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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 9 July

Earth and Planetary Astrophysics

A Retrieval Framework for Observationally Constraining the Parameters of Circumplanetary Disks

Aster Taylor and Fred Adams

As they form, giant planets are surrounded by disks of gas and dust sourced from the background circumstellar disk. Although there have been few detections to date, upcoming instruments are likely to discover many more of these systems in the coming decades. Accurate spectral modeling will enable these observations to constrain the properties of these forming systems. Towards this end, we have constructed a semianalytic model for the structure and radiative signatures of geometrically thick circumplanetary disks and their planet hosts. Fitting these radiative signatures to synthetic observations of a two-dimensional disk model then quantifies the parameter constraints that can be derived (subject to model assumptions). This machinery provides estimates of the values and uncertainties in system parameters, and some combinations of parameters have significantly smaller uncertainties than others. This model is then used to fit observations of real protoplanets, with good results. The derived parameters provide useful context about the local extinction, formation history, and initial entropy of these objects.
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Instrumentation and Methods for Astrophysics

On-Orbit Calibration of Danuri/PolCam. II. Image Artifact Correction

Kilho Baek, Sungsoo S. Kim, Minsup Jeong et al. (+1 more)

Danuri, South Korea's first lunar orbiter, was launched on 2022 August 5, and has completed its two-year nominal mission phase. The wide-angle Polarimetric Camera (PolCam) onboard Danuri is the first instrument to conduct global polarimetric observations from lunar orbit. This paper presents the image artifact correction pipeline for PolCam's on-orbit data. It encompasses the primary steps of the radiometric calibration, consisting of dark current removal, smear correction, and flat-fielding, except for inter-channel relative response and the final radiance calculation. Notably, PolCam's raw data exhibit severe smear artifacts induced by the frame-transfer CCD architecture, which degrade both radiometric fidelity and the accuracy of polarimetric measurements. These smear artifacts have been mitigated through a rigorous correction algorithm, restoring data quality to a level sufficient for scientific analysis and facilitating the precise derivation of the degree of linear polarization. These steps serve as an essential prerequisite for conducting subsequent absolute radiance and photometric calibrations. Finally, we present representative examples of polarimetric measurements to validate the calibration performance. Although the current calibration focuses on restoring data quality for qualitative scientific analysis, these results demonstrate the expected inverse linear relationship between intensity and polarization.
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All authors Kilho Baek, Sungsoo S. Kim, Minsup Jeong, Young-Jun Choi

Wednesday 8 July

High Energy Astrophysical Phenomena

A Diagnostic Inverse-PINN Study of Identifiability in Reduced Black-Hole Spin Inference

Stella Menziltsidou

Black-hole spin is a fundamental parameter in relativistic astrophysics, influencing accretion efficiency, jet launching, and perturbative modes. This work investigates a hybrid physicsinformed inverse framework for reduced black-hole spin inference. Spin recovery is formulated as an inverse problem constrained by a reduced scalar angular Teukolsky-like equation. A Physics-Informed Neural Network approximates the angular mode function, while the spin parameter is treated as a trainable physical quantity linked to the residual of the governing differential operator. The framework is evaluated under controlled synthetic and noisecontaminated angular-mode configurations across multiple reference spin values. The main result is diagnostic rather than confirmatory. The PINN reproduces angular-mode profiles qualitatively; however, the inferred spin values cluster near the upper part of the allowed interval rather than accurately recovering the full range of reference spins. This reveals a weak-identifiability regime in which accurate angular-profile reconstruction and low residual loss do not necessarily imply accurate spin recovery. The results highlight the diagnostic value of physics-informed constraints for reduced black-hole spin-inference experiments, while also showing the need for further identifiability analysis, loss reweighting, joint eigenvalue inference, full Kerr perturbation modeling, realistic uncertainty models, and validation against numerical solvers.
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Cosmology and Nongalactic Astrophysics

Remembering George Smoot

John Berliner, Tom Broadhurst, Martin Bucher et al. (+30 more)

George Smoot (1945-2025) was a major figure in observational cosmology, particularly through his role in the precision measurement of the CMB dipole and the discovery of the primordial CMB temperature anisotropy as part of the COBE team. This collection of 33 essays from collaborators, colleagues, students, and friends offers varied insights into the work, career, and life of George Smoot.
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All authors John Berliner, Tom Broadhurst, Martin Bucher, Robert Cahn, Jorge Cervantes-Cota, Steven Chu, Nóra Csiszár, Razieh Emami, Leo Fung, Ken Ganga, Alison Goldwyn, Bill Green, Paula Keeney, Dhiraj Kumar Hazra, Albert Wai Kit Lau, Sean Li, Eric Linder, Charley Lineweaver, Tao Liu, Omar López-Cruz, Philip Lubin, Kam-Biu Luk, John Mather, Saul Perlmutter, Federico Piazza, Graciela Tiburcio Pintos, Barbara Rittner, Uroš Seljak, Mehdi Shafiee, Tony Spadafora, Henry Tye, Ann Whetstone, Alex Zhavoronkov

Astrophysics of Galaxies

There is no single density: star-forming regions and galaxies hold more dense ionized gas than long assumed

J. Eduardo Méndez-Delgado, Christophe Morisset, William J. Henney et al. (+29 more)

Ionized gas fills star-forming regions and galaxies, and nearly everything we know about its temperature, pressure, mass, and composition is inferred from its emission lines [1-3]. The electron density is needed for all of these, yet a longstanding puzzle has resisted explanation: different density-sensitive lines, applied to the same gas, return values that disagree by up to two orders of magnitude. This is usually attributed either to each line tracing a physically distinct ionization zone or to imperfect atomic data [4-7]. Here we show that the disagreement is neither a flaw in the atomic data nor an ionization-stratification effect, but something more fundamental. Each diagnostic is tuned to a particular density, and when a nebula contains gas across a wide range of densities, as real nebulae do, each line reports the part of that range it is most sensitive to. The diagnostics do not measure a representative average density; they respond to different parts of a broad density distribution. This resolves the discrepancy with a simple relation between the density each line returns and the density it is most sensitive to, a relation that holds from individual H II regions to whole galaxies, near and far, and reveals that ionized nebulae contain far more dense gas than any one diagnostic implies. A nebula has no single electron density to measure, but a broad density distribution, and the masses, pressures, abundances and energetics built on the single-density assumption must be reconsidered, from nearby star-forming regions to galaxies across cosmic time.
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All authors J. Eduardo Méndez-Delgado, Christophe Morisset, William J. Henney, Niv Drory, Oleg V. Egorov, Sebastián F. Sánchez, Juna A. Kollmeier, Kathryn Kreckel, Guillermo Blanc, Grażyna Stasińska, Evelyn J. Johnston, Héctor J. Ibarra-Medel, Alfredo J. Mejía-Narváez, César Esteban, Jorge García-Rojas, Amrita Singh, Ivan Yu. Katkov, Evan D. Skillman, Rogelio Orozco-Duarte, Igor A. Zinchenko, Alejandra Z. Lugo-Aranda, Aida Wofford, Simon C. O. Glover, Evgeniya Egorova, Rodolfo de J. Zermeño, Lesly C. Castañeda-Carlos, Fu-Heng Liang, Natascha Sattler, Irene Cruz-González, Joel R. Brownstein, Thomas Hilder, Donald P. Schneider

Astrophysics of Galaxies

Enhancing Photometric Redshift Estimation for LSST with a Hybrid LSTM-Mixture Density Network

