Current date: 2025-09-15

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Datestamp limit: 2025-09-15 (0 days ago)

Created/updated limit: 2025-09-08 (7 days ago)

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OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2025-09-15&until=2025-09-15&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 508

Keyword score statistics

score 11 -- 1 abstracts

score 8 -- 1 abstracts

score 7 -- 3 abstracts

score 6 -- 5 abstracts

score 4 -- 3 abstracts

score 3 -- 6 abstracts

score 2 -- 15 abstracts

in total -- 34 abstracts

Articles that appeared on 2025-09-15

[abstract 1 / 34] Wow! (score: 11)
arXiv:2509.09883 [pdf, ps, other]

Title: PeV particle acceleration and non-thermal emission in the `minimalist' model of the extended JETs in W50/SS433

Authors: A. M. Bykov, S. M. Osipov, V. I. Romansky, Y. A. Uvarov, E. Churazov, I. Khabibullin,

Comments: 14 pages, 12 figures

Subjects: astro-ph.GA astro-ph.HE

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

The W50 nebula around microQUASAR SS~433, powered by supercritical accretion, features two `extended JETs' (tens of pc long and a few pc wide) from which polarized X-ray and very high energy radiation above 100 TeV is detected. Here we present a model of very high energy particle acceleration in these extended JETs. In the `minimalist' model (discussed in Churazov, Khabibullin, and Bykov, 2024), a collimated outflow aligned with the rotation axis is propagating through a more isotropic wind produced by the accretion disk. The observed extended X-ray JETs with bright knots in this model are associated with the formation of strong recollimation MHD shocks after the collision of the collimated outflow with the isotropic wind termination surface. The spectra of electrons and protons up to PeV energies are simulated with a nonlinear Monte Carlo model of diffusive shock acceleration with turbulent MAGNETic field amplification. The overall efficiency of the JETs power transfer to accelerated protons in this model is above 10\% and about 0.5\% for electrons above 50 TeV. The MAGNETic field amplification by Bell's instability due to the electric current of COSMIC RAYs escaping the accelerator produces highly anisotropic MAGNETic turbulence in the shock downstream. This results in the polarized SYNCHROTRON X-ray emission with the photon electric vector predominantly transverse to the JET direction and the degree of POLARIZATION above 20\%. The model is able to reproduce the observed spectra and intensity profiles of non-thermal X-ray and gamma-ray emission, which are both dominated by the leptonic radiation.

[abstract 2 / 34] Wow! (score: 8)
arXiv:2509.10319 [pdf, ps, other]

Title: The merger of spinning, accreting supermassive BLACK HOLE binaries

Authors: Lorenzo Ennoggi, Manuela Campanelli, Julian Krolik, Scott C. Noble, Yosef Zlochower, Maria Chiara de Simone,

Comments: 6 pages, 3 figures. See Supplemental Material in the ancillary files section

Subjects: astro-ph.HE gr-qc physics.comp-ph physics.plasm-ph

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Because they are likely to accrete substantial amounts of interstellar gas, merging supermassive binary BLACK HOLEs are expected to be strong multimessenger sources, radiating gravitational waves, photons from thermal gas, and photons from RELATIVISTIC electrons energized by RELATIVISTIC JETs. Here we report on a numerical simulation that covers the late inspiral, merger, and initial postmerger phase of such a system where both BLACK HOLEs have the same mass and spin, and both spin axes are parallel to the orbital angular momentum. The simulation incorporates both 3D general RELATIVISTIC MAGNETohydrodynamics and numerical relativity. The thermal photon power during the late inspiral, merger, and immediate postmerger phases is drawn from strong shocks rather than dissipation of turbulence inside a smoothly structured accretion disk as typically found around accreting single BLACK HOLEs. We find that the thermal photon and JET Poynting flux outputs are closely related in time, and we posit a mechanism that enforces this relation. The power radiated in both photons and JETs diminishes gradually as merger is approached, but jumps sharply at merger to a noisy plateau. Such a distinct lightcurve should aid efforts to identify supermassive BLACK HOLE mergers, with or without accompanying gravitational wave detections.

[abstract 3 / 34] Wow! (score: 7)
arXiv:2503.06209 [pdf, ps, other]

Title: Study of mass outflows from MAGNETized accretion disks around rotating BLACK HOLEs with thermal conduction

Authors: Camelia Jana, Monu Singh, Suvendu Rakshit, Santabrata Das,

Comments: 13 pages, 6 figures, To appear in JCAP

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

We examine mass outflows from a low-angular momentum, viscous, advective, and MAGNETized accretion disk around a rotating BLACK HOLE in presence of thermal conduction. We consider the disk is primarily threaded by the toroidal component of the MAGNETic field and an effective potential satisfactorily mimicked the spacetime geometry around the rotating BLACK HOLE. With this, we self-consistently solve the coupled governing equations for inflow and outflow and compute the mass outflow rate $R_{\dot m}$ (ratio of mass flux of inflow to outflow) in terms of the inflow parameters, namely energy ($\mathcal{E}$), angular momentum ($λ$), plasma-$β$ and conduction parameter ($Υ_{\rm s}$) around weakly rotating ($a_{\rm k} \rightarrow 0$) as well as rapidly rotating ($a_{\rm k} =0.99$) BLACK HOLEs. Our findings reveal that the present formalism admits coupled inflow-outflow solutions across a wide range of inflow parameters yielding substantial mass loss. We observe that $R_{\dot m}$ monotonically increases with $Υ_{\rm s}$, irrespective of BLACK HOLE spin. We also find that for a fixed $Υ_{\rm s}$, when energy, angular momentum, and MAGNETic field strength of the inflowing matter is increased, $R_{\dot{\rm m}}$ is enhanced resulting the outflows even more pronounced. We further estimate the maximum outflow rate ($R^{\rm max}_{\dot{\rm m}}$) by varying the inflow parameters and find that thermal conduction leads to maximum mass outflow rate $R^{\rm max}_{\dot{\rm m}} \sim 25\%$ for rapidly rotating BLACK HOLE of spin $a_{\rm k} = 0.99$. Finally, we employ our formalism to explain the kinetic JET power of $68$ radio-loud low-luminosity ACTIVE GALACTIC NUCLEi (LLAGNs), indicating that it is potentially promising to account for the observed JET power of substantial number of LLAGNs.

[abstract 4 / 34] Wow! (score: 7)
arXiv:2505.03942 [pdf, ps, other]

Title: Variability of X-ray POLARIZATION of Cyg X-1

Authors: Vadim Kravtsov, Anastasiia Bocharova, Alexandra Veledina, Juri Poutanen, Andrew K. Hughes, Michal Dovčiak, Elise Egron, Fabio Muleri, Jakub Podgorny, Jiři Svoboda, Sofia V. Forsblom, Andrei V. Berdyugin, Dmitry Blinov, Joe S. Bright, Francesco Carotenuto, David A. Green, Adam Ingram, Ioannis Liodakis, Nikos Mandarakas, Anagha P. Nitindala, Lauren Rhodes, Sergei A. Trushkin, Sergey S. Tsygankov, Maimouna Brigitte, Alessandro Di Marco, Noemi Iacolina, Henric Krawczynski, Fabio La Monaca, Vladislav Loktev, Guglielmo Mastroserio, Pierre-Olivier Petrucci, Maura Pilia, Francesco Tombesi, Andrzej A. Zdziarski,

Comments: 12 pages, 10 figures, accepted for publication in Astronomy & Astrophysics

