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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 1 December

High Energy Astrophysical Phenomena

Slow-Light Effect in the Jet-Launching Region of M87

Yuh Tsunetoe, Dominic W. Pesce and Ramesh Narayan

We explore the impact of "slow-light" radiative transfer - i.e., general relativistic radiative transfer (GRRT) calculations in which the simulated fluid evolves while light rays are propagating through it - in general relativistic magnetohydrodynamic (GRMHD) models of the M87 jet. Because the plasma in the jet-launching region is accelerated to relativistic velocities, and because the jet in M87 is nearly aligned with the line of sight (offset by ~17 degrees), a slow-light treatment is important for accurately modeling the observable structure. While fast-light images exhibit prominent helical or loop-shaped features in the jet - which we associate with narrow bundles of magnetic field lines - these features become stretched and smoothed-out in slow-light images. Our slow-light images instead exhibit a double-edged, cone-like morphology that is more consistent with observations of M87 than corresponding fast-light images. We find that the radius at which the plasma transitions from sub-relativistic to relativistic velocities is imprinted on slow-light images via a transition from loop-dominated at small distances from the black hole to edge-dominated at a larger distance, with the loop-edge transition occurring at larger distances for lower black hole spins. The jet image dynamics also vary with black hole spin, with low-spin models producing jets that exhibit substantial "wobbling", while high-spin models produce jets that are straighter and more stable in time. The spin-dependent jet morphology and variability are revealed by slow-light imaging because slow-light effects become more enhanced as the plasma velocity becomes more relativistic, and because the plasma acceleration is itself a strong function of the spin.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Exceptional Points and Resonance in Black Hole Ringdown

Rodrigo Panosso Macedo, Takuya Katagiri, Kei-ichiro Kubota et al. (+1 more)

We propose an exceptional-point (EP) framework for black-hole ringdown beyond the standard quasinormal-mode (QNM) paradigm. It provides a first-principles characterization of the resonance associated with avoided crossings near EPs, an effect that conventional QNM analysis cannot fully capture. Employing a phenomenological environmental black-hole model with the hyperboloidal framework, we identify near-coalescence of both QNM eigenvalues and eigenfunctions, and directly demonstrate that the resonance produces enhanced mode contributions in the time domain, resulting in characteristic departures from exponentially damped oscillations. Our formulation further reveals that the EP frequency, given by the average of the resonant modes, emerges as the physically relevant observable in the near-EP regime, and offers a robust foundation for modeling and extracting resonant ringdown signals.
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All authors Rodrigo Panosso Macedo, Takuya Katagiri, Kei-ichiro Kubota, Hayato Motohashi

Cosmology and Nongalactic Astrophysics

Cosmic chronometers with galaxy clusters: a new avenue for multi-probe cosmology

E. Tomasetti, M. Moresco, G. Granata et al. (+9 more)

We provide a new measurement of the expansion history of the Universe at $z=0.54$ with the cosmic chronometers (CC) method, exploiting the high-quality spectroscopic VLT/MUSE data for three galaxy clusters in close-by redshift bins: SDSS J2222+2745 ($z=0.49$), MACS J1149.5+2223 ($z=0.54$), and SDSS J1029+2623 ($z=0.59$). The central one, MACS J1149.5+2223, hosts the well-known supernova 'Refsdal', which allowed for $H_0$ measurements via time delay cosmography (TDC). This represents the first step for a self-consistent probe combination, where different methods are applied to the same data sample. After selecting the most passive and massive cluster members (38 CCs), we derive their age and physical parameters via full spectrum fitting. We use the code Bagpipes, specifically modified to remove the cosmological prior on ages. On average, the CC sample shows super-solar metallicities $Z/Z_{\odot} = 1.3 \pm 0.7$, low dust extinction $A_{\rm{V}} = 0.3 \pm 0.3$ mag and to have formed in short bursts $\tau = 0.6 \pm 0.2$ Gyr. We also observe both an ageing trend in redshift and a mass-downsizing pattern. From the age-redshift trend, implementing the CC method through a bootstrap approach, we derive a new $H(z)$ measurement: $H$($z$=0.542) = $66_{-29}^{+81}$ (stat) $\pm$13 (syst) km/s/Mpc. We also simulate the impact of increased statistics and extended redshift coverage, finding that $H$($z$) uncertainties can be reduced by up to a factor of 4 with $\sim$100 CCs and a slightly broader redshift range (d$z\sim$0.2).
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All authors E. Tomasetti, M. Moresco, G. Granata, M. D'Addona, P. Bergamini, C. Grillo, A. Mercurio, P. Rosati, A. Cimatti, L. Tortorelli, S. Schuldt, M. Meneghetti

Earth and Planetary Astrophysics

The Dependence of Earth Milankovitch Cycles on Martian Mass

Stephen R. Kane, Pam Vervoort and Jonathan Horner

The Milankovitch cycles of Earth result from gravitational interactions with other bodies in the Solar System. These interactions lead to slow changes in the orbit and angular momentum vector of Earth, and correspondingly influence Earth's climate evolution. Several studies have shown that Mars may play a significant role in these Milankovitch cycles, such as the 2.4 Myr eccentricity cycle related to perihelion precession dynamics. Here we provide the results of a detailed dynamical analysis that explores the Earth Milankovitch cycles as a function of the Martian mass to quantify the extent that Mars influences variations in Earth's orbital eccentricity, the longitude of perihelion, the longitude of the ascending node, and obliquity (axial tilt). Our results show that, although the 405 kyr long-eccentricity metronome driven by $g_2$ (Venus) and $g_5$ (Jupiter) persists at all Mars masses, the $\sim$100 kyr short-eccentricity bands driven by $g_4$ (Mars) lengthen and gain power as Mars becomes more massive, consistent with enhanced coupling among inner-planet $g$-modes. The 2.4 Myr grand cycle is absent when Mars approaches zero mass, reflecting the movement of $g_4$ with the Martian mass. Meanwhile, Earth's obliquity cycles driven by $s_3$ (Earth) and $s_4$ (Mars) lengthen from the canonical $\sim$41 kyr with increasing Mars mass, relocating to a dominant 45–55 kyr band when the mass of Mars is an order of magnitude larger than its present value. These results establish how Mars' mass controls the architecture of Earth's climate-forcing spectrum and that the Milankovitch spectrum of an Earth-like planet is a sensitive, interpretable probe of its planetary neighborhood.
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Earth and Planetary Astrophysics

JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS

Jason T. Hinkle, Bin Yang, Karen J. Meech et al. (+4 more)

Interstellar objects (ISOs), particularly those with cometary activity, provide unique insight into the primordial physical and chemical conditions present during the formation of the planetary system in which they originated. Observations in the sub-mm regime allow for direct measurements of several parent molecules released from the comet nucleus into the coma. Here we present observations of the third ISO, 3I/ATLAS, with the `Ū`ū heterodyne receiver on the James Clerk Maxwell Telescope (JCMT), which targeted emission from HCN($J = 3 - 2$) and CO($J = 2 - 1$). Our observations, taken between 16 July 2025 and 21 July 2025 (UT), when 3I/ATLAS was at a heliocentric distance between 4.01 and 3.84 au, provide the earliest sub-mm constraints on its activity. We do not detect HCN or CO in these epochs, with 3$\sigma$ upper-limits on the production rates of $Q(HCN) < 1.7 \times 10^{24}$ s$^{-1}$ at $r_h = 4.01 - 3.97$ au and $Q(CO) < 1.1 \times 10^{27}$ s$^{-1}$ at $r_h = 3.94 - 3.84$ au, respectively. We combine this HCN limit with later JCMT observations of HCN to constrain its temporal evolution. Fitting the HCN detections with a $Q(HCN) \propto r_h^{-n}$ model and accounting for the upper-limits yields $n = 12.7^{+6.9}_{-2.5}$. This slope is steeper than those of typical Solar System comets, but consistent with the production rate slopes measured for other species in the coma of 3I/ATLAS.
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All authors Jason T. Hinkle, Bin Yang, Karen J. Meech, Andrew Hoffman, Benjamin J. Shappee, W. B. Hoogendam, James J. Wray

High Energy Astrophysical Phenomena

Possible $\nu$ Source Class: 3-sigma Detection of High-Energy Neutrinos from Supermassive Black Hole Binary Candidates

Pugazhendhi A D, Subhadip Bouri, Bei Zhou et al. (+2 more)

Identifying the sources of high-energy (TeV-PeV) astrophysical neutrinos is crucial for studies in both astrophysics and particle physics. Despite extensive searches for more than a decade, which revealed several individual potential sources and only one potential source class, the origins of these neutrinos remain largely unresolved; thus, more source classes should be investigated. In this work, we conduct the first search for high-energy neutrino emission from a new source class, supermassive black hole binaries (SMBHBs), which are also theoretically motivated. We perform an unbinned maximum-likelihood-ratio analysis on our constructed catalog of 693 SMBHB candidates and 10 years of IceCube public data. Our results show positive correlations, with higher significance in more physically motivated scenarios and the highest significance at 3.0$\sigma$. In addition, we also study potential connections between SMBHBs' high-energy neutrino and nano-Hz gravitational-wave emissions, the latter being the main target of pulsar timing arrays. Our results provide the first evidence of SMBHBs being high-energy neutrino emitters.
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All authors Pugazhendhi A D, Subhadip Bouri, Bei Zhou, Rachana, Ranjan Laha

Astrophysics of Galaxies

Discovery of two little red dots transitioning into quasars

Shuqi Fu, Zijian Zhang, Danyang Jiang et al. (+9 more)

James Webb Space Telescope (JWST) has uncovered a new population of compact objects that show a unique V-shaped spectral energy distribution (SED) in the UV and optical wavelength range. These so-called "little red dots" (LRDs) often exhibit broad Balmer emission lines, indicative of the presence of active galactic nuclei (AGNs). They generally lack detection of X-ray, radio, and mid-IR radiation, which is fundamentally different from typical AGNs. Various models, including super-Eddington-accreting black holes enshrouded in dense and dust-poor gas, have been proposed to explain these features. However, the nature of LRDs remains debated, and their evolutionary fate is unclear. Here we report two unusual LRDs at redshift z = 2.868 and 2.925 that are in a transitional phase towards typical AGNs. Their V-shaped SEDs, compact optical morphology, and broad emission lines satisfy the defining criteria of LRDs. On the other hand, they exhibit intense X-ray, radio, and mid-IR radiation that is much stronger than previously known LRDs. These hybrid properties suggest that the dense gas envelope around their central black holes is dispersing, allowing high-energy photons and radio emission to escape. Meanwhile, a dust torus is forming. This finding provides a direct insight into the nature of LRDs and indicates that at least some LRDs will evolve into AGNs or quasars at later times.
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All authors Shuqi Fu, Zijian Zhang, Danyang Jiang, Jie Chen, Linhua Jiang, Luis C. Ho, Kohei Inayoshi, Kaiyuan Chen, Jianwei Lyu, Fengwu Sun, Feige Wang, Jinyi Yang

Astrophysics of Galaxies

The DREAMS Project: Disentangling the Impact of Halo-to-Halo Variance and Baryonic Feedback on Milky Way Satellite Galaxies

Jonah C. Rose, Mariangela Lisanti, Paul Torrey et al. (+24 more)