Zhijian Luo, Yangyang Li, Xinyu Luo et al. (+4 more)

Accurate photometric redshift (photo-$z$) estimation and robust uncertainty quantification are essential for the LSST to achieve its precision cosmology goals. Traditional machine learning algorithms are largely restricted to point estimates, struggling to characterize the multimodal nature of redshift PDFs and the degeneracies within the color-redshift space. To address this, we present and validate the LSTM-MDNz architecture, which integrates sequential feature extraction with flexible probability density modeling to enhance both prediction accuracy and uncertainty calibration across a broad redshift range, thereby meeting the stringent data quality requirements necessitated by next-generation cosmological analysis. The LSTM-MDNz framework treats multi-band photometry as wavelength-ordered sequences, utilizing LSTM networks to capture non-linear evolutionary correlations across the SED. A Mixture Density Network (MDN) is then employed to explicitly model posterior PDFs via Gaussian mixture models (GMMs). Performance is evaluated on the HSC GalaxiesML dataset (which serves as a small-scale proxy for next-generation surveys like LSST) and benchmarked against the BNN architecture established by Jones et al. (2024). The proposed model consistently outperforms the BNN baseline, achieving a $\sim 10\%$ improvement in point-estimation accuracy (specifically across RMSE, MAE, scatter, and $\sigma_{\text{NMAD}}$) and a $\sim 20\%$ reduction in the rates of both general and catastrophic outliers. A uniform probability integral transform (PIT) distribution confirms well-calibrated probabilistic outputs. Furthermore, the PDF-based confidence metric $z_{\text{conf}}$ enables high-purity catalog construction: excluding just approximately $4\%$ of extremely low-confidence ($z_{\text{conf}} < 0.05$) samples reduces the overall outlier rate by $\sim 48\%$.
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All authors Zhijian Luo, Yangyang Li, Xinyu Luo, Hubing Xiao, Wei Fang, Shaohua Zhang, Chenggang Shu

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

Multipolar Dark Matter Freeze-out in an Early Matter-Dominated Universe

Debajit Bose, Prolay Chanda, Suvam Maharana et al. (+1 more)

The relic abundance of thermal dark matter depends not only on its particle interactions but also on the expansion history of the early Universe. We study the freeze-out of fermionic dark matter interacting with the Standard Model through higher-dimensional electromagnetic operators in an early matter-dominated cosmology. In particular, we consider magnetic dipole, electric dipole, anapole, and charge-radius interactions, and compute the couplings required to reproduce the observed dark matter relic abundance in the presence of entropy injection from the decay of a long-lived heavy field. The resulting parameter space is compared with that obtained in the standard radiation-dominated freeze-out scenario and confront it with current constraints from direct-detection experiments and solar neutrino observations. We find that the entropy dilution associated with an early matter-dominated epoch significantly reduces the interaction strength required to obtain the observed relic abundance, thereby rendering viable regions of parameter space that are excluded in the conventional cosmological history. Our results demonstrate that the cosmological history prior to Big Bang nucleosynthesis can have an important impact on the phenomenology and experimental viability of electromagnetic multipole dark matter.
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All authors Debajit Bose, Prolay Chanda, Suvam Maharana, Poulami Mondal

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

Nonlinear hydrodynamics in spinning neutron stars: Theoretical universal relations and equilibrium solutions

Hang Yu, Giorgio Nicolini, Shu Yan Lau et al. (+6 more)

We study tides during the inspiral of a binary neutron star system, including nonlinear hydrodynamical interactions. Using an affine approximation that treats the perturbed neutron star (NS) as an ellipsoid, we analytically derive coupling coefficients among the quadrupolar f-modes and the radial mode to the four-wave order (next-to-next-to-leading order) in the Hamiltonian, allowing for arbitrary (aligned or anti-aligned) spin of the background star. Our model reveals a series of universal relations from first-principles arguments. We show that the three-wave (next-to-leading-order) interaction coefficients in a non-spinning star are fully determined by the properties of the linear tide. They do not probe new physics of the NS. Nonetheless, three-wave nonlinear tides are significant corrections to the gravitational waveform. We support this via a hybrid approach that simultaneously captures mode resonances expected in Newtonian hydrodynamics and is consistent with relativistic calculations in the low-frequency expansion. The nonlinear tide in a single NS can cause a phase shift of around 1.8 radians accumulated up to merger compared to the linear tide model; for a binary, the phase shift is approximately doubled. In a low-frequency expansion, the nonlinear tide is degenerate with the finite-frequency correction of the linear tide, introducing systematic bias when ignored. Our calculation extends to four-wave interactions, which, for a slowly spinning neutron star, provide only small corrections. For a rapidly rotating neutron star, the nonlinear centrifugal drive of the f-mode provides a window to study the internal buoyancy that cannot be probed by the linear and three-wave f-mode tides in slowly spinning systems. The four-wave anharmonicity cannot lead to resonance locking of the f-mode.
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All authors Hang Yu, Giorgio Nicolini, Shu Yan Lau, K.J. Kwon, Tejaswi Venumadhav, Nils Andersson, Pantelis Pnigouras, Fabian Gittins, Amlan Nanda

Solar and Stellar Astrophysics

Cluster-Weighted Training of Deep Surrogate Models for Subgrid Turbulent Transport

Rimsha Hameed Syeda, Dustin Kempton, Viacheslav Sadykov et al. (+2 more)

Turbulence in the solar interior and atmosphere plays a crucial role in energy transport, yet modeling its subgrid-scale effects remains a major challenge. This study leverages machine learning (ML) models to predict components of the Reynolds stress tensor using high-resolution StellarBox simulations of the quiet Sun. Previously, we have compared a Multi-Layer Perceptron (MLP) and a 3D Convolutional Neural Network (CNN) against physics-based baselines to achieve a lower Mean Squared Error (MSE) and better generalization across various heights and depths in the solar atmosphere. To enhance learning, in this work, we investigate cluster-weighted training using K-Means and Hierarchical Agglomerative Clustering (HAC). By weighing the loss function based on cluster-specific prediction errors, we direct the model's attention to high-error regions. It significantly improves CNN performance, achieving 34% lower MSE and a significantly higher R2 score indicating that integrating deterministic clustering with ML is a promising technique for modeling subgrid turbulence, in particular, and regression in diverse environments, in general.
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All authors Rimsha Hameed Syeda, Dustin Kempton, Viacheslav Sadykov, Irina Kitiashvili, Rafal Angryk

Solar and Stellar Astrophysics

Node-locked phase of annual modulations from the gravitational chiral anomaly in the solar Kerr field

M. Misiaszek

The leading parity-odd mass–spin curvature invariant of the solar exterior, $P_{\odot}\equiv{}^{*}\!R\,R\simeq 288\,G^{2}M_{\odot}^{2}a_{\odot}\cos\theta/c^{4}r^{7}$, changes sign when the Earth crosses the solar equatorial plane and acts as the geometric source of the gravitational chiral anomaly. We study two minimal phenomenological responses to this structure: a long-memory reservoir $Q\propto\int(P_{\odot}-\langle P_{\odot}\rangle)\,dt$ and the local worldline derivative $D=u^{\mu}\nabla_{\mu}P_{\odot}$. Both have an annual Fourier phase fixed by ephemerides, $t^{*}=158.7$~d (June 7–8) or the opposite branch $t^{*}=341.4$~d, with a calculable secular drift of $+0.014$~d\,yr$^{-1}$ and an energy-independent geometric input phase, while predicting different semiannual fractions, $3.75\%$ and $15\%$, respectively. The response amplitudes and their microscopic origin are not predicted; the phase is. Single-amplitude fits to the digitized DAMA/LIBRA–phase2 1–3~keV residuals give $\chi^{2}/\mathrm{dof}=62.7/51$ for the reservoir and $63.6/51$ for the derivative, against $60.9/51$ for the standard-halo cosine. The most precise published phase, $t^{*}=153.5\pm3.8$~d, lies $0.3\sigma$ from the halo value and $1.4\sigma$ from the node-locked one; phase metrology at the two-day level ($\simeq3\sigma$), together with the phase-locked semiannual component, discriminates between the two clocks.
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Solar and Stellar Astrophysics