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

We present the results of a three-year X-ray, optical, and radio polarimetric monitoring campaign of the prototypical BLACK HOLE X-ray binary Cyg X-1, conducted from 2022 to 2024. The X-ray POLARIZATION of Cyg X-1 was measured 13 times with the Imaging X-ray Polarimetry Explorer (IXPE), covering both hard and soft spectral states. The X-ray POLARIZATION degree (PD) in the hard state was found to be $\approx4.0\%$, roughly twice as high as in the soft state, where it was around $2.2\%$. In both states, a statistically significant increase of PD with the energy was found. Moreover, a linear relation between PD and spectral hardness suggests a gradual and continuous evolution of the POLARIZATION properties, rather than an abrupt change of POLARIZATION production mechanism between states. The POLARIZATION angle (PA) was independent of the spectral state and showed no trend with the photon energy. The X-ray PA is well aligned with the orientation of the radio JET, as well as the optical and radio PAs. We find significant orbital changes of PA in the hard state, which we attribute to scattering of X-ray emission at intrabinary structure. No significant superorbital variability in PD or PA was found at the period $P_{\rm{so}}$ = 294 d. We also find no correlation between the X-ray and optical POLARIZATION; if any, there is a long-term anti-correlation between the X-ray PD and the radio PD.

[abstract 5 / 34] Wow! (score: 7)
arXiv:2509.09827 [pdf, ps, other]

Title: Discovery and Analysis of Afterglows from Poorly Localised GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey

Authors: Amit Kumar, B. P. Gompertz, B. Schneider, S. Belkin, M. E. Wortley, A. Saccardi, D. O'Neill, K. Ackley, B. Rayson, A. de Ugarte Postigo, A. Gulati, D. Steeghs, D. B. Malesani, J. R. Maund, M. J. Dyer, S. Giarratana, M. Serino, Y. Julakanti, B. Kumar, D. Xu, R. A. J. Eyles-Ferris, Z. -P. Zhu, B. Warwick, Y. -D. Hu, I. Allen, G. Ramsay, R. L. C. Starling, J. Lyman, K. Ulaczyk, B. Godson, D. K. Galloway, V. S. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, D. Pollacco, J. Casares, T. L. Killestein, M. R. Kennedy, N. Habeeb, S. Moran, K. Wiersema, I. Worssam, D. L. Coppejans, C. A. Phillips, A. Martin-Carrillo, N. S. Pankov, J. F. Agüí Fernández, M. A. Aloy, J. An, G. E. Anderson, A. Bochenek, A. J. Castro-Tirado, X. Chen, L. Cotter, R. Dastidar, M. De Pasquale, V. D'Elia, Y. Fang, S. Y. Fu, J. P. U. Fynbo, D. H. Hartmann, L. B. He, L. Izzo, S. Q. Jiang, Y. Kawakubo, E. V. Klunko, A. J. Levan, X. -W. Liu, X. Liu, G. Lombardi, E. Maiorano, J. T. Palmerio, D. A. Perley, D. L. A. Pieterse, A. S. Pozanenko, G. Pugliese, A. Rossi, B. Sbarufatti, S. Bijavara Seshashayana, N. R. Tanvir, C. C. Thöne, A. J. van der Horst, S. D. Vergani, A. A. Volnova, R. A. M. J. Wijers, J. L. Wise,

Comments: 50 pages, including 27 figures and 15 tables (with Appendix). Submitted to MNRAS

Subjects: astro-ph.HE

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

Gamma-ray bursts (GRBs), particularly those detected by wide-field instruments such as the FERMI/GBM, pose a challenge for optical follow-up due to their large initial localisation regions, leaving many GRBs without identified afterglows. The Gravitational-wave Optical Transient Observer (GOTO), with its wide field of view, dual-site coverage, and robotic rapid-response capability, bridges this gap by rapidly identifying and localising afterglows from alerts issued by space-based facilities including FERMI, SVOM, SWIFT, and the EP, providing early optical positions for coordinated multi-wavelength follow-up. In this paper, we present optical afterglow localisation and multi-band follow-up of seven FERMI/GBM and MAXI/GSC triggered long GRBs (240122A, 240225B, 240619A, 240910A, 240916A, 241002B, and 241228B) discovered by GOTO in 2024. Spectroscopy for six GRBs (no spectroscopic data for GRB 241002B) with VLT/X-shooter and GTC/OSIRIS yields precise redshifts spanning $z\approx0.40-$3.16 and absorption-line diagnostics of host and intervening systems. Radio detections for four events confirm the presence of long-lived SYNCHROTRON emission. Prompt-emission analysis with FERMI and MAXI data reveals a spectrally hard population, with two bursts lying $>3σ$ above the Amati relation. Although their optical afterglows resemble those of typical long GRBs, the prompt spectra are consistently harder than the long-GRB average. Consistent modelling of six GOTO-discovered GRB afterglows yields JET half-opening angles of a few degrees and beaming-corrected kinetic energies ($E_{JET}\sim10^{51-52}$) erg, consistent with the canonical long-GRB population. These findings suggest that optical discovery of poorly localised GRBs may be subject to observational biases favouring luminous events with high spectral peak energy, while also providing insight into JET microphysics and central engine diversity.

[abstract 6 / 34] Yes (score: 6)
arXiv:2504.05600 [pdf, ps, other]

Title: A universal natal spin in stellar-mass BLACK HOLEs

Authors: Shu-Xu Yi, Tian-Yong Cao, Shuang-Nan Zhang,

Comments: 16 pages, 6 figures. Comments are welcome!

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

A stellar mass BLACK HOLE (BH) is believed to be formed as the result of the core collapse of a massive star at the end of its evolution. For a class of Gamma-Ray Bursts (GRBs), it is widely believed that their centre engines are just these stellar-mass BHs, which accrete the collapsing matter in hyper-accretion mode. In such systems, a popular scenario is that the MAGNETic field supported in the accretion disk extracts the rotational energy of the spinning BH and launches a JET on one hand, and the accretion of the infalling matter of the collapse will increase the BH's rotational energy on the other hand. Here we report that when the accretion process is dominated by a Magnetically-Arrested-Disk (MAD), the above-mentioned two competing processes link to each other, so that the spin evolution of the BH can be written in a simple form. Most interestingly, when the total accreted mass is enough, the BH spin will always reach an equilibrium value. This value does not depend on the initial mass and spin of the BH, as well as the history of accretion but is a function of the accretion physics near the event horizon. This model predicts that there is a population of stellar-mass BH that possess a universal spin at the end of the collapsing accretion. We test this prediction against the 4th gravitational wave (GW) catalogue (GWTC-4.0) and found that there is a dominating population with high significance, in which the distribution of the spin of the secondary BH is centred narrowly around a single value ~0.017. The above-mentioned scenario is supported and the parameters of the accretion physics near the event horizon can be thus constrained. The result is also consistent with previous numerical simulations.

