heaviest such merger detected to date. Whilst much of the post-discovery literature has focused on its astrophysical origins, primary analyses have exhibited considerable discrepancies in the measurement of source properties between waveform models, which cannot reliably be reproduced by simulations. Such discrepancies may arise when an unaccounted overlapping signal is present in the data, or from phenomena that produce similar effects, such as gravitational lensing or overlapping noise artifacts. In this work, we analyse GW231123 using a flexible model that allows for two overlapping signals, and find that it is favoured over the isolated signal model with Bayes factors of $\sim 10^2 - 10^{4}$, depending on the waveform model. These values lie within the top few per cent of the background distribution. Similar effects are not observed in GW190521, another high-mass event. Under the overlapping signals model, discrepancies in the measurement of source properties between waveform models are largely mitigated. We also find that neglecting an additional signal in overlapping-signal data can lead to discrepancies in the estimated source properties resembling those reported in GW231123. Although the overlapping signal model provides a higher Bayesian evidence, the astrophysical prior probability of two short signals overlapping is low. However, we find that the two recovered sources show similar properties. This, taken with the higher evidence of the two signal model, suggests that gravitational lensing may provide an alternative explanation.
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All authors Qian Hu, Harsh Narola, Jef Heynen, Mick Wright, John Veitch, Justin Janquart, Chris Van Den Broeck

High Energy Astrophysical Phenomena

Constraining black hole spin in PG 1535+547 amidst complex multi-layered absorption

A. Madathil-Pottayil, D.J. Walton, Jiachen Jiang et al. (+7 more)

We present a spectroscopic analysis of XMM-Newton and NuSTAR observations of the 'complex' NLS1 PG 1535+547 at redshift $z=0.038$. These observations span three epochs: 2002 and 2006 with XMM-Newton alone, covering the $0.3-10$ keV energy range, and a coordinated XMM-Newton and NuSTAR observation in 2016, covering the $0.3-60$ keV energy range. The X-ray spectra across all epochs exhibit both neutral and ionized absorption, along with reflection features from the accretion disc, including a prominent Compton hump in the broadband data. Notably, the spectral shape varies across epochs. Our analysis suggests this variability is attributed to changes in both line-of-sight absorption and the intrinsic emission from PG 1535+547. The source is obscured by multiple layers of partially and/or fully covering neutral and ionized absorbers, with neutral column densities ranging from undetectable levels in the least obscured phase to $\sim0.3-5\times10^{23}\mathrm{cm^{-2}}$ in the most obscured phase. A clear warm absorber is revealed during the least obscured phase. The continuum remains fairly consistent ($\Gamma\approx 2.2\pm0.1$) during the first two observations, followed by a substantial flux decrease (by a factor of $\sim7$ in the $2-10$ keV band) in 2016 compared to 2006. The 2016 data indicates the source is in a reflection-dominated state during this epoch, with a reflection fraction of $R>7$ and an X-ray source located at a height $\leq 1.72r_g$. Simultaneous fitting of the multi-epoch data suggests a rapidly rotating black hole with a spin parameter, $a>0.99$. These findings imply that strong light-bending effects may account for the observed continuum flux reduction.
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All authors A. Madathil-Pottayil, D.J. Walton, Jiachen Jiang, T. Dauser, Andrew Fabian, D. Stern, Luigi C. Gallo, Mark T. Reynolds, Emanuele Nardini, Javier A. Garcia

High Energy Astrophysical Phenomena

Radio studies of supernovae 1979C, 1986J and 2006X with LOFAR

Peter Lundqvist, Deeepika Venkattu, Miguel Pérez Torres et al. (+3 more)