Physics of Eclipsing Binaries. VI. Hot, compact stars

David Jones, Nicole Reindl, Kyle Conroy et al. (+9 more)

Models of eclipsing binaries require the assignment of appropriate emergent intensities to the surface elements of the binary components. For distance-dependent modelling of flux-calibrated light curves, this necessitates an approximation of the absolute normal intensities of both components of the binary, as well as how their brightness varies across the stellar disks (limb darkening). Such surface intensities are often inferred from other physical properties of the synthetic binary (effective temperature, surface gravity, etc.) through the use of model atmospheres, which in turn are generally suited to a particular range of stellar types or parameters. Here, we present the major developments included in the PHOEBE 2.5 release (publicly available from http://phoebe-project.org), which improve the fidelity of model binaries comprising hot, compact stars. These developments include the incorporation model atmospheres produced using the Tubingen Model Atmosphere Package (TMAP) and Montreal/Tremblay codes (complementing the already incorporated PHOENIX and Castelli & Kurucz models, primarily suited to main sequences stars and low-temperature giants). Similarly, PHOEBE v2.5 now allows for blending/extrapolation of model atmospheres, meaning one can continue to make use of model atmospheres in cases when a small number of surface elements have parameters outside the model atmosphere grid. As an added value product, we also present tables of limb-darkening coefficients derived from the newly incorporated model atmospheres, such that they can be used as inputs in other binary modelling codes.
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All authors David Jones, Nicole Reindl, Kyle Conroy, James Munday, Pier-Emmanuel Tremblay, Michael Abdul-Masih, Matthias Fabry, Joseph Giammarco, Kelly Hambleton, Herbert Pablo, Marcin Wrona, Andrej Prsa

Cosmology and Nongalactic Astrophysics

Alcock-Paczynski Blinding Scheme for the Ly-$\alpha$ Forest Analysis

G. Perez-Sanchez, S. F. Beltran, G. Niz et al. (+45 more)

We present and validate a blinding method for the Lyman-$\alpha$ (Ly$\alpha$) forest analysis based on a modification of the Alcock-Paczynski test. In order to hide the background expansion history, the method employs a geometrical shift of each quasar (QSO) forest in wavelength space, once the quasar continuum has been fitted and the fluctuation field is extracted. The redshift positions for the QSO sample are also changed in a consistent manner. We show that the method remains effective when applied to real data, where contamination from metals and Lyman-$\beta$ is intrinsically mixed with the Lyman-$\alpha$ forest. This limitation is primarily visible in the 1D correlation function, where other blinding strategies can mitigate the effect. To assess its effectiveness, the prescription is tested against a series of datasets of increasing complexity: from idealized low-noise mocks, to realistic DESI year one synthetic datasets, and finally to data from DESI first data release (DR1), using both the auto (Ly$\alpha\times$Ly$\alpha$) and cross (Ly$\alpha\times$ QSO) correlations. We find that the method robustly shifts the BAO peak position from the 3D correlation functions to the expected value for cosmology changes of around 5% in the matter content, without altering the shape of the posteriors in the model parameters. In conclusion, this catalog-level blinding strategy is a viable method for cosmological inference with the Lyman-$\alpha$ forest, particularly if a cross-analysis with other tracers using the same blinding strategy is pursued.
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All authors G. Perez-Sanchez, S. F. Beltran, G. Niz, S. Brieden, L. Verde, A. Font-Ribera, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. Cuceu, A. de la Macorra, B. Dey, P. Doel, S. Ferraro, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, A. X. Gonzalez-Morales, G. Gutierrez, H. K. Herrera-Alcantar, K. Honscheid, D. Huterer, M. Ishak, R. Joyce, A. Kremin, O. Lahav, A. Lambert, M. Landriau, L. Le Guillou, M. Manera, P. Martini, R. Miquel, S. Nadathur, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, E. F. Schlafly, D. Schlegel, M. Schubnell, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver

Astrophysics of Galaxies

On the detection of Population III galaxies: Emission Line Diagnostics for Hybrid Stellar Populations

S. Goswami, J. M. Vílchez, C. Kehrig et al. (+2 more)

Identifying Population III (Pop III) stars, the first generation of metal-free stars in the early Universe, remains a central challenge in astrophysics. High-ionization emission lines, such as HeII are commonly used as tracers of Pop III signatures. However, realistic galaxies may host hybrid stellar populations, including both Pop III and metal-enriched Population II (Pop II) stars, complicating the interpretation of observed spectra. We aim to investigate how hybrid Pop III/Pop II stellar populations affect emission line diagnostics and assess the detectability of Pop III stars across different galactic environments and redshifts. We select galaxies with varying Pop III-to-total mass ratios from the IllustrisTNG cosmological simulations. Using self-consistent photoionisation models, we compute integrated spectra by adopting local physical conditions from the simulations to study the resulting emission line diagnostics. We find that emission line diagnostics are strongly dependent on the relative Pop III contribution. Current diagnostics can identify galaxies dominated totally by Pop III stars but fail for systems where Pop II stars contribute significantly, introducing degeneracies in interpreting observed spectra. Our results highlight the limitations of existing emission line diagnostics in hybrid systems and emphasize the need for additional methods that account for mixed stellar populations to reliably detect Pop III stars during and after the epoch of reionization.
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All authors S. Goswami, J. M. Vílchez, C. Kehrig, A. Ferrara, J. Iglesias-Páramo

Cosmology and Nongalactic Astrophysics

Multipolar structure of the local expansion rate from incomplete sky data

João G. Vicente, Thiago S. Pereira, Ricardo G. Rodrigues et al. (+2 more)

Using the Cosmicflows-4 data, we reconstruct the first multipolar moments of a general function describing the local expansion rate. In addition to the conventional harmonic approach, we employ a basis of symmetric and trace-free tensors to characterize the anisotropies of the expansion rate, allowing us to identify all directions associated with each of its multipoles. Focusing on objects in $z\in[0.01,0.05]$ in the CMB rest frame, we derive all $2\ell+1$ degrees of freedom in the multipoles $\ell=1,2$ and 3, which are split into one amplitude and $\ell$ unit vectors per multipole. To mitigate anisotropies induced by incomplete sky coverage, we introduce a pixel-based mask that removes poorly sampled pixels. The full-sky expansion rate is reconstructed using two independent approaches: a pseudo-inverse of the multipole-coupling kernel induced by the mask, and a maximum-likelihood estimate of the underlying full-sky field. These approaches are validated through simulations that explore different mask resolutions, cosmic variance and statistical noise. We find that the quadrupole and octupole amplitudes are consistent (at $95\%$ C.L.) with the expectations of a $\Lambda$CDM universe with linear and mild nonlinear perturbations, where the anisotropies of the expansion rate result from small peculiar velocities. The dipole amplitude, however, is inconsistent with $\Lambda$CDM predictions at 3.3$\sigma$, with a direction $(l, b) = (290^\circ, -4^\circ) \pm 5^\circ$ consistent with a bulk flow. This signal comes predominantly from sources in $z\in[0.03,0.05]$. Finally, we conduct alignment tests between the dipole, quadrupole, and octupole vectors. We confirm recent findings showing that the maxima of these multipoles are approximately located at $(290^\circ,-4^\circ)$. However, detailed tests using the complete vector structure of these multipoles reveal no evidence of alignments.
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All authors João G. Vicente, Thiago S. Pereira, Ricardo G. Rodrigues, Sandro D.P. Vitenti, Vitoria M. Gomes

