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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 3 September

High Energy Astrophysical Phenomena

Nebular Spectra of the Extremely Metal-Poor SN II 2023ufx Over a Year After Explosion: A Massive Progenitor and Unique Circumstellar Environment

Evan Jennerjahn, Michael A. Tucker, Christopher S. Kochanek et al. (+3 more)

We present new observations of the metal-poor ($< 0.1$ $\rm Z_\odot$) Type II supernova 2023ufx and its host galaxy. The deep nebular spectrum, obtained roughly a year after explosion, has a triple-peaked [O I] emission profile suggesting an asymmetric explosion. Comparison to nebular spectra models suggests a zero-age main sequence mass of $ M_{\rm ZAMS} \sim 25-35$ $\rm M_\odot$, which is supported by the low [Ca II]/[O I] emission-line ratio of $\approx0.4$. The diminishing, broad, boxy H$\alpha$ emission and flattening of the light curve in the late ($\sim2$ yr) photometry suggest a complex mass-loss history in the centuries to millennia before explosion. New optical and near-infrared imaging of the host galaxy confirms that it is a dwarf, with a stellar mass of $10^{6.6\pm0.1}$ $\rm M_\odot$ and a SFR of $10^{-2.5\pm0.1}$ $\rm M_\odot$/yr. Results from both SED fitting and galaxy stellar mass-metallicity scaling relations all lead to an environmental metallicity estimate of $0.02-0.07$ $\rm Z_\odot$. Taken together, these observations confirm that SN 2023ufx is the explosion of a very metal-poor, heavily stripped red supergiant.
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All authors Evan Jennerjahn, Michael A. Tucker, Christopher S. Kochanek, Luc Dessart, Willem B. Hoogendam, Benjamin J. Shappee

Instrumentation and Methods for Astrophysics

TNFlow: Amortized Posterior Inference for Trans-Neptunian Object Surface Composition

Agastya Gaur, Cristina M. Dalle Ore and Alessandra Ricca

We present TNFlow, a transformer and normalizing flow architecture for inferring the surface composition of Trans-Neptunian Objects (TNOs) from their reflectance spectra. TNFlow is trained on synthetic spectra generated by the Shkuratov radiative transfer model to act as its inverse. TNFlow takes ${\sim}$0.7s to invert one spectrum on a single CPU core, returning a multimodal posterior over simplex-valid compositions and grain sizes. On synthetic spectra, the highest-weight mode achieves a mean total-variation distance of 0.149 from ground truth on the test split, and the model generalizes well to unseen combinations of known components. Qualitative tests on real JWST spectra show blindness or bias towards some materials. We suggest this could be attributed to either simulator fidelity or the training set.
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Cosmology and Nongalactic Astrophysics

Euclid preparation. The shape of halo profiles in $\Lambda$CDM and non-standard cosmologies

Euclid Collaboration: L. Pizzuti, G. Y. Ferron, A. Ragagnin et al. (+303 more)

We study the shape of three-dimensional and projected dark-matter halo profiles extracted from cosmological $N$-body simulations in $\Lambda$CDM and non-standard cosmologies, using the DUSTGRAIN-PF and DEMNUni suites. The models considered include massive neutrinos, $f(\mathcal{R})$ gravity, and dynamical dark energy. By comparing density, mass, velocity-dispersion, and excess-surface-density profiles up to $5\,r_{500{\rm c}}$, we quantify the differential imprint of non-standard physics on halo structure in view of Euclid cluster WL studies. Our main analysis is performed at $z=1.1$, a high-redshift regime where the weak-lensing signal-to-noise starts to degrade, providing a conservative stress test for detectability; for DUSTGRAIN-PF we additionally analyse $z=0.5$ and $z=0.3$ snapshots. In low-mass haloes ($M_{\rm 200c}<7\times10^{13}\,M_\odot$), $f(\mathcal{R})$ gravity produces deviations of order $10\,\%$ in projected and three-dimensional profiles, especially in the outskirts where screening is less efficient. Massive neutrinos partially reduce this signal, reflecting the competition between free streaming and fifth-force-enhanced growth. Dynamical dark energy and massive-neutrino cosmologies generally induce smaller, few-percent deviations, with the largest effects again found in low-mass haloes and at large radii. Under simplified assumptions for \Euclid WL, detecting such profile differences at $z=1.1$ requires stacks of $\sim10^5$ haloes, while a few thousands haloes may be sufficient at $z\lesssim0.5$. This further calls for the need of integrating such precise modelling of non-standard effects – along with other observational effects – in any likelihood involving Euclid WL masses to avoid non-negligible systematic biases. Concentration–mass relations show weaker cosmology dependence, typically at the $\sim5\,\%$ level. [...]
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All authors Euclid Collaboration: L. Pizzuti, G. Y. Ferron, A. Ragagnin, A. M. C. Le Brun, P.-S. Corasaniti, T. Gayoux, G. Rácz, E. Altamura, Z. Sakr, C. Carbone, M. Baldi, C. Giocoli, T. Castro, F. Pace, J. E. Taylor, S. Borgani, O. Luongo, C. T. Mpetha, R. E. Angulo, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, S. Bardelli, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, S. Camera, V. Capobianco, V. F. Cardone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, F. Faustini, S. Ferriol, F. Finelli, P. Fosalba, S. Fotopoulou, M. Frailis, E. Franceschi, M. Fumana, L. Gabarra, S. Galeotta, K. George, B. Gillis, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, S. Hemmati, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, K. Kuijken, M. Kunz, H. Kurki-Suonio, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, M. Magliocchetti, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, N. Mauri, S. Maurogordato, E. Medinaceli, S. Mei, M. Meneghetti, E. Merlin, G. Meylan, P. Monaco, A. Mora, M. Moresco, C. Moretti, L. Moscardini, E. Munari, C. Neissner, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, V. Pettorino, A. Pezzotta, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, I. Risso, E. Romelli, M. Roncarelli, R. Saglia, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, A. Secroun, E. Sefusatti, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, J.-L. Starck, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, E. A. Valentijn, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, A. Zacchei, G. Zamorani, F. M. Zerbi, E. Zucca, M. Ballardini, P. Bergamini, A. Boucaud, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, F. Caro, J. A. Escartin Vigo, J. García-Bellido, T. Gasparetto, J. Macias-Perez, R. Maoli, R. B. Metcalf, M. Pöntinen, E. Sarpa, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, J. A. Acevedo Barroso, Y. Akrami, I. T. Andika, S. Anselmi, M. Archidiacono, G. Aricò, F. Atrio-Barandela, M. Baes, L. Bazzanini, D. Bertacca, M. Bethermin, F. Beutler, A. Blanchard, L. Blot, H. Böhringer, M. L. Brown, S. Bruton, A. Calabro, B. Camacho Quevedo, C. S. Carvalho, F. Cogato, T. E. Collett, S. Conseil, A. R. Cooray, P. Corcho-Caballero, M. Costanzi, B. Csizi, O. Cucciati, T. de Boer, F. De Paolis, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, Y. Fang, A. Farina, A. Finoguenov, F. Fontanot, A. Franco, Y. Fu, K. Ganga, R. Gavazzi, E. Gaztanaga, Z. Ghaffari, F. Giacomini, F. Gianotti, E. J. Gonzalez, G. Gozaliasl, A. Gruppuso, M. Guidi, C. M. Gutierrez, A. Hall, N. A. Hatch, C. Hernández-Monteagudo, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, J. Kim, C. C. Kirkpatrick, A. Kovács, I. Kovačić, K. Koyama, S. Kruk, M. C. Lam, M. Lattanzi, L. Legrand, M. Lembo, G. Leroy, G. F. Lesci, J. Lesgourgues, L. Linke, A. Manjón-García, F. Mannucci, F. R. Marleau, C. J. A. P. Martins, M. Migliaccio, M. Miluzio, G. Morgante, S. Nadathur, K. Naidoo, A. Navarro-Alsina, S. Nesseris, F. Oppizzi, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, C. Pattison, R. Paviot, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, G. Rodighiero, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, A. Schneider, D. Sciotti, E. Sellentin, S. Serjeant, F. Shankar, L. C. Smith, J. G. Sorce, I. Szapudi, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, C. Uhlemann, C. Valieri, A. Venhola, D. Vergani, G. Verza, P. Vielzeuf, S. Vinciguerra, M. von Wietersheim-Kramsta, L. Wang, A. H. Wright, H. W. Yeung

