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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 24 February

Instrumentation and Methods for Astrophysics

A Path to an All-Sky Survey with Roman

Jiwon Jesse Han, Anirudh Chiti, Kai-Feng Chen et al. (+93 more)

A deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$\sigma$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint Gaia-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.
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All authors Jiwon Jesse Han, Anirudh Chiti, Kai-Feng Chen, Keith Bechtol, Andrea Bellini, Robert Benjamin, Adam Bolton, Ana Bonaca, Alex Broughton, Esra Bulbul, Susan Clark, Charlie Conroy, Suchetha Cooray, John Franklin Crenshaw, Tansu Daylan, Arjun Dey, Alex Drlica-Wagner, Tim Eifler, Kareem El-Badry, Richard M. Feder, Peter Ferguson, Shenming Fu, Sebastian Gomez, Ryan Hickox, Christopher Hirata, Easton J. Honaker, Xiaosheng Huang, Alexander P. Ji, Michael Liu, Kevin A. McKinnon, Geoffrey Mo, Burcin Mutlu-Pakdil, Adrian M. Price-Whelan, Alessandro Savino, David J. Schlegel, Nora Shipp, Jay Strader, Federica Tarsitano, Adrien C.R. Thob, Kim-Vy Tran, Roeland P. van der Marel, Feige Wang, Risa Wechsler, Daniel R. Weisz, Dennis Zaritsky, Tianqing Zhang, Shreya Anand, Amirnezam Amiri, Abhijeet Anand, Matthew L. N. Ashby, Finian Ashmead, Leandro Beraldo e Silva, Aliza Beverage, Michael R. Blanton, Warren R. Brown, Anthony G.A. Brown, Priyanka Chakraborty, Yi-Kuan Chiang, Jose M. Diego, Denis Erkal, Simone Ferraro, Lluís Galbany, Marla Geha, Oleg Y. Gnedin, Lars Hernquist, Jason A. S. Hunt, Valentin D. Ivanov, Venu Kalari, Nitya Kallivayalil, András Kovács, Kyle Kremer, Ting-Wen Lan, Denis Leahy, Jiaxuan Li, Ivan Minchev, GyuChul Myung, Ethan O. Nadler, Joan R. Najita, Melissa K. Ness, Jacob Nibauer, Fabio Pacucci, David Parkinson, Ekta Patel, R. Michael Rich, Marina Ricci, Graziano Rossi, Nikolina Sarcevic, Arnab Sarkar, Andrew K. Saydjari, Arman Shafieloo, Zachary Slepian, Sangmo Tony Sohn, David N. Spergel, Róbert Szabó, Christina C. Williams, John F. Wu

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

Inflationary branch decoherence and the cosmological arrow of time

Ali Nayeri

We analyze branch decoherence in inflationary quantum cosmology by computing reduced density matrices and branch-overlap factors for long-wavelength perturbations. The Hartle-Hawking no-boundary state is real in the semiclassical regime and contains both expanding and contracting WKB components, whereas the tunneling state is selected as an outgoing complex WKB branch; expanding-contracting decoherence is therefore central for the former and mainly diagnostic for the latter. Using the influence-functional formalism, we derive the noise kernel for a light spectator environment and evaluate decoherence under horizon-based and EFT-motivated coarse grainings. We then compute the single-mode branch overlap directly from the Bunch-Davies mode functions, obtaining $|\mathcal{D}_k(z)|=[z^2/(z^2+1)]^{1/4}$ in the massless limit and $|\mathcal{D}_k(z)|\sim z^\nu$ on superhorizon scales for massive fields, where $z=-k\eta$ is the dimensionless wavenumber with $\eta$ the conformal time. In the massless case, the accumulated geometric branch functional is evaluated in closed form, with a leading cutoff-sensitive phase-space term and a universal subleading contribution. The calculation provides an explicit quantitative bridge between quantum-cosmological boundary conditions, inflationary squeezing, and the emergence of effectively classical cosmological histories.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Using thermodynamics to learn gravitational wave physics

Caio César Rodrigues Evangelista and Níckolas de Aguiar Alves

Black holes are some of the most interesting objects in the universe. While they first arise in the complicated behavior of general relativity, the physical laws ruling their behavior are surprisingly simple. For example, one of the core facts about black holes is that their area never decreases, much like the entropy in thermodynamics. In this note directed at introductory physics students and their instructors, we use this similarity to understand properties of black hole physics using standard techniques from an undergraduate course in thermal physics. We explore the never-decreasing nature of black hole area to obtain bounds on the energy emitted in a black hole merger (a calculation originally done by Hawking). We show how this allows us to think of black holes in manners very similar to heat engines, and how these ideas have been used in modern gravitational wave observatories to test general relativity. This allows a research-level topic to be discussed in introductory physics lectures.
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Astrophysics of Galaxies

The JWST Resolved Stellar Populations Early Release Science Program. IX. The RR Lyrae Population in WLM with HST and JWST

Catherine M. Slaughter, Evan D. Skillman, Alessandro Savino et al. (+16 more)

RR Lyrae stars are a common, dependable Population II distance indicator, and provide an independent tracer of early star formation. Here, we utilize archival HST/ACS and JWST/NIRCam observations of the nearby dwarf star-forming galaxy WLM to study RR Lyrae in JWST filters. We independently identify RR Lyrae in HST and JWST imaging in order to evaluate JWST's efficacy at characterizing RR Lyrae in the near-IR. We use an MCMC template-fitting technique to obtain periods, amplitudes, and mean magnitudes from the RR Lyrae time-series data. The spatially overlapping HST and JWST observations allow us to directly compare the same sources observed with the instruments, and calibrate the NIRCam F090W and F150W RR Lyrae period-Wesenheit-metallicity (PWZ) relation to the Gaia-consistent HST PWZ. We additionally assess the epoch-to-epoch consistency of NIRCam photometry, and find evidence of burn-in. We conclude that the zero-point offset is negligible compared to the uncertainties from the template fitting. We conduct an MCMC fit of the PWZ with both HST and JWST data. Our results are three-fold. First, we find that we can reliably identify RR Lyrae in NIRCam data, but light-curve template fitting proves difficult on short-baseline observations. Second, the HST PWZ fit yields a distance modulus to WLM of $\mu = 24.85\pm0.05$ ($0.93\pm0.02$ Mpc). This is closer than previous measurements, primarily attributed to consistency with the Gaia scale. Lastly, although the JWST PWZ fit has large uncertainties and a poorly-constrained slope, it represents a first-of-its-kind PWZ calibration in NIRCam filters.
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All authors Catherine M. Slaughter, Evan D. Skillman, Alessandro Savino, Daniel R. Weisz, Meredith Durbin, Jay Anderson, Martha L. Boyer, Roger E. Cohen, Andrew A. Cole, Matteo Correnti, Andrew E. Dolphin, Marla C. Geha, Mario Gennaro, Nitya Kallivayalil, Evan N. Kirby, Kristen B. W. McQuinn, Max J. B. Newman, Jack T. Warfield, Benjamin F. Williams