[abstract 7 / 34] Yes (score: 6)
arXiv:2509.09770 [pdf, ps, other]

Title: Early Stages of Dusty Tori: The First Infrared Spectra from a Highly Multiscale Quasar Simulation

Authors: Jaeden Bardati, Philip F. Hopkins, Gordon T. Richards,

Comments: 21 pages, 11 figures. Submitted to ApJ

Subjects: astro-ph.GA astro-ph.CO astro-ph.HE

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

We present the first infrared spectral predictions from a self-consistent simulation of the formation of a QUASAR in a starburst galaxy, spanning cosmological to innermost stable circular orbit (ISCO) scales. The infrared emission is dominated by a torus-like dust structure composed of the highly MAGNETized, turbulence-supported outer accretion disk and of accreting gas tidally torn from the interstellar medium (ISM). At these early stages, the AGN is buried and Compton-thick. The near- to mid-IR escaping luminosity varies by almost an order of magnitude across sightlines, largely due to extinction from the inflowing stream of cold dust. Self-absorption within the torus suppresses silicate emission features, and further reprocessing by the ambient ISM leads to prominent silicate absorption and colder IR emission. The sublimation structure is stratified by composition and size, producing sightline-dependent extinction curves that intrinsically vary in shape. However, after repeated scattering in the optically thick dusty medium, these curves emerge substantially grayed. We also demonstrate that bipolar outflows from the central BLACK HOLE that carve biconical cavities and reveal the central engine in later stages can preserve IR anisotropy and silicate features. These results suggest that dusty starburst QUASARs can undergo a buried, IR-bright phase early in their evolution.

[abstract 8 / 34] Yes (score: 6)
arXiv:2509.09929 [pdf, ps, other]

Title: Laplace-Fourier linear stability analysis of non-RELATIVISTIC MAGNETized rotational JETs: mode identification by Hamiltonian analysis and the occurrence of mode transitions

Authors: Wu Fan, Yamada Shoichi,

Comments: 25 pages, 10 figures

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

In this paper, we conduct a linear stability analysis of MAGNETized and/or rotating JETs propagating in ambient matter that is also MAGNETized and/or rotating, having in mind the application to the JET penetrating the core/envelope of a massive star. We solve the linearized MAGNETo-hydrodynamic (MHD) equations in the non-RELATIVISTIC regime by Laplace transform in time and Fourier transform in space. In this formulation all unstable modes with the same translational and azimuthal wave numbers can be obtained simultaneously by searching for pole singularities in the complex plane. In order to determine unambiguously their driving mechanisms, we evaluate the second-order perturbation of the MHD Hamiltonian for individual eigenfunctions derived at these singular points. We identify in our non-rotating models the Kelvin-Helmholtz instability (KHI) as one of the shear-driven modes and the current-driven instability such as the kink instability (KKI). In rotational models we also find the MAGNETorotational instability (MRI) as another shear-driven mode. In some cases, we find that a mode changes its character continuously from KKI to KHI (and vice versa) or from MRI to KHI as the JET velocity is increased.

[abstract 9 / 34] Yes (score: 6)
arXiv:2509.10037 [pdf, ps, other]

Title: Multi-GeV FERMI-LAT Detection of PSR B1259-63

Authors: D. Malyshev, M. Chernyakova, A. Finn Gallagher, A. Kuzin, N. Matchett, A. Santangelo, Iu. Shebalkova, B. van Soelen,

Comments:

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

PSR B1259-63 is a classical gamma-ray binary detected from radio to TeV energies near periastron. In the GeV band, it had previously been detected only up to a few GeV, with the extrapolation of the TeV spectrum overestimating the measured GeV flux. Using over 17 years of FERMI-LAT observations, we report the first detection of PSR B1259-63 in the 10 GeV to $\gtrsim 100$ GeV range, from -400 to +100 days relative to periastron. The FERMI-LAT spectrum is well described by a hard power law with index $Γ= 1.9 \pm 0.1$, and has a flux level consistent with that measured at TeV energies by H.E.S.S. The apparent transition from the hard FERMI-LAT spectrum to the softer TeV spectrum suggests that the detected GeV emission traces the rising tail of the inverse-Compton component extending into the TeV regime. We note that the detection of PSR B1259-63 as early as -400 days before periastron is difficult to reconcile with existing theoretical models.

[abstract 10 / 34] Yes (score: 6)
arXiv:2509.10275 [pdf, ps, other]

Title: A MeerKAT view of the parsec-scale JETs in the black-hole X-ray binary GRS 1758-258

Authors: I. Mariani, S. E. Motta, P. Atri, J. H. Matthews, R. P. Fender, J. Martí, P. L. Luque-Escamilla, I. Heywood,

Comments: 14 pages, 6 figures

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Jets from accreting BLACK HOLE (BH) X-ray binaries (XRBs) are powerful outflows that release a large fraction of the accretion energy to the surrounding environment, providing a feedback mechanism that may alter the interstellar medium (ISM) properties. Studying accretion and feedback together enables estimates of matter and energy input/output around accreting BHs. We focus on the extended JET structures of the BH-XRB GRS1758-258. First seen in VLA data, these parsec-scale JETs arise from JET-ISM interaction and show a Z-shaped morphology. Using the MeerKAT telescope we observed GRS1758-258 in L-band for a total exposure of 7 hr. Applying a calorimetry-based method developed for AGN and later used for XRBs, we estimated the properties of the JETs and of the surrounding ISM. We detect a JET and counter-JET terminating in bow-shocks. Within the northern JET lobe we identify SYNCHROTRON and bremsstrahlung emission, while the southern lobe is dominated by thermal emission. We measure ISM densities between 10-40 cm-3 across both JETs, slightly lower in the northern region. The estimated ages of the two lobes range from 6-51 kyr. The time-averaged JET power lies between 4.4x10^33 and 3.3x10^36 erg/s, with differences between north and south likely due to different local ISM conditions. Comparing new MeerKAT with archival VLA data, we measured a proper motion of 130 mas/yr in a portion of the northern JET. Jet-ISM interaction structures on both sides of GRS1758-258 reveal different ISM properties. The comparison between these structures and those from other XRBs suggests that the lobes in GRS1758-258 are younger and may result from different JET activity phases. The time-averaged energy transferred to the environment is slightly lower than in other XRBs, consistent with the younger age of the lobes in GRS1758-258 relative to those of other systems.

[abstract 11 / 34] Yes (score: 4)
arXiv:2501.16881 [pdf, ps, other]

Title: Influence of the Galactic Halo on the UHECR Multipoles

Authors: Vasundhara Shaw, Arjen Van Vliet, Andrew M. Taylor,

Comments:

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

We examine the effects of a giant MAGNETized halo around the Galaxy on the angular distribution of the arriving ultra-high energy COSMIC RAYs (UHECR) observed at Earth. We investigate three injection scenarios for UHECRs, and track them through isotropic turbulent MAGNETic fields of varying strengths in the Galactic halo. We calculate the resultant dipole and quadrupole amplitudes for the arriving UHECRs detected by an observer in the Galactic plane region. We find that, regardless of the injection scenario considered, when the scattering length of the particles is comparable to the size of the halo, the UHECRs skymap resembles a dipole. However, as the scattering length is increased, the dipolar moment always increases, and the quadrupolar moment increases rapidly for two of the three cases considered. Additionally, the quadrupole amplitude is highlighted to be a key discriminator in discerning the origin of the observed dipole. We conclude that, to understand the origin of the UHECR dipole, one has to measure the strength of the quadrupole amplitude as well.