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

Confronting the Higgsino Interpretation of the LZ Event with the High-Energy Sideband

Nicholas L. Rodd, Benjamin R. Safdi, Tracy R. Slatyer et al. (+1 more)

The LZ experiment has reported a single 248 keV nuclear recoil event in their $2.84$ ton-yr exposure on a xenon target. The absence of lower nuclear recoil events is naturally explained by inelastically scattering dark matter (DM), for which the nuclear recoil energy spectra are shifted upwards from zero. Excitingly, the observed rate and spectra are consistent with a thermal $1.1$ TeV higgsino that explains all of DM with a mass splitting $\delta \sim 370 - 490$ keV between the two lowest-lying Majorana states, with the range depending on the underlying DM velocity distribution. In this work, however, we show that higgsino DM with these properties would generically produce more higher-energy recoil events in a high-energy sideband along the LZ $S1c$ energy axis, while the LZ experiment reports no events in that bin. This suggests a possible tension which could be further explored by the LZ Collaboration, as the acceptance in that bin is not public. We further show that a non-thermal $\sim$500 GeV higgsino may evade the sideband constraint and that future experiments using heavy targets can potentially test the higgsino interpretation of the event either way.
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All authors Nicholas L. Rodd, Benjamin R. Safdi, Tracy R. Slatyer, Weishuang Linda Xu

High Energy Astrophysical Phenomena

Low-angular-momentum accretion shocks can power weak-to-moderate X-ray flares from SgrA*

Samik Mitra, Bożena Czerny, Michal Zajaček et al. (+1 more)

X-ray flares from Sgr~A* span broad ranges in duration, fluence, and luminosity, but their origin remains unsettled. We test whether standing shocks in low-angular-momentum magnetized accretion flows can provide a viable energy reservoir to account for these events. Using semi-analytic trans-magnetosonic shock solutions, we estimate the kinetic energy available in the downstream post-shock flow and compare it with the 25-year Chandra X-ray flare catalog. For each theoretical solution, we compute the required efficiency $\epsilon=E_{\rm data}/E_{\rm sh}$, where $E_{\rm data}$ is the observed radiated energy for each flare and $E_{\rm sh}$ is the available energy in the shocked flow. Notably, the weak flares require $\epsilon\sim10^{-3}$–$10^{-2}$, while moderate flares require a few percent. We perform the analyses for weakly and highly spinning cases, and the resulting weak-to-moderate flare energy budget remains unchanged. For the fiducial accretion rate and bolometric correction, the kinetic energy reservoir in standing shock is sufficient for the observed weak-to-moderate flare population, whereas the strongest events likely require higher efficiency which can be mediated via additional magnetic energy dissipation channel.
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All authors Samik Mitra, Bożena Czerny, Michal Zajaček, Zach Sumners

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

Inelastic Signatures of Electroweak Dark Matter

Juri Smirnov, Spencer Griffith and John F. Beacom

Minimal dark matter extended to include a Majorana and a Dirac multiplet coupled through the Higgs — the HC-MDM model — provides a compelling and predictive framework. We show that in certain limits of this model, the mass splitting and the inelastic interaction are representation-independent, while the thermal-relic masses are representation-dependent. We then show that this model can account for the high-energy recoil event recently reported by LUX-ZEPLIN (LZ) while also respecting thermal-relic, elastic-scattering, and solar-capture constraints. Generic inelastic DM models do not connect all these tests and generic Higgsino models do not survive them.
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Cosmology and Nongalactic Astrophysics

The moving lens effect: analytical modelling and foreground suppression

Amy Wayland, David Alonso and William Coulton

The moving lens (ML) effect is a secondary anisotropy of the cosmic microwave background (CMB) generated by the transverse motion of gravitational potentials, providing a direct probe of the large-scale cosmic velocity field. Its detection relies on cross-correlating a CMB map with the transverse galaxy momentum field, constructed from the galaxy overdensity and a velocity field reconstructed from it. Restricting the reconstruction to large-scale modes strongly suppresses contamination from small-scale astrophysical foregrounds while preserving the ML signal. In this work, we develop a theoretical framework for the ML estimator and its foreground contamination. We show that the signal and foregrounds have a distinct dependence on the direction of the long-wavelength mode represented by the reconstructed galaxy velocity. In the squeezed limit enforced by the velocity reconstruction filter, the bispectrum sourcing the foreground correlation becomes independent of this direction, causing its leading contribution to vanish after angular averaging. In turn, the ML signal survives by matching this directional dependence, with its amplitude reduced only by the filtered velocity variance. Using the halo model, we derive the leading corrections beyond the squeezed limit and show that the residual contamination remains parametrically suppressed. Finally, we model the cross-correlation exactly in the curved sky, and show that it is sourced solely by the longitudinal component of the galaxy momentum field, in the form of a spin-1 $E$-mode, with all other contributions either strongly suppressed on small scales or exactly zero.
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Astrophysics of Galaxies

Fundamental differences in the X-ray accretion properties of low and high-excitation radio galaxies

