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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 6 July

Instrumentation and Methods for Astrophysics

CausticFlow: An Efficient Machine Learning Framework Combining Neural Differential Equations and Normalizing Flows for Binary Microlensing Parameter Inference

Haibin Ren and Wei Zhu

We introduce CausticFlow, a machine learning framework that combines neural controlled differential equations with normalizing flows to infer binary microlensing parameters. This architecture naturally handles irregularly sampled time series and data gaps while flexibly capturing strongly correlated and multimodal posterior distributions. Trained on simulated KMTNet-like light curves, CausticFlow generates posterior samples in a fraction of a second, with maximum-a-posteriori estimates achieving typical precisions of $\sim17\%$ for the mass ratio $q$ and $\sim3\%$ for the projected separation $s$. When used as a proposal distribution for downstream local optimization, the framework improves these precisions to $<5\%$ and $<1\%$, respectively, and recovers model $\chi^2$ for $\sim80\%$ of simulated events. We test the generalizability of the framework on 10 real binary lensing events characterized by higher-order effects, varied cadences, and real-world noise. Despite these mismatches between simulation and reality, CausticFlow successfully recovers the model parameters, light-curve morphology, and lensing geometry for 7 of the 10 events after simple local refinement, achieving precision levels comparable to those found for simulated data in 10 CPU minutes per event. These results demonstrate that CausticFlow acts as a fast and robust proposal engine that provides informative starting points for downstream local optimization, bridging the gap between the rapid influx of data and the need for systematic modeling in large-scale microlensing surveys such as Roman, CSST, and ET.
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Astrophysics of Galaxies

MICONIC: The spatial relationship between star formation and the AGN in Centaurus A revealed by JWST/MIRI

O. C. Jones, M. L. Jones, D. Dicken et al. (+21 more)

Centaurus A (Cen A), the nearest active radio galaxy, hosts a warped dust disc formed in a gas-rich merger. We present JWST/MIRI imaging in three filters, F560W, F770W, and F1130W, of this central disc over a ~4 x 2 kpc region to characterise its resolved mid-infrared stellar populations. The images reveal a system of extended dusty structures, previously identified with Spitzer as an "oval dusty shell", now resolved into multiple loop-like features that are brightest in F1130W and closely associated with the warped disc. Colour-magnitude and colour-colour diagnostics reveal a distinct population of 928 red point sources with strong infrared excess, accounting for ~36 per cent of sources with high-quality photometry in all three bands, spatially confined to the disc. These sources exhibit rising mid-infrared spectral slopes indicative of emission from warm dust. Their colours and spatial distribution are consistent with a population dominated by embedded young stellar objects, tracing recent (~10^5-10^6 yr) star formation within the disc. The strong geometric alignment of these sources with the disc, together with the lack of correlation with the radio jet, suggests that star formation in the central regions of Cen A is primarily regulated by merger-accreted gas, with no strong evidence for AGN jet-ISM interactions.
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All authors O. C. Jones, M. L. Jones, D. Dicken, G. S. Wright, M. García Marín, A. Alonso Herrero, P. Guillard, K. Justtanont, M. Meixner, A. Labiano, D. Rouan, P. van der Werf, L. Pantoni, V. A. Buiten, T. Böker, G. Östlin, L. Evangelista, M. Baes, L. Colina, L. Hermosa Muñoz, Th. Henning, M. Güdel, T. P. Ray, P.-O. Lagage

Cosmology and Nongalactic Astrophysics

Inverse-k Primordial Oscillations from a Symbolic Regression Search

Ze-Yu Peng, Qing-Yu Lan and Yun-Song Piao

Oscillatory features in the primordial power spectrum, potential signatures of new physics in the early universe, are usually searched for using fixed templates. In this work, we perform a template-free search for primordial features using symbolic regression. We find that both Planck and the combined Planck+ACT+SPT-3G datasets independently select an inverse-$k$ oscillation, $\cos(B/k)$ with $B\simeq4\,\mathrm{Mpc}^{-1}$, as the leading low-complexity feature. Comparing this inverse-$k$ template with standard linear and logarithmic oscillating templates, we find that it fits the data best, showing a weak preference for a non-zero amplitude. Our results show that symbolic regression as a powerful machine learning technique can provide an interpretable, model-independent approach to cosmological discovery.
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Instrumentation and Methods for Astrophysics

HRMOS: A High-Resolution Multi-Object Spectrograph for the VLT

Laura Magrini, Thomas Bensby, Sofia Randich et al. (+174 more)