Instrumentation and Methods for Astrophysics · Cross-listed from hep-ex

Low-Energy Radon Backgrounds from Electrode Grids in Dual-Phase Xenon TPCs

D.S. Akerib, A.K. Al Musalhi, F. Alder et al. (+264 more)

The dual-phase xenon time projection chamber (TPC) is a powerful technology to detect rare interactions such as scatters of dark matter particles on nuclei. In particular, the built-in gain of ionization signals in a dual-phase TPC makes it sensitive to events in the few-electron regime, as expected from low-mass dark matter interactions. The pursuit of this low-energy sensitivity through ionization-only signal detection has so far been hindered by excessive electron backgrounds observed across experiments. Much of this background is attributed to the plate-out of $^{222}$Rn decay chain isotopes on the high voltage electrode grid surfaces that span the full cross section of the TPC. This work presents a first-principle model constructed for this background, the predictions of which are consistent with data from the LZ and LUX experiments. We then discuss mitigation strategies of this background in future dual-phase TPCs and the possibility of applying this grid background model to ionization-only dark matter searches.
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All authors D.S. Akerib, A.K. Al Musalhi, F. Alder, B.J. Almquist, S. Alsum, C.S. Amarasinghe, A. Ames, T.J. Anderson, N. Angelides, H.M. Araújo, J.E. Armstrong, M. Arthurs, X. Bai, A. Baker, J. Balajthy, S. Balashov, J. Bang, J.W. Bargemann, E.E. Barillier, A. Baxter, K. Beattie, T. Benson, E.P. Bernard, A. Bernstein, A. Bhatti, T.P. Biesiadzinski, H.J. Birch, E. Bishop, G.M. Blockinger, E.M. Boulton, B. Boxer, C.A.J. Brew, P. Brás, S. Burdin, D. Byram, M.C. Carmona-Benitez, M. Carter, C. Chan, A. Chawla, H. Chen, Y.T. Chin, N.I. Chott, S. Contreras, M.V. Converse, R. Coronel, A. Cottle, G. Cox, D. Curran, J.E. Cutter, C.E. Dahl, I. Darlington, S. Dave, A. David, J. Delgaudio, S. Dey, L. de Viveiros, L. Di Felice, C. Ding, J.E.Y. Dobson, E. Druszkiewicz, S. Dubey, C.L. Dunbar, S.R. Eriksen, A. Fan, N.M. Fearon, N. Fieldhouse, S. Fiorucci, H. Flaecher, E.D. Fraser, T.M.A. Fruth, P.W. Gaemers, R.J. Gaitskell, A. Geffre, J. Genovesi, C. Ghag, J. Ghamsari, A. Ghosh, S. Ghosh, R. Gibbons, M.G.D. Gilchriese, S. Gokhale, J. Green, M.G.D.van der Grinten, C. Gwilliam, J.J. Haiston, C.R. Hall, T. Hall, R.H Hampp, E. Hartigan-O'Connor, S.J. Haselschwardt, M.A. Hernandez, S.A. Hertel, D.P. Hogan, G.J. Homenides, M. Horn, D.Q. Huang, D. Hunt, C.M. Ignarra, R.G. Jacobsen, E. Jacquet, O. Jahangir, R.S. James, K. Jenkins, W. Ji, A.C. Kaboth, A.C. Kamaha, K. Kamdin, M.K. Kannichankandy, K. Kazkaz, D. Khaitan, A. Khazov, J. Kim, Y.D. Kim, J. Kingston, D. Kodroff, E.V. Korolkova, H. Kraus, S. Kravitz, L. Kreczko, V.A. Kudryavtsev, C. Lawes, E. Leason, D.S. Leonard, K.T. Lesko, C. Levy, J. Liao, J. Lin, A. Lindote, R. Linehan, W.H. Lippincott, J. Long, M.I. Lopes, W. Lorenzon, C. Lu, S. Luitz, W. Ma, V. Mahajan, P.A. Majewski, A. Manalaysay, R.L. Mannino, N. Marangou, R.J. Matheson, C. Maupin, M.E. McCarthy, G. McDowell, D.N. McKinsey, J. McLaughlin, J.B. McLaughlin, R. McMonigle, D.-M. Mei, B. Mitra, E. Mizrachi, M.E. Monzani, K. Morå, J.A. Morad, E. Morrison, B.J. Mount, M. Murdy, A.St.J. Murphy, A. Naylor, C. Nehrkorn, H.N. Nelson, F. Neves, A. Nguyen, A. Nilima, C.L. O'Brien, F.H. O'Shea, I. Olcina, K.C. Oliver-Mallory, J. Orpwood, K.Y Oyulmaz, K.J. Palladino, N.J. Pannifer, N. Parveen, S.J. Patton, B. Penning, G. Pereira, E. Perry, T. Pershing, A. Piepke, S.S. Poudel, Y. Qie, J. Reichenbacher, C.A. Rhyne, Q. Riffard, G.R.C. Rischbieter, E. Ritchey, H.S. Riyat, R. Rosero, P. Rossiter, N.J. Rowe, T. Rushton, D. Rynders, S. Saltão, D. Santone, A.B.M.R. Sazzad, R.W. Schnee, G. Sehr, B. Shafer, S. Shaw, W. Sherman, K. Shi, T. Shutt, C. Silva, G. Sinev, J. Siniscalco, A.M. Slivar, R. Smith, A.M. Softley-Brown, M. Solmaz, V.N. Solovov, P. Sorensen, J. Soria, A. Stevens, T.J. Sumner, A. Swain, N. Swanson, M. Szydagis, D.J. Taylor, R. Taylor, W.C. Taylor, B.P. Tennyson, P.A. Terman, D.R. Tiedt, M. Timalsina, W.H. To, Z. Tong, D.R. Tovey, J. Tranter, M. Trask, K. Trengove, M. Tripathi, L. Tvrznikova, U. Utku, A. Usón, A. Vacheret, A.C. Vaitkus, O. Valentino, V. Velan, A. Wang, J.J. Wang, Y. Wang, R.C. Webb, L. Weeldreyer, J.T. White, T.J. Whitis, K. Wild, M. Williams, J. Winnicki, M.S. Witherell, L. Wolf, F.L.H. Wolfs, S. Woodford, D. Woodward, C.J. Wright, Q. Xia, X. Xiang, J. Xu, Y. Xu, M. Yeh, D. Yeum, J. Young, W. Zha, C. Zhang, H. Zhang, T. Zhang, Y. Zhou