R. Kondapally, T. Holc, J. Aird et al. (+7 more)

We characterise the accretion rate properties of radio-detected AGN by combining deep radio and X-ray observations of the Boötes field. We used deep international LOFAR telescope observations to identify 2840 radio-AGN across $0.3 < z \leq 2$, divided into samples that are complete in radio luminosity. We further split this sample into four different classes: radio-quiet AGN (RQ-AGN), high-excitation radio galaxies (HERGs), and low-excitation radio galaxies (LERGs) hosted by star-forming (SF-LERGs) and quiescent galaxies (Q-LERGs). Through performing X-ray stacking, we determined the average X-ray luminosities, $L_{\rm{X, 2-10\,keV}}$ and average specific X-ray luminosities, $\lambda_{sL_{X}}$ (X-ray luminosity scaled by the stellar mass; a proxy for the accretion rate). We studied how these X-ray properties depend on radio luminosity, stellar mass, and redshift for each of the four AGN classes. We found that the LERGs, regardless of their star-formation activity, show significantly lower $L_{\rm{X, 2-10\,keV}}$ and $\lambda_{sL_{X}}$ than both HERGs and RQ-AGN across all redshifts. The average X-ray luminosities for the HERGs, RQ-AGN, and SF-LERGs typically increase with redshift, which may be associated with the increased cold gas fractions at earlier times, resulting in more enhanced black hole accretion. The average X-ray luminosities show weak-to-no correlation with radio luminosity at a given redshift, suggesting that the physical processes producing the X-ray and radio emission may not be coupled on spatial and/or temporal scales.
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All authors R. Kondapally, T. Holc, J. Aird, K. J. Duncan, P. N. Best, D. M. Alexander, S. Das, L. K. Morabito, S. Shenoy, D. J. B. Smith

High Energy Astrophysical Phenomena

A targeted search for fast radio bursts from magnetars in elliptical galaxies

S. Paine, D. R. Lorimer, S. Sirota et al. (+12 more)

Motivated by predictions that globular clusters associated with nearby giant elliptical galaxies are prime environments for detecting fast radio bursts (FRBs) from magnetars, we report on a targeted high-sensitivity search across five local massive elliptical galaxies. We utilized the GREENBURST single-pulse search pipeline and the VEGAS backend on the Green Bank Telescope (GBT) to conduct an L-band (1.4 GHz) survey for FRBs in each target environment. We discovered FRB 20240817A in the direction of M49 (NGC 4472) which has a pulse width of 15 ms, a signal-to-noise ratio of 13, and a dispersion measure (DM) of $983~\rm{cm}^{-3}$ pc. Although a Bayesian spatial association framework initially flags M49 as the host, carefully accounting for the foreground electron column contributions from the Milky Way and both the Virgo intracluster medium and M49's hot gaseous halo ($\sim300-400~\rm{cm}^{-3}$ pc combined) strongly disfavours a physical connection. We conclude that FRB 20240817A is a background event. We also identified a repeating cluster of three low-significance pulses from the direction of M49 at a physically plausible DM of $150-160~\rm{cm}^{-3}$ pc. Accounting for the fraction of each target's extended globular cluster distribution observed, the absence of unambiguous, host-localized bursts allows us to place a joint upper limit on the intrinsic burst rate of a single active source within these systems of $R_0 < 0.028~\rm{hr}^{-1}$ (and an integrated rate limit of $<1.0$~hr$^{-1}$ for M49), lowering previous upper limits and suggesting that magnetar formation within dynamical clusters is less efficient than previously assumed.
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All authors S. Paine, D. R. Lorimer, S. Sirota, G. M. Doskoch, S. Tabassum, M. Flanagan, J. Lituchy, A. Stone, J. W. Kania, M. Bhardwaj, S. Mehta, M. A. McLaughlin, B. Kharel, D. Agarwal, M. P. Surnis

Cosmology and Nongalactic Astrophysics

Consistency between cosmological and standard siren observations in evolving dark energy

Macarena Lagos and William J. Wolf

A scalar field non-minimally coupled to gravity can be the driver of cosmic acceleration. Such a non-minimal coupling (NMC) can produce a non-zero gravitational-wave (GW) friction function $\alpha_M(z)$, which modifies the luminosity distance inferred from GW sources relative to its electromagnetic counterpart. We use a particular NMC scalar-tensor model, that explains time-varying dark energy in good alignment with DESI, to predict $\alpha_M(z)$ and the expected GW/EM luminosity-distance ratio $D_L^{\rm GW}/D_L^{\rm EM}$, and map it onto two common parametrizations—the $c_M$ and the $(\Xi_0,n)$ models. We find $c_M = -0.5\pm 0.2$ and $\Xi_0 = 0.88\pm 0.05$, $n=3.2\pm 0.3$, both consistent with GWTC-5 constraints at the $\lesssim 1\sigma$ level. This consistency is mostly driven by current large uncertainties in GW data, which lead to measurements consistent with both $\Lambda$CDM and the NMC model. By contrast, the dark energy constraints derived from analyzing cosmological data, under the common parametric scalar-tensor model using $\alpha_M(z)=c_M\Omega_\Lambda(z)/\Omega_{\Lambda 0}$ and the CPL parametrized equation of state $w_0w_a$, are in $2.2\sigma$ ($3.6\sigma$) tension with the NMC predictions for the $c_M$ ($w_0w_a$) parameter. We confirm that, in order to avoid cosmological instabilities, this parametrized model imposes strong implicit priors that are incompatible with physically-motivated scalar-tensor models when dark energy is dynamical.
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Astrophysics of Galaxies

Absolute Motion of the Infrared Counterpart to Sagittarius A* in the Gaia Celestial Reference Frame 3 and Limits on an Intermediate-mass Black Hole Companion

Rebecca A. Lewis-Merrill, Tuan Do, Matthew W. Hosek Jr. et al. (+9 more)

We report the first proper motion and acceleration measurements of the infrared (IR) counterpart to Sagittarius A* (Sgr A*-IR), the supermassive black hole (SMBH) at the center of our Galaxy, in the Gaia-Celestial Reference Frame (Gaia-CRF3). This reference frame realizes the International Celestial Reference System (ICRS), which is an absolute reference coordinate system defined by quasars. A combination of Gaia and Hubble Space Telescope data was used to transform Keck adaptive optics (AO) observations into Gaia-CRF3. We developed a method for selecting reference stars that minimizes astrometric transformation errors (statistical error = $0.10-0.63$ mas) and drift of the coordinate system (systematic error $\sim 0.01$ mas/yr). We find the proper motion of Sgr A*-IR in Gaia-CRF3 to be $\mu_{\alpha^{*}} = -3.093 \pm 0.085$ mas yr$^{-1}$ and $\mu_{\delta}= -5.62 \pm 0.13$ mas yr$^{-1}$ with the initial position at $t_{0} = 2016.0$ of R.A. = 266.41680848 $\pm$ 0.00000029 deg and DEC = -29.00783947 $\pm$ 0.00000050 deg, which translates to a precision of 1.05 mas in R.A. and 1.79 mas DEC. This is consistent with the astrometric measurements of the radio counterpart to Sgr A* by \citet{Xu_2022}. We also place a $2\sigma$ upper constraint of the acceleration of Sgr A*-IR on the sky at 0.061 mas yr$^{-2}$. This acceleration limit on Sgr A*-IR excludes any intermediate-mass black hole companion with mass $\gtrsim 4\times 10^{4}$ $M_{\odot}$ within a distance of $\sim$0.01 pc, consistent with previous studies. With the release of Gaia Data Release 4, we predict these limits will be improved by at least a factor of two.
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All authors Rebecca A. Lewis-Merrill, Tuan Do, Matthew W. Hosek Jr., Gregory David Martinez, Shoko Sakai, Kelly Kosmo O'Neil, Grant Weldon, Abhimat Gautam, Zoë Haggard, Andrea M. Ghez, Jessica R. Lu, Keith Matthews