This White Paper presents the scientific rationale and instrument concept for HRMOS (High-Resolution Multi-Object Spectrograph), a next-generation instrument proposed for the ESO Very Large Telescope within the VLT 2030 roadmap. Current and planned facilities offer either multi-object spectroscopy or ultra-high spectral resolution, but not both. HRMOS fills this gap by combining very high spectral resolution, multi-object capability, and radial-velocity stability, enabling transformative studies in Galactic and extragalactic astrophysics. The baseline design provides a resolving power of R = 80000, radial-velocity precision of 10 m s-1 (goal: 5 m s-1), simultaneous observations of 50-60 targets, and broad optical coverage down to 385 nm. These capabilities enable precise measurements of elemental abundances, isotopic ratios, line profiles, and radial velocities for large stellar samples, including crowded fields, star clusters, the Galactic bulge, and nearby dwarf galaxies. HRMOS will address key questions on the age of the oldest stellar populations through nucleocosmochronology, the formation and survival of planetary systems, the assembly history of the Milky Way and satellites, the origin of the heaviest elements, stellar evolution, and the chemical and dynamical properties of the interstellar and circumgalactic medium. It will bridge large spectroscopic surveys and the next generation of extremely large telescopes, with strong synergies with 4MOST, Gaia, TESS, PLATO, the proposed Haydn mission, and future ELT instruments. Building on VLT/FLAMES heritage, HRMOS represents a strategic investment for European astronomy in the 2030s.
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All authors Laura Magrini, Thomas Bensby, Sofia Randich, Andrea Bianco, Oscar Gonzalez, Emma Fernandez-Alvar, Sergio G. Sousa, Letizia Caito, Marco Riva, Vardan Adibekyan, Anish M. Amarsi, Maria Teresa Belmonte, Maria Benito, Christian P. Clear, Camilla Danielski, Valentina D'Orazi, Riano Giribaldi, Camilla J. Hansen, Vanessa Hill, Robin D. Jeffries, Georges Kordopatis, Andrea Miglio, Dinko Milakovic, Germano Sacco, Jose Schiappacasse-Ulloa, Asa Skuladottir, Rodolfo Smiljanic, Maria Tsantaki, Almudena Arcones, Jose Maria Arroyo-Polonio, Martina Baratella, Beatriz Barbuy, John R. Barnes, Giuseppina Battaglia, Holger Baumgardt, Katia Biazzo, Manuela Bischetti, Angela Bragaglia, Tobias Buck, Sven Buder, Sema Caliskan, Gabriele Cescutti, Andrew Collier Cameron, Ryan Cooke, Sergio Cristallo, Francesco Damiani, Arnas Drazdauskas, Heitor Ernandes, Antonio Frasca, Mark Gieles, Valeria Grisoni, Moira Jardine, Evan N. Kirby, Jonas Klevas, Andreas Korn, Ioanna Koutsouridou, Cis Lagae, Nadege Lagarde, Romain Lucchesi, Francesca Lucertini, Luca Malavolta, Fabiola Marino, Tadafumi Matsuno, Thibault Merle, Sapna Mishra, Marta Molero, Mario Montalto, Michele Moresco, Alessio Mucciarelli, Domenico Nardiello, Valerio Nascimbeni, Brunella Nisini, Joana Oliveira, Elenia Pacetti, Marco Palla, Marco Pignatari, Danae Polychroni, Federico Rizzuti, Donatella Romano, Stefania Salvadori, Luca Sbordone, Emanuele Spitoni, Matthew R. Standing, Grazina Tautvaivsiene, Yuan-Sen Ting, Andrea Travascio, Diego Turrini, Sophie Van Eck, Kim Venn, Diego Vescovi, C. Clare Worley, Nick Wright, Robert Yates, Alice Zocchi, Laura Affer, Carlos Allende, Paul Barklem, Michele Bellazzini, Serena Benatti, Leda Berni, Francesco Borsa, Maurizio Busso, Tiago Campante, Roberta Carini, Brad Carter, Giada Casali, Mario Damasso, Elisa Delgado Mena, Ignacio Del Moral Castro, Silvano Desidera, Maria Pia Di Mauro, Ana Escorza, Sergio Fonte, Elena Franciosini, Xiaoting Fu, Paolo Giacobbe, Terese Thidemann Hansen, Henrik Hartman, Keith Hawkins, Neda Heidari, Krzysztof Helminiak, H. Jens Hoeijmakers, Stavro Lambrov Ivanovski, Pascale Jablonka, Chiaki Kobayashi, Arunas Kucinskas, Carmela Lardo, Sebastiano Ledda, Alesandra Lehtmets, Karin Lind, João J.G. Lima, Sara Lucatello, Fatemeh Zahra Majidi, Sarah Martell, Anna McLeod, Sergio Molinari, Stephanie Monty, Benjamin Montet, Michael T. Murphy, Henryka Netzel-Iłkiewicz, Belinda Nicholson, Patrick Palmeri, Luca Pasquini, Lorenzo Pino, Romolo Politi, Francesca Primas, Pascal Quinet, Monica Rainer, Heleri Ramler, Yassin Rany Khalil, Martina Rossi, Eugenio Schisano, Federico Sestito, Paolo Simonetti, Arianna Vasini, Silvia Vicente, Carlos Viscasillas Vazquez, Manuela Zocchi, Michele Zusi, Andrea Baruffolo, Martin Black, Anna Brucalassi, Simone D'Auria, Vincenzo De Caprio, Michele Frangiamore, Enrico Giro, Robert J. Harris, Alen Khanbekyan, Enrique Joven, Tom Louth, Matteo Munari, Graham J. Murray, Luis Fernando Rodriguez Ramos, Bernardo Salasnich, William Taylor, Andrea Tozzi, Steven Watson