We analyze the properties of satellite galaxies around 1,024 Milky Way-mass hosts from the DREAMS Project, simulated within a $\Lambda$CDM cosmology. Utilizing the TNG galaxy-formation model, the DREAMS simulations incorporate both baryonic physics and cosmological uncertainties for a large sample of galaxies with diverse environments and formation histories. We investigate the relative impact of the physical uncertainty from the galaxy-formation model on predicted satellite properties using four metrics: the satellite stellar mass function, radial distribution, inner slope of dark matter density profile, and stellar half-light radius. We compare these predictions to observations from the SAGA Survey and the DREAMS N-body simulations and find that uncertainties from baryonic physics modeling are subdominant to the scatter arising from halo-to-halo variance. Where baryonic modeling does affect satellites, the supernova wind energy has the largest effect on the satellite properties that we investigate. Specifically, increased supernova wind energy suppresses the stellar mass of satellites and results in more extended stellar half-light radii. The adopted wind speed has only a minor impact, and other astrophysical and cosmological parameters show no measurable effect. Our findings highlight the robustness of satellite properties against uncertainties in baryonic physics modeling.
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All authors Jonah C. Rose, Mariangela Lisanti, Paul Torrey, Francisco Villaescusa-Navarro, Alex M. Garcia, Arya Farahi, Carrie Filion, Alyson M. Brooks, Nitya Kallivayalil, Kassidy E. Kollmann, Ethan Lilie, Jiaxuan Li, Olivia Mostow, Akaxia Cruz, Tri Nguyen, Sandip Roy, Andrew B. Pace, Niusha Ahvazi, Stephanie O'Neil, Xuejian Shen, Francis-Yan Cyr-Racine, Adrian M. Price-Whelan, Marla Geha, Lina Necib, Mark Vogelsberger, Julian B. Muñoz, Julianne J. Dalcanton

Cosmology and Nongalactic Astrophysics

Photon (Non)Conservation in the Reduced Speed of Light Approximation and How to (Almost) Fix It

Nickolay Y. Gnedin

The "Reduced Speed of Light" (RSL) approximation is commonly used to speed up radiative transfer calculations in cosmological simulations. However, it has been shown previously that the RSL approximation leads to photon non-conservation when the radiation field is rapidly evolving in time. I show that these missing photons can be counted exactly for some numerical schemes. Adding them back into a simulation, however, is a much harder task. I show one example of such a scheme, which achieves sub-percent accuracy on simple tests. Unfortunately, the scheme performs much worse on semi-realistic simulations of cosmic reionization, leading to a faster overlap and significant errors in the point-wise comparison of the RSL radiation field with the reference simulation that maintains the full speed of light for the radiative transfer.
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Astrophysics of Galaxies

COSMOS-3D: Dense Circumnuclear Gas across Black Hole Growth Phases at z ~ 3

Zi-Jian Li, Siwei Zou, Jianwei Lyu et al. (+25 more)

We report the discovery of two broad-line X-ray AGNs (cid_414 and cid_947) at z ~ 3 identified in the JWST Cycle 3 COSMOS-3D program using NIRCam F444W grism spectroscopy. Both exhibit prominent HeI+Pa$\gamma$ emission and absorption, indicative of circumnuclear dense gas that is traced in these systems. Complementary UV and optical spectroscopy in the COSMOS field provides Ly$\alpha$, Si IV, and C IV measurements. Both sources are detected in MIRI F1000W, and cid_414 is also detected in F2100W, indicating hot dust emission. The two AGNs show distinct black hole and obscuration properties. The source cid_414 displays little red dots (LRD)-like V-shape spectra energy distribution (SED) shape with a turnover near the Balmer 4000 Å break, and a narrow Ly$\alpha$ line with $\log L_{\rm Ly\alpha}=42.49\pm0.01~\mathrm{erg\ s^{-1}}$, with no additional metal lines detected. In contrast, cid_947 exhibits a higher HeI absorption column density, larger X-ray–inferred $N_{\rm H}$, lower intrinsic 2–10 keV luminosity, and strong blueshifted features in He I, Si IV, and C IV absorption with velocity offsets exceeding $5000~\mathrm{km\ s^{-1}}$. Photoionization modeling implies gas densities of $\sim10^{9-10} \mathrm{cm^{-3}}$ and sizes comparable to the broad-line region, consistent with dense gas envelopes predicted for LRDs. Together with previous detections of HeI absorption in compact little red dots, these results suggest that dense circumnuclear gas is likely prevalent at high redshift and may regulate obscuration and black hole–host co-evolution across AGN types.
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All authors Zi-Jian Li, Siwei Zou, Jianwei Lyu, Jaclyn B. Champagne, Jia-Sheng Huang, Cheng Cheng, Shuqi Fu, Zijian Zhang, Danyang Jiang, Khee-Gan Lee, Feige Wang, Xiaohui Fan, Jinyi Yang, Ruancun Li, Hollis B. Akins, Fuyan Bian, Y. Sophia Dai, Andreas L. Faisst, Luis C. Ho, Kohei Inayoshi, Linhua Jiang, Xiangyu Jin, Koki Kakiichi, Jeyhan S. Kartaltepe, Zihao Li, Weizhe Liu, Jan-Torge Schindler, Wei Leong Tee

Astrophysics of Galaxies · Cross-listed from physics.atom-ph

Effect of the avoided crossing on the rovibrational energy levels, resonances, and predissociation lifetimes within the ground and first excited electronic states of lithium fluoride

V. G. Ushakov, A. Yu. Ermilov and E. S. Medvedev

We investigate the LiF spectrum up to $7800$ cm$^{-1}$ above the first dissociation limit. The ab initio calculations of the adiabatic potentials and other molecular functions are performed in a wide range of interatomic separations, $r=1$-17 bohr. We consider the model of two interacting electronic states including both the bound states and the resonances of two kinds, the tunneling resonances and the predissociative ones. The Born-Oppenheimer potentials are modeled with use of two functions imitating the diabatic terms whereas the coupling between them was set constant equal to the half of the minimum separation between the adiabatic terms, and then we define the final diabatic terms and the final diabatic coupling via the adiabatic potentials and the angle of the adiabatic-to-diabatic basis rotation obtained by integration of the nonadiabatic coupling matrix element. The energies of the bound states, as well as the positions and widths of the resonances are calculated. The observed transition frequencies are reproduced with the standard deviation of 0.0009 cm$^{-1}$ for $^7$LiF, 0.0006 cm$^{-1}$ for $^6$LiF, and within the experimental uncertainties for the most of the lines. The line lists for the bound-bound $X$-$X$ rovibrational transitions are calculated for quantum numbers $v\le50,\Delta v\le15,J\le170$ ($J\le200$ for the 0-0 and 1-0 bands).
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Earth and Planetary Astrophysics