High Energy Astrophysical Phenomena

Sgr A* as a Galactic PeVatron: Multimessenger Signatures of the Magnetic Penrose Process

Marina Cermeño, Pedro De la Torre Luque, Cristina Fernández-Suárez et al. (+5 more)

The magnetic Penrose process (MPP) is one of the most efficient mechanisms for extracting rotational energy from a magnetized Kerr black hole (BH), enabling charged particles to reach very-high energies. We investigate this process in Sagittarius A* (Sgr A*), the supermassive BH at the Galactic center (GC), focusing on its ultra-high-efficiency regime, in which neutrons undergo beta decay inside the BH ergosphere. As a key novelty, we compute the neutron production spectrum in the accretion flow directly from the nuclear reaction kinematics and follow neutron trajectories in the Kerr spacetime to determine the population that reaches the ergosphere and undergoes the MPP. From this population, we derive the spectrum of accelerated protons and show that Sgr A* can accelerate them up to PeV energies, strengthening its interpretation as a candidate Galactic PeVatron. We further compute the gamma-ray and neutrino emission produced through hadronic interactions of the escaping protons in the Central Molecular Zone. The predicted gamma-ray fluxes exhibit distinctive spectral features that could provide an observational signature of the MPP and may constitute a non-negligible contribution to the very-high-energy emission detected by H.E.S.S. and HAWC. The associated neutrino fluxes remain below the diffuse Galactic component inferred by IceCube, but may still contribute to the high-energy emission from the GC. Remarkably, the predicted signals lie within the projected sensitivity of SWGO for all scenarios considered here and, for some models, only a factor of a few below the nominal CTAO sensitivity, while KM3NeT/ARCA and IceCube-Gen2 will provide complementary tests. Our results establish the MPP as an observable mechanism for extracting BH rotational energy, providing a direct connection between horizon-scale physics and multimessenger observations that can be extended to other magnetized BHs.
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All authors Marina Cermeño, Pedro De la Torre Luque, Cristina Fernández-Suárez, Viviana Gammaldi, Enrique Mier-Alonso, María J. Rodríguez, Miguel Á. Sánchez-Conde, Jaume Zuriaga-Puig

Solar and Stellar Astrophysics

Ionized Nebulae Around Two New Symbiotic Stars: GR Cygni and [D75] 141

Howard E. Bond, Calvin Carter, Sven E. Eklund et al. (+4 more)

In the course of selecting targets for a spectroscopic survey of faint planetary-nebula nuclei, we encountered two anomalous cases of late-type variable stars surrounded by nebulosities discovered by amateur astronomers. We obtained follow-up deep narrow-band images of the two nebulae: StDr Objet 14 (diameter 1.5 arcmin) and StDr 4 (diameter 2.5 arcmin). StDr Objet 14 is found to be a low-excitation nebula, bright only in Ha+[N II], and showing a unique double-ring "bull's-eye" morphology. StDr 4 exhibits a bow-shock structure, bright in Halpha and [S II], embedded in an extended emission nebula. Both central stars, respectively GR Cygni and [D75] 141, are found to be pulsating semiregular variable stars. Our spectroscopic observations show GR Cyg to be a cool carbon star of type C9,2, with emission lines of the Balmer series, [O II] and [O III], [Ne III], [S II], and Fe II. A synthetic narrow-band image of GR Cyg shows that the source of its strong [O II] 3727 A emission line is a knot displaced from the star by about 1.6 arcsec, indicative of a recent collimated ejection event. [D75] 141 is a M6 III red giant, with weak Balmer-series emission. Both stars show a blue excess, and GR Cyg was detected in the near-UV by the GALEX spacecraft. These data establish both stars as new symbiotic binaries, containing a late-type red giant and a hot companion accreting from its stellar wind. We speculate that the double rings surrounding GR Cyg were ejected during helium-shell thermal pulses (or conceivably from recurring nova outbursts), while the nebula around [D75] 141 may be the result of a collision of the symbiotic star's ejecta with an interstellar cloud. Our accidental discoveries of these two binaries because they are surrounded by faint nebulae supports the view that there is a significant population of "missing" symbiotic stars yet to be discovered.
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All authors Howard E. Bond, Calvin Carter, Sven E. Eklund, Peter Goodhew, Ulisse Munari, Jonathan Talbot, Gregory R. Zeimann

Astrophysics of Galaxies

Two sets of potential-density basis pairs for the study of radial perturbations in collisionless spherical stellar systems

E. V. Polyachenko and I. G. Shukhman

The Kalnajs matrix method is a widely used framework for studying the global linear stability and possible Landau damping of collisionless stellar systems. However, for radial perturbations ($l=0$) in three-dimensional spherical models with infinite boundaries, standard biorthogonal sets such as the Clutton-Brock basis often converge slowly. This stems from a physical constraint: mass-conserving radial modes force the perturbed potential to decay faster than a point mass at infinity, whereas individual Clutton-Brock elements carry a fictitious net mass and decay only as $\mathcal{O}(1/r)$, producing unphysical asymptotic tails. We construct two new families of potential-density basis pairs that are free of these tails by construction. The first modifies the Clutton-Brock set: a specific linear combination of adjacent elements analytically cancels the leading $\mathcal{O}(1/r)$ term, giving potentials that decay as $\mathcal{O}(1/r^3)$ and densities as $\mathcal{O}(1/r^5)$. This breaks strict biorthogonality but yields a compact tridiagonal Gram matrix that enters the response equation at negligible additional cost. The second family is built from Jacobi polynomials that embed the required $\mathcal{O}(1/r^2)$ potential decay directly into their construction while retaining strict diagonal biorthogonality. Numerical tests demonstrate convergence that is uniform in radius for both expansions: the truncation error decreases exponentially when the asymptotic tail of the expanded potential matches the parity of the basis elements, and algebraically otherwise. Both bases reduce the dimension of the response matrix required for a given accuracy and are suited to studying radial perturbations in open stellar systems.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Eight Local Couplings of Gravitational Waves from Unified Field Equations