[abstract 12 / 34] Yes (score: 4)
arXiv:2509.10177 [pdf, ps, other]

Title: Interaction between disk and extended corona in general RELATIVISTIC framework. I. Static slab corona in global energy balance with the underlying disk

Authors: Sudeb Ranjan Datta, Michal Bursa, Michal Dovciak, Wenda Zhang,

Comments: Under review in A&A

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

The energy equilibrium between the corona and the underlying disk in a two-phase accretion flow sets a lower limit on the achievable photon index. A slab corona may not explain the hard state observations of X-ray binaries (XRBs). We incorporate energy feedback to the accretion disk resulting from illumination by an extended corona, and vice versa. The interaction between these two components allows for the possibility of finding an energetically self-consistent equilibrium solution for a given disk-corona system. We have upgraded the existing Monte Carlo radiative transfer code, MONK, to incorporate the interaction between the disk and the extended corona within the general RELATIVISTIC framework. We introduce an albedo parameter to specify the fraction of the incident flux that is reflected by the disk, while the remainder is absorbed and added to the intrinsic dissipation. Reflection is modeled assuming a semi-infinite electron atmosphere. We find global equilibrium solutions by iterating interaction between disk and extended slab corona. A higher BLACK HOLE spin, higher coronal temperature, and higher albedo all lead to harder spectra. For typical coronal temperatures and disk albedo, the lowest achievable photon index with a static slab corona fully covering the disk is approximately 1.7-1.8. With the upgraded version of MONK, we are now able to achieve global energy equilibrium for a given disk-corona system. This approach holds significant potential for constraining the coronal geometry using not only the observed flux but also POLARIZATION. A static slab does not appear to be a favorable coronal geometry for the hard state of XRBs, even when global energy balance is taken into account. In future work, we will explore truncated disk geometries and outflowing coronae as potential alternatives. (shortened)

[abstract 13 / 34] Yes (score: 4)
arXiv:2509.10271 [pdf, ps, other]

Title: Stellar populations of QUASAR host galaxies with MFICA decomposition

Authors: Sahyadri Devidatt Krishna, Vivienne Wild, Paul C. Hewett, Carolin Villforth,

Comments: 21 pages, 14 figures, 2 tables in the main text. Accepted for publication in MNRAS

Subjects: astro-ph.GA

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Galaxy evolution theories require co-evolution between accreting supermassive BLACK HOLEs (SMBH) and galaxies to explain many properties of the local galaxy population, yet observational evidence for the mechanisms driving this co-evolution is lacking. The recent star-formation histories of the host galaxies of accreting SMBHs (Active Galactic Nuclei, AGNs) can help constrain the processes that feed SMBHs and halt STAR FORMATION in galaxies, but are difficult to obtain for the most luminous AGNs (QUASARs). We introduce Mean-Field Independent Component Analysis (MFICA) to decompose QUASAR spectra and obtain recent STAR FORMATION histories of their host galaxies. Applying MFICA to QUASAR spectra from the Sloan Digital Sky Survey (SDSS) DR7 Quasar Catalogue in the redshift range $0.16 \leq z \leq 0.76$, we find that 53 per cent of QUASAR host galaxies are star-forming, 17 per cent lie in the green-valley, while only 5 per cent are quiescent. This contrasts with 14, 11, and 74 per cent of a mass-matched control sample that are star-forming, green-valley, and quiescent, respectively. We find that $\sim25$ per cent of QUASARs are hosted by post-starburst galaxies, an excess of $28\pm1$ compared to our control sample. While the heterogeneity of recent STAR FORMATION histories implies multiple SMBH feeding mechanisms, the excess of post-starburst host galaxies demonstrates the link between accreting SMBHs and a recent starburst followed by rapid quenching. Given that massive post-starburst galaxies are predominantly caused by gas-rich major mergers, our results indicate that $30-50$ per cent of QUASARs originate from merger-induced starbursts.

[abstract 14 / 34] (score: 3)
arXiv:2502.06203 [pdf, ps, other]

Title: Different physical and numerical sources of scatter in the $M_{\star}$-$M_{\mathrm{BH}}$ relation and their connection to galaxy evolution

Authors: Bocheng Zhu, Volker Springel,

Comments: 18 pages, 13 figures, accepted for publication in MNRAS

Subjects: astro-ph.GA

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Observations have established that the masses of supermassive BLACK HOLEs (SMBHs) correlate tightly with the stellar masses of their host galaxies, albeit with substantial scatter. The magnitude of this scatter as a function of galaxy mass and redshift contains valuable information about the origin of SMBHs and the physical nature of their co-evolution with galaxies. In this work, we highlight this connection by studying the scatter in the $M_{\rm BH}$-$M_\star$ relation for massive galaxies in the Illustris, TNG100, and EAGLE cosmological simulations. We find that TNG100 shows significantly lower scatter than Illustris and EAGLE, reflecting different BH feedback models. Using numerical experiments, we separate different contributions to the scatter, including an intrinsic component. At $z=0$, Illustris and EAGLE show $\sim 0.3$ dex intrinsic scatter dominated by BH accretion, while the smaller scatter in TNG100 is dominated by hierarchical merging, implying more tightly quenched massive galaxies. BH seed mass variations can add scatter, though their impact at $z=0$ depends on the feedback model. Without AGN feedback the scatter is much larger for low-mass galaxies ($\gtrsim 0.5$ dex for $\log M_\star < 10^{10.5},\mathrm{M_\odot}$ at $z=0-3$), underscoring the crucial role of feedback in SMBH-galaxy co-evolution. In contrast, hierarchical merging of quenched systems is the main factor reducing scatter for massive galaxies. Based on our results, we expect that the scatter in the $M_{\rm BH}$-$M_\star$ relation at high redshift could be particularly powerful in providing clues to the origin of SMBHs.

[abstract 15 / 34] (score: 3)
arXiv:2506.13519 [pdf, ps, other]

Title: General-RELATIVISTIC MAGNETar MAGNETospheres in 3D with physics-informed neural networks

Authors: Petros Stefanou, Arthur G. Suvorov, José A. Pons,

Comments: 12 pages, 12 figures. v2 (accepted manuscript). Published by MNRAS. Comments are welcome

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Magnetar phenomena are likely intertwined with the location and structure of MAGNETospheric currents. General-RELATIVISTIC effects are important in shaping the force-free equilibria describing static configurations, though most studies have quantified their impact only in cases of axial symmetry. Using a novel methodology based on physics-informed neural networks, fully three-dimensional configurations of varying stellar compactness are constructed. Realistic profiles for surface currents, qualitatively capturing the geometry of observed hotspots, are applied as boundary conditions to deduce the amount of free energy available to fuel outburst activity. It is found that the lowest-energy solution branches permit only a $\approx 30\%$ excess relative to current-starved solutions in axisymmetric cases with global twists, regardless of compactness, reducing to $\approx 5\%$ in 3D models with localised spots. Accounting for redshift reductions to their inferred dipole moments from timing data, explaining MAGNETar burst energetics therefore becomes more difficult unless the field hosts non-negligible multipoles. Discussions on other aspects of MAGNETar phenomena are also provided.