The Astrometric Resoeccentric Degeneracy: Eccentric Single Planets Mimic 2:1 Resonant Planet Pairs in Astrometry

Daniel A. Yahalomi, Tiger Lu, Philip J. Armitage et al. (+4 more)

Detections of long-period giant exoplanets will expand dramatically with Gaia Data Release 4 (DR4), but interpreting these signals will require care. We derive the astrometric resoeccentric degeneracy: an astrometric analogue of the well-known radial velocity degeneracy in which a single eccentric planet can mimic two circular planets near a 2:1 period ratio. To first order in eccentricity, the sky-projected motion of a single eccentric orbit decomposes into a fundamental mode and first harmonic with an amplitude proportional to that eccentricity. A pair of coplanar, circular planets in a 2:1 orbital resonance produces the same harmonic structure: the outer planet sets the fundamental mode, while the inner planet supplies an apparent first harmonic. We present a mapping between the harmonic amplitudes and effective eccentricity ($e_\mathrm{eff}$) of a single planet that mimics a 2:1 configuration, demonstrating that $e_\mathrm{eff} = \, 2^{1/3}(M_{p,2}/M_{p,1})$, the masses of the inner and outer planets, respectively. Using simulated Gaia data we show that (1) coplanar 2:1 systems are statistically indistinguishable from a single eccentric planet and (2) mutual inclination can break this degeneracy. This bias favors detecting mutually inclined systems, often fingerprints of a dynamically hot history – traces for processes such as planet-planet scattering or secular chaos. Determining the planetary architectures in which this degeneracy holds will be essential for measuring cool-giant occurrence rates with Gaia and for inferring their dynamical evolution histories.
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All authors Daniel A. Yahalomi, Tiger Lu, Philip J. Armitage, Megan Bedell, Andrew R. Casey, Adrian M. Price-Whelan, Malena Rice

Astrophysics of Galaxies

JWST & the Waz Arc I: Spatially Resolving the Physical Conditions within a Post-Starburst Galaxy at Redshift 5 with NIRSpec IFS

Taylor A. Hutchison, Gourav Khullar, Jane R. Rigby et al. (+22 more)

We present NIRSpec/IFS observations of a rest-frame UV-bright, massive ($M_* \sim 10^{10}$ M$_\odot$, $z_{AB}=20.5$) galaxy highly magnified by gravitational-lensing observed just after the end of the epoch of reionization ($z=5.04$, $\bar{\mu}\sim90$). With JWST accessing the restframe UV and optical spectrum of this galaxy with high fidelity, we classify this UV-bright galaxy as post-starburst in nature – due to weak/absent emission lines and strong absorption features – making this an example of a new class of UV-bright but significantly quenched galaxies being discovered in this epoch. With a median $E(B-V)=0.44\pm0.14$, we identify the presence of stellar absorption across the arc both in Balmer lines and the MgII doublet, indicative of older stellar populations dominated by A stars (and potentially B stars). Using spatially-resolved maps of rest-optical strong emission lines, we find a heterogeneous distribution of nebular metallicities across the arc, potentially hinting at different enrichment processes. With a low median lensing-corrected H$\alpha$ star formation rate of SFR$_{H\alpha} = 0.024 \pm 0.001$ M$_\odot$ yr$^{-1}$, we find in the most "star-forming" clumps indications of lower ionization (log$_{10}$U $\sim -3.2$), lower nebular metallicities (12+log$_{10}$O/H $\lesssim$ 8.3), and hints of higher densities that suggest a possible recent infall of more pristine (low metallicity) gas onto the galaxy. Investigating the regions with no detectable H$\beta$ emission, we find (for the first time at $z>5$) signatures of diffuse ionized gas (DIG). Separating DIG from HII regions within a galaxy has predominantly been demonstrated at lower redshifts, where such spatial resolution allows clear separation of such regions – highlighting the immense power of gravitational lensing to enable studies at the smallest spatial scales at cosmic dawn.
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All authors Taylor A. Hutchison, Gourav Khullar, Jane R. Rigby, Brian Welch, Michael K. Florian, Keren Sharon, Isaac Sierra, Julissa Sarmiento, Guillaume Mahler, Nikko J. Cleri, Rachel Bezanson, Michael D. Gladders, Matthew B. Bayliss, Juliana S. M. Karp, Dylan Berry, Alex Ross, T. Emil Rivera-Thorsen, Suhyeon C. Choe, Håkon Dahle, John Chisholm, Erini L. Lambrides, Rebecca L. Larson, Grace M. Olivier, Riley Owens, Erik Solhaug

Cosmology and Nongalactic Astrophysics

Constraining Dark Acoustic Oscillations with the High-Redshift UV Luminosity Function

Jared Barron, David Curtin, Hongwan Liu et al. (+2 more)

Dark acoustic oscillations (DAOs) in the matter power spectrum can arise in many different dark sector models, and can imprint on a variety of cosmological observables. In this work we use measurements of the galactic UV luminosity function (UVLF) at high redshifts to constrain the dark acoustic oscillation feature at small scales in a model-agnostic way. We introduce a phenomenological transfer function model for a dark sector with a species undergoing DAOs which can accommodate sub-dominant dark matter abundances, and obtain constraints on its parameters. In order to predict the UVLF, we employ an Extended Press-Schechter formalism which we calibrate using N-body simulations with initial conditions featuring DAOs. Using measurements from the Hubble Space Telescope, James Webb Space Telescope, Subaru Telescope, and Canada-France-Hawaii Telescope, we constrain the wave number of the first DAO peak to be at $k \gtrsim 50\ h/\mathrm{Mpc}$, unless the fraction of dark matter undergoing DAOs is less than $0.07$.
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All authors Jared Barron, David Curtin, Hongwan Liu, Julian B. Munoz, Sandip Roy

Instrumentation and Methods for Astrophysics

Real-time RFI Mitigation Techniques in Radio Astronomy and Their Practical Limitations