Hong-Bo Jin and Yue-Liang Wu

A gravitational-wave (GW) detector records a linear mixture of local couplings under the assumption that extra polarizations enter geodesic deviation. Vacuum general relativity (GR) admits two transverse-traceless (TT) amplitudes. It remains to determine the largest set of couplings that can sit in that mixture, and whether a tensor-only arm-length result selects GR uniquely. The little group \(E(2)\) of a null four-momentum classifies the strain amplitudes \(\mathbf{p}=(p_{+},p_{\times},p_{x},p_{y},p_{b},p_{\ell})\), commonly written \(h_{P}\), which determine the electric tidal tensor along a ray. Geodesic deviation, recorded as differential arm length, therefore contains only those \(p_{P}\) that enter that tensor. Lorentz mixing at helicity \(\pm1\) supplies a gravito-magnetic (GEM) field that does not enter the tidal tensor. if GEM field is static, that does not propagate as a wave. A time-varying helicity-\(\pm1\) current sources a GEM wave that enters the mixture as a coupling, to be isolated by its measured quantity. For a radiation-zone wave that depends only on retarded time, \(\betag_{\perp}=\hat{\mathbf{k}}\times\partial_{t}(p_{x},p_{y})\), and the eight couplings are \(\Pvec=(\mathbf{p},\betag_{\perp})\). Here we adopt unified field equations on \(\mathbf{p}\) to clarify the origin of each component of \(\Pvec\); the measured quantity of each coupling then isolates the polarizations in that mixture, which favors identification of distinct polarizations and model tests.
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Earth and Planetary Astrophysics

Detection of hydrocarbons in Titan using high-resolution cross-correlation spectroscopy

Maria Coelho, Rafael Rianço-Silva, Diogo Gonçalves et al. (+2 more)

High-resolution cross-correlation spectroscopy (HRCCS) is a powerful technique for detecting molecules whose individual spectral lines are too weak to be identified directly, but its sensitivity is limited by the availability and quality of high-resolution opacity data. Many molecules of atmospheric and astrobiological interest lack complete line lists, restricting traditional template-based searches. In this work, we use Titan as a controlled testbed to develop and validate a new cross-section-based methodology for HRCCS template construction. We analyse K-band CRIRES+ observations of Titan (1.99 - 2.48 {\mu}m), and compute cross-correlation functions using both line-by-line and cross-section-based templates. Our analysis recovers known hydrocarbons such as methane (CH4) and acetylene (C2H2), and yields the first HRCCS detection of ethane (C2H6) with a significance of SNRpeak = 5.17 {\pm} 0.07. The ethane detection was made possible exclusively through cross-section-based templates, as no high-resolution line list currently exists for this molecule. These results demonstrate that cross-section-based template construction is a practical and powerful strategy for extending HRCCS to molecules that currently lack reliable line lists, and establish Titan as a benchmark for calibrating molecular detection techniques that can be applied to both solar system and exoplanet atmospheres. Future applications of this approach to other ground-based high-resolution spectrographs, as well as to JWST's highest-resolution modes and next-generation facilities such as the ELT, could significantly expand the inventory of molecules detectable in planetary atmospheres.
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All authors Maria Coelho, Rafael Rianço-Silva, Diogo Gonçalves, Pedro Machado, Zita Martins

High Energy Astrophysical Phenomena

Ultra-compact twin stars with hybrid equations of state from bosonic dark matter

Ishfaq Ahmad Rather, Sarah Louisa Pitz and Jürgen Schaffner-Bielich

The properties of compact stars with a strong first-order phase transition to quark matter and with an additional fluid of self-interacting bosonic dark matter (DM) are studied. We find that the inclusion of DM changes considerably the stability of mass-radius configurations relative to the naive one-fluid criterion. For compact star configurations with similar masses and different radii, so-called twin stars, the presence of DM removes the unstable segment between the hadronic and the hybrid branch, so that the stable mass-radius sequence becomes continuous after the onset of the phase transition to quark matter. We furthermore find stable ultra-compact objects (UCOs), defined by a total compactness $C = M_\text{tot}/R_\text{grav} \ge 1/3$. We observe two distinct classes of UCOs: a DM-halo class with $f_\text{DM} \gtrsim 0.9$, and a DM-core class at $f_\text{DM} \lesssim 0.02$. The two classes can be separated by the surface redshift of the normal matter, which reaches $z=0.73$–$0.77$ for the DM-core class and stays below $0.45$ for the DM-halo class. Finally, we find hybrid star solutions of 'ultimate twins' with similar mass and visible radius, but different dark matter content, leading to different tidal deformabilities and surface redshifts. Future X-ray and gravitational measurements of ultra-compact neutron stars with radii and masses outside the allowed neutron star range can thereby probe the presence and the properties of DM in addition to a first-order phase transition to quark matter.
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Solar and Stellar Astrophysics

Interferometric Survey of Stellar Parameters: Mass of the metallic A-type binary $\beta$ Aur

J. Jonák, D. Mourard, J. D. Monnier et al. (+23 more)

With the capabilities of the new visible CHARA/SPICA instrument and the multiple spectral band operation of CHARA, our goal is to resolve orbits of short-period binaries and develop a robust framework for combining interferometric, spectroscopic, and photometric observations into a single consistent model. For our target sample, we selected suitable binaries based on brightness, angular separation, and orbital properties based on the expected performance of the CHARA/SPICA instrument. As a case study, we analysed the bright eclipsing binary $\beta$ Aurigae, composed of two slightly evolved A1 stars. We combined new interferometric observations of $\beta$ Aur obtained with CHARA/SPICA, MIRC-X, and MYSTIC with archival MIRC data, radial velocities, and light curves. We first derived astrometric positions from interferometric observables and computed an orbital solution. Afterwards, we implemented a unified model, capable of tying interferometric modelling with the ellc code to simultaneously fit all observables using MCMC sampling. We performed a detailed analysis of the noise statistics of each data set and in the end we adopted a profile likelihood approach to account for underestimated noise and systematics. We derived a consistent orbital and physical solution for $\beta$ Aur through joint modelling. The inclusion of interferometric data tightly constrains the angular semi-major axis and inclination. Using profile likelihood to account for the different intrinsic levels of uncertainty of the fundamentally different observables, we derived the masses of the two stars, $M_1 = 2.359 \pm 0.005$ M$_S$ and $M_2 = 2.293 \pm 0.004$ M$_S$, their radii $R_1 = 2.752 \pm 0.002$ R$_S$ and $R_2 = 2.622 \pm 0.002$ R$_S$, and the distance to the binary, $d = 24.30\pm0.05$ pc.
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All authors J. Jonák, D. Mourard, J. D. Monnier, S. Hoin, M. Brož, A. Oplištilová, K. A. Kubiak, N. Ebrahimkutty, R. V. Ibañez-Bustos, H. Nowacki, M. Vrard, M. Bailleul, P. Bério, J. Dejonghe, R. Ligi, F. Morand, N. Nardetto, D. Salabert, S. Deheuvels, A. Domiciano de Souza, A. Meilland, K. Perraut, M. Wittkowski, S. Kraus, N. Anugu, M. Gutierrez