Astrophysics of Galaxies

Scattering, Migration, Re-circularization and Relaxation to Build Out Galaxy Disks with Exponential Profiles

Curtis Struck, Bruce G. Elmegreen and Elena DOnghia

Scattering of stars by interstellar clouds or massive clumps increases the stellar velocity dispersion and promotes a radial disk profile that is exponential. Here we show that such scattering reaches a steady-state distribution function of stellar eccentricity, after which eccentricity increases and decreases occur at equal rates. The implication is that clump/cloud scattering recircularizes eccentric stellar orbits, keeping the stellar velocity dispersion in a limited range. This re-circularization regulates disk heating and maintains kinematic coherence, contributing to the longevity of disk structures. The eccentricity distribution function and the presence of recircularizing cloud-star interactions are independent of cloud mass but the timescale to reach equilibrium decreases with increasing mass. The calculations are made in the simplest possible disk system to highlight the effects of scattering without contamination from spiral waves, star formation, and other processes. The calculations also reveal a bifurcation in the disk evolutions whereby in a minority of cases temporary asymmetries in the clump spatial distribution drive the disks to an end state of increased velocity dispersion and orbital eccentricity corresponding to early type disks. Overall the models emphasize an important physical process that can make and maintain an exponential stellar disk in all galaxies with a cloudy interstellar medium.
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Cosmology and Nongalactic Astrophysics

Revisiting CPL with sign-switching density: To cross or not to cross the NECB

Mine Gökçen, Özgür Akarsu and Eleonora Di Valentino

Recent DESI DR2 BAO measurements, when combined with CMB and SNeIa data, exhibit a $3.2\sigma$-$3.4\sigma$ preference for dynamical dark energy (DE) described by the CPL-parametrized equation of state. A particularly striking feature of these reconstructions is an apparent transition from an early-time phantom-like regime to a late-time quintessence-like behavior. For positive-definite DE densities, this transition is often phrased as a crossing of the phantom divide line (PDL) at $w(a)=-1$. Allowing the DE density to become negative, however, renders the PDL (in the sense of $w(a)=-1$) non-diagnostic as a global separator: the physically meaningful criterion is instead the null energy condition boundary (NECB), $\rho_{\rm DE}+p_{\rm DE}=0$. We therefore test whether the data-driven preference for NECB-crossing in CPL reconstructions persists once alternative realizations of phantom behavior are admitted, specifically through sign-switching DE densities. To this end, we introduce and constrain two controlled phenomenological extensions of the CPL framework featuring a negative DE phase in the past. In the CPL$\to-\Lambda$ model, the switching epoch is tied to the CPL-inferred NECB-crossing scale factor, yielding an early-time negative cosmological-constant phase, while the post-switch evolution follows the CPL branch. In the sCPL model, the CPL equation of state is maintained at all times, while the sign switch in the energy density occurs at an independent transition redshift. We find that late-time BAO and SNeIa data drive the negative-density phase beyond their effective redshift coverage, and that this requirement is the primary driver of the inferred parameter behavior. While both models are statistically disfavored relative to the baseline CPL, admitting a negative DE phase generally reduces the significance of deviations from a cosmological constant.
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High Energy Astrophysical Phenomena

RAMSES-MCR: A consistent multi-group treatment of cosmic rays physics in momentum-space with the RAMSES code

Nimatou-Seydi Diallo, Yohan Dubois, Alexandre Marcowith et al. (+2 more)

Cosmic rays (CRs) are known to play a key role in many astrophysical environments: they can modify shock dynamics, influence the thermochemistry and the ionization of the interstellar medium, regulate galaxy mass content by driving galactic winds, and be released by jets from active galactic nuclei. They also serve as important observational tracers through $\gamma$-ray emission, radio synchrotron, and secondary particle production. Since CR particles follow power-law distributions in momentum space spanning many decades in energy, and because diffusion and radiative losses further shape these spectra, it is crucial to model spectrally resolved CRs in numerical simulations and to assess the impact of this modeling on gas dynamics and observational signatures. We present a consistent multi-group spectral method in momentum space for CR protons called RAMSES-MCR in the adaptive mesh refinement code RAMSES, based on the two-moment formalism that evolves both CR energy and number density in momentum space, together with their associated flux. The modeled CR processes include advection, anisotropic/isotropic diffusion, streaming instability, Coulomb and hadronic losses, adiabatic changes, and feedback onto the gas. We also show that the method can be naturally extended to CR electrons (e.g. including synchrotron losses) and generalized to multiple CR species. The implementation is validated against a suite of standard multi-dimensional tests. We finally apply RAMSES-MCR to the three-dimensional expansion of a supernova remnant including CRs with anisotropic diffusion and energy losses, and demonstrate how CR energy redistributes in a momentum-dependent manner and modifies the gas momentum during the snowplough phase.
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All authors Nimatou-Seydi Diallo, Yohan Dubois, Alexandre Marcowith, Joki Rosdahl, Benoît Commerçon

Astrophysics of Galaxies

Experimental and computational studies of the hydrogenation of carbon disulfide (CS2) on ice analogues

Thanh Nguyen, Germán Molpeceres, Yasuhiro Oba et al. (+4 more)

Carbon disulfide (CS$_2$) is one of the sulfur-bearing species expected to be present in the interstellar medium (ISM). In this study, we investigated the surface reactions of solid CS$_2$ with hydrogen (H) atoms on amorphous solid water (ASW) using laboratory experiments supported by computational calculations. Our results show that CS$_2$ reacts with H atoms through quantum tunneling in the initial step, followed by successive H addition reactions, with or without activation barriers, on icy surfaces. These processes lead to the formation of several sulfur-bearing species, including hydrogen sulfide (H$_2$S), methyl mercaptan (CH$_3$SH), and small amounts of dithioformic acid (HC(S)SH) and methanedithiol (CH$_2$(SH)$_2$). The observed reactivity of CS$_2$ with H atoms provides a plausible explanation for the non-detection of CS$_2$ in interstellar ices. Furthermore, the efficient hydrogenation of the complex molecules derived from CS$_2$, namely HC(S)SH and CH$_2$(SH)$_2$, suggests that these species could be easily undergone with H atoms to produce other S-bearing species under ISM conditions.
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All authors Thanh Nguyen, Germán Molpeceres, Yasuhiro Oba, Marcelino Agúndez, Gisela Esplugues, José Cernicharo, Naoki Watanabe