Kaushal D. Buch, Thushara Gunaratne, Gregory Hellbourg et al. (+2 more)

Radio astronomy is facing critical challenges due to an ever-increasing human-made signal density filling up the radio spectrum. With the rise of satellites, mobile networks, and other wireless technologies, radio telescopes are struggling with radio frequency interference (RFI), which can masquerade, block or distort astronomical signals. In this chapter, we explain where RFI comes from, how it affects observations, and discuss different ways to reduce or remove interference. The techniques presented here reflect the state of the art in real-time RFI mitigation at the time of publication and include methods such as filtering, digital processing, and optimal scheduling. The proposed catalogue also explores new ideas like satellite avoidance through scheduling, the use of intelligent surfaces to block interference, and advanced computer algorithms to clean up data. The chapter also highlights the need for strong cooperation between astronomers and spectrum regulators to protect radio frequencies for future discoveries. By combining technical solutions and better policies, we can help ensure that radio astronomy continues to provide important insights into the universe.
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All authors Kaushal D. Buch, Thushara Gunaratne, Gregory Hellbourg, Cedric Viou, Benjamin Winkel

Instrumentation and Methods for Astrophysics

Pixel-Based Non-Linearity Correction for the WFC3 IR Detector

Sachindev S. Shenoy, Ky Huynh, Varun Bajaj et al. (+1 more)

The current non-linearity correction for the Wide Field Camera 3 Infrared (WFC3/IR) channel is based on ground-based data acquired during WFC3's Thermal Vacuum 3 (TV3) testing campaign. In the current reference file, the correction coefficients derived for each pixel are averaged over each of the four detector quadrants. In this work, we compute a new pixel-based non-linearity correction using in-flight calibration observations with the internal tungsten lamp flats acquired between 2011 and 2013. We derive the new correction coefficients by fitting a third-order polynomial to the accumulated signal “up-the-ramp" for each pixel. Approximately 2% of IR detector pixels are flagged as bad, and a solution cannot be computed. For these, we use the quadrant averages of the new correction coefficients. An accompanying report (\cite{huynh2025}) provides detailed testing results using both internal flats and external science targets acquired in a variety of observing modes. The report highlights improvements in photometry derived from “\_flt.fits" data products calibrated using the new reference file, with the largest improvement for pixels with fluence levels approaching the full well limit of $\sim$80,000 $e^- $. A new NLINFILE reference file was delivered in October 2025 and will be used to reprocess all WFC3/IR imaging and grism observations in the MAST archive.
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All authors Sachindev S. Shenoy, Ky Huynh, Varun Bajaj, Jennifer Mack

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

Quantum Recoherence in Presence of Excited States in the Early Universe

Mattia Cielo, Simone Scarlatella, Gianpiero Mangano et al. (+2 more)

We investigate the quantum-to-classical transition of primordial perturbations within a two-field inflationary framework where an adiabatic mode interacts with an entropic environment. In the case of a massive entropic environment, the attractor Bunch–Davies vacuum plays a special role: it is the only state that can undergo full recoherence, whereas all excited initial states exhibit persistent loss of purity. To characterize this behavior, we parameterize excited Gaussian initial states by their Bogoliubov coefficients and compute the purity and Rényi-2 entropy of the reduced adiabatic state as information-theoretic indicators of decoherence dynamics. We find that excited states display purity-freezing at a non-zero plateau, where residual quantum correlations persist indefinitely, a qualitative departure from the complete recoherence observed for the Bunch–Davies vacuum. This sensitivity to initial conditions highlights the non-generic nature of full recoherence in the quantum-to-classical transition of inflationary perturbations.
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All authors Mattia Cielo, Simone Scarlatella, Gianpiero Mangano, Ofelia Pisanti, Louis Hamaide

Instrumentation and Methods for Astrophysics

Nested Sampling for ARIMA Model Selection in Astronomical Time-Series Analysis

Ajinkya Naik and Will Handley

The era of large-scale, high-cadence astronomical surveys demands efficient and robust methods for time-series analysis. ARIMA models provide a versatile parametric description of stochastic variability in this context. However, their practical use is limited by the challenge of selecting optimal model orders while avoiding overfitting. We present a novel solution this problem by combining Autoregressive Integrated Moving Average (ARIMA) models with the Nested Sampling algorithm. Our method yields Bayesian evidences for model comparison and also incorporates an intrinsic Occam's penalty for unnecessary model complexity. Using JAX and Blackjax, a vectorized ARIMA-Nested Sampling framework with GPU-acceleration support is implemented, allowing us to perform model selection across grids of Autoregressive (AR) and Moving Average (MA) orders, with efficient inference of selected model parameters. We validate the approach using simulated time series with known ground-truth parameters and demonstrate accurate recovery of both model order and parameters. We then apply the method to several astronomical datasets, including the historical sunspot number record, stellar light curves of KIC 12008916 and Kepler 17 from the Kepler mission, and quasar light curves of 3C 273 and S4 0954+65 from the TESS mission. For all cases, except Kepler 17, the ARIMA models selected by this method were able to accurately model the stochastic variability in the time series data as well as produce accurate multi-step ahead forecasts for the sunspot number time series. Our results demonstrate that nested sampling offers a rigorous and computationally tractable alternative to autoregressive model selection in astronomical time-series analysis.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

No Love for black holes: tightest constraints on tidal Love numbers of black holes from GW250114

M. Andrés-Carcasona and G. Caneva Santoro

Tidal Love numbers of black holes, zero in classical general relativity for Kerr black holes in vacuum, become non-vanishing in the presence of exotic matter or in alternative theories of gravity, making them a powerful probe of fundamental physics. The gravitational-wave event GW250114, observed with an unprecedented signal-to-noise ratio, provides a unique opportunity to test this prediction. By analyzing this event, we conclude that the data is consistent with the binary black hole hypothesis, and we place a 90% upper limit on the effective tidal deformability of $\tilde{\Lambda} < 34.8$. These bounds imply that any environment surrounding the black holes must contribute less than $\sim 7\times 10^{-3}$ of their mass, and they rule out some models of boson stars. Our findings provide the strongest observational constraints yet on black hole tidal deformability and show that the data remain fully consistent with the Kerr black hole prediction of vanishing tidal Love numbers.
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Earth and Planetary Astrophysics