Astrophysics of Galaxies

FRANZ: Framework for analytical one-zone blastwave dynamics

Leonard E. C. Romano

(abridged) We develop a flexible analytical framework for modeling blastwave evolution in arbitrary environments and use it to investigate how large-scale galactic structure affects the dynamics and morphology of evolved SNRs and SBs. We introduce FRANZ (FRamework for ANalytical one-Zone blastwave dynamics), a modular thin-shell model that follows the local evolution of a shock-surface segment in environments characterized by arbitrary density, velocity and gravitational fields. After validating the model against well-established analytical results, we apply it to study the effects of vertical stratification, galactic shear and dense galactic substructure on blastwave evolution. FRANZ reproduces the classical evolution of blastwaves in uniform media while extending to complex environments. We derive criteria for disk break out in stratified media, characterize the timescales on which differential rotation deforms blastwaves and identify a new mechanism, by which it can suppress the momentum coupling in continuously-driven blastwaves. Interactions with dense filaments modify both shock-surface morphology and dynamics and confound the interpretation of the expansion history of observed remnants, which depends on the density distribution prior to the onset of explosions, which is fundamentally inaccessible from the observed state. In highly structured media with a high volume-filling factor of diffuse gas, ages inferred from the observed state may be systematically overestimated. FRANZ provides a computationally inexpensive and extensible framework for studying blastwaves in realistic galactic environments. It offers a useful complement to numerical simulations for interpreting observations of evolved SNRs and SBs and for developing improved models of stellar feedback in large-scale simulations.
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Cosmology and Nongalactic Astrophysics

Collisionless damping of the gravitational instability in fuzzy dark matter: spectral shape and quantum-to-thermal crossover

Yosuke Matsumoto, Kohji Yoshikawa and Naoki Yoshida

We present a quantum-kinetic linear theory of the gravitational instability in the context of fuzzy dark matter universe. Starting from the Wigner transport equation, we apply Landau's approach to the linearized Wigner–Poisson system and derive a kinetic dispersion relation that incorporates quantum effects exactly by introducing the plasma dispersion function. The growth rate as a function of wavenumber is characterized by a dimensionless quantum-to-thermal ratio $\alpha = k_{\mathrm{qJ}}/k_{\mathrm J}$, where $k_{\mathrm{qJ}}$ and $k_{\mathrm J}$ represent the quantum and thermal Jeans wavenumbers, respectively. We derive an analytic expression for the spectral slope at the cutoff wavenumber, revealing that the spectral shape undergoes a sharp transition across $\alpha \sim 0.5$. This implies a crossover from a thermally dominated kinetic regime, in which collisionless damping occurs via phase mixing and Landau resonance, to a regime dominated by quantum pressure. By applying these results to fuzzy dark matter, we show that the cutoff scale and its spectral shape depend sensitively on both the particle mass and the initial velocity dispersion, suggesting a method for simultaneously constraining these parameters through observations of the matter power spectrum. This framework provides a theoretical basis for future studies on the transition from early-phase thermal states to the formation of Bose-Einstein condensates in galactic structures.
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Astrophysics of Galaxies

Shared star formation in the Milky Way and Magellanic Clouds

Xunchuan Liu and Yu Cheng

We investigate the structural and evolutionary similarities between star formation patterns in different environments by comparing the dense clump populations in the Milky Way (MW) from the ATLASGAL survey with those from the Herschel HERITAGE survey in the Magellanic Clouds (MCs). Our analysis reveals that MW and MC clumps behave as physical analogs, sharing consistent dust temperature distributions, mass spectra, and luminosity evolutionary trends. We establish that the warmest MC clumps and the most distant MW clumps share an identical fiducial parent structure bounded by a natural spatial scale of $\sim 1$~parsec, serving as the direct precursors to open clusters. Closer MW clumps are resolved into discrete sub-clumps, whereas colder MC clumps suffer from peripheral envelope mass blending. Furthermore, the global spatial layout of clumps in the LMC and the MW shares a remarkably similar pattern when adjusting for galaxy size, suggesting a nested, hierarchical distribution. The clump-based star formation rates are calibrated to be $\sim 0.4~M_\odot\,\rm yr^{-1}$ for the LMC and $\sim 0.1~M_\odot\,\rm yr^{-1}$ for the SMC, confirming that the LMC is currently experiencing an active, ongoing star formation burst captured within a short ($< 10^6$~yr) snapshot timescale.
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Instrumentation and Methods for Astrophysics

Star-Planet Interactions: The Instrumentation Perspective

H. Korhonen, P. Figueira, B. Montet et al. (+4 more)

Star-Planet Interactions (SPIs) produce observable phenomena across the electromagnetic spectrum, from X-ray and ultraviolet emission tracing magnetic activity and atmospheric escape to optical, infrared, and radio signatures probing stellar variability, planetary atmospheres, and magnetospheric interactions. This work reviews the current observational capabilities for SPI research, focusing on the instruments and facilities currently used, or technically capable of being used, for SPI studies. Particular emphasis is placed on the instrumental characteristics required to detect often weak and transient SPI signatures, as well as on the observational challenges associated with such measurements. The chapter concludes with an outlook on upcoming facilities that are expected to enhance our ability to detect, characterise, and understand SPI phenomena in the coming years.
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All authors H. Korhonen, P. Figueira, B. Montet, S.P. Jarvinen, H. Vedantham, S. Narendranath, P. Chaturvedi