High Energy Astrophysical Phenomena

Compact Objects Merging with Stars as an Origin of Ultra-Long Gamma-Ray Bursts and Luminous Fast Blue Optical Transients

V. Ashley Villar, Anya E. Nugent, Eric Burns et al. (+4 more)

Ultra-long gamma-ray bursts (ULGRBs) and luminous fast blue optical transients (LFBOTs) are two rare classes of engine-driven transients whose physical connection remains unknown. It has been suggested that both may arise from the mergers of a massive helium core with a compact object. We investigate this common origin by reanalyzing the optical counterpart of the highly unusual GRB 111209A/SN 2011kl associated with an ULGRB in the context of a recently developed, analytical LFBOT model. We find that SN 2011kl is broadly consistent with an LFBOT origin, exhibiting a rapid, luminous and blue early emission. However, compared to the LFBOT population, SN~2011kl features a longer "plateau" of emission ~2 weeks post-merger, suggesting an extended pre-merger mass-loss history, as well as stronger UV suppression. We additionally compare the host galaxy environments of five ULGRBs to those of LFBOTs and classical LGRBs. We find that ULGRBs, similar to LFBOTs and long GRBs, tend to occur in lower mass (<10^10 solar masses) galaxies with higher amounts of active star formation than observed for field galaxy populations at similar redshifts. Together, these results support a shared progenitor for at least a subset of ULGRBs and LFBOTs.
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All authors V. Ashley Villar, Anya E. Nugent, Eric Burns, Brian D. Metzger, Tarraneh Eftekhari, Jakub Klencki, Christopher L. Fryer

Astrophysics of Galaxies

The DESI View of the Faint Radio Source Population in LoTSS DR2

M. I. Arnaudova, L. R. Holden, D. J. B. Smith et al. (+10 more)

The faint radio-source population includes galaxies dominated by both star formation (SF) and active galactic nuclei (AGN), which are two key processes shaping galaxy evolution. To investigate this population, we probabilistically classified 251,413 radio sources from the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2) using spectroscopic data from the first release of the Dark Energy Spectroscopic Instrument (DESI DR1). Our classification method includes: (i) the identification of radio excess relative to SF, (ii) the Baldwin, Philips & Terlevich (BPT) diagram, (iii) a modified Mass Excitation (MEx) diagram, and (iv) the [OIII]5007 equivalent width. These are combined with Monte Carlo methods to estimate the probability that each source is a star-forming galaxy (SFG), a radio-quiet AGN (RQ AGN), or a low- or high-excitation radio galaxy (LERG or HERG), allowing various thresholds to be applied depending on science goals. Considering classifications above a 90 per cent probability threshold, we identify 68,820 SFGs, 32,288 RQ AGN, 35,210 LERGs and 3,085 HERGs, representing the largest radio sample to date with high-confidence spectroscopic classifications. Using this sample, we show with higher statistical power than previous studies that LERGs typically accrete below 1 per cent of the Eddington limit and HERGs above it. We also identify a small subset of high-accreting LERGs whose stacked spectra reveal prominent star-forming features, highlighting difficulties in interpreting their accretion properties. Our results demonstrate the power of large spectroscopic samples to characterise the radio-source population, providing a foundation for studies in the SKA era.
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All authors M. I. Arnaudova, L. R. Holden, D. J. B. Smith, P. N. Best, R. Kondapally, K. J. Duncan, A. Bushi, S. Das, S. R. Flury, C. L. Hale, M. J. Hardcastle, H. J. A. Rottgering, S. Shenoy

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

Causal Horizons, Geodesic Completeness and Stability in Slow Contraction Cosmology

Mariam Khaldieh, Anna I. Rosenzweig and Paul J. Steinhardt

We show that cosmological models with a semi-infinite phase of slow contraction (ekpyrosis) possess a combination of properties that can address several fundamental problems in cosmology, otherwise faced in contracting de Sitter phases or standard big bang expansion. In particular, slow contraction admits a stable past attractor asymptoting to Minkowski space, as well as a stable, flat, homogeneous, and isotropic future attractor with negligible Weyl curvature (and, therefore, negligible gravitational entropy). In bouncing cosmologies, this contracting attractor is terminated by a smooth, non-singular bounce that transforms the attractor properties at the end of contraction into the initial conditions for the subsequent expanding phase. Cosmologies incorporating a slow contraction phase have no particle horizon and therefore avoid the causal horizon problem. The past Minkowski attractor also generates an initial spectrum of vacuum-like quantum fluctuations on all wavelengths. Moreover, because the averaged expansion rate along past-directed geodesics is non-positive, models incorporating a semi-infinite phase of slow contraction also evade the Borde,Guth and Vilenkin theorem and are past geodesically complete. By contrast, contracting de Sitter space possesses a finite particle horizon and becomes unstable in the presence of scalar fields, matter, or radiation.
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Cosmology and Nongalactic Astrophysics

Intensity fluctuations of radio halo in galaxy cluster: Insights from power spectrum estimation

Srijita Pal, Nirupam Roy, Sameer Salunkhe et al. (+3 more)

Non-thermal synchrotron emissions from radio halo allow us to study mechanisms of particle (re)acceleration, magnetic field distribution, merger history, and turbulence in the intra-cluster medium. We propose power spectrum estimation as a novel and complementary method to study galaxy clusters. We use 610 MHz observations of MACSJ0014.3-302 and MACSJ0152.5-2852 to estimate the angular power spectrum (C_l) from the central halo regions. The C_l shows excess emission only for MACSJ0014.3-302. Using simulations, we find that a halo model with power-law fluctuations, in addition to the smooth exponential radial profile, is required to explain the observed C_l. We compare the observed power-law with existing models of MHD turbulence. The method may be useful for large data from SKA, finding megahalos in other sources, or detecting faint cluster emissions beyond the visible extent.
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All authors Srijita Pal, Nirupam Roy, Sameer Salunkhe, Surajit Paul, Tanu Sharma, Samir Choudhuri

Astrophysics of Galaxies

Scaling Relations for Binary Black Hole Merger Times from Cosmological Initial Conditions