[abstract 16 / 34] (score: 3)
arXiv:2508.14316 [pdf, ps, other]

Title: Machine learning classification of BLACK HOLEs in the mass--spin diagram

Authors: Nathan Steinle, Samar Safi-Harb,

Comments: submitted to PRD

Subjects: astro-ph.HE astro-ph.CO gr-qc

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

We present the mass--spin diagram for classifying BLACK HOLEs and studying their formation pathways providing an analogue to the Hertzsprung-Russell diagram. This allows for BLACK HOLE evolutionary tracks as a function of redshift, combining formation, accretion, and merger histories for the variety of BLACK HOLE populations. A realistic BLACK HOLE continuum constructed from initial mass and spin functions and approximate redshift evolution reveals possible BLACK HOLE main sequences, such as sustained coherent accretion through cosmic time or hierarchical merger trees. In the stellar-mass regime, we use a binary population synthesis software to compare three spin prescriptions for tidal evolution of Wolf-Rayet progenitors, showing how the mass--spin diagram exposes interesting modeling differences. We then classify BLACK HOLE populations by applying supervised and unsupervised machine learning clustering methods to mass--spin datasets. While bare unsupervised clustering can nearly recover canonical population boundaries (stellar-mass, intermediate-mass, and supermassive), a more sophisticated approach utilizing deep learning via variational autoencoders for latent space representation learning aids in clustering of realistic datasets with subclasses that highly overlap in mass--spin space. We find that a supervised random forest can accurately recover the correct clusters from the learned latent space representation depending on the complexity of the underlying dataset, semi-supervised methods show potential for further development, and the performance of unsupervised classifiers is a great challenge. Our findings motivate future machine learning applications and demonstrate that the mass--spin diagram can be used to connect gravitational-wave and electroMAGNETic observations with theoretical models.

[abstract 17 / 34] (score: 3)
arXiv:2509.09768 [pdf, ps, other]

Title: Spatially Offset Active Galactic Nuclei in the Very Large Array Sky Survey: Tracers of Galaxy Mergers and Wandering Massive Black Holes

Authors: R. Scott Barrows, Julia M. Comerford,

Comments: 21 pages, 12 figures, 3 tables. Accepted for publication in the Astrophysical Journal

Subjects: astro-ph.GA

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

The remnants of galaxy mergers may host multiple off-nuclear massive BLACK HOLEs (MBHs), some of which may wander indefinitely within the host galaxy halos. Tracing the population of offset MBHs is essential for understanding how the distribution of MBHs in the Universe evolves through galaxy mergers, the efficiency of binary MBH formation, and the rates at which MBHs are seeded in low-mass satellite galaxies. Offset MBHs can be observationally traced if they are accreting and detectable as spatially offset ACTIVE GALACTIC NUCLEi (AGN). In this work, we build the largest uniform sample of spatially offset AGN candidates (328) by matching sources from the Very Large Array Sky Survey (VLASS) to galaxies in the Sloan Digital Sky Survey (SDSS). Based on the radio source surface density, 29+/-3% are unrelated chance projections. The offset AGN occupation fraction is positively correlated with host galaxy stellar mass, consistent with predictions that most offset MBHs will reside in massive halos. However, this trend vanishes, and may reverse, at the lowest stellar masses, potentially reflecting the weaker host galaxy gravitational potentials. The offset AGN occupation fraction shows no significant evolution with orbital radius, and the agreement with predictions suggests a binary MBH formation rate of <0.5 per merger. Finally, for offset MBHs down to masses of 10^5 Solar masses, the occupation fraction is ~30-70 times lower than the expected value assuming all accreted satellites host a MBH. This result may suggest a relatively low MBH seeding efficiency.

[abstract 18 / 34] (score: 3)
arXiv:2509.09860 [pdf, ps, other]

Title: Propeller effect in action: unveiling quenched accretion in the transient X-ray pulsar 4U 0115+63

Authors: Hua Xiao, Sergey S. Tsygankov, Valery F. Suleimanov, Alexander A. Mushtukov, Long Ji, Juri Poutanen,

Comments: 8 pages, 6 figures, 2 tables, accepted for publication in Astronomy & Astrophysics

Subjects: astro-ph.HE

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

The Be/X-ray pulsar 4U 0115+63 underwent a type II outburst in 2023. After the outburst, similar to the outbursts in 2015 and 2017, the source decayed into a quiescent state. Two out of three XMM-Newton observations conducted after the 2023 outburst confirmed the source to be in a low-luminosity state at a level of $L_{\rm X} \sim 10^{33}\,\rm erg\,s^{-1}$. X-ray pulsations were detected at $\approx$0.277 Hz in both observations with a pulsed fraction exceeding 50%. The power density spectra show no significant low-frequency red noise in both observations, suggesting that the radiation is not driven by accretion. The energy spectra in this state can be described by a single blackbody component, with an emitting area smaller than the typical size of the polar caps during the accretion phase. Based on the timing and spectral properties, we suggest that the propeller effect is active during the quiescent state, resulting in a total quenching of accretion. We discuss possible mechanisms for the generation of pulsations in this regime and consider the scenario of neutron star crust cooling.

[abstract 19 / 34] (score: 3)
arXiv:2509.10352 [pdf, ps, other]

Title: Can a gamma-ray dim radio BLAZAR produce a 200-PeV neutrino? The case of PMN J0606$-$0724 and KM3-230213A

Authors: Polina Kivokurtseva, Sergey Troitsky,

Comments: 17 pages, 3 figures

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

An extremely energetic muon has been recently detected by the Cubic Kilometre Neutrino Telescope (KM3NeT), indicating the observation of a neutrino with the estimated energy of $\left( 2.2^{+5.7}_{-1.0} \right)\times 10^{17}$~eV. Radio BLAZAR PMN~J0606$-$0724, not detected in gamma rays, is located within the reported error region of the neutrino arrival direction, and was flaring at the time of the event. Here we demonstrate that the neutrino could be produced in a photohadronic interaction in its radio core. The necessary proton power is of order of the source's photon luminosity, and protons can be accelerated to the required energies in the core, while high-energy gamma rays cannot leave the source because of intense production of electron-positron pairs. Expected contribution of the population of similar flaring sources matches non-observation of energetic events by other neutrino telescopes.

[abstract 20 / 34] (score: 2)
arXiv:2305.15181 [pdf, ps, other]

Title: Gravitational wave signatures from the phase-transition-induced collapse of a MAGNETized neutron star

Authors: Anson Ka Long Yip, Patrick Chi-Kit Cheong, Tjonnie Guang Feng Li,

Comments: 11 pages, 7 figures

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Strong MAGNETic fields make neutron stars potential sources of detectable electroMAGNETic and gravitational-wave signals. Hence, inferring these MAGNETic fields is critical to understand the emissions of neutron stars. However, due to the lack of direct observational evidence, the interior MAGNETic field configuration remains ambiguous. Here, for the first time, we show that the internal MAGNETic field strength along with the composition of a neutron star can be directly constrained by detecting the gravitational waves from the \emph{phase-transition-induced collapse} of a MAGNETized neutron star. By dynamically simulating this collapsing event, we first find that the dominant peaks in the gravitational waveform are the fundamental $l=0$ quasi-radial $F$ mode and the fundamental $l=2$ quadrupolar $^2f$ mode. We next show that the maximum gravitational wave amplitude $|h|_\mathrm{max}$ increases with the maximum MAGNETic field strength of the interior toroidal field $\mathcal{B}_\mathrm{max}$ until the maximum rest-mass density at bounce $ρ_\mathrm{max,b}$ decreases due to the increasing $\mathcal{B}_\mathrm{max}$. We then demonstrated that the MAGNETic suppression of fundamental modes found in our previous work remains valid for the hybrid stars formed after the phase-transition-induced collapses. We finally show that measuring the frequency ratio between the two fundamental modes $f_{^2f}/f_{F}$ allows one to infer $\mathcal{B}_\mathrm{max}$ and the baryonic mass fraction of matter in the mixed phase $M_\mathrm{mp} / M_{0}$ of the resulting hybrid star. Consequently, taking $\mathcal{B}_\mathrm{max}$ and $M_\mathrm{mp} / M_{0}$ as examples, this work has demonstrated that much information inside neutron stars could be extracted similarly through measuring the oscillation modes of the stars.