Astrophysics of Galaxies

MHD Simulations of Strongly Magnetized HII Region Evolution: Evidence for Ionized Gas Filamentation

Samuel Crowe, Yisheng Tu, Zhi-Yun Li et al. (+2 more)

Recent JWST observations of HII regions in the Central Molecular Zone have shown a highly filamentary morphology distinct from HII regions in other parts of the galaxy. We present magnetohydrodynamic (MHD) simulations of strongly magnetized (plasma-$\beta$ << 1) HII region evolution that investigate and describe the formation of these ionized gas filaments. HII region evolution has been simulated in a 30 pc$^3$ box, in distinct models with pre-placed overdensities in the ambient medium and overdensities that have been generated with driven turbulence. We find that when these overdensities are seeded in the ambient medium before the birth of the ionizing source, the photoionized plasma stripped off of these dense blobs is funneled into long filaments along the magnetic field lines. The length and emission measure of these ionized gas filaments are similar to the filaments observed in the Central Molecular Zone. Given that these filaments are effectively magnetically-confined flows of photoionized gas, their density and curvature are influenced by the density of the blob and the geometry of the configuration.
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All authors Samuel Crowe, Yisheng Tu, Zhi-Yun Li, Jeong-Gyu Kim, John Bally

High Energy Astrophysical Phenomena

The no-hair theorems at work in the tidal disruption event AT2020afhd

Lorenzo Iorio

Recently, the coprecession of both the accretion disk and the jet formed following the tidal disruption event associated with the optical transient AT2020afhd, driven by a supermassive black hole of almost ten million solar masses, were independently measured in both the X and radio bands, respectively, showing a periodicity of nearly 20 days over about 300 days. An analytical model of the general relativistic gravitomagnetic Lense-Thirring precession of the effective orbit of a fictitious test particle revolving about a spinning primary can explain the observed precessional features. It yields allowed regions in the system's parameter space which, as far as the hole's dimensionless spin parameter is concerned, are essentially in agreement with those obtained in the literature with general relativistic magnetohydrodynamic simulations. The present analytical approach can be extended to include the precession due to the hole's quadrupole mass moment as well. It breaks the degeneracy in the allowed regions occurring for negative and positive values of the spin parameter when only the Lense-Thirring effect is considered. The best estimate for the hole's mass yields the range $0.185-0.215$ for the dimensionless spin parameter. Using the same strategy with the gravitomagnetic frequency for an extended disk of finite size with a parameterized power-law mass density yields to distinct, generally non-overlapping allowed regions for each value of the power-law index adopted.
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Cosmology and Nongalactic Astrophysics

Simulations of the 21cm emission line for upcoming large-scale HI galaxy surveys

Joël Mayor, Marta Spinelli, Gabriella De Lucia et al. (+5 more)

Upcoming galaxy surveys with the SKA Observatory will detect neutral hydrogen (HI) across unprecedented volumes, and their scientific return will crucially depend on predictive models for HI observables. In this work, we present a framework to simulate the neutral hydrogen 21cm emission line in such large-scale HI galaxy surveys. This framework is developed as a modular layer that builds on semi-analytical models. In particular we use as bases the Galaxy Evolution and Assembly (GAEA) and L-Galaxies semi-analytical models, coupled to merger trees from the Millennium Simulation suite. We validate our framework against local Universe observations, demonstrating consistency with velocity functions, and generalised Tully-Fisher relations. Predictions based on GAEA and L-Galaxies exhibit mutual consistency despite the distinct underlying physical prescriptions. We construct mock galaxy catalogues that incorporate forward-modelled selection functions, inclination effects, and redshift broadening, reproducing the statistical distributions of HI-selected galaxies in the ALFALFA survey. Finally, we present redshift distribution forecasts for future SKA Observatory HI galaxy surveys. This framework offers a flexible tool for interpreting upcoming large-scale radio surveys and studying HI line observables as cosmological probes.
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All authors Joël Mayor, Marta Spinelli, Gabriella De Lucia, Robert Yates, Alexandre Refregier, Fabio Fontanot, Lizhi Xie, Michaela Hirschmann

Solar and Stellar Astrophysics

The hybrid Nova Vul 2024 (=V615 Vul)

Paolo Valisa, Ulisse Munari and Irene Albanese

We present daily optical, absolute-fluxed spectroscopy of the heavily reddened Nova Vul 2024 (=V615 Vul), obtained in both low- and high-resolution echelle modes from discovery on 29 July 2024 through the nebular phase. Refined astrometry confirms the positional consistency with a potential progenitor. Reliable estimates of the decline time (t3=10.7 +/- 0.5 d) and reddening (E(B-V)=1.6 +/- 0.1) enabled the application of the Maximum Magnitude - Rate of Decline relation, yielding a distance of 5.0 +/- 1.0 kpc in excellent agreement with 3D Galactic extinction maps. Around maximum light, the nova displayed a Fe II-type spectrum with very broad emission lines (FWZI 5800 km s-1) and high-velocity P-Cygni absorptions. Shortly after t3, coincident with the onset of hard X-ray emission, it showed pronounced photometric oscillations driven mainly by continuum variations. At the same time, He/N features developed alongside Fe II lines, identifying V615 Vul as a rare hybrid nova. During the nebular phase, the ionization level increased up to [Fe VII] and likely [Fe X]. The ejecta show no evidence of neon overabundance and expand ballistically, as indicated by the constant line widths, stable profiles, and characteristic castellation of the high-resolution emission lines.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

5PN eccentric waveforms for intermediate-mass-ratio-inspirals (IMRIs) from post-Newtonian and black hole perturbation theory

M Laxman, Ryuichi Fujita and Chandra Kant Mishra

Detection of gravitational waves from compact binaries involving at least one intermediate mass black hole, and component mass ratios in the range $0.1$-$10^{-4}$, are among the primary sources for future space detectors with target strain sensitivities in the deci-Hertz (dHz) band. Tuned to the waveform requirements for analyzing such sources, a hybrid model is obtained by combining waveforms from the post-Newtonian (PN) and black hole perturbation (BHP) theory. Components of the binary are assumed to be nonspinning and on eccentric orbits. This hybrid model is 3PN accurate in terms of results from PN theory and 5PN in results from BHP theory. In terms of eccentricity, corrections through the order $\mathcal{O}(e^{10})$ are included. Further, using number of gravitational wave cycles estimates for a few representative binaries observable in the dHz band, we demonstrate the significance of the mass ratio information from the PN approach, of contributions from the BHP theory at high PN orders, and also of higher order eccentricity corrections. In particular, we find an almost 10-fold increase in number of gravitational wave cycles for a fixed mass ratio of 0.1 and $e_0\sim0.3$ (evaluated at $0.01$Hz) when contributions beyond the leading order in eccentricity are accounted for. We also confirm the requirement to go beyond 5PN order in the circular part of the waveform from BHP theory.
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Solar and Stellar Astrophysics