Earth and Planetary Astrophysics

Properties of Seasonal Ice at Sisyphi Cavi and Implications for Current Modification of Martian Gullies

Apolline Leclef, Mathieu Vincendon, Cateline Lantz et al. (+7 more)

Martian gullies are geologically recent landforms that may form either through liquid-water activity and/or through processes involving CO2 ice. We investigated the mechanisms responsible for the formation or modification of these features by focusing on the active site of Sisyphi Cavi (68{\deg}S, 1{\deg}E), located outside the typical latitude range of gully presence. Using CRISM and OMEGA infrared data, we characterized the composition and physical state of seasonal surface ices to test the relevance of H2O and CO2 ice driven mechanisms. Our analysis shows that H2O ice is not detected as an independent surface deposit, although it may be present as minor inclusions within the CO2 ice layer. In particular, during the final phase of CO2 ice sublimation in late spring, no H2O ice signature is observed. In the area, faint spectral signatures of sulfate salts are observed, but their distribution and amount do not suggest any direct link with gully activity. Available observations during early and mid-spring reveal that CO2 ice is translucent during these times, suggesting that it likely remains in this state through most of the ice season. However, a temporal mismatch between dark spot formation - indicative of CO2 geysers through translucent ice - and gully modification (respectively occurring late winter to early spring, and mid to late spring) exists. This does not suggest a systematic link between both processes. Overall, the available observations provide no evidence that liquid water contributes to present-day gully activity at Sisyphi Cavi, while offering no support either for the hypothesis that gully modifications are mainly driven by the formation of CO2 geysers. Gully modifications at Sisyphi Cavi, observed during the late sublimation stages of CO2 ice, may be rather more appropriately explained by CO2-ice-based fluidization or avalanche processes.
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All authors Apolline Leclef, Mathieu Vincendon, Cateline Lantz, François Andrieu, Marie Ausseresse, John Carter, Susan J. Conway, Marion Massé, Kelly Pasquon, Frédéric Schmidt

Instrumentation and Methods for Astrophysics

nufftcf: Fast Auto- and Cross-Correlation Function Estimation for Irregularly-Sampled Time Series via the Non-Uniform FFT

Jean-Eric Campagne

Estimating the auto-correlation function (ACF) and cross-correlation function (CCF) of sampled series is a standard task in many physics fields, including astronomy and environmental sciences. We present nufftcf, an ACF/CCF estimator designed primarily for irregularly sampled series, numerically consistent with established kernel-weighted definitions and scaling as O(nK) for K requested lags, rather than O(n^2). nufftcf was initially developed to evaluate the Wiener-Khinchin theorem for irregularly sampled data using the Non-Uniform Fast Fourier Transform (NUFFT), through the Flatiron Institute FINUFFT library, with Gaussian and rectangle kernels. An O(n)-per-lag two-pointer scan replaces the naive O(n^2) computation of the effective pair count used to normalize each lag bin. This enabled real-space estimators using the same kernels, providing exact reference implementations with the same O(nK) complexity and, in some cases, lower cost than the NUFFT path. The library also provides dedicated classical-FFT estimators for regularly sampled data. All estimators share a common calling convention. Using synthetic time series, we validate nufftcf for ACF against pastas, a library used in groundwater time-series analysis, and for CCF against pyZDCF, used in astronomical time-series analysis. Benchmarks confirm O(nK) scaling for the NUFFT and real-space nufftcf estimators, compared with O(n^2) for the pastas slotting technique. nufftcf is already advantageous at moderate series lengths because of its low millisecond-scale overhead. For regularly sampled data, the FFT path further reduces computational cost. We also demonstrate nufftcf on a simulated ground-based stellar light curve combining quasi-periodic rotation, correlated flicker noise, seasonal sampling gaps, and heteroscedastic measurement errors. Notebooks and scripts are provided to reproduce the examples and explore other use cases.
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High Energy Astrophysical Phenomena

A catalogue of insights from the fourth LIGO-Virgo-KAGRA observing run

Christopher P L Berry and Daniel Williams

Over the last decade, gravitational-wave science has developed from an era where a single detection was a Nobel-winning achievement to an (almost) everyday occurrence. The LIGO-Virgo-KAGRA (LVK) Collaboration's flagship scientific results are now their catalogues of detections, which include a comprehensive set of analysis results characterising the astrophysical properties of sources, and their implications for fundamental physics and cosmology. We review discoveries from the fourth observing run (O4) of the LVK network. The most recent catalogues each include $\sim100$ new detections. Among these new detections are remarkable single discoveries: the loudest signals detected so far, and sources unlike those seen before. However, significant advances in the field are coming from population-level analyses, leveraging the increasing sample size to infer constraints on the astrophysical distribution of merging compact binaries, potential deviations to general relativity, and the expansion rate of the Universe. Analyses of the latest data have revealed evidence for multiple subpopulations of sources. These observations provide a unique probe into the evolution of massive stars and the formation of coalescing binaries. Our understanding of gravitational-wave signals and their sources will continue to deepen with more observations. The final catalogue from O4}is due for release in December 2026, and future observing runs with even greater detector sensitivity are planned. These will bring even larger catalogues, and additional loud signals, continuing to advance gravitational-wave science.
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Instrumentation and Methods for Astrophysics

Morphology of Radio Sources in Representation Space

Nicolas Baron Perez, Marcus Brüggen and Luisa Lucie-Smith

Understanding radio source morphologies and their classification remains challenging. We previously developed a deep clustering method based on self-supervised learning to classify a subsample of radio sources from the LOFAR Two-meter Sky Survey DR2. This yielded a labelled subset used to fine-tune an ensemble of classifiers. We aim to identify rare morphological classes in a subsample of LoTSS-DR3, which contains > 13 million sources, beyond the 12 classes previously recognised in the DR2 sample. We further aim to characterise the resulting class distribution. We applied the classifier ensemble to derive class probabilities and representations for our samples. Among DR3 sources with low class probabilities, we searched for new clusters in representation space. Moreover, we use these clusters as centroids to classify the low-probability subset. We found that 88% of the sources fall into clearly separated clusters in representation space, coinciding with the DR2 clusters. Within the remaining sources, we identified representatives of six additional morphological classes, including rare morphologies like winged and FR-ambiguous sources. The number of sources in the resulting 18 classes exhibit a strongly skewed distribution, with four dominant classes constituting 69% of the DR3 sample, while rare morphologies account for only a small fraction. The identification of additional morphological classes shows the possibility of open-set recognition with representation learning in an unexplored dataset. Unlike anomaly detection, which flags individual sources as uncommon, this approach identifies representatives of novel morphological classes, providing a framework for discovering novel source populations. The highly skewed class distribution poses a fundamental challenge for constructing balanced training datasets and highlights the need for open-set approaches in future observations.
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Earth and Planetary Astrophysics