Solar and Stellar Astrophysics

How Magnetic Field Strength Affects Stellar Coronal Mass Ejection Dynamics

Zheng Sun, Julián D. Alvarado-Gómez and Hui Tian

Observations show that stellar coronal mass ejection (CME) candidates display relatively lower kinetic energies compared to expectations from solar flare-CME relations extrapolated to the stellar regime. This behaviour was predicted by studies of magnetic confinement of CMEs by strong large-scale stellar magnetic fields. However, the possible promoting role of stronger small-scale magnetic fields has not yet been properly explored in previous studies. In this work, we present the first parametric study that simultaneously incorporates both the promoting and confining effects of magnetic field strength on CME dynamics. We perform CME simulations with scaled solar magnetograms spanning <B_star> = 1, 5, 10, 50, 100 B_sun and inserting flux ropes whose magnetic energy is set to scale as E_FR \propt <B_star>^2. Our results show that CME speed and mass increase with magnetic field strength in this restrictive scenario, approximately following v_CME \propt <B_star> and M_CME \propt <B_star>^1.5. These trends indicate that, within this idealized solar-scaled framework, increasing the magnetic field strength enhances the net promoting forces relative to the confining forces and drives faster, more massive CMEs. We further identify the upward Lorentz force as the dominant contributor to the acceleration and the mass enhancement. We also conducted additional cases with different flux rope energies that do not follow the above scaling assumption, and found that stronger flux ropes produce faster and more massive CMEs for each given stellar model. The adopted scaling assumptions are intended as a controlled parametric experiment rather than a realistic model of young solar-type stars, and future work using more realistic stellar magnetic maps will be required to determine which regions of the parameter space explored here are most relevant to active stars.
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Instrumentation and Methods for Astrophysics · Cross-listed from stat.ME

Multivariate Bayesian P-spline estimation of spectral density matrices, with application to LISA TDI noise

Avi Vajpeyi, Renate Meyer, Patricio Maturana-Russel et al. (+1 more)

We present a Bayesian P-spline method for estimating the frequency-dependent cross-spectral density matrix of stationary multivariate time series. The inverse spectral matrix is parametrised through its frequency-varying Cholesky decomposition, which guarantees Hermitian positive definiteness at every frequency. Each real log-diagonal entry and each real and imaginary off-diagonal entry is given an independent penalised B-spline prior that controls smoothness. Inference uses a blocked, coarse-grained Whittle likelihood with safe-Bayes $\eta$-tempering to stabilise posterior calibration, sampled by the No-U-Turn Sampler from a variational initialisation. On synthetic VAR(2) benchmarks with known ground truth, the method recovers both diagonal and cross-spectral structure, attains near-nominal credible-interval coverage, and achieves a relative integrated squared (Frobenius) error (RISE) that decreases with sample size. We then apply the method to publicly released simulated LISA time-delay interferometry (TDI) data in two noise configurations. In the idealised symmetric case, the full multivariate model and a reduced model that assumes a diagonal AET noise covariance agree to within $\sim10^{-3}$ in RISE. Under realistic noise that is asymmetric across the six Movable Optical Sub-Assemblies (MOSAs), the AET-diagonal assumption fails by more than an order of magnitude in RISE ($\sim\!3.3\!\times\!10^{-2}$ versus $\sim\!10^{-3}$), whereas the full multivariate model recovers the cross-spectral structure.
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All authors Avi Vajpeyi, Renate Meyer, Patricio Maturana-Russel, Jianan Liu

Solar and Stellar Astrophysics

On the feasibility of inverting the rotation of the solar core with mixed f/g modes

Armand Leclerc, Arthur Le Saux, J. M. Joel Ong et al. (+1 more)

Context: Thanks to helioseismology, the rotation profile of the Sun has been measured with great precision down to 20% of its total radius. This rotation profile is used as a calibration to infer the rotation of other stars as well as a test of angular momentum transport theory in stellar interiors. However, the deepest 20% of the layers remain out of reach of current observations, preventing astronomers to discriminate between currently competing angular momentum transport mechanisms. Aims: The main obstacle is that no global oscillations modes sensitive to rotation (non-zero degree l) reaching the solar core have been detected yet, as nonradial p modes cannot reach it and g modes are evanescent at the surface and still elude detection. In this work, we propose and examine a new method to constrain the rotation of the core of the Sun, which does not require direct observation of solar g modes. Methods: It is based on a recent prediction that g modes in the radiative interior couple with f modes in the outer parts of the star. These mixed f /g are at the same time sensitive to the rotation of the core and able to reach the surface. These modes can be used together to build average inversion kernels and perform an inversion of the rotation of the solar core. Results: We find that the oscillations' spectrum of the Sun should present 6 mixed f /g modes that can be used to measure the rotation rate of the Sun at r = 0.07 and 0.2R. We estimate that the uncertainty on the measurements should be small enough to distinguish between competing scenarios of angular momentum transport in the Sun.
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All authors Armand Leclerc, Arthur Le Saux, J. M. Joel Ong, Rafael A. Garcia

Astrophysics of Galaxies

ALMA observations of Magnetic Fields in the Massive Star-forming Region IRAS 18360-0537

Shixian Mo, Keping Qiu, Qizhou Zhang et al. (+6 more)

Assessing the significance of magnetic fields in high-mass star formation remains one of the most challenging topics in astrophysics. In this study, we present full polarization observations obtained from the Atacama Large Millimeter/Submillimeter Array (ALMA) of the high-mass star-forming region IRAS18360-0537. The polarized dust emission at 1.3 mm reveals a clear hourglass-shaped morphology of the magnetic field. Interestingly, the magnetic field orientation is nearly perpendicular to both the outflow and core rotation axes, while it aligns with the elongation of the core. This orientation poses challenges for interpretation, particularly in light of the strong magnetic field strength estimated using the Davis-Chandrasekhar-Fermi method. Several scenarios provide insights into the underlying reasons for this magnetic field morphology. A clear velocity gradient seen in high-density tracing of molecular spectral lines indicates that the core is fast-rotating. The curved outskirts of the magnetic fields coincide with the outflow cavity, suggesting a possible influence from the outflow. The accretion flows along the core's elongation are also notable. Our study shows that the morphology of the magnetic field is probably highly influenced by the gas bulk motions.
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All authors Shixian Mo, Keping Qiu, Qizhou Zhang, Junhao Liu, Josep Miquel Girart, Hauyu Baobab Liu, Zhi-Yun Li, Shanghuo Li, Huei-Ru Vivien Chen