Giant Outer Transiting Exoplanet Mass (GOTEM) Survey.VII. TOI-6041: a multi-planet system including a warm Neptune exhibiting strong TTVs

N. Heidari, A. Alnajjarine, H.P. Osborn et al. (+101 more)

We present the characterization of the TOI-6041 system, a bright ($V = 9.84 \pm 0.03$) G7-type star hosting at least two planets. The inner planet, TOI-6041b, is a warm Neptune with a radius of $4.55^{+0.18}_{-0.17}\,R_\oplus$, initially identified as a single-transit event in TESS photometry. Subsequent observations with TESS and CHEOPS revealed additional transits, enabling the determination of its $26.04945^{+0.00033}_{-0.00034}$~d orbital period and the detection of significant transit timing variations (TTVs), exhibiting a peak-to-peak amplitude of about 1~hour. Radial velocity (RV) measurements obtained with the APF spectrographs allow us to place a $3\sigma$ upper mass limit of $28.9\,M_\oplus$ on TOI-6041b. In addition, the RV data reveal a second companion, TOI-6041c, on an 88~d orbit, with a minimum mass of $0.25\,M_{\mathrm{Jup}}$. A preliminary TTV analysis suggests that the observed variations could be caused by gravitational perturbations from planet c; however, reproducing the observed amplitudes requires a relatively high eccentricity of about 0.3 for planet c. Our dynamical stability analysis indicates that such a configuration is dynamically viable and places a $1\sigma$ upper limit on the mass of TOI-6041c at $0.8\,M_{\mathrm{Jup}}$. An alternative is the presence of a third, low-mass planet located between planets b and c, or on an inner orbit relative to planet b – particularly near a mean-motion resonance with planet b – which could account for the observed variations. These findings remain tentative, and further RV and photometric observations are essential to better constrain the mass of planet b and to refine the TTV modeling, thereby improving our understanding of the system's dynamical architecture.
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All authors N. Heidari, A. Alnajjarine, H.P. Osborn, D. Dragomir, P. Dalba, W. Benz, G. Hébrard, J. Laskar, N. Billot, M.N. Günther, T.G. Wilson, Y. Alibert, A. Bonfanti, A. Bieryla, C. Broeg, A.C.M. Correia, J.A. Egger, Z. Essack, E. Furlan, D. Gandolfi, N. Grieves, S. Howell, D. LaCourse, C. Pezzotti, T. Pritchard, S.G. Sousa, S. Ulmer-Moll, S. Villanueva, R. Alonso, J. Asquier, T. Bárczy, D. Barrado, S.C. Barros, W. Baumjohann, L. Borsato, A. Brandeker, M. Buder, A. Collier Cameron, S. Csizmadia, P.E. Cubillos, M.B. Davies, M. Deleuil, X. Delfosse, A. Deline, O.D.S. Demangeon, B. Demory, A. Derekas, B. Edwards, D. Ehrenreich, A. Erikson, A. Fortier, L. Fossati, M. Fridlund, K. Gazeas, M. Gillon, M. Güdel, J. Hasiba, A. Heitzmann, C. Helling, J.M. Jenkins, T. Keller, K.G. Stassun, L. Kiss, J. Korth, K.W.F. Lam, D.W. Latham, A. Lecavelier des Etangs, A. Leleu, M. Lendl, P.F.L. Maxted, S. McDermott, B. Merín, C. Mordasini, V. Nascimbeni, G. Nowak, G. Olofsson, I. Pagano, E. Pallé, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, H. Rauer, I. Ribas, G. Ricker, N.C. Santos, G. Scandariato, S. Seager, D. Ségransan, A.E. Simon, A.M.S. Smith, M. Stalport, S. Striegel, S. Sulis, G.M. Szabó, S. Udry, V. Van Grootel, R. Vanderspek, J. Venturini, E. Villaver, V. Viotto, N.A. Walton, J.N. Winn, S. Wolf

Astrophysics of Galaxies

Weak, extended water vapor emission in the Horsehead nebula

Dariusz C. Lis, Vincent Maillard, Emeric Bron et al. (+4 more)

We analyzed archival Herschel observations of water vapor emission toward the Horsehead photon dominated region (PDR), along with supporting ground-based and airborne observations of CO isotopologues and fine structure lines of ionized and atomic carbon to determine the distribution and abundance of water vapor in this low-UV illumination PDR. Water emission in the Horsehead nebula is very weak and, surprisingly, extends outward beyond other PDR tracers such as $^{12}$CO or [CI] 609 $\mu$m, reaching as far out as [CII] 158 $\mu$m. We model the observations using a newly developed PDR wrapper that takes into account the geometry of this region. PDR modeling of the molecular and atomic lines studied here provides strong constraints on the thermal pressure, but not on the UV illumination. Maximum model line intensities %typically agree to within ~40% with the observations. and spatial profiles are well reproduced, except for CO isotopologues, where the increase on the illuminated side of the PDR is steeper than observed. Water vapor abundance in the model reaches $3.6 \times 10^{-7}$ at $A_V \sim 3$ mag. However, the ground state $o$-H$_2$O 557 GHz line is systematically overestimated by the models by at least a factor of 7 for any values of the model parameters. This line has a very high optical depth and the emergent line intensity is sensitive to radiative transfer effects such as line scattering by water molecules in a low-density halo surrounding the dense PDR and the assumed microturbulent line width. A more accurate model of the water surface chemistry is required.
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All authors Dariusz C. Lis, Vincent Maillard, Emeric Bron, Franck Le Petit, Javier R. Goicoechea, Ducheng Lu, David Teyssier