Disk survey in the Serpens star-forming region: Environmental effects in nearby star-forming regions

Simin Tong, Nienke van der Marel, Jonathan P. Williams et al. (+1 more)

The external environment where protoplanetary disks are embedded regulates disk evolution. External irradiation, which heats and evaporates gas, as well as frequent stellar encounters, which truncate disks, can reduce disk sizes and masses. Disk surveys in nearby star-forming regions with various environments can help us understand how external environments impact disk evolution. The Serpens star-forming region, which is thought to be dense but not highly irradiated by massive stars, is an ideal laboratory to study the dynamical effects on disk properties. We aim to study how dynamical interactions modify disk dust masses by comparing Serpens with other nearby star-forming regions through their disk masses and 3D stellar densities. We survey 321 young stellar objects from Class I to III in Serpens using ALMA at 0.25 arcsec. We measure disk dust masses from millimeter observations under the optically thin assumption and recompute the 3D stellar density using Gaia data. We apply the same method to other nearby star-forming regions for direct comparison with Serpens. The cumulative disk dust mass distribution of Serpens is similar to those of similarly aged nearby star-forming regions, such as Lupus and Taurus. Along with re-assessment of the 3D stellar density, it suggests that Serpens is not likely to have experienced strong tidal truncation capable of producing lower disk dust masses. We also find that the low disk dust mass tension in Ophiuchus and Corona Australis can be resolved when only disks that have been explicitly identified as members of young (1-2 Myr) sub-clusters are considered. Disks without Gaia identifications, especially in Ophiuchus, are spatially clustered in the 2D projected sky plane and less massive than nearby disks with Gaia identifications, possibly tracing the effects of tidal truncation in denser environments at earlier evolutionary stages.
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All authors Simin Tong, Nienke van der Marel, Jonathan P. Williams, Alexa R. Anderson

High Energy Astrophysical Phenomena

The Physics of the Nebular Phase in Black Hole X-ray Binaries: Modelling V404 Cygni

A. Ambrifi, T. Muñoz-Darias, J. A. Fernández-Ontiveros et al. (+3 more)

Some of the most extreme galactic black hole transients exhibit a nebular phase at the end of their outbursts. This stage was first identified in the 2015 outburst of V404 Cygni, when it dominated the optical spectrum for ~4 days. It is characterised by exceptionally strong optical emission lines, together with a significant increase in the Balmer decrement. The emission features show broad wings reaching velocities consistent with outflow speeds derived from prominent P-Cygni profiles that preceded the nebular phase. They are thus interpreted as arising from previously launched ejecta that expand and recombine as X-ray irradiation declines. In this work, we modelled this phase using the photoionisation code Cloudy. Adopting simple assumptions for the irradiating continuum and emitting gas, we quantitatively reproduced key observables, such as the Balmer decrement and the H$\alpha$ equivalent width, and qualitatively reproduced the observed spectra. Our simulations show that the Balmer decrement remains roughly stable within the observed range across orders-of-magnitude changes in the density and ionisation parameter, spanning $n_\mathrm{H} \sim 10^{10.5}-10^{12.5}\,\text{cm}^{-3}$ and $-1.5 \lesssim \log\xi \lesssim 1$. This supports the scenario in which the nebular phase can persist through moderate ejecta expansion and cooling, consistent with observations. Finally, we used different approaches to constrain the general properties of the nebular phase, which we propose is produced by clumpy, partially ionised ejecta whose total mass likely exceeds the mass accreted during the outburst.
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All authors A. Ambrifi, T. Muñoz-Darias, J. A. Fernández-Ontiveros, J. Casares, D. Mata Sánchez, J. H. Matthews

Solar and Stellar Astrophysics

New scaling relations from MESA models for mass and radius of subgiant stars: application to Kepler targets

T. Çak{\i}r Alsaç, M. Y{\i}ld{\i}z and S. Örtel

The precise determination of the fundamental parameters of stars is crucial for understanding stellar structure and evolution. In this regard, the asteroseismic parameters of solar-like oscillating stars obtained from space telescopes are very useful for determining the mass ($M$) and radius ($R$) of single stars using classical scaling relations. These relations still need to be improved. In this study, we develop alternative scaling relations based on reference frequencies ($\nu_{\rm min}$) due to helium ionization zone glitches, specifically for subgiant (SG) stars. We compile main-sequence and SG {\small{MESA}} models from the literature and derive new scaling relations for stellar $R$ and surface gravity ($g$) of evolved stars. The expressions for $R$ and $g$ are obtained simultaneously as functions of the large frequency separation, $\nu_{\rm min}$, and metallicity. These new relations allow $M$ and $R$ to be reliably determined only from observational parameters, without the need for detailed stellar modelling. The resulting $\nu_{\rm min}$-based relations are applied to a sample of 31 SG stars observed by the Kepler mission, with masses in the range 0.85-1.74 M$_\odot$ and radii between 1.03 and 2.82 R$_\odot$. Using simultaneous solutions, we estimate new mass and radius ranges of 0.89-1.62 M$_\odot$ and 1.04-2.95 R$_\odot$, respectively. The results demonstrate significant improvements in the determination of $M$ and $R$ for evolved Kepler target stars, highlighting the potential of the new scaling relations in asteroseismic analyses.
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Solar and Stellar Astrophysics

The Role of Preceding CMEs and SIRs in Enhancing Shock Acceleration of Electrons

Xiaomin Chen, Seve Nyberg, Rami Vainio et al. (+3 more)

The role of large-scale pre-existing interplanetary structures, including preceding coronal mass ejections (CMEs) and stream interaction regions (SIRs), in shaping the shock acceleration environment for energetic electrons remains not fully understood. In this study, we investigate nine interplanetary shocks observed by the Solar Terrestrial Relations Observatory (STEREO) that are associated with significant MeV electron enhancements, as such enhancements are rarely observed at interplanetary shocks. We combine remote-sensing observations, drag-based modeling, and in-situ measurements to analyze the shock propagation through pre-existing interplanetary structures. Eight of the nine events are associated with a preceding slow or intermediate-speed CME, while six shocks are in-situ observed propagating within preceding ICMEs, indicating that large-scale upstream trapping structures are a common feature of these events. Further analysis identifies three distinct scenarios associated with enhanced electron acceleration: shocks propagating through preceding ICMEs, shock-SIR interactions, and direct injection of flare-accelerated electrons into SIRs. As a representative shock-in-ICME event, the 2012 January 29 low-$\beta$, quasi-perpendicular shock ($\theta_{Bn}\sim87^\circ$) is further investigated using observations together with one-dimensional Monte Carlo test-particle simulations of a shock propagating into a large-scale upstream magnetic loop. The simulation suggests that the upstream loop prolongs electron residence near the shock and substantially enhances acceleration efficiency. These results demonstrate that large-scale interplanetary structures can precondition the upstream magnetic environment, providing favorable conditions for prolonged electron residence and efficient shock acceleration.
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All authors Xiaomin Chen, Seve Nyberg, Rami Vainio, Immanuel Christopher Jebaraj, Chuan Li, Nina Dresing