Astrophysics of Galaxies

Sutra : An integrated framework for identification and characterization of filaments in the interstellar medium

Shivam Kumaram, Ushasi Bhowmick, Vipin Kumar et al. (+3 more)

Observations of the interstellar medium (ISM) at Far-infrared(FIR) and sub-millimetre (sub-mm) wavelengths reveal a complex filamentary structure of dust and gas, which plays a pivotal role in both low and high mass star formation. Large scale identification and characterization of filaments is crucial to establish a link between the ISM and the star formation. We present Sutra, a machine learning based framework that unifies filament identification and beam-scale physical characterization within a single automated pipeline. The framework employs a U-Net architecture to perform supervised segmentation on column density maps and is trained on five nearby (<500pc) molecular clouds from the Herschel Gould Belt Survey (HGBS), using consensus skeletons constructed from the union of filaments identified by DisPerSE and getsf. Rather than reproducing broad intensity-based masks, Sutra predicts crest-likelihood maps focused on filament spines. Beyond identification, Sutra characterizes the filaments at the beam resolution by extracting radial profiles perpendicular to the crest and deriving local structural parameters. The framework provides a parameter-free, computationally efficient approach for consistent filaments identification and systematic investigation of their local properties and shows stable behaviour across varying background conditions in controlled synthetic tests. We demonstrate its application on selected regions from Aquila, Orion and Polaris molecular clouds, and compare the derived filament characteristics with those obtained using existing algorithms. Sutra robustly recovers filamentary structures consistent with cylindrical profiles, including in relatively low-intensity and low-contrast environments, making it well suited for both region-specific studies and large-scale statistical analyses of early-stage star formation and ISM structure.
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All authors Shivam Kumaram, Ushasi Bhowmick, Vipin Kumar, Manish Chauhan, Munn V Shukla, Mehul R Pnadya

High Energy Astrophysical Phenomena

Evidence for a Delayed Progenitor Population for CHIME non-repeating Fast Radio Bursts from a Self-Consistent Forward and Backward Inference Framework

Zi-Liang Zhang and Bing Zhang

Fast radio bursts (FRBs) are luminous extragalactic radio transients whose physical origins remain uncertain. Using over one thousand non-repeating events from CHIME/FRB Catalog 2, we infer the intrinsic FRB demographics with a self-consistent framework that combines backward non-parametric inference and forward population synthesis while accounting for probabilistic dispersion measure–redshift estimates, baseband-to-catalog fluence corrections, and the latest fuzzy multidimensional selection function. We first apply a backward non-parametric method, the weighted Lynden–Bell $C^{-}$ estimator, to recover the intrinsic redshift and energy distributions without assuming any population model. Independently, we perform forward Monte Carlo population synthesis in observable dispersion measure–fluence space, treating candidate intrinsic redshift and energy distributions as population hypotheses and comparing the resulting selected synthetic catalogs with observations. We find that the intrinsic redshift distribution peaks at $z\sim1$, significantly lower than the cosmic star formation history (SFH) peak at $z\sim1.7$, indicating clear tension with a pure SFH-tracking scenario, suggesting that at least some FRBs are delayed with respect to SFH. The intrinsic energy distribution is consistent with a power law of index $\alpha\approx1.9$ and steepens at higher energies. We find no significant evidence for a redshift-energy distribution correlation.
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Instrumentation and Methods for Astrophysics

Emulation of non-linear 1D spectral models: relativistic X-ray reflection

Benjamin J. Ricketts, Tin Hadži Veljković, Daniela Huppenkothen et al. (+4 more)

The use of machine learning techniques to approximate computationally expensive models has become increasingly prevalent in a wide variety of fields within astronomy. We discuss the implementation of emulators for 1-dimensional models in the context of the astrophysical numerical model reltrans, a black hole X-ray spectral model that models the effects of relativistically smeared emission from an accretion disk. We argue that the decision of whether and how to emulate should follow from a systematic characterisation of the target model, and we demonstrate a diagnostic workflow: examining how the spectrum varies with individual parameters. We adopt a modular strategy, emulating only the relativistically convolved reflection spectrum (1-10% of the total flux) rather than the full model. Using an operator-learning architecture with Fourier feature embeddings and FiLM conditioning, we reproduce the reflection spectrum to O(0.1)% precision across 0.1-100 keV with a 4-10x speed-up that scales considerably better under vectorised evaluation. This emulator, RTFAST2, recovers the true parameters of simulated observations without the systematic posterior biases of our previous work. We conclude that no architecture is universally transferable and bespoke emulators motivated by a model's specific structure are required. The modular approach taken in this work presents a promising strategy for future emulators of numerical models.
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All authors Benjamin J. Ricketts, Tin Hadži Veljković, Daniela Huppenkothen, Adam Ingram, Matteo Lucchini, Guglielmo Mastroserio, Fergus J. E. Baker