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

Astrophysical viability of extremal black holes

Chiara Coviello and Ruth Gregory

We take a fresh look at the viability of physically realistic extremal black holes within our (non-supersymmetric) low energy physics. By incorporating prefactors and volume effects, we show that Schwinger discharge in charge neutral environments is far more efficient than commonly assumed. Using ionisation estimates for neutral hydrogen, we obtain a new and robust lower bound on the mass of an extremal electrically charged black hole, exceeding $10^{14} M_\odot$. For magnetic black holes, we compute the Lee-Nair-Weinberg instability and revisit early universe pair creation rates, including singular instantons that substantially enhance production, to demonstrate that the extreme charges required for stability are cosmologically implausible. Finally, we speculate that an extremal Kerr black hole could shed angular momentum via superradiant scattering from the stochastic gravitational wave background. Taken together, our results provide a unified picture that extremal black holes are unlikely to persist in our universe.
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Solar and Stellar Astrophysics

Active chromospheric fibril singularity: Coordinated observations from Solar Orbiter, SST, and IRIS

Reetika Joshi, Luc Rouppe van der Voort, Guillaume Aulanier et al. (+6 more)

The fine structures of the solar chromosphere, driven by photospheric motions, play a crucial role in the dynamics of solar magnetic fields. Many have been already identified such as fibrils, filament feet, and arch filament systems. Still, high resolution observations show a wealth of structures that remain elusive. We have observed a puzzling, unprecedented chromospheric fibril singularity in close vicinity of a blow-out solar jet and a flaring loop. We aim to understand the magnetic nature of this singularity and the cause of its activity using coordinated high-resolution multi-wavelengths observations. We aligned datasets from Solar Orbiter, SST, IRIS, and SDO. We re-projected the Solar Orbiter datasets to match the perspective of the Earth-based instruments. We performed potential field extrapolations from Solar Orbiter/PHI data. We analysed the spatial and temporal evolution of the plasma structures and their link with the surface magnetic field. This leads us to derive a model and scenario for the observed structures which we explain in a general schematic representation. We have discovered a new feature, a singularity in the chromospheric fibril pattern. It is formed in a weak magnetic field corridor between two flux concentrations of equal sign, at the base of a vertically inverted-Y shape field line pattern. In this specific case some activity develops along the structure. Firstly a flaring loop at one end, secondly a blow-out jet at the other end, where a coronal null-point was present and associated with a chromospheric saddle point being located onto the fibril singularity. The observations sugge
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All authors Reetika Joshi, Luc Rouppe van der Voort, Guillaume Aulanier, Sanja Danilovic, Avijeet Prasad, Carlos J. Díaz Baso, Daniel Nóbrega-Siverio, Nicolas Poirier, Daniele Calchetti

Astrophysics of Galaxies

First detections of methanol maser lines from a rare transition family

Bradley R. Johnson, Simon P. Ellingsen, Shari L. Breen et al. (+3 more)

We report the first observations in a rare family of class II methanol maser transitions in both CH$_3$OH and $^{13}$CH$_3$OH toward three southern high-mass star formation regions, along with the first maser detected in the $^{13}$CH$_3$OH line. The $8_2 \rightarrow 9_1 A^{-}$ methanol transition was observed in both CH$_3$OH and $^{13}$CH$_3$OH (at 28.9 GHz and 41.9 GHz respectively) toward three sources; G358.93-0.03, NGC6334I and G345.01+1.79, all of which are star formation regions with recent maser flaring events. We report the first maser detection of the 41.9 GHz line in $^{13}$CH$_3$OH toward G358.93-0.03 and the first confirmed maser detection of the 28.9 GHz line in CH$_3$OH toward NGC6334I. Additionally we report a maser detection of the 28.9 GHz line in CH$_3$OH toward G358.93-0.03, meaning that with our detection of the 41.9 GHz line, this is the first isotopic detection of these lines toward G358.93-0.03. The newly detected maser transitions are associated with the primary millimetre continuum sources (MM1) in both G358.93-0.03 and NGC6334I, within the varying positional uncertainties.
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All authors Bradley R. Johnson, Simon P. Ellingsen, Shari L. Breen, Maxim A. Voronkov, Tiege P. McCarthy, Lucas J. Hyland

Earth and Planetary Astrophysics

A window for water-hydrogen demixing on warm metal-rich sub-Neptunes

Caroline Piaulet-Ghorayeb, Daniel P. Thorngren, Eliza M.-R. Kempton et al. (+4 more)

Sub-Neptunes represent the largest exoplanet demographic, yet their bulk compositions remain poorly understood. Recent studies suggested that only very cold planets, such as Uranus and Neptune, could experience stratification of volatiles in their envelopes. Transiting warm sub-Neptunes, with $10^3$ to $10^4$ times more stellar irradiation, were therefore believed to have fully-miscible compositions. Here, we present ATHENAIA, an interior-atmosphere composition inference framework we leverage to assess the potential for water-hydrogen demixing on warm sub-Neptunes and for the 350 K planet TOI-270 d as a case study, using radiative-convective atmosphere models coupled to interior models. We find that the higher temperatures at which hydrogen and water demix in water-rich environments open a window for demixing on sub-Neptunes with bulk envelope metallicities of $\sim 150$ to $700\times$ solar, compatible with TOI-270 d. Demixing is easier to achieve on more massive and colder planets, but still broadly affects warm ($\simeq $330 to 450 K) metal-rich sub-Neptunes. Therefore, combining atmosphere metallicities with models of fully-miscible envelopes may lead to underestimated bulk envelope metallicities and mass fractions. Further, we find that considering the increased greenhouse effect in metal-rich atmospheres in concert with the composition-dependent adiabatic gradient in the convective envelope increases the range of compositions under which molten mantle conditions should be expected on sub-Neptunes. This work encourages a reconsideration of the current paradigm for linking sub-Neptune atmospheres to their interiors and motivates evolutionary modeling describing the onset of metallicity gradients in sub-Neptune envelopes.
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All authors Caroline Piaulet-Ghorayeb, Daniel P. Thorngren, Eliza M.-R. Kempton, Justin Lipper, Leslie Rogers, Fernanda Correa Horta, Shi Lin Sun