A Catalog of 486 Barium Stars Identified in GALAH DR4

Guochao Yang, Jingkun Zhao, Nian Liu et al. (+4 more)

We present a catalog of 486 Ba stars identified in the GALAH DR4 survey using high-resolution spectra and precise abundance measurements. The sample was selected based on s-process enrichment criteria involving the abundances of Ba and La relative to Eu, and further refined using the signed-distance method, resulting in the largest sample of Ba stars to date, including five newly identified Ba dwarfs. Using astrometric and kinematic parameters from Gaia DR3 and StarHorse, we derived the Galactic velocity components for 367 Ba stars and found that most belong to the thin or thick disk, while 18 exhibit halo-like kinematics. Chemical abundance analysis suggests that most Ba stars are of in situ origin, whereas two stars (4077588766331013248 and 6692980582560946304) display signatures of accreted populations. The E-Lz diagram further shows that star 4077588766331013248 lies within the region of substructure ED-8. The observed decline of [Ba/Fe] and [La/Fe] with increasing metallicity implies that s-process elements originate from nucleosynthetic sites distinct from those of iron-peak elements, while the decreasing [hs/ls] ratio toward higher metallicity indicates higher neutron capture efficiency at lower metallicity. Both giant and dwarf Ba stars-except for 6053735173729807872-are confirmed binaries hosting white dwarf companions. Moreover, we estimated the masses of the former asymptotic giant branch (AGB) companions to these Ba stars based on the good agreement between the FRUITY AGB model predictions and their observed abundance patterns.
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All authors Guochao Yang, Jingkun Zhao, Nian Liu, Xiaokun Hou, Zhenxin Lei, Xianhao Ye, Gang Zhao

Astrophysics of Galaxies

HINORA II: Testing the Existence of the Council of Giants in {\Lambda}CDM simulations

Edward Olex, Alexander Knebe, Noam I. Libeskind et al. (+2 more)

The discovery of the galaxy ring known as the Council of Giants (CoG) highlights the need to explain such structures in the Local Universe. In the first paper of this series we presented HINORA - a code to locate (ring-like) structures in 3D point sets - and used it to identify the CoG in the most complete observations of the Local Volume. Here, in Part II, we apply the same method to cosmological simulations to quantify the possible existence of such objects in the LCDM model of structure formation. We analyze DM-only simulations with random and constrained initial conditions, selecting regions that reproduce the properties of the Local Group and Volume, respectively. In order to use the same selection criteria as previsouly done for observations, we relate K-band luminosities to halo masses through semi-empirical relations. After confirming that the selected regions from the simulations match the observed mass function and density of the Local Universe, we use HINORA to search for ring-like structures in them. We find that the existence of CoGs in LCDM simulations is a rather unusual phenomenon. The observed CoG represents an anomaly of more than 2.7 sigma from what is expected in the distribution of massive galaxies in LCDM. These results hint that the CoG could either be a rare chance configuration or the imprint of physical processes at intermediate scales that standard DM-only simulations fail to capture.
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All authors Edward Olex, Alexander Knebe, Noam I. Libeskind, Stefan Gottlöber, Dmitry I. Makarov

High Energy Astrophysical Phenomena

Molecular bipolar outflow in SN 1987A supports the jittering-jets explosion mechanism

Noam Soker

I examine high-quality CO and SiO molecular maps of the core-collapse supernova (CCSN) remnant SN 1987A from the literature and find that the molecular gas exhibits a bipolar structure, correlated with the visible bipolar morphology (termed the keyhole) and the bipolar morphology of the iron emission map. I apply a method commonly used in the study of jet-shaped planetary nebulae. The keyhole has a morphology similar to that of many jet-shaped pairs of bubbles in cooling-flow clusters of galaxies and planetary nebulae. Therefore, the findings of this study, which make the bipolar structure of SN 1987A robust, strengthen the claim that a pair of energetic jets shaped the keyhole and its surroundings. According to the jittering-jets explosion mechanism (JJEM), this pair of jets was the most energetic of several pairs that exploded SN 1987A. This study adds to the accumulating evidence that the JJEM is the primary explosion mechanism for CCSNe, responsible for the majority, if not all, CCSNe.
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Astrophysics of Galaxies

Constraints on dynamically-formed massive black holes in Little Red Dots from X-ray non-detections

M. Liempi, D.R.G. Schleicher, M. A. Latif et al. (+4 more)

The existence of massive, compact galaxies (Little Red Dots, LRDs) at $z \sim 2$ challenges early structure formation models, suggesting rapid stellar and black hole (BH) assembly. While LRDs are efficient environments for BH growth, many show no X-ray evidence of strong AGN emission. We utilize a subsample of X-ray non-detected LRDs to test the compatibility of collision-based BH formation scenarios and constrain physical parameters like metallicity and column density. Our results indicate LRDs are ideal birthplaces for massive BHs, particularly given a mass-radius relation $R_{gal} \propto M_{gal}^{0.6}$. Collision-based models suggest seed masses larger than those in the local Universe, consistent with high-redshift BH mass-radius relations. We modeled BH seed formation and X-ray emission (0.3-7 keV) against observed upper limits. We find that mass-radius exponents $> 0.55$ favor the collision-based scenario; however, consistency with stacked X-ray analysis requires specific accretion and obscuration parameters. Constant or increasing SFR scenarios with high Eddington ratios are feasible but necessitate larger column densities or higher metal enrichment. Alternatively, moderate sub-Eddington accretion reconciles massive seeds with observed masses and X-ray weakness. We conclude that even if LRDs began as starbursts, they should eventually evolve into AGNs.
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All authors M. Liempi, D.R.G. Schleicher, M. A. Latif, R. Schneider, F. Flammini Dotti, A. Escala, M.C. Vergara

High Energy Astrophysical Phenomena

Black hole-Neutron star distinction based on long-term MAXI and Swift study of 42 low mass X-ray binaries

Prakhar Maheshwari, Mayukh Pahari, Anish Sarkar et al. (+1 more)