Astrophysics of Galaxies

A new model of quasar mass evolution

Z. Li, M. Zhang, Q.-H. Peng et al. (+1 more)

Magnetic monopoles have been a trending topic among physicists and astronomers since the 1930s. Researchers have been working hard to find evidence of magnetic monopoles in laboratories. The existence of magnetic monopoles can rationally explain the stability of charges, the quantization of charges, the structure of leptons, the unified composition of leptons and hadrons, and the symmetry of leptons and quarks. The presence of these mysterious particles in the universe could have significant implications for theoretical physics and astrophysics. The Grand Unified Theory has also predicted the existence of magnetic monopoles, which is interestingly implied by some astronomical observations. Noticing that the growth of supermassive black holes in the early universe is an increasingly challenging difficulty faced by astronomers, here we argue that it could be solved with the help of magnetic monopoles. As suggested by Peng et al. in A Monopole Model for Galactic Nuclei. In: Structure and Evolution of Active Galactic Nuclei, vol. 121, p. 663 (1986), quasars containing magnetic monopoles at the center can continuously catalyze the decay of protons to release energy. We examine this model by using quasar data from the Sloan digital sky survey. It is shown that the initial mass distribution of quasars derived from the magnetic monopole model exhibits a Gaussian distribution. At the same time, the initial mass function is also slightly higher than previously expected, which could be verified by future observations.
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All authors Z. Li, M. Zhang, Q.-H. Peng, X. Liu

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

Constraining inflationary models via de-Sitterization of Bianchi Cosmologies

Apurba Samanta and Rahul Kothari

Our Universe is isotropic and homogeneous when we observe it on $\gtrsim$ Mpc length scales. It is desirable that present state of the Universe has no dependence on its initial geometry. In case of Bianchi Universes, i.e., anisotropic but homogeneous Universe, this has already been demonstrated via cosmological constant in a process that we call de Sitterization. In this letter, we show that for Bianchi Universe, the same state can be achieved by a homogeneous inflaton field with a general potential and satisfying a criterion without the need of a cosmological constant. More importantly, we show that the same condition can constrain models of inflation and explain our idea with examples.
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Astrophysics of Galaxies

Observational Study of Multi-wavelength Synergistic Effects in 3C 120

Yuting He, Ming Zhang, Qi Yuan et al. (+1 more)

The energy dissipation and particle acceleration mechanisms within relativistic jets remain fundamental questions in active galactic nuclei (AGN) research. In this paper, we present a comprehensive 13-year (2012-2025) multi-wavelength study of the broad-line radio galaxy 3C 120, utilizing Fermi-LAT ($\gamma$-ray), ASAS-SN (optical), and high-resolution VLBA (15 GHz and 43 GHz) monitoring. Cross-correlation analyses reveal that $\gamma$-ray flares lead radio emission by $11.08_{-1.88}^{+4.03}$ months at 15 GHz and $8.27_{-5.55}^{+3.45}$ months at 43 GHz. This frequency-dependent temporal hierarchy positions the high-energy dissipation zone upstream of the radio core, corroborating the opacity-driven core-shift effect. By tracking the parsec-scale jet morphology during major $\gamma$-ray flaring epochs, we demonstrate that radio outbursts systematically coincide with compact core brightening, pronounced surges in polarized flux, abrupt electric vector position angle rotations, and the subsequent ejection of superluminal knots. Ultimately, our internal radio correlations suggest that jet dynamics are governed by a dual mechanism: long-term kinematic and flux baseline variations are geometrically modulated by a secular jet precession, while rapid, highly energetic polarimetric bursts are driven by short-lived internal shocks propagating down the jet channel.
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All authors Yuting He, Ming Zhang, Qi Yuan, Nenghui Liao

High Energy Astrophysical Phenomena

Exploring Hierarchical Merger Scenarios for GW241011 and GW241110

Lei He, Liang-Gui Zhu, Zheng-Yan Liu et al. (+4 more)

GW241011 and GW241110 are asymmetric binary black hole mergers with rapidly spinning primaries, unequal component masses, and nonzero spin–orbit tilts, making them natural candidates for hierarchical mergers. We use a Bayesian framework to compare a fiducial first-generation (1G+1G) binary black hole population with second-generation plus first-generation (2G+1G) hierarchical merger models in star clusters and active galactic nucleus (AGN) disks. Both events favor the 2G+1G interpretation over the 1G+1G hypothesis, with $\ln\mathcal{B}^{\rm 2G+1G}_{\rm 1G+1G}\simeq6.5$–$8.6$ for GW241011 and $\ln\mathcal{B}^{\rm 2G+1G}_{\rm 1G+1G}\simeq3.0$–$4.5$ for GW241110, depending on the waveform model and assumed environment. The AGN disk models yields slightly larger evidence than the star cluster models, mainly due to their spin tilt distribution, but the data do not provide a decisive environmental classification. We further consider a third-generation plus first-generation (3G+1G) interpretation, but it is not robustly preferred over 2G+1G scenarios. Finally, we also search for optical counterparts by examining AGNs within the three-dimensional localization volumes using ZTF and ATLAS forced photometry, and find one candidate source with weak flare, which might be associated with GW241110 event.
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All authors Lei He, Liang-Gui Zhu, Zheng-Yan Liu, Rui Niu, Chao Wei, Ken Chen, Wen Zhao

Earth and Planetary Astrophysics

Self-Consistent Evolution Models Show Weak Double-Diffusive Mixing in Jupiter and Saturn