Thibaut L. Francois, Alessia Gualandris and Walter Dehnen

Recent evidence from Pulsar Timing Arrays (PTAs) for a nanohertz gravitational wave background is broadly consistent with theoretical expectations from a population of massive black hole binaries (MBHBs), although the inferred amplitude appears somewhat higher than predicted by standard models. Interpreting these observations requires a robust understanding of the merger timescales of MBHBs, and of their connection to host galaxy properties. In this work, we investigate the evolution of MBHBs selected from cosmological galaxy mergers in the IllustrisTNG simulation. We re-simulate these systems at high resolution using the N-body code Griffin to accurately resolve the dynamical friction and stellar hardening phases, and follow their evolution to coalescence with a semi-analytical model. We find that cosmological galaxy encounters and the resulting MBHBs are typically highly eccentric. We characterise the distribution of binary eccentricities at formation and at entry into the PTA band, and quantify the corresponding residence times. We identify the key parameters governing the duration of the different stages of MBHB evolution, and derive scaling relations linking galaxy and orbital properties to dynamical friction, hardening, and total coalescence times. These relations provide a framework for subgrid prescriptions in cosmological simulations. Applying these scaling relations to the full IllustrisTNG merger population, we infer the probability distributions of galaxy merger and black hole coalescence times. We find that galaxy mergers typically complete within $\sim 0.7$ Gyr, while the total black hole coalescence time is $\sim 1.0$ Gyr. These short timescales imply efficient binary evolution, consistent with current PTA constraints.
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Astrophysics of Galaxies

Boötes III is a Tidally Disrupting Ultra-Faint Dwarf Galaxy on an Eccentric Polar Orbit

Ting S. Li, Denis Erkal, Andrew B. Pace et al. (+20 more)

We present updated systemic properties of the ultra-faint dwarf galaxy Boötes III from the Southern Stellar Stream Spectroscopic Survey (S$^5$). We identify 21 high-probability members and measure a velocity dispersion of $\sigma_{v} = 1.69^{+1.03}_{-0.85}$ km s$^{-1}$, about six times smaller than the previously reported $10.7 \pm 3.5$ km s$^{-1}$, and a mean metallicity of [Fe/H] $= -2.34 \pm 0.11$. The revised dispersion brings Boötes III in line with other tidally disrupting dwarfs such as Antlia II and Crater II. Orbit integrations in a Milky Way (MW) + Large Magellanic Cloud (LMC) potential confirm a highly eccentric ($e \approx 0.8$), polar ($i \approx 89.5^\circ$) orbit with a recent pericentric passage $\sim 0.14$ Gyr ago at $r_{\rm peri} \approx 9.5$ kpc. Boötes III is thus likely actively tidally disrupting, as its tidal radius at pericenter, $r_t \approx 164$ pc, is only $\sim 0.35$ of its half-light radius. The unusually low dispersion also implies that Boötes III has either lost most of its dark matter to tides or hosts a cored inner density profile, making it a probe of the nature of dark matter. Simulated tidal streams are broadly consistent with the Styx stellar stream, though the predicted track and kinematics are sensitive to the MW halo mass, LMC mass, and solar velocity. Boötes III overlaps the Typhon stream in integrals-of-motion space but has a much lower mean metallicity, suggesting the two are not the same system but may have had a common group infall origin. Sagittarius-stream contamination prevents a direct tidal-tail detection, so deep spectroscopic follow-up remains essential, both to confirm Styx as a genuine stream and to establish it as Boötes III's tidal tail.
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All authors Ting S. Li, Denis Erkal, Andrew B. Pace, Jiaxun Yang, Sergey E. Koposov, Jo Bovy, Nathan R. Sandford, Andrew P. Li, Gustavo E. Medina, Lara R. Cullinane, Gary S. Da Costa, Alexander P. Ji, Kyler Kuehn, Geraint F. Lewis, Guilherme Limberg, Sarah L. Martell, Aldo Mura-Guzmán, Nora Shipp, Yong Yang, Daniel B. Zucker, Kaia R. Atzberger, Joss Bland-Hawthorn, John D. Dixon

Astrophysics of Galaxies

The incidence of eROSITA X-ray AGN in the local Universe: from dwarf to massive galaxies

Z. Igo, A. Merloni, A. Georgakakis et al. (+22 more)

Combining deep, wide-area X-ray surveys with multi-wavelength catalogues provides insights into rare, highly-accreting AGN and low-mass galaxies at low redshift, the latter potentially representing local analogues of the first galaxies in the early Universe. We use the four-pass eROSITA All Sky Survey to select the largest catalogue of X-ray AGN in a highly complete sample of low-redshift galaxies, including low-mass (logM*/Msol<10) ones. We probe their distribution of specific accretion rates, $\lambda$_SAR, and the cumulative AGN fraction above varying $\lambda$_SAR thresholds. Our parent sample consists of ~5.35 million galaxies selected from the Legacy Survey DR10 with z-band fluxes brighter than 20 mag and redshifts 0.03<z<0.2. We place particular emphasis on the detailed characterisation of our sample, including estimating unbiased physical galaxy properties and rigorous cleaning and validation of the X-ray aperture photometry and host-galaxy associations. We identify 874 X-ray AGN in low-mass galaxies, most of them newly discovered as X-ray emitters. Thanks to a Bayesian framework that makes use of the X-ray information from all parent sample galaxies, we constrain the specific accretion rate distribution, p(log$\lambda$_SAR | M*, z), across a wide range of $\lambda$_SAR and uncover second-order mass-dependent effects. We detect a break at high $\lambda$_SAR, possibly indicating Eddington-limited, self-regulated black hole growth. Integrating p(log$\lambda$_SAR | M*, z) above $\lambda$_SAR>10^-3, we find a cumulative AGN fraction of ~1% for low-mass galaxies, placing a firm lower limit on the black hole occupation fraction in this regime. Overall, our specific accretion rate distributions, sampling down to the as-of-yet unexplored low-mass regime, highlight a more nuanced, mass-dependent view of AGN growth and accretion history that must be taken into account in future modelling.
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All authors Z. Igo, A. Merloni, A. Georgakakis, J. Buchner, R. Arcodia, M. Salvato, J. Aird, K. Nandra, B. Trakhtenbrot, P. G. Boorman, J. Comparat, G. Lamer, B. Laloux, M. Kluge, W. Roster, E. Bulbul, F. Balzer, T. Dwelly, W. N. Brandt, R. Seppi, S. Morrison, E. Kyritsis, J. Gelfand, S. F. Anderson, D. P. Schneider

Astrophysics of Galaxies

Tracing black hole and galaxy growth across environments since cosmic noon

Emma Jane Weller, Priyamvada Natarajan, Colin J. Burke et al. (+1 more)

The distribution of systems in the black hole (BH) mass-stellar mass ($M_\mathrm{BH}-M_\star$) plane encodes both the integrated growth of galaxies and their central black holes, and the processes that shape their evolution. Using the ASTRID and TNG300 cosmological simulations, we track massive BHs from cosmic noon ($z=2$) to $z=0.5$. TNG300 repositions BHs to the centers of their host galaxies at every time step, while ASTRID instead advances them under the resolved gravitational forces plus a subgrid dynamical friction model, allowing BHs to wander off-center when orbital decay is inefficient. We follow the BHs rather than their original host galaxies, thereby capturing central BHs, BHs in satellites, and wandering BHs. We find that central BHs in both simulations evolve along a tight, nearly redshift-invariant $M_\mathrm{BH}-M_\star$ relation that is broadly consistent with local empirical constraints. Departures from this relation trace distinct evolutionary channels in which mergers play a key role. Major galaxy mergers drive BH-BH coalescence that dominates the growth of the most massive central BHs. These BHs subsequently quench their hosts through active galactic nucleus (AGN) kinetic feedback. Minor mergers tidally strip satellites to lower $M_\star$ at nearly fixed $M_\mathrm{BH}$, producing weakly accreting, overmassive central BHs in gas-poor systems. In ASTRID, satellite accretion and inefficient dynamical friction generate wandering BHs that are undermassive relative to their new hosts and experience minimal accretion or merger-driven growth. A BH's location in the $M_\mathrm{BH}-M_\star$ and specific BH accretion rate-specific star formation rate planes is therefore a fossil record of its dynamical, accretion, merger, and feedback history.
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All authors Emma Jane Weller, Priyamvada Natarajan, Colin J. Burke, Shashank Dattathri