In this study, we analysed about $\sim$13 years of publicly available data from MAXI and Swift/BAT to examine the long-term source evolution of 42 transient low-mass X-ray binaries. The sample consists of 11 confirmed black hole X-ray binaries (BHXBs), 10 black hole candidates (BHC), and 21 neutron star X-ray binaries (NSXBs). Outbursts and flaring activities studied over 13 years show that 19/21 NSXBs spend significantly longer time in the hard state (observations for which hardness ratio is $\geq$ 0.2) while 15/21 BHXB+XRC spend substantially longer time in the soft state (observations for which hardness ratio is $<$ 0.2). The frequency distribution of the hardness ratio clearly shows two distinct distributions for BHXBs and NSXBs, with their peaks separated: NSXBs prefer harder values, while BHXBs prefer softer values of hardness. Our model-independent analysis for 42 transient sources shows that statistically NSXBs do not prefer to show a canonical high soft state as observed in BHXBs. Additionally, the probability distribution of the duration of the 2-20 keV X-ray outburst is observed to peak at a significantly longer duration ($>$100 days) for BHXBs than for NSXBs (15-60 days). Our analysis shows that among candidate sources, Swift J1728.9-3613, MAXI J1535-571, MAXI J1659-152, EXO 1846-031 show a `q' diagram in the HID and prefer to align with the HID frequency distribution of BHXBs that show `q' diagram, MAXI J1305-704 and MAXI J1836-194 align with frequency distribution of black hole sources without `q' diagram while MAXI J1848-015 shows the HID distribution similar to NSXBs, indicating a neutron star accretor. Therefore, a long-term statistical study of MAXI and Swift/BAT X-ray outbursts from a large sample of transient sources may be used to distinguish BHXB from NSXB.
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All authors Prakhar Maheshwari, Mayukh Pahari, Anish Sarkar, Saurabh Sharma

High Energy Astrophysical Phenomena

Turbulent AGN coronae as the origin of diffuse neutrinos up to PeV energies

Qi-Rui Yang, Ruo-Yu Liu and Xiang-Yu Wang

It has been shown that the turbulence acceleration in AGN coronae can account for 1-10 TeV neutrinos from some AGNs, such as the Seyfert galaxy NGC 1068. Based on this, there are attempts to explain the diffuse neutrinos observed by IceCube with the accumulated contribution from a population of AGNs, but it is found that the maximum neutrino energy is less than tens of TeV, and as a result, additional source classes are needed to explain the high-energy component above this energy. Recently, motivated by the detection of $>100$ TeV neutrinos from the Seyfert galaxy NGC 7469, it was shown that the turbulence acceleration in the corona can explain $>$100 TeV neutrinos given a larger magnetization parameter ($\sigma\sim 1$) in the corona, which leads to a larger maximum proton energy and a hard proton spectrum. In this paper, we extend this assumption to the population of AGNs and study whether the population of AGNs with a wide range of magnetization can explain the entire diffuse neutrino flux. We find that AGN coronae could account for the diffuse neutrinos up to PeV energies if a significant fraction of AGNs have magnetizations as large as $\sigma\sim 1-10$. This conclusion is insensitive to the shape of the magnetization parameter distribution as long as the range of the magnetization parameter is sufficiently wide and the distribution is flat towards high magnetization. Interestingly, this model can also explain the peak of the diffuse neutrino spectrum at $\sim30$ TeV.
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Solar and Stellar Astrophysics

Multiple Extreme Ultraviolet Peaks Attributed to Three-dimensional Magnetic Reconnection in a Long-duration Solar Flare

Shihan Li, Jinhan Guo, Wensi Wang et al. (+5 more)

Solar flares are a major driver of hazardous space weather, whose intense electromagnetic emissions and energetic particles can significantly disturb the near-Earth space environment. Therefore, understanding the physical processes during a solar flare and predicting its radiation profiles are of great importance. In this study, we analyze and model an M1.4 two-ribbon long-duration flare, whose multiple extreme-ultraviolet (EUV) emission peaks are found to correspond to different three-dimensional (3D) magnetic reconnections driven by the continuous evolution of a flux rope. In particular, the second and third peaks in the 335 Å EUV channel originate from longer and higher flare loops with extended cooling times, formed by reconnection between flux-rope field lines and ambient sheared-arcade field lines ($ar\text{--}rf$) and between flux-rope field lines themselves ($rr\text{--}rf$). These results are supported by the drifting of the flux-rope footpoint (and flare ribbon) and the decrease in toroidal flux of the flux rope, as well as by the connectivity transfer of representative field lines in the magnetohydrodynamic (MHD) simulation. This work points out, for the first time, new manifestations of the 3D flare scenario in EUV light curves. On the one hand, it provides an explanation for two-ribbon late-phase flares. On the other hand, the conclusions presented here help bridge the gap between imaging observations, EUV light-curve diagnostics, and the magnetic structures of the associated coronal mass ejections.
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All authors Shihan Li, Jinhan Guo, Wensi Wang, Yu Dai, Brigitte Schmieder, Jaroslav DudÍk, Yang Guo, Mingde Ding

High Energy Astrophysical Phenomena

Relativistic Dissipative Magnetohydrodynamics from the Boltzmann equation for 2-particle species gas

Khwahish Kushwah and Gabriel Silveria Denicol

We derive the equations of motion of relativistic magnetohydrodynamics from the Boltzmann equation using the method of moments. We consider a locally electrically neutral system composed of two particle species with opposite charges, with vanishing dipole moment or spin, so that the fluid has vanishing magnetization and polarization. We find that the dynamics of this fluid changes dramatically in the presence of a magnetic field. The shear stress tensor no longer adheres to a single differential equation; instead, it splits into three non-degenerate components, each evolving according to distinct dynamical equations. Exploring these equations in a Bjorken flow scenario, we find that for large magnetic fields, our theory predicts oscillatory behavior beyond the scope of an Israel-Stewart-like theory.
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Cosmology and Nongalactic Astrophysics

Constraints on CMBR flux due to high-z dust emission

Martin Lopez-Corredoira

Gjergo & Kroupa (2025) have proposed a new foreground CMBR component produced by dust associated with the progenitor clouds at $z=15-20$ that led to the formation of massive early-type galaxies, calculating that a minimum of 1.4% and a maximum of 100% of the whole CMBR radiation would be produced by this mechanism. Here, I check how much dust emission is compatible with the spectrum of the CMBR monopole flux measurements within the corresponding errors. COBE-FIRAS monopole is fitted to different models with different dust emissivity spectral indexes ($\beta $) and dispersion of redshifts of the progenitor clouds ($\sigma _d$). Within the realistic values of $\beta \ge 0.5$, $\sigma _d\ge 0.8$, the contamination of CMBR flux by high $z$ dust should be $<1.3$% (95% CL).
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Instrumentation and Methods for Astrophysics