J. R. Fuentes, Ankan Sur, David J. Stevenson et al. (+1 more)

Double-diffusive convection in the “fuzzy” cores of giant planets has been widely discussed as a mechanism for redistributing heavy elements, but its efficiency in evolutionary models remains uncertain. Previous estimates rely on idealized compositional structures and have not treated double-diffusive transport self-consistently in planetary evolution calculations. Here we implement a prescription for transport across convective staircases in the planetary evolution code APPLE and apply it to post-formation interior models of Jupiter and Saturn containing compositional gradients produced during formation. These models are evolved for 4.56 Gyr including convection, diffusion, and double-diffusive transport. We find that double-diffusive convection produces limited mixing between the deep interior and the envelope. In both Jupiter and Saturn, less than $\sim 1\,M_\oplus$ of heavy material is redistributed over the full cooling history, leaving the primordial compositional gradients largely intact. This inefficiency arises because the buoyancy work available to drive compositional transport is constrained by the thermal energy budget of the deep interior, in contrast to idealized Boussinesq simulations that operate in regimes more favorable to layer merging and efficient mixing. As a result, double-diffusive convection alone cannot significantly erode the compositional gradients generated during formation. The observed heavy-element distributions in Jupiter and Saturn therefore likely require additional transport mechanisms or formation pathways, including large collisional events, that produce broader initial mixing than standard accretion models predict.
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All authors J. R. Fuentes, Ankan Sur, David J. Stevenson, Peter Bodenheimer

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

Neutron stars in $f(Q) = Q +\xi Q^2$ gravity

J. C. N. de Araujo and H. G. M. Fortes

Modified theories of gravity based on the symmetric teleparallel framework have recently attracted considerable attention as viable alternatives to General Relativity. In this context, f(Q) gravity, in which the gravitational interaction is encoded in the nonmetricity scalar Q, provides a consistent geometrical formulation that differs from the standard curvature-based description. In this work, we investigate the structure of neutron stars within a family of f(Q) gravity models by employing realistic equations of state, namely FPS, SLy, ENG and MPA1. Using the covariant formulation of f(Q) gravity, we derive the corresponding Tolman-Oppenheimer-Volkoff equations and apply them to model compact stellar configurations. Numerical integration of the field equations provides the mass-radius relations and the maximum masses supported by each equation of state, enabling a direct comparison with current observational constraints. Furthermore, we analyze the behavior of the nonmetricity scalar both inside and outside the stellar object, providing additional insight into the gravitational structure of compact stars in this framework.
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Earth and Planetary Astrophysics

Four Cold Giant Planets Discovered by High-Cadence Microlensing Surveys

Cheongho Han, Chung-Uk Lee, Andrzej Udalski et al. (+52 more)

We report the discovery of four cold giant planets identified through the analysis of microlensing events detected by high-cadence surveys: OGLE-2016-BLG-0261, KMT-2025-BLG-0026, KMT-2025-BLG-0030, and KMT-2025-BLG-2272. The planetary signals appear as short-duration anomalies in the light curves and are well described by binary-lens single-source models with mass ratios between the lens components of order $q \sim 10^{-3}$. Finite-source effects are securely measured in three out of four events, enabling determinations of the angular Einstein radius. A Bayesian analysis incorporating the measured event timescale and angular Einstein radius yields host masses of $\sim 0.07$–$0.6~M_\odot$ and companion masses of $\sim 0.2$–$2.5~M_{\rm J}$, confirming that all companions lie in the giant-planet regime. The projected separations are ~ 0.7–6 au, placing all planets at or beyond the snow lines of their host stars. The inferred lens distances span $\sim 6.6$–$7.9$ kpc, with all systems consistent with bulge lenses. These detections expand the sample of cold giant planets from homogeneous high-cadence surveys and highlight the sensitivity of microlensing to planetary systems beyond the snow line, providing further constraints on the occurrence and properties of giant planets around low-mass stars.
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All authors Cheongho Han, Chung-Uk Lee, Andrzej Udalski, Ian A. Bond, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Youn Kil Jung, Kyu-Ha Hwang, Yoon-Hyun Ryu, Yossi Shvartzvald, In-Gu Shin, Jennifer C. Yee, Weicheng Zang, Hongjing Yang, Doeon Kim, Dong-Jin Kim, Seung-Lee Kim, Dong-Joo Lee, Sang-Mok Cha, Yongseok Lee, Byeong-Gon Park, Richard W. Pogge, Przemek Mróz, Michał K. Szymański, Jan Skowron, Radosław Poleski, Igor Soszyński, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof A. Rybicki, Patryk Iwanek, Krzysztof Ulaczyk, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mróz, David P. Bennett, Chihiro Ueda, Ryusei Hamada, Yuki Hirao, Shuma Makida, Shota Miyazaki, Tutumi Nagai, Seiya Nakayama, Kansuke Nunota, Ryo Ogawa, Ryunosuke Oishi, Hideaki Ose, Nicholas J. Rattenbury, Yuki K. Satoh, Takahiro Sumi, Daisuke Suzuki, Motohide Tamura, Takuto Tamaoki, Hibiki Yama

Sunday 5 July

Cosmology and Nongalactic Astrophysics

Reflection polarization of close binaries as a probe of axion dark matter birefringence

Tomoki Matsuoka, Kimihiro Nomura and Hidetoshi Omiya

We propose close binary polarimetry as a probe of birefringence induced by ultralight axion dark matter. In a close binary, reflection or scattering can generate a small linear polarization whose time dependence is locked to the orbital phase. This phase-locked polarization provides a template against which an oscillatory rotation of the polarization angle induced by the axion can be searched for. We show that axion birefringence appears as sidebands around the orbital harmonics. For a single bright binary, with parameters motivated by observed systems and current high-precision optical polarimetry, we estimate the sensitivity to the axion-photon coupling under white noise assumption to be the level of $10^{-12}$ GeV$^{-1}$ at an axion mass of $10^{-20}$ eV. A future array of suitable binaries could further improve the sensitivity to $10^{-13}$ GeV$^{-1}$ in an optimistic scenario. This method could provide a complementary high-cadence optical probe of axion birefringence, compared to existing astrophysical searches.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Shifted Hybrid Realization of Non-Minimal Higgs Inflation in Light of ACT DR6 and Planck Data