Earth and Planetary Astrophysics

Inferring planet occurrence rates from radial velocities

J. P. Faria, J.-B. Delisle and D. Ségransan

We introduce a new method to infer the posterior distribution for planet occurrence rates from radial-velocity (RV) observations. The approach combines posterior samples from the analysis of individual RV datasets of several stars, using importance sampling to reweight them appropriately. This eliminates the need for injection-recovery tests to compute detection limits and avoids the explicit definition of a detection threshold. We validate the method on simulated RV datasets and show that it yields unbiased estimates of the occurrence rate in different regions, with increasing precision as more stars are included in the analysis.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Search for Peak Structures in the Stochastic Gravitational-Wave Background in LIGO-Virgo-KAGRA O1-O4a Datasets

Catalina-Ana Miritescu, Mario Martinez and Oriol Pujolas

We present a dedicated search for gravitational-wave backgrounds with nontrivial peak structures using data from the first three and the initial part of the fourth observing runs of the LIGO-Virgo-KAGRA network. The analysis is motivated by a variety of early-Universe models characterized by signals with multiple peaks. We introduce a model independent parameterization of double-peaked spectra based on the superposition of two normalized broken power laws and perform a Bayesian inference study using the LIGO-Virgo-KAGRA isotropic cross-correlation data. While no statistically significant evidence for a multi-peak background is found, the analysis provides constraints on the inter-peak slopes in correlation with the signal amplitude. These results exhibit LIGO-Virgo-KAGRA's ability to probe signals beyond a single peak structure and establish a foundation for future targeted searches for nontrivial gravitational waves background spectral shapes in future observing runs and the advanced detector era.
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High Energy Astrophysical Phenomena

LST-1 follow-up of the exceptionally bright gamma-ray burst GRB 221009A

Arnau Aguasca-Cabot, Alessandro Carosi, Alice Donini et al. (+6 more)

On 9 October 2022, the brightest gamma-ray burst (GRB) ever recorded (GRB 221009A) was detected. Its remarkably bright emission, partially due to its close distance to Earth ($z\sim0.15$), makes this GRB a unique event. The outstanding characteristics of GRB 221009A, including the TeV detection by the LHAASO experiment, triggered deep follow-up observations of the source across all wavebands, including very-high-energy gamma rays with the first Large-Sized Telescope (LST-1) of the future Cherenkov Telescope Array Observatory. LST-1 observations started about one day after the onset of the prompt emission, under strong moonlight conditions. This resulted in a hint of a signal with a statistical significance of about 4$\sigma$. The monitoring of this source continued until the end of November 2022. This constitutes the deepest observation campaign performed on a GRB with LST-1. Here we show the results of this follow-up campaign.
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All authors Arnau Aguasca-Cabot, Alessandro Carosi, Alice Donini, Susumu Inoue, Yuri Sato, Monica Seglar Arroyo, Kenta Terauchi, Pol Bordas, Marc Ribó

Solar and Stellar Astrophysics

Identification of new Galactic symbiotic stars with SALT – II. New discoveries and characterization of the sample

J. Merc, J. Mikołajewska, K. Iłkiewicz et al. (+2 more)

We present the continuation of a systematic search for new southern Galactic symbiotic stars, selecting candidates from the SuperCOSMOS H$\alpha$ Survey and 2MASS. Follow-up spectroscopy with the Southern African Large Telescope (SALT) was used to confirm their symbiotic nature and to characterize the cool and hot components of the full sample, including systems from earlier work. We report 14 newly confirmed bona fide symbiotic stars and identify 6 additional strong candidates. Photometric variability was examined using our data and archival light curves from multiple all-sky surveys. Most systems are variable, with the majority showing periodic modulation consistent with orbital motion or pulsations. Possible photometric orbital periods are reported for 19 confirmed and 3 candidate systems, pending spectroscopic confirmation. Eight objects exhibit signs of outburst activity. In one of the systems, multiple brightenings occur at similar orbital phases, closely resembling the evolution of FN Sgr, a symbiotic binary with a magnetic white dwarf. The peculiar variability of another symbiotic star is best explained by dust-obscuration events. These results expand the census of Galactic symbiotic stars.
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All authors J. Merc, J. Mikołajewska, K. Iłkiewicz, B. Monard, A. Udalski

Earth and Planetary Astrophysics

The chemical diversity of giant-planet nurseries as revealed by ALMA

Alice S. Booth, Jenny Calahan, Milou Temmink et al. (+9 more)

With the giant exoplanet occurrence rate peaking around stars of 1.5-2 solar masses, there is strong motivation to characterize the disks that set their formation conditions. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) allow us to investigate both the availability of different molecules in disks and infer the radial distribution of elemental abundances, enabling us to make connections to exoplanet systems. Here we present a survey of six transition disks around young F-, A-, and B-type stars using ALMA. We find 13C18O, CS, SO, and H2CO in all six systems, as well as ten additional molecules in a subset of disks, including detections of H2S, 33SO, and CH3OCH3. Using these data, and literature data where available, we construct the first comprehensive picture of Herbig disk chemistry. We find clear correlations between molecular tracers of C/O>1 environments (e.g., CS, C2H) and disk mass, as traced by C18O line flux. In contrast, tracers of C/O<1 environments (e.g., SO, CH3OH) do not show significant correlations with disk mass. Interestingly, these molecules are relatively brighter in lower-mass disks, with their presence primarily linked to disks with central cavities and spirals. Finally, we show that the observed chemical diversity seen across Herbig disks leads to varying C/O regimes at the orbital radii of candidate proto-planets identified within these disks. When comparing these inferred disk C/O ratios with those measured for directly imaged exoplanets, we find a notable overlap and show that low C/O gas is common on 10's of au scales in Herbig disks.
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All authors Alice S. Booth, Jenny Calahan, Milou Temmink, Lisa Wölfer, Jamila Pegues, Charles J. Law, Lucy Evans, Margot Leemker, Shota Notsu, Karin Öberg, Catherine Walsh, Ewine F. van Dishoeck