We present LOw Frequency ARray (LOFAR) studies of supernovae SN 1979C, SN 1986J, and SN 2006X, focusing on new observations from the LOFAR Two-metre Sky Survey (LoTSS) and the International LOFAR Telescope (ILT). For Type Ia SN 2006X, we derive a 3$\sigma$ upper limit of 0.7 mJy at 0.146 GHz, and using radio emission models based on the CS15DD2 explosion model, we constrain the circumstellar density to $n_{\rm H} \lesssim 10$ cm$^{-3}$ for the microphysical parameters $\epsilon_{\rm rel} = \epsilon_{\rm B} = 0.01$. SN 1979C is clearly detected in the LoTSS image with a flux density of $4.6 \pm 0.36$ mJy nearly 40 years postexplosion. Modeling its radio evolution suggests a steep flux decay ($F_{\nu} \propto t^{-2.1}$) between 22 and 42 years, a break in the spectrum near 1.5 GHz possibly due to synchrotron cooling, a progenitor mass of $\sim 13$ solar masses, and a progressive steepening with velocity for the density slope of the supernova ejecta. Our findings for SN 1979C contradict scenarios involving central compact object emission, and we obtain X-ray temperatures close to those derived from recent observations. For SN 1986J, we present the first ILT image showing a flux density of $6.77\pm0.2$ mJy at 0.146 GHz. The spectral index of the shell emission is found to be $0.66\pm0.03$, consistent with previous estimates, although variations at low frequencies warrant further investigation. Our results highlight the power of LOFAR for studying long-term radio evolution in supernovae.
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All authors Peter Lundqvist, Deeepika Venkattu, Miguel Pérez Torres, Javier Moldón, Vijay Mahatma, Poonam Chandra

Cosmology and Nongalactic Astrophysics

CLiENT: A new tool for emulating cosmological likelihoods using deep neural networks

Luca Janken, Steen Hannestad, Thomas Tram et al. (+1 more)

Cosmological emulation of observables such as the Cosmic Microwave Background (CMB) spectra and matter power spectra have become increasingly common in recent years because of the potential for saving computation time in connection with cosmological parameter inference or model comparison. In this paper we present CLiENT (Cosmological Likelihood Emulator using Neural networks with TensorFlow), a new method which circumvents the computation of observables in favour of directly emulating the likelihood function for a data set given a model parameter vector. We find that the method is competitive with observable emulators in terms of the required number of function evaluations, but has the distinct advantage of producing a surrogate likelihood which is completely auto-differentiable. Using less than $2 \times 10^4$ function evaluations CLiENT typically achieves credible intervals within better than $0.1 \sigma$ of those obtained using the true likelihood and single-point emulator precision better than $\Delta \chi^2 \sim 0.5$ across relevant regions in parameter space.
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All authors Luca Janken, Steen Hannestad, Thomas Tram, Andreas Nygaard

High Energy Astrophysical Phenomena

High-Resolution Measurements with the CTAO Southern Array: The Case for Pulsar Wind Nebulae

Georg Schwefer and Jim Hinton

The advent of the Cherenkov Telescope Array Observatory (CTAO) and recent advances in reconstruction of gamma-ray photons with Cherenkov telescopes are bound to push the limit of angular resolution to an unprecedented precision of less than one arcminute at tens of TeV. Naturally, such instrumental improvements open up possibilities for new and interesting scientific studies. We aim to show that the study of pulsar wind nebulae (PWNe) in particular is bound to profit from these high-resolution measurements. This is because PWNe are the dominant Galactic source population at TeV energies, exhibit hard spectra up to hundreds of TeV and from X-ray observations are known to possess plentiful structure on arcminute scales. Using HESS J1813-178 and MSH 15-52 as examples, we create simple leptonic models of the TeV morphology of these sources based on X-ray observations and existing gamma-ray measurements. Then, assuming different models for the exposure and point spread function of the observatory, we create mock observations with the future CTAO southern array. We use these to assess the ability of these observations to differentiate between models and study the physics of these sources, in particular to infer the structure of the magnetic field and electron distributions. We find that future observations with the CTAO southern array at multi-TeV energies - in combination with existing X-ray measurements - will likely be able to constrain the distributions of magnetic field and high-energy electrons in these sources. We demonstrate that the sensitivity of these measurements can be significantly enhanced with the improved angular resolution achievable with novel reconstruction algorithms. However, we also show that in the relevant multi-TeV regime, signal-photon statistics remain a limitation and trading event statistics for improved angular resolution is not necessarily advantageous.
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