Gaia Data Release 4: Modelling of drift-scan related effects in Gaia's point spread function

Nicholas Rowell, Michael Davidson, Nigel C. Hambly et al. (+5 more)

An accurate model of the point spread function is required in order to estimate positions and brightnesses of stars in digitized images. The PSF of the Gaia space telescope is unusual due to the use of drift-scan mode and time-delayed integration, in which the satellite spins and precesses while images are captured. This induces several systematic and periodic distortions in the PSF that are unique to Gaia. These include systematic variations in the stellar image drift rate with respect to the charge transfer rate, and spatial variations in the CCD response that are, contrary to expectations, not marginalised by the use of TDI mode. These must be incorporated into the PSF model in order to reduce systematic errors in Gaia's data products. We have developed a semi-analytic model of the PSF, in which the blurring effects of along- and across-scan stellar image motion are modelled analytically, and dependences of the PSF shape on source colour and position within the CCD are calibrated empirically. Constraints on the PSF origin are introduced in order to break a degeneracy with the geometric instrument calibration. Our new PSF model leads to significant improvements in the modelling of observations, particularly around the 11-13 magnitude range in G. This will contribute to reductions in the astrometric and photometric uncertainties in the derived data products. Our PSF model was deployed in the Gaia cyclic data processing systems and used in the production of the forthcoming Data Release 4. The linear part of Gaia's PSF is now well understood. Future development work will focus on the handling of several nonlinear effects that depend on the signal level, including charge transfer inefficiency and the brighter-fatter effect. This work will provide a useful reference for users of Gaia data and for other missions that use the same observing principles, such as the proposed GaiaNIR mission.
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All authors Nicholas Rowell, Michael Davidson, Nigel C. Hambly, Lennart Lindegren, Javier Castañeda, Claus Fabricius, Jose Hernández, Dafydd W. Evans

High Energy Astrophysical Phenomena

XRISM Discovery of Multiple Ionized Fe-K Emission and Absorption Components in Centaurus A

Taishu Kayanoki, Yasushi Fukazawa, Junjie Mao et al. (+13 more)

We present the first clear detection of ionized Fe-K emission and absorption components in the nearby radio galaxy Centaurus A, revealed by the high-resolution XRISM/Resolve detector. In the 6.5-6.9 keV band, XRISM reveals multiple Fe XXV and Fe XXVI emission components. One is a broad (with a width of sigma = 3000 km/s) and redshifted (+3400 km/s) component, originating at D = 0.02 pc from the central black hole. The other two components are narrow (with a width of sigma = 500 km/s) and exhibit redshifted and blueshifted velocities (+2600 km/s and -1500 km/s), originating from more distant regions (D = 0.1 pc). The photo-ionized model explains the broader component, while the two narrower components can be explained by either photo-ionization or collisional ionization. One interpretation is that the broader component is an outflow at ~10^2 R_S (R_S; Schwarzschild radius) and the narrow component is a shock-heated plasma close to the torus, with a possible connection to the JWST-discovered outflow outside the torus. Two blueshifted absorption lines are detected at ~7.1 keV (~10^4 km/s) and ~10.6 keV (~10^5 km/s). The line significance of the 10.6 keV line is above 98%. The absorption line components might be attributed to the broad emission component. These results demonstrate the high potential of XRISM/Resolve to characterize ionized emission and absorption features in the Fe-K band. Our findings establish a new benchmark in the study of circumnuclear environments in low-luminosity radio galaxies, thereby contributing to a broader understanding of AGN unification.
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All authors Taishu Kayanoki, Yasushi Fukazawa, Junjie Mao, Jon M. Miller, Luigi Gallo, Tahir Yaqoob, Richard Mushotzky, David Bogensberger, Misaki Mizumoto, Kouichi Hagino, Hirofumi Noda, Yoshihiro Ueda, Makoto Tashiro, Yuya Nakatani, Toshiya Iwata, Misaki Urata

High Energy Astrophysical Phenomena

The magnetic filling in magnetically arrested accretion disk simulations and its impact on the jet in M87

Felix Glaser, Christian M. Fromm, Yosuke Mizuno et al. (+2 more)

Magnetically arrested accretion disks (MADs) in black hole jet launching simulations are very successful in modelling low-luminosity active galactic nuclei (AGN) like M87*. The Fishbone-Moncrief torus is well established for this purpose in numerical astrophysics. The extent of the magnetic vector potential inside the torus that we coin the filling factor has not been studied before in the case of MAD simulations. We employ five 3D general relativistic magneto-hydrodynamics (GRMHD) simulations initialized with large-scale tori, that are immersed in weak, poloidal magnetic fields. To study the impact of the spatial extent of the initial magnetic field, hence the magnetic energy content in the torus, we scale it with the filling factor w.r.t. the poloidal geometric area of the mass density distribution. A common choice of the filling factor is complimented and investigated in terms of altered energetics and angular momentum transport. Further, we investigate the polarized, radiative imprints of synchrotron emission on M87 at 86 GHz, comparing them with VLBI observations. Our simulations show that elevated filling factors significantly increase the electromagnetic energy contributions and outward angular momentum transport in the jet, due to the initially increased magnetic energy-content in the torus. High magnetic fillings exhibit increased linear polarization fractions, agreeing with the observed 15$\%$ in M87*. We find the jet morphology more prone to disk-vertical flux tubes generated by MAD events. We show, that GRMHD simulations bracket the jet width measurements at the jet base in M87*. Increased magnetic filling of the torus produces jets that are noticeably brighter downstream compared to our reference models, hence, we find high fillings well suited for extended GRMHD jet models of other low-luminosity AGN, as well.
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All authors Felix Glaser, Christian M. Fromm, Yosuke Mizuno, Matthias Kadler, Karl Mannheim

Astrophysics of Galaxies

A Salpeter IMF and an NFW halo: Disentangling the dark and stellar mass of an elliptical galaxy through precise lens modelling of a double-source-plane system

Tian Li, Thomas E. Collett, Coleman M. Krawczyk et al. (+7 more)