[abstract 21 / 34] (score: 2)
arXiv:2411.17303 [pdf, ps, other]

Title: Inner crust of neutron stars: Polymorphism and superconductivity in the liquid drop model

Authors: Dmitry Kobyakov, Xavier Viñas,

Comments: Revised version. 25 pages, 11 figures, 3 tables

Subjects: nucl-th astro-ph.HE astro-ph.SR hep-th physics.plasm-ph

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Within the liquid drop model built up with the nuclear interaction parametrization Sk$χ$450, which is based on the chiral effective field theory, we calculate numerically the internal energy density for each of nuclear pasta phases and for the uniform nuclear matter. We provide quantitative arguments in favor of coexistence of various nuclear matter phases at a significant range of total pressure within the inner crust of neutron stars, a concept known as crystal polymorphism. Specifically, we find that differences of the internal energy per baryon for various phases are typically less than the thermal energy per a freedom degree at temperature about $10^8$--$10^9$ K, which sets the energetic scale for thermal fluctuations of state of FERMI liquid from the ground state. The nuclear energy contributions are described using the same parametrization Sk$χ$450 for the bulk, plain surface and curvature terms. We find that the introduction of the curvature correction changes the ground state in a relevant way. This may be understood as a consequence of the corresponding change in size of the nucleus, which significantly modifies the phase transition densities. Using the calculated structural parameters from liquid drop model, we explore the physical consequences of the expected Cooper pairing of protons in lasagna phase. In this case, we find a crossover between the discreet layered and the three-dimensional anisotropic regimes of superconductivity. Additionally, we study the MAGNETic stress in lasagna accounting for a rotational lag between superfluid neutrons and the crystal lattice, which is believed to develop naturally in pulsars and MAGNETars. Our results offer a preliminary insight into rich MAGNETic properties of the inner crust of neutron stars.

[abstract 22 / 34] (score: 2)
arXiv:2502.10206 [pdf, ps, other]

Title: Turbulent Mixing Dynamics of Under-Expanded Hydrogen Jets in Propulsion Systems

Authors: Francesco Duronio, Andrea Di Mascio,

Comments:

Subjects: physics.flu-dyn

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

Underexpanded JETs are present in various engineering applications; in recent years, they have gained special attention because of the development of gas-fueled propulsion systems. In these apparatuses, the direct injection of fuels such as hydrogen in innovative low-emission engines' chambers induces turbulent under-expanded JETs. In this study, we performed high-fidelity Large Eddy Simulations of under-expanded hydrogen JETs to investigate mixing characteristics and provide valuable insights for developing injectors suitable for hydrogen and, more generally, gaseous-fueled propulsion systems. We initially assessed the method's accuracy, evaluating the convergence and uncertainty of the numerical results and validating them against experimental particle image velocimetry and Schlieren data. The simulated JETs, the Mach disc dimensions, and the resulting velocity field align closely with the experimental observations. Then, we analysed the JET structure for pressure ratios of 4 to 25 and examined the effects of the geometrical configuration of the nozzle on the characteristics of the air-fuel mixture obtained. We compared the JETs resulting from a round-hole nozzle with annular ones resembling outward-opening injectors.

[abstract 23 / 34] (score: 2)
arXiv:2509.08765 [pdf, ps, other]

Title: PCGBandit: One-shot acceleration of transient PDE solvers via online-learned preconditioners

Authors: Mikhail Khodak, Min Ki Jung, Brian Wynne, Edmond Chow, Egemen Kolemen,

Comments: code available at https://github.com/mkhodak/PCGBandit

Subjects: physics.comp-ph cs.LG cs.NA math.NA stat.ML

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Data-driven acceleration of scientific computing workflows has been a high-profile aim of machine learning (ML) for science, with numerical simulation of transient partial differential equations (PDEs) being one of the main applications. The focus thus far has been on methods that require classical simulations to train, which when combined with the data-hungriness and optimization challenges of neural networks has caused difficulties in demonstrating a convincing advantage against strong classical baselines. We consider an alternative paradigm in which the learner uses a classical solver's own data to accelerate it, enabling a one-shot speedup of the simulation. Concretely, since transient PDEs often require solving a sequence of related linear systems, the feedback from repeated calls to a linear solver such as preconditioned conjugate gradient (PCG) can be used by a bandit algorithm to online-learn an adaptive sequence of solver configurations (e.g. preconditioners). The method we develop, PCGBandit, is implemented directly on top of the popular open source software OpenFOAM, which we use to show its effectiveness on a set of fluid and MAGNETohydrodynamics (MHD) problems.

[abstract 24 / 34] (score: 2)
arXiv:2509.09876 [pdf, ps, other]

Title: Trends in the Population of Binary Black Holes Following the Fourth Gravitational-Wave Transient Catalog: a Data-Driven Analysis

Authors: Nir Guttman, Ethan Payne, Paul D. Lasky, Eric Thrane,

Comments: 20 pages, 19 figures

Subjects: astro-ph.HE gr-qc

Created: 2025-09-11; Updated: 2025-09-15; Datestamp: 2025-09-15

Current population models of binary BLACK HOLE distributions are difficult to interpret because standard population inferences hinge on modeling choices, which can mask or mimic real structure. The maximum population likelihood ``$\pistroke$ formalism'' provides a means to investigate and interpret features in the distribution of binary BLACK HOLEs using only data -- without specifying a population model. It tells us if features inferred from current population models are truly present in the data or if they arise from model misspecification. It also provides guidance for developing new models by highlighting previously unnoticed features. In this study, we utilize the $\pistroke$ formalism to examine the binary BLACK HOLE population in the LIGO--Virgo--KAGRA (LVK) fourth Gravitational-Wave Transient Catalog (GWTC-4). Our analysis supports the existence of a gap around $45\,M_\odot$ in the secondary BLACK HOLE mass distribution and identifies a widening in the distribution of the effective inspiral spin parameter $χ_\text{eff}$ near this mass as recently reported by Tong et al. (2025). Similar to earlier studies, we find support for an anti-correlation between $χ_\text{eff}$ and mass ratio. However, we argue that this may be a spurious correlation arising from misspecification of the joint distribution of BLACK HOLE masses. Furthermore, we identify support for dimensionless BLACK HOLE spin magnitudes at approximately $χ\approx 0.2$ and $χ\approx0.7$. The data support the existence of a correlation between the spin magnitudes $χ_1$ and $χ_2$, though subsequent study is required to determine if this feature is statistically significant. The accompanying data release includes $\pistroke$ samples, which can be used to compare theoretical predictions to LVK data and to assess assumptions in parameterised models.