Astrophysics of Galaxies

Probing the origins. III. Exoplanet demographics across Galactic birth radii

Juan José García-Delgado, M. L. L. Dantas, Isabel Rebollido et al. (+1 more)

We quantify radial mixing in exoplanet hosts and explore links between birth environment, orbital evolution, planetary architecture, and Galactic habitability. We constructed a homogeneous catalogue by cross-matching the Encyclopaedia of Exoplanetary Systems with Gaia DR3 astrometry and infrared photometry from 2MASS and AllWISE. Stellar orbits were integrated using Galpy. Stellar birth radii were inferred by combining Galactic chemical enrichment models with the generalised additive model introduced in Paper I. Giant-planet hosts preferentially trace inner-Galaxy birth sites, whereas brown-dwarf hosts span a broader, less localised range of radial displacements. Rocky-only systems show smaller radial excursions and less centrally concentrated birth radii, while rocky+giant systems are intermediate, retaining a stronger link to inner-disc birth environments than rocky-only systems. We also find that outward-migrators host more compact outer detected companions than inward-migrators, with non-migrators in between. This trend remains tentative because of heterogeneous detection biases. Giant-planet hosts retain a strong connection to metal-rich inner-Galaxy birth environments, whereas brown-dwarf hosts span a broader range of radial displacements, and rocky-only systems are less centrally concentrated. The older ages of rocky and rocky+giant hosts, especially among outward migrators, make them useful reference populations for future habitability and technosignature searches. Dynamically heated outer-Galaxy-born hosts show that planet-hosting systems can survive significant Galactic perturbations, although whether their architectures retain causal imprints of this evolution remains uncertain. No clear connection is found between radial displacement and the number of detected planets.
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All authors Juan José García-Delgado, M. L. L. Dantas, Isabel Rebollido, Rodolfo Smiljanic

High Energy Astrophysical Phenomena

The SANE, the MAD, and the Chimera

George N. Wong and James M. Stone

Non-radiative black hole accretion flows are commonly classified by their magnetic flux state, with standard and normal evolution (SANE) disks and magnetically arrested disks (MADs) marking the usual weak- and strong-flux regimes. We compare three-dimensional general relativistic magnetohydrodynamics simulations of a weakly magnetized SANE flow, a standard MAD, and a Chimera flow fed by a different reservoir of mass, angular momentum, and coherent magnetic flux. The Chimera reaches a MAD-level horizon magnetic flux and launches a powerful electromagnetic jet during an extended non-eruptive interval, showing that a flow can maintain large horizon flux and jet power without sharing the standard MAD's bursty horizon-flux variability, mass-flow distribution, or inner-flow morphology. In the SANE flow, we show that radial support is primarily hydrodynamic and provided by gas pressure gradients, whereas in MAD flows, magnetic pressure and tension enter the radial force budget at comparable order and help regulate the inner flow dynamics. The Chimera remains distinct from the standard MAD in its density structure, funnel-wall geometry, mass-flow channels, radial force budget, and angular-momentum transport throughout the analyzed evolution. We therefore argue that MAD-like behavior is not captured by any single diagnostic, but by a dynamical coupling among horizon flux, jet power, magnetic support, Maxwell transport, surface-layer flow, disk morphology, and eruption activity. The Chimera shows that these outcomes can be separated by accretion history and magnetic-flux supply.
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Instrumentation and Methods for Astrophysics

Blind Line Search System: BLiSS

Luis Abalo, Graciela Sanjurjo-Ferrín, Jessica Planelles-Villalva et al. (+2 more)

The increasing sensitivity and spectral resolution of current and forthcoming X-ray observatories, including XRISM and NewAthena, are expected to reveal increasing numbers of weak and blended emission lines, motivating reproducible tools for their systematic identification. Existing workflows often rely on manual inspection or source-specific analysis pipelines, making homogeneous analyses of large datasets difficult. To address this need, we present BLiSS (Blind Line Search System), an open-source Python package for the fast, blind detection and characterization of emission-line candidates in one-dimensional X-ray spectra without requiring a prior physical continuum model. BLiSS is intended as an exploratory analysis tool that complements subsequent physical spectral modelling. The package estimates an empirical baseline directly from the observed spectrum, identifies positive excesses, groups them into candidate regions, and characterizes them with Gaussian models. Candidate reliability is estimated by comparison with synthetic spectra using a Gaussian Mixture Model classifier. Finally, optional routines perform a simultaneous multi-Gaussian fit and associate detected features with compatible atomic transitions. The methodology implemented in BLiSS has already enabled published spectroscopic studies and is presented here as a documented, modular, and publicly available software package. Its performance is demonstrated using Chandra/HETGS and XRISM/Resolve observations of the high-mass X-ray binary Vela X-1, one of the best-studied X-ray sources. BLiSS recovers the principal emission features reported in previous studies while providing a fast, reproducible, and instrument-independent workflow for exploratory line searches.
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All authors Luis Abalo, Graciela Sanjurjo-Ferrín, Jessica Planelles-Villalva, José Joaquín Rodes-Roca, José Miguel Torrejón

Astrophysics of Galaxies

Supersonic Motion in the Driving Region of M82

Skylar Grayson, Evan Scannapieco, Philipp Grete et al. (+5 more)

The prototypical starburst galaxy M82 is host to an expansive, multiphase outflow whose driving mechanism is not fully understood. Longstanding models suggest that energy and mass injection from supernova into the hottest phase of the galactic wind could drive the cooler phases, but validating these models has been difficult due to the lack of constraints on the hot wind energetics. The high-resolution spectral capabilities of XRISM have generated the tightest constraints to date on the temperatures of the hot wind, as well as the first direct measurement of its velocity dispersion. In this work, we use these new observational constraints to test a model of a supernova-driven free wind. We generate a suite of highly idealized hydrodynamic simulations varying the energy and mass loading of the starburst and construct mock spectra to compare against the XRISM results. We find that the observed velocity dispersion is impossible to replicate using our free-wind model alone, and extra broadening is required to fit the spectrum. We interpret this broadening to be due not to bulk outflow, but rather to smaller scale non-thermal motions in the driving region of the starburst. This implies supersonic motion (Mach 1.71-3.14) of the hot gas in the central region of the galaxy. As supersonic motions are unexpected, it is possible that a significant amount of the energy that should go into heating the gas is instead going towards other sources such as amplifying magnetic fields and driving cosmic rays.
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All authors Skylar Grayson, Evan Scannapieco, Philipp Grete, Erin Boettcher, Marcus Brüggen, Edmund Hodges-Kluck, John ZuHone, Yutaka Fujita

Solar and Stellar Astrophysics

Stellar J-Harvesting: a novel angular momentum technosignature and first search in the Kepler field