Astrophysics of Galaxies

Rapid Growth of Intermediate-Mass Black Holes through Disk-induced Stellar Disruptions

Mengye Wang, Yiqiu Ma, Qingwen Wu et al. (+3 more)

Dense nuclear star clusters provide unique environments for studying the dynamical interactions between stars and massive black holes. When an accretion disk is present, dissipative star–disk interactions can capture surrounding stars, drive their inward migration, and ultimately lead to disk-induced tidal disruption events\,(dTDEs). The long-term feeding rate from this process, however, cannot be inferred from single-orbit migration estimates alone, as it depends on the coupled evolution of disk capture, collisional relaxation, stellar depletion and replenishment, and physical mergers within the star cluster. In this work, we use high-performance direct $N$-body simulations combined with analytic prescriptions for star–disk interactions to follow this coupled evolution for intermediate-mass black holes\,(IMBHs) with accretion disks embedded in dense stellar clusters. The simulations track the formation of the stellar cusp, the capture of stars by repeated disk crossings, their subsequent orbital damping and migration, and their eventual consumption by the central IMBH. We find that dTDEs can sustain stellar mass supply rates of $\sim10^{-3}\,M_\odot \,\mathrm{yr}^{-1}$, which exceeds the Eddington-limited gas accretion rate for IMBHs with $M_\bullet<10^5\,M_\odot$. These results identify dTDEs as an efficient stellar feeding channel for IMBHs in gas-rich dense stellar systems. As one possible application, this mechanism may help transform $\sim10^3\,M_\odot$ IMBHs into more massive black-hole seeds, provided that compact stellar clusters and accretion disks persist for $>30$ Myr.
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All authors Mengye Wang, Yiqiu Ma, Qingwen Wu, Boyuan Liu, Zijian Wang, Zhili Wang

Cosmology and Nongalactic Astrophysics

Prospects for probing dark matter with filamentary 21cm emission

Yizhou Liu, Yingjie Jing, Haoran Shi et al. (+1 more)

The cosmic web contains most of the matter in the Universe, and its filamentary structure is closely related to the properties of dark matter. Compared with the cold dark matter (CDM) model, warm dark matter (WDM) suppresses the formation of low-mass halos and produces smoother cosmic filaments. In this work, we explore whether filamentary 21cm emission can be used to distinguish between these two dark matter models at $z=4$ and $2.5$. We generate intrinsic 21cm brightness temperature maps from cosmological hydrodynamical simulations and produce mock observations by convolving them with Gaussian beams of different angular resolutions. We then compare the predicted filament signals with the expected sensitivities of SKA1-Low and SKA2-Low. We find that the intrinsic 21cm emission clearly reflects the different filament morphologies in the CDM and WDM models, particularly at $z=4$. However, these differences rapidly disappear as the beam size increases, especially for beam sizes larger than 6 arcsec. Although larger beams improve the observational sensitivity, they also erase the small-scale structures that encode the dark matter information. As a result, neither SKA1-Low nor the planned SKA2-Low can directly resolve individual filaments with sufficient sensitivity to distinguish between the two models. We therefore conclude that direct imaging of cosmic filaments and constraining dark matter through their morphology are unlikely to be feasible with current and planned SKA-Low facilities.
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All authors Yizhou Liu, Yingjie Jing, Haoran Shi, Huijie Hu

High Energy Astrophysical Phenomena

NuSTAR View of the 2025 Mini-Outburst of the Black Hole X-ray Binary GRS 1739-278: Spectral and Timing Evolution in the Soft State

Arshad Hussain and Umananda Dev Goswami

We present a dedicated timing and spectral analysis of three NuSTAR observations of the Galactic black hole candidate GRS 1739-278 obtained during the decay of its 2025 mini-outburst (September 18-30, 2025). The source is found in a soft, disk-dominated state throughout, with a declining $3$-$79$ keV count rate (from $112.4$ to $99.4$ cts s$^{-1}$), a low and only mildly evolving hardness ratio ($\approx0.14$-$0.16$) and a fractional variability that drops from $3.2\%$ to $1.1\%$; no periodic or quasi-periodic signal is detected in the power spectrum or the Lomb-Scargle periodogram of any observation. Joint FPMA+FPMB spectral fits with an absorbed disk-blackbody plus thermal-Comptonization continuum, together with a broad, high-significance ($11.7$-$15.0\sigma$) curvature feature near $10$-$12$ keV (an empirical proxy for a strong disk-reflection/returning-radiation component) describe the $4$-$30$ keV spectra well ($\chi^2/{\rm dof}=1.04$-$1.15$). The inner-disk temperature cools steadily from $1.021\pm0.001$ to $1.002^{+0.003}_{-0.002}$ keV while the disk normalization and hence the derived inner radius, $R_{\rm in}\simeq27.7$ km $\simeq0.95\,R_{ISCO}$ remains constant to within $0.3\%$, consistent with a disk anchored at the innermost stable circular orbit throughout. The unabsorbed $4$-$30$ keV luminosity declines from $1.35\times10^{37}$ to $1.15\times10^{37}$ erg s$^{-1}$ ($0.67\%$ to $0.57 L_{Edd}$). These results of the spectral-timing characterization of the 2025 mini-outburst are broadly consistent with a high-spin black hole accreting at a low, steadily declining rate in the canonical soft state.
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High Energy Astrophysical Phenomena

KM3NeT/ARCA stacking search for high-energy neutrino point sources: the case of ultra-luminous infrared galaxies and blazars

The KM3NeT Collaboration

A stacking search for high-energy astrophysical neutrino emission is presented using three candidate source populations: ultra-luminous infrared galaxies and two categories of blazars, specifically high-synchrotron-peaked BL Lacs and extreme blazars. The analysis is based on 336 days of data from the Astroparticle Research with Cosmics in the Abyss component of the KM3NeT research infrastructure (KM3NeT/ARCA), collected with detector configurations comprising 19-21 detection units, yielding 1544 selected track-like neutrino candidates. The sample of ultra-luminous infrared galaxies consists of 75 sources, for which conventional power-law spectra are assumed in modelling their signal emission. The blazar samples comprise 232 high-synchrotron-peaked BL Lac objects and 88 extreme synchrotron-peaked emitters, respectively. Their expected neutrino fluxes are obtained from numerical tools constrained by multi-wavelength observational data. No statistically significant excess above the atmospheric background is found for the three catalogues and 90% confidence level upper limits are set.
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