[abstract 25 / 34] (score: 2)
arXiv:2509.09944 [pdf, ps, other]

Title: Supra-arcade downflows in an extensive fan associated with a giant quiescent solar filament eruption

Authors: Xiaoyan Xie, Katharine Reeves, Chengcai Shen, Nishu Karna, Yan Xu, Christopher Moore, Crisel Suarez, Ritesh Patel, Daniel Seaton,

Comments:

Subjects: astro-ph.SR

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

We investigate the aftermath of a giant quiescent solar filament eruption on December 24, 2023. One feature of the eruption is an extensive fan above the filament channel that is about three times as wide as similar structures that appear above active regions (ARs) during solar flares. The fan contains numerous supra-arcade downflows (SADs), and we investigate the largest SADs with continuous Hinode X-ray Telescope (XRT) observations. The measured maximum width of the SADs in this event is at least three times the maximum width of SADs observed in AR flares, whereas the velocities of the largest SADs are similar to the typical values of AR SADs. The kinetic characteristics of the largest SADs observed in this event align with previous model predictions, where SADs originate from the non-linear development of Rayleigh-Taylor type instabilities. In this scenario, the larger system size allows the existence of larger-scale instabilities, while the development of the velocities of these instabilities is expected to be independent of the system size. Compared to AR flares, the temperature and emission measure in this event are lower, and there is less overall radiation, resulting in no evident Geostationary Operational Environmental Satellite (GOES) signature. Similar to those in AR flares, SADs show lower temperatures compared to the surrounding fan plasma. Our observations show that SADs are present in a wide variety of eruptions. The RECONNECTion mechanisms present in quiescent filament eruptions are similar to those driving more compact eruptions originating from ARs.

[abstract 26 / 34] (score: 2)
arXiv:2509.09949 [pdf, ps, other]

Title: The growth of MAGNETic energy during the nonlinear phase of the subsonic and supersonic small-scale dynamo

Authors: Neco Kriel, James R. Beattie, Mark R. Krumholz, Jennifer Schober, Patrick J. Armstrong,

Comments: 9 pages, 4 figures, submitted to PRL

Subjects: physics.plasm-ph physics.comp-ph

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

Small-scale dynamos (SSDs) amplify MAGNETic fields in turbulent plasmas. Theory predicts nonlinear MAGNETic energy growth $E_\mathrm{mag} \propto t^{p_\mathrm{nl}}$, but this scaling has not been tested across flow regimes. Using a large ensemble of SSD simulations spanning sub- to supersonic turbulence, we find linear growth ($p_\mathrm{nl} = 1$) in subsonic flows and quadratic growth ($p_\mathrm{nl} = 2$) in supersonic flows. In all cases, we find a dynamo efficiency of $\sim 1/100$ and a duration $Δt \approx 20\,t_0$, with $t_0$ the turnover time, establishing the universal timescales and efficiencies of the nonlinear SSD across astrophysical and laboratory plasmas.

[abstract 27 / 34] (score: 2)
arXiv:2509.09996 [pdf, ps, other]

Title: A star-by-star correspondence between X-ray activity and rotation in the young open cluster NGC 2516 with eROSITA

Authors: Dario J. Fritzewski, Sydney A. Barnes, Samet Ok, Georg Lamer, Axel Schwope,

Comments: Accepted for publication in A&A

Subjects: astro-ph.SR astro-ph.GA astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

The coronal soft X-ray emission of cool stars, especially when taken in combination with their measured rotation periods, offers insights into their levels of MAGNETic activity and related transitions. We study the X-ray properties of low-mass members of the open cluster NGC 2516 to explicate their detailed dependencies on mass and rotation. We analysed the pointed SRG/eROSITA satellite observations of NGC 2516 obtained during the calibration and performance verification phase of the mission. We found 1561 X-ray sources within the field of view and related 1007 of them to their optical stellar counterparts, including 655 members of NGC 2516 (433 with rotation periods). We combined these detections with auxiliary optical data to facilitate their interpretation. Furthermore, we extracted X-ray spectra for all sources and fit two-component APEC models to them. To aid the analysis, we grouped stars with similar mass and rotational properties together, which allowed us to investigate the influence of rotation on various X-ray properties. The colour-activity diagram of NGC 2516 displays a general increase in the fractional X-ray luminosity with spectral type change from F through G and K to M-type. However, the behaviour of K-type stars, representing the ones that best sample the fast-to-slow rotational transition, is more complex, with both increased and decreased X-ray emission relative to G-type stars for fast and slow rotators, respectively. The rotation-activity diagram is analogous, with an identifiable desaturated group of X-ray emitters that corresponds to stars in the rotational gap between the fast and slow rotator sequences. We prefer to describe the normalised X-ray emission for all cluster stars as declining logarithmically with Rossby number over those using broken power laws. Coronal temperatures appear to be largely independent of mass or rotation. (abridged)

[abstract 28 / 34] (score: 2)
arXiv:2509.10017 [pdf, ps, other]

Title: Rotating twisted MAGNETosphere of MAGNETars: approximate analytical solutions

Authors: H. Tong, L. Chen,

Comments: 7 pages, submitted

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

An approximate analytical solution for the rotating twisted MAGNETosphere of MAGNETars is presented. The poloidal flux is approximated by the self-similar twisted dipole field. The toroidal field is obtained by the minimum torque model. Under this approximation, it is found that: (1) The Y-point radius decreases with the increase of twist of the MAGNETic field. (2) The polar cap is larger for larger twist. (3) The particle outflow luminosity is larger for larger twist. (4) The maximum acceleration potential, pulse width of MAGNETar radio emission etc all increase with the twist. (5) For an untwisting MAGNETosphere, the physical properties general evolves towards that of the normal pulsars. The above findings are consistent with previous analytical and numerical results. The larger polar cap may corresponds to the hot spot during MAGNETar outburst. In general, a rotating twisted MAGNETosphere has larger open field line regions. The radio emission of MAGNETars and fast radio burst may both originates in the larger and evolving open field line regions of MAGNETars.

[abstract 29 / 34] (score: 2)
arXiv:2509.10115 [pdf, ps, other]

Title: An ultraviolet burst oscillation candidate from the low-mass X-ray binary EXO 0748-676

Authors: A. Miraval Zanon, F. Ambrosino, G. Illiano, A. Papitto, G. L. Israel, F. Coti Zelati, L. Stella, T. Di Salvo, S. Campana, G. Benevento, N. O. Pinciroli Vago, M. C. Baglio, P. Casella, P. D'Avanzo, D. de Martino, M. Imbrogno, R. La Placa, S. E. Motta,

Comments: accepted for publication by A&A

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

X-ray burst oscillations are quasi-coherent periodic signals at frequencies close to the neutron star spin frequency. They are observed during thermonuclear Type I X-ray bursts from a number of low-mass X-ray binaries (LMXBs) hosting a fast-spinning, weakly MAGNETic neutron star. Besides measuring the spin frequencies, burst oscillations hold the potential to accurately measure neutron star mass and radius, thus providing constraints on the equation of state of matter at nuclear densities. Based on far-ultraviolet (FUV) observations of the X-ray binary EXO 0748-676 taken with the Hubble Space Telescope in 2003, we report a possible indication of ultraviolet burst oscillations at the neutron star spin frequency ($\sim$552 Hz), potentially the first such case for an LMXB. The candidate signal is observed during an $\sim$8 s interval in the rising phase of an FUV burst, which occurred $\sim$4 s after a Type I X-ray burst. Through simulations, we estimated that the probability of detecting the observed signal power from pure random noise is 3.7$\%$, decreasing to 0.3$\%$ if only the burst rise interval is considered, during which X-ray burst oscillations had already been observed in this source. The background-subtracted folded pulse profile of the candidate FUV oscillations in the (120-160 nm) band is nearly sinusoidal with a $\sim$16$\%$ pulsed fraction, corresponding to a pulsed luminosity of $\sim$8$\times$10$^{33}$ erg/s. Interpreting the properties of this candidate FUV burst oscillations in the light of current models for optical-ultraviolet emission from neutron star LMXBs faces severe problems. If signals of this kind are confirmed in future observations, they might point to an unknown coherent emission process as the origin of the FUV burst oscillations observed in EXO 0748-676.