Sahin Torlakcik

We introduce Stellar J-Harvesting (SJH), a technosignature in which an engineered system extracts rotational angular momentum from a star. Unlike a classical Dyson sphere, such a system need not produce a detectable mid-infrared excess; its clearest signature would be a star rotating more slowly than comparable peers. We derive the energy-period relation for this effect, outline several possible coupling channels, and apply a population-relative slow-rotator search to Kepler stars using colour-gravity bins. After eight false-positive filters, the clean sample contains 6,725 FGK main-sequence stars. We find two >4 sigma slow rotators, but Gaia DR3 indicators and WISE imaging point to more ordinary explanations, including unresolved binaries and low metallicity. We therefore make no detection claim and place a conservative pilot upper limit on the occurrence of strong SJH-like signals, f_SJH < 4.5e-4. The main result is a search framework: angular-momentum technosignatures are testable with existing stellar-rotation catalogues, and the strongest outliers define concrete targets for spectroscopic, imaging, and radio follow-up.
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Cosmology and Nongalactic Astrophysics

The Status of Single Scalar Field Dark Energy

Carlos García-García, Pedro G. Ferreira and William J. Wolf

We present an assessment of the current observational status of single scalar field models of dark energy. Motivated by recent cosmological measurements – including baryon acoustic oscillations, Type Ia supernovae, and CMB data – we examine whether a dynamical scalar field offers a viable explanation for the accelerated expansion of the Universe. Working within an effective field theory (EFT) framework, we argue that cosmological observations are fundamentally limited and can at most constrain a small number of parameters that govern scalar field dynamics. We show that quintessence remains only marginally distinguishable from a cosmological constant, $\Lambda$, and that more general EFT extensions exhibit modest statistical preference, though such evidence is sensitive to data set selection and prior assumptions. These extended models generically predict fifth forces and modifications to the growth of structure, raising challenges from astrophysical constraints. We compare their predictions with current growth rate measurements, Integrated Sachs-Wolfe (ISW) effect and Solar System constraints. We emphasize that viable screening mechanisms remain theoretically non-trivial and observationally testable. On the other hand, we find that current ISW and growth data remain largely in agreement. Looking ahead to Stage IV surveys we forecast improvements in constraints on the dark energy behaviour; although there will be some tightening of bounds, we argue that the problem of underdetermination will persist. We conclude that while single scalar field dark energy remains a natural and flexible framework, its ultimate viability will hinge on improved low-redshift growth measurements and a clearer understanding of gravitational screening.
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Cosmology and Nongalactic Astrophysics

Infrared-enhanced Photometric Redshifts for the Dark Energy Survey Y6 Gold catalogue

M. M. Puebla, I. Sevilla-Noarbe, J. de Vicente et al. (+13 more)

The Dark Energy Survey (DES) provides optical data across 5000 square degrees of the southern sky, enabling a broad range of extragalactic and cosmological studies. Combining DES data with infrared surveys offers the opportunity to improve its photometric redshift (photo-z) estimates. We aim to investigate improvements in photometric redshift estimation achieved by combining DES optical data with infrared measurements from the VISTA Hemisphere Survey (VHS) and the Wide-field Infrared Survey Explorer (WISE), and release an updated version of the catalogue. We performed a positional sky cross-match between the DES Y6 Gold catalogue matched to a spectroscopic dataset, the 2013 AllWISE Data Release, and VHS Data Release 5, in order to test these improvements using the Directional Neighbourhood Fitting (DNF) algorithm (Y6 Gold catalogue reference estimator). We additionally matched it to the unWISE catalogue to verify the performance against this deeper dataset. Adding infrared data reduces all the metrics (scatter, bias and outlier fraction) in photo-z estimates, particularly at higher redshifts in comparison with only using optical data from DES. The obtained results are globally better for the DES+WISE sample, with improvements that are statistically significant. On the other hand, the addition of the VHS bands to available depth is only marginal. The combined use of DES and WISE W1 and W2 data improves the photometric redshift metrics analysed here. The addition of VHS data at the DES and VHS depths explored here does not provide any further improvement at z less than 1.5, indicating that, under these constraints, WISE data may already capture the key infrared features and depth needed for accurate photo-z estimation. In addition, low signal-to-noise (less than 10) infrared data does not contribute to any improvement beyond the DES optical dataset.
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All authors M. M. Puebla, I. Sevilla-Noarbe, J. de Vicente, L. Toribio San Cipriano, J. Carretero, A. Drlica-Wagner, J. García-Bellido, D. Gruen, J. Gschwend, T. A. Manning, M. de la Osa, A. Porredon, N. Reynes, E. Sánchez, P. Tallada, N. Weaverdyck

High Energy Astrophysical Phenomena

Sub-Torque-Balance Upper Limits on Continuous Gravitational Waves from Scorpius X-1

The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration et al. (+1833 more)