We present a strong lensing analysis of the double source plane lens J0946+1006 (colloquially "Jackpot" lens) to measure the inner dark matter density profile, the stellar-to-halo mass ratio, and the stellar initial mass function normalisation using a two component stellar plus dark matter mass model. The stellar mass follows a multi-Gaussian expansion light model with a free global mass-to-light ratio and an allowed radial $M/L$ gradient, while the dark matter is described by an elliptical generalised NFW halo. The double-source-plane geometry provides additional leverage against the mass-sheet transformation and helps constrain the radial mass profile. Despite allowing both a radial stellar $M/L$ gradient and a generalised NFW halo, the data prefer the canonical picture: an approximately constant stellar mass-to-light ratio with a Salpeter-like IMF normalisation, and a dark matter halo consistent with NFW. We infer $M_{\star} = 4.4^{+0.25}_{-0.39}\times 10^{11}\,M_{\odot}$ and an inner halo slope $\gamma_{\rm in}^{\rm halo} = 1.04^{+0.10}_{-0.14}$. The halo mass is $M_{200}^{\rm halo} = 1.11^{+0.37}_{-0.32}\times 10^{13}\,M_{\odot}$, implying $\log_{10}(M_{200}/M_{\star})=1.41^{+0.13}_{-0.14}$. At fixed halo mass, the inferred stellar mass lies $\sim0.1$ dex above typical literature stellar halo mass relations at similar redshift, which is comparable to the intrinsic scatter of these relations. We expect this approach to provide a practical template for future dark matter studies with the large double-source-plane lens samples from Euclid.
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All authors Tian Li, Thomas E. Collett, Coleman M. Krawczyk, Giovanni Granata, Wolfgang J. R. Enzi, Daniel J. Ballard, Natalie E. P. Lines, Ana Sainz de Murieta, Luke Weisenbach, Dan Ryczanowski

High Energy Astrophysical Phenomena

Revisiting the Geminga halo at GeV energies with Fermi-LAT data

Yu Meng, Yun-Feng Liang, Ben-Yang Zhu et al. (+2 more)

Nearby pulsars within $\sim1\,{\rm kpc}$ are considered to be possible sources of 10-500 GeV cosmic-ray positron excess measured by PAMELA and AMS-02. A TeV halo around Geminga is detected by HAWC, and the measurements of its surface brightness profile indicate a slow particle diffusion surrounding the source. This result challenges the pulsar interpretation of the positron excess. The observations at GeV energies provide direct information on the electron/positron density in the GeV nebula, which can offer more direct constraints on the origin of the positron excess. Two previous works have performed analyses on the GeV emission of the pulsar halo, but focused on the energy band above 8 GeV. In this work, we use a longer dataset from the Fermi Large Area Telescope (LAT) to re-analyze the GeV halo emission of Geminga, extending the analysis to cover the energy range of 1-1000 GeV. We find that the analysis in this wider energy range results in a low significance of the halo emission. This can be attributed to the Galactic interstellar emission model being unable to perfectly fit the background over this broader energy range, and due to the low measured halo flux at $<$ 10 GeV energies leading to a mismatch between the observation and model expectation. We also derive the spectral energy distribution of the tentative halo emission, which shows a very hard spectrum in the 1-10 GeV range.
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All authors Yu Meng, Yun-Feng Liang, Ben-Yang Zhu, Xiao-Na Sun, En-Wei Liang

Solar and Stellar Astrophysics

Stellar structure, magnetism and the variational principle

Andrej Čadež, Aleš Mohorič and Massimo Calvani

Matter interacts through two long range forces: gravity and electromagnetism. While all matter contributes to the gravitational potential, electromagnetic effects were traditionally expected to cancel in large systems because positive and negative charges balance. Yet astrophysical objects clearly show long range electromagnetic behavior, so the cancellation cannot be perfect. This paper develops a model for stationary aggregation of matter into a star that consistently includes angular momentum and electromagnetic effects. We reformulate the standard polytropic stellar model as a variational problem and extend it to include the kinetic energy of rigid rotation and the electromagnetic interaction energy between oppositely charged baryonic matter. The electromagnetic contribution to the action is taken to be the minimal energy required to generate the stellar magnetic dipole moment. This energy has two parts: the pure electromagnetic contribution, expressible as a surface integral, and the free energy difference between magnetized and unmagnetized matter, obtained by analyzing a degenerate electron gas in a background of cold ions. Differential forms provide a convenient mathematical framework. The resulting model incorporates electromagnetic effects into stellar structure in a way consistent with linearized general relativity. Although the full system forms a complex open boundary problem, exact solutions exist under simplifying assumptions. The phase diagram predicted by the simplified model shows patterns that may motivate further study of the balance between matter, gravitation, and electromagnetism
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High Energy Astrophysical Phenomena

Pulsar Discoveries from the TRAPUM UHF Survey of Fermi-LAT Sources

Tinn Thongmeearkom, Colin J. Clark, Rene P. Breton et al. (+25 more)

The Fermi Large Area Telescope (LAT) provides advantages for radio pulsar searches by enabling efficient target selection. We can confidently point radio telescopes to the positions of Fermi unidentified gamma-ray sources that have a high probability of hosting a pulsar. As part of Transients and Pulsars with MeerKAT (TRAPUM), we conducted a survey of Fermi-LAT sources using the Ultra High Frequency (UHF; 544-1088 MHz) receiver of the MeerKAT radio telescope. We observed 79 sources that were identified as pulsar-like candidates using a random forest technique from the Fermi-LAT Fourth Source Catalogue. We observed each target for 10 minutes at two separate epochs. As a result, we discovered nine new millisecond pulsars (MSPs) and six slow pulsars. Based on the radio discoveries, we also searched for gamma-ray pulsations, confirming that seven of the newly discovered MSPs are associated with Fermi-LAT sources, and performed joint radio and gamma-ray pulsar timing. Companion mass estimates and evidence of radio eclipses indicate that among the nine MSPs there are three black widows and three redbacks. Lastly, we compared the discovered pulsars in the MeerKAT UHF survey against the previous Fermi sources TRAPUM survey at L band, concluding the superiority of UHF observations in sensitivity to fainter pulsars and in detection rate than L band for finding new gamma-ray MSPs.
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All authors Tinn Thongmeearkom, Colin J. Clark, Rene P. Breton, Marta Burgay, Lars Nieder, Oliver G. Dodge, Brian McGloughlin, Ewan D. Barr, Sarah Buchner, Benjamin W. Stappers, Joanna Berteaud, Elizabeth C. Ferrara, Paulo C. C. Freire, Lina Levin, Scott M. Ransom, Laila Vleeschower, Sergio Belmonte Díaz, Francesca Calore, Ismaël Cognard, Vik S. Dhillon, Jean-Mathias Grießmeier, Ramesh Karuppusamy, Mark R. Kennedy, Michael Kramer, Prajwal V. Padmanabh, Maria A. Papa, Adipol Phosrisom, Benjamin Steltner