[abstract 30 / 34] (score: 2)
arXiv:2509.10150 [pdf, ps, other]

Title: Magnetic effects on fundamental modes in rotating neutron stars with a purely toroidal MAGNETic field

Authors: Anson Ka Long Yip, Tjonnie Guang Feng Li,

Comments: 14 pages, 4 figures

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

ElectroMAGNETic and gravitational-wave signals from neutron stars are shaped by rapid rotation and strong MAGNETic fields. Determining these properties is essential to interpret such signals, but current measurements are limited: rotation estimates rely on electroMAGNETic detections and assume uniform rotation, while inferring interior MAGNETic fields remains ambiguous due to a lack of direct observations. Measuring the excited fundamental modes of neutron stars in gravitational-wave signals offers a promising solution, as these modes encode information about stellar composition, structure, and dynamics. Previous studies have examined the individual effects of rotation and MAGNETic fields on these modes, identifying MAGNETic suppression and establishing linear relations for the frequencies of the fundamental $l=0$ quasi-radial mode $f_F$ and $l=2$ quadrupolar mode $f_{^2f}$. However, few have investigated the combined influence of rotation and MAGNETic fields. Here, for the first time, we consider both rotation and a toroidal MAGNETic field to construct linear relations for quantifying $f_F$ and $f_{^2f}$, showing that their combined effects can be constrained by detecting these modes. Using 2D axisymmetric simulations, we demonstrate that quasi-linear relations between $f_F$, $f_{^2f}$, stellar compactness $M/R$, and kinetic-to-binding energy ratio $T/|W|$ persist even with a toroidal MAGNETic field. The slope of these relations depends on the toroidal MAGNETization constant $K_\mathrm{m}$. Additionally, measuring the frequency ratio $f_{^2f}/f_F$ enables inference of $T/|W|$ and the maximum MAGNETic field strength $\mathcal{B}_\mathrm{max}$. Lastly, we show that differential rotation causes only minor deviations from predictions for uniform rotation. Thus, this work demonstrates that rotational and MAGNETic properties of neutron stars can be inferred from their fundamental modes.

[abstract 31 / 34] (score: 2)
arXiv:2509.10256 [pdf, ps, other]

Title: UV-irradiated outflows from low-mass protostars in Ophiuchus with JWST/MIRI

Authors: I. M. Skretas, A. Karska, L. Francis, W. R. M. Rocha, M. L. van Gelder, Ł. Tychoniec, M. Figueira, M. Sewiło, F. Wyrowski, P. Schilke,

Comments: 35 pages, 40 figures. Accepted for publication in A&A

Subjects: astro-ph.GA astro-ph.SR

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

The main accretion phase of protostars is characterized by the ejection of material in the form of JETs/outflows. External UV irradiation can potentially have a significant impact on the excitation conditions within these outflows. High-resolution observations in the mid-infrared allow us to investigate the details of those energetic processes through the emission of shock-excited H$_2$ . Our aim is to spatially resolve H$_2$ and ionic/atomic emission within the outflows of low-mass protostars, and investigate its origin in connection to shocks influenced by external ultraviolet irradiation. We analyze spectral maps of 5 Class I protostars in the Ophiuchus molecular cloud from the James Webb Space Telescope (JWST) Medium Resolution Spectrometer (MIRI/MRS). Four out of five protostars show strong H$_2$, [\ion{Ne}{II}], and [\ion{Fe}{II}] emission associated with outflows/JETs. Pure rotational H$_2$ transitions from S(1) to S(8) are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of $\sim$500-600 K and $\sim$1000-3000 K respectively. Both $C$-type shocks propagating at high pre-shock densities (n$_\text{H} \ge$10$^4$ cm$^{-3}$) and $J$-type shocks at low pre-shock densities (n$_\text{H} \le$10$^3$ cm$^{-3}$) reproduce the observed line ratios. However, only $C$-type shocks produce sufficiently high column densities of H$_2$, whereas predictions from a single $J$-type shock reproduce the observed rotational temperatures of the gas better. A combination of various types of shocks could play a role in protostellar outflows as long as UV irradiation is included in the models. The origin of this radiation is likely internal, since no significant differences in the excitation conditions of outflows are seen at various locations in the cloud.

[abstract 32 / 34] (score: 2)
arXiv:2509.10276 [pdf, ps, other]

Title: Power coupled to the slow wave resonance cone in cold plasma

Authors: Wouter Tierens,

Comments:

Subjects: physics.plasm-ph

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

We consider the power coupled to the plasma from a cylindrical source emitting resonance cones, propagative slow waves which exist in low density MAGNETized plasmas when the signs of the Stix parameters S and P differ. In this work, we calculate this power for the first time for any collisionality, and show that it remains finite in the cold collisionless limit, even as the radiofrequency electric field itself, and the associated power absorption density, is singular. We give the main parameter dependencies of the coupled power.

[abstract 33 / 34] (score: 2)
arXiv:2509.10346 [pdf, ps, other]

Title: The electron temperature distribution and the high ionization just behind the shock in the Cygnus Loop

Authors: Masahiro Ichihashi, Aya Bamba, Dai Tateishi, Kouichi Hagino, Satoru Katsuda, Hiroyuki Uchida, Hiromasa Suzuki, Ryo Yamazaki, Yutaka Ohira,

Comments: 14 pages, 6 figures, ApJ, Accepted

Subjects: astro-ph.HE

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

The physical processes behind astrophysical collisionless shocks, such as thermal relaxation and ionization after shock passage, remain poorly understood. To investigate these processes, we analyze the northeastern region of the Cygnus Loop with XMM-Newton. The electron temperature is found to increase towards the interior of the remnant ranging from 0.15-0.19 keV energy range within a spatial scale of 6 arcmin (or 1.27 pc at a distance of 725 pc) from the shock front. This can be explained well by a modified Sedov solution with radiative cooling. We also show that the ionization timescales determined from our spectroscopy are significantly larger than those estimated based on the electron density of the surrounding materials and the shock velocity. This excess can be qualitatively explained by a mixing of inner multiple plasma components with different ionization states due to turbulence.

[abstract 34 / 34] (score: 2)
arXiv:2509.10431 [pdf, ps, other]

Title: Primordial Black Hole Formation in a Scalar Field Dominated Universe: Investigation of the Critical nature of the Collapse

Authors: Luis E. Padilla, Ethan Milligan, David J. Mulryne, Juan Carlos Hidalgo,

Comments: 13 pages and 6 figures. Comments are welcome!

Subjects: astro-ph.CO

Created: 2025-09-12; Updated: 2025-09-15; Datestamp: 2025-09-15

In this paper, we investigate the critical collapse leading to primordial BLACK HOLE (PBH) formation in a universe dominated by a self-interacting scalar field with a quartic potential, comparing it to the well-known radiation-dominated case. Using fully RELATIVISTIC nonlinear numerical simulations in spherical symmetry, based on the Misner--Sharp formalism, we analyze the dynamics near the collapse threshold and track the scaling of the BLACK HOLE mass. Our results confirm that both the scalar field and radiation cases exhibit type II critical behavior with similar -- though not identical -- critical exponents, differing by about $2σ$. This suggests that, while a quartic scalar field effectively mimics a radiation fluid even in the nonlinear collapse regime, small differences in the critical exponent persist. Our findings provide direct numerical evidence for the near universality of the critical exponent in PBH formation, with only mild dependence on whether the collapse is driven by a scalar field or a perfect fluid.