We present the results of a search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1 using LIGO data from the first part of the fourth LIGO-Virgo-KAGRA observing run. By applying the resampling version of the cross-correlation pipeline to search for signal frequencies $f_0$ between $25$ and $200\un{Hz}$ (corresponding to neutron star spin frequencies of $12.5$ to $100\un{Hz}$ for GW due to triaxiality, or $\sim15-20$ to $\sim120-150\un{Hz}$ for GW due to $r$-modes), we set upper limits below the standard torque balance level, independent of neutron star spin inclination, for $50\un{Hz}\lesssim f_0\lesssim200\un{Hz}$. While uncertainties in the modelling of torque and equation of state limit the strength of our inference, our results nonetheless argue against torque balance in this spin range for a neutron star described by a hadronic equation of state. The most sensitive upper limits on the gravitational wave amplitude $h_0$, at the upper end of the frequency band searched, approach $5\times10^{-26}$ marginalized over inclination angle and $2\times10^{-26}$ assuming the most favorable inclination. The marginalized upper limits correspond to a sensitivity depth of $70-75\un{Hz}^{-1/2}$, improving sensitivity considerably over previous searches. Expressed as constraints on the triaxial deformation of the neutron star, the limits correspond to an ellipticity of $3\times10^{-5}$ if the GW frequency $f_0$ is $75\un{Hz}$ and $3\times10^{-6}$ if $f_0=200\un{Hz}$, approaching deformations which could be supported by ordinary nuclear matter. Outliers from the search were ruled out as potential signals by a combination of hierarchical followup and analysis of additional data from later in the observing run.
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All authors The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, the Precision Ephemerides for Gravitational-Wave Searches Project: A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, A. Adam, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I.-L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu, S. Albanesi, L. Albers, W. Ali, S. Al-Kershi, C. Alléné, A. Allocca, S. Al-Shammari, P. A. Altin, S. Alvarez-Lopez, W. Amar, O. Amarasinghe, A. Amato, F. Amicucci, C. Amra, C. Anand, A. Ananyeva, S. B. Anderson, W. G. Anderson, M. Andia, M. Ando, M. Andrés-Carcasona, J. L. Andrey, T. Andrić, J. Anglin, J. Anna, S. Ansoldi, J. M. Antelis, S. Antier, M. Aoumi, E. Z. Appavuravther, S. Appert, S. K. Apple, K. Arai, A. Araya, M. C. Araya, M. Arca Sedda, F. Arciprete, J. S. Areeda, N. Aritomi, F. Armato, S. Armstrong, N. Arnaud, M. Arogeti, S. M. Aronson, G. Ashton, Y. Aso, L. Asprea, M. Assiduo, S. Assis de Souza Melo, S. M. Aston, P. Astone, F. Attadio, F. Aubin, K. AultONeal, G. Avallone, E. A. Avila, S. Babak, C. Badger, S. Bae, S. Bagnasco, L. Baiotti, R. Bajpai, T. Baka, K. A. Baker, T. Baker, G. Balbi, G. Baldi, N. Baldicchi, M. Ball, G. Ballardin, S. W. Ballmer, S. Banagiri, B. Banerjee, D. Bankar, T. M. Baptiste, P. Baral, M. Baratti, J. C. Barayoga, K. Baric, B. C. Barish, D. Barker, N. Barman, P. Barneo, F. Barone, B. Barr, M. Barrios, L. Barsotti, M. Barsuglia, D. Barta, M. A. Barton, I. Bartos, A. Basalaev, R. Bassiri, A. Basti, M. Bawaj, P. Baxi, J. C. Bayley, A. C. Baylor, P. A. Baynard II, M. Bazzan, V. M. Bedakihale, F. Beirnaert, M. Bejger, D. Belardinelli, A. S. Bell, C. Bellani, L. Bellizzi, D. Beltran-Martinez, W. Benoit, I. Bentara, M. Ben Yaala, S. Bera, F. Bergamin, B. K. Berger, S. Bernuzzi, M. Beroiz, I. Berry, D. Bersanetti, T. Bertheas, A. Bertolini, J. Betzwieser, D. Beveridge, G. Bevilacqua, N. Bevins, R. Bhandare, R. Bhatt, A. Bhattacharjee, D. Bhattacharjee, S. Bhattacharyya, S. Bhaumik, V. Biancalana, A. Bianchi, F. Bianchi, I. A. Bilenko, G. Billingsley, A. Binetti, S. Bini, C. Binu, S. Biot, O. Birnholtz, S. Biscoveanu, A. Bisht, M. Bitossi, M.-A. Bizouard, S. Blaber, J. K. Blackburn, L. A. Blagg, C. D. Blair, D. G. Blair, N. Bode, N. Boettner, P. Bogdan, G. Boileau, M. Boldrini, G. N. Bolingbroke, A. Bolliand, L. D. Bonavena, R. Bondarescu, F. Bondu, V. A. Bonhomme, E. Bonilla, M. S. Bonilla, A. Bonino, R. Bonnand, A. Borchers, N. Borghi, V. Boschi, S. Bose, V. Bossilkov, Y. Bothra, A. Boudon, M. Boyle, A. Bozzi, C. Bradaschia, M. J. Brady, P. R. Brady, A. Branch, M. Branchesi, T. Briant, A. Brillet, M. Brinkmann, P. Brockill, E. Brockmueller, A. F. Brooks, B. C. Brown, D. D. Brown, M. L. Brozzetti, S. Brunett, G. Bruno, R. Bruntz, J. Bryant, Y. Bu, F. Bucci, J. Buchanan, O. Bulashenko, T. Bulik, H. J. Bulten, A. Buonanno, K. Burtnyk, R. Buscicchio, D. Buskulic, C. Buy, R. L. Byer, R. Cabrita, V. Cáceres-Barbosa, L. Cadonati, G. Cagnoli, C. Cahillane, A. Calafat, T. A. Callister, E. Calloni, S. R. Callos, M. Canepa, G. Caneva Santoro, K. C. Cannon, H. Cao, L. A. Capistran, E. Capocasa, G. Capoccia, E. Capote, G. Capurri, G. Carapella, F. Carbognani, K. J. Cardona-Martínez, M. Carlassara, J. B. Carlin, T. K. Carlson, M. F. Carney, M. Carpinelli, G. Carrillo, J. J. Carter, G. Carullo, A. Casallas-Lagos, J. Casanueva Diaz, C. Casentini, S. Caudill, M. Cavaglià, R. Cavalieri, G. Cella, S. Cepic, P. Cerdá-Durán, E. Cesarini, N. Chabbra, W. Chaibi, A. Chakraborty, P. Chakraborty, S. Chakraborty, S. Chalathadka Subrahmanya, R. Chalmers, C. Chan, J. C. L. Chan, M. Chan, K. Chang, P. Charlton, E. Chassande-Mottin, C. Chatterjee, Debarati Chatterjee, Deep Chatterjee, M. Chaturvedi, S. Chaty, A. Chen, A. H.-Y. Chen, D. Chen, H. Chen, H. Y. Chen, S. Chen, Y. Chen, G. Cheng, H. P. Cheng, P. Chessa, T. Cheunchitra, H. T. Cheung, S. Y. Cheung, F. Chiadini, G. Chiarini, A. Chiba, A. Chincarini, D. Chintala, M. L. Chiofalo, A. Chiummo, C. Chou, S. Choudhary, N. Christensen, S. S. Y. Chua, G. Ciani, P. Ciecielag, M. Cieślar, M. Cifaldi, B. Cirok, F. Clara, J. A. Clark, T. A. Clarke, P. Clearwater, S. Clesse, F. Cleva, S. M. Clyne, E. Coccia, E. Codazzo, P.-F. Cohadon, D. E. Cohen, S. Colace, E. Colangeli, O. Cole, M. Colleoni, C. G. Collette, J. Collins, S. Colloms, A. Colombo, C. M. Compton, G. Connolly, L. Conti, T. R. Corbitt, I. Cordero-Carrión, S. Corezzi, N. J. Cornish, I. Coronado, A. Corsi, L. A. Corubolo, L. Cotnoir, R. Cottingham, M. W. Coughlin, P. Couvares, D. M. Coward, D. C. Coyne, R. Coyne, A. Cozzumbo, J. D. E. Creighton, T. D. Creighton, S. Crook, R. Crouch, J. Csizmazia, J. R. Cudell, T. J. Cullen, A. Cumming, E. Cuoco, M. Cusinato, L. V. Da Conceição, T. Dal Canton, S. Dall'Osso, S. Dal Pra, G. Dálya, O. Dan, Y. Dang, B. D'Angelo, S. Danilishin, S. D'Antonio, K. Danzmann, K. E. Darroch, L. P. Dartez, R. Das, A. Dasgupta, V. Dattilo, A. Daumas, I. Dave, A. Davenport, M. Davier, T. F. Davies, D. Davis, L. Davis, M. C. Davis, P. Davis, E. J. Daw, M. Dax, J. De Bolle, M. Deenadayalan, J. Degallaix, M. De Laurentis, C. J. Delgado Mendez, F. De Lillo, S. Della Torre, W. Del Pozzo, O. M. del Rio, A. Demagny, F. De Marco, G. Demasi, F. De Matteis, N. Demos, T. Dent, A. Depasse, N. DePergola, R. De Pietri, R. De Rosa, C. De Rossi, M. Desai, V. Deshmukh, R. De Simone, S. Determan, A. Dhani, R. Dhurkunde, R. Diab, C. Diaz, M. C. Díaz, M. Di Cesare, G. Dideron, T. Dietrich, L. Di Fiore, C. Di Fronzo, M. Di Giovanni, T. Di Girolamo, D. Diksha, J. Ding, S. Di Pace, I. Di Palma, D. Di Piero, F. Di Renzo, Divyajyoti, A. Dmitriev, J. P. Docherty, Z. Doctor, N. Doerksen, E. Dohmen, A. Doke, A. Domiciano De Souza, L. D'Onofrio, F. Donovan, K. L. Dooley, T. Dooney, S. Doravari, O. Dorosh, F. Dosopoulou, W. J. D. Doyle, M. Drago, J. C. Driggers, M. Dubois, R. R. Dumbreck, L. Dunn, U. Dupletsa, D. D'Urso, P. Dutta Roy, H. 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