Nadir Ijaz, Pirzada and Mansoor Ur Rehman

We investigate non-minimal Higgs inflation in a no-scale-inspired supergravity framework and confront its predictions with the latest CMB constraints from ACT DR6 and Planck. Working within a shifted hybrid inflation scenario, we construct an effective single-field description in which the GUT Higgs direction serves as the inflaton after stabilization of the orthogonal scalar fields. We show that the inclusion of the leading nonrenormalizable operator in the superpotential induces a controlled deformation of the Starobinsky attractor, allowing the scalar spectral index to be shifted into the range favored by recent ACT and related CMB datasets while maintaining a small tensor-to-scalar ratio, $r \sim 10^{-3}-10^{-2}$. The resulting inflationary dynamics remain theoretically consistent, with controlled supergravity corrections and sub-Planckian inflaton field values. We perform a detailed numerical analysis of the model parameter space, including reheating and nonthermal leptogenesis, and identify regions that simultaneously satisfy current observational constraints and yield a viable post-inflationary cosmological history.
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Solar and Stellar Astrophysics

Asteroseismic imprints of strong non-axisymmetric fields in the cores of red giants

Nicholas Z. Rui, J. M. Joel Ong, Armand Leclerc et al. (+5 more)

To date, magnetic fields have been asteroseismically measured in nearly one hundred red giant cores. However, most analyses assume weak magnetic fields and slow rotation so that perturbation theory can be applied. The "traditional approximation of rotation and magnetism" (TARM) method can predict gravity-mode frequencies under strong magnetic fields and rapid rotation rates. So far, this formalism requires the magnetic field to be symmetric about the rotation axis. We generalize the TARM formalism to apply to arbitrary magnetic field geometries, including cases where the magnetic and rotation axes are misaligned, as well as fields with no symmetry axis at all. The resulting gravity modes exhibit a rich diversity of wave behavior, including oblique pulsation and avoided crossings. We also clarify the domains of validity of perturbation theory and the TARM formalism.
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All authors Nicholas Z. Rui, J. M. Joel Ong, Armand Leclerc, Daniel Lecoanet, Lisa Bugnet, Janosz W. Dewberry, Bastien Liagre, Stéphane Mathis

Cosmology and Nongalactic Astrophysics

Strong gravitational lensing constraints on interacting dark energy models

F. Villalobos, T. Verdugo, P. Troncoso-Iribarren et al. (+2 more)

The possible interaction between dark matter and dark energy has been proposed as a mechanism to alleviate the coincidence problem and the Hubble tension. Strong gravitational lensing observations provide valuable constraints to test the properties of the dark components of the Universe. We present estimates of cosmological parameters employing strong lensing data for an interaction model Q, proportional to the dark matter density and dependent on the deceleration parameter q. The obtained results are consistent with an accelerating Universe. Furthermore, these results agree with previous studies suggesting that an interaction in the dark sector may help alleviate existing tensions in the expansion history of the Universe and highlight the potential of strong gravitational lensing as an independent cosmological probe.
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All authors F. Villalobos, T. Verdugo, P. Troncoso-Iribarren, N. Piña, J. Magaña

Cosmology and Nongalactic Astrophysics · Cross-listed from physics.plasm-ph

Turbulent Magnetogenesis and Large-scale Magnetic Dynamo Amplification in Ion–electron Plasmas

Fabio Bacchini, Francesco Pucci, Sergio Servidio et al. (+2 more)

Using fully kinetic simulations that capture unprecedentedly large (from electron to ion) scales, we study magnetogenesis driven by continuous large-scale forcing until nonlinear dynamo saturation. We uncover a two-stage mechanism in collisionless ion-electron plasmas whose dynamics diverge dramatically from the pair-plasma case. In the first phase, electron pressure anisotropy triggers electron-Weibel modes, seeding small-scale magnetic fields. Then, a second growth phase emerges when the more massive ions develop their own strong anisotropy and drive ion-Weibel-type modes; concurrently, a Biermann-battery mechanism contributes to amplifying the magnetic field. This combined dynamics provides a tenfold amplification of the magnetic field in comparison to the pair-plasma case. Over long times, dynamo action continues until the system reaches a statistical steady state. This self-consistent kinetic mechanism provides a plausible explanation for robust magnetogenesis wherever an external forcing continuously stirs the plasma.
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All authors Fabio Bacchini, Francesco Pucci, Sergio Servidio, Francesco Valentini, William H. Matthaeus

Solar and Stellar Astrophysics

A Catalog of Automatically Identified Multi-Signature ICMEs Observed by Solar Orbiter

Felix N. Minta, Stefano A. Livi, George C. Ho et al. (+2 more)

In this study, we present a catalog of 138 interplanetary coronal mass ejections (ICMEs) identified using multiple distance-normalized ICME criteria within sliding time windows applied to Solar Orbiter in-situ measurements. We observe sub-adiabatic proton cooling, a near-spherical radial density decrease, a steep decline in dynamic pressure indicative of enhanced expansion in the inner heliosphere, and a magnetic-field profile shallower than Parker-spiral expectations. Approximately $55\%$ of the ICMEs are associated with a preceding shock and sheath, while $45\%$ are not. Compared with non-sheath ICMEs, sheath-associated events are $\approx27\%$ longer, $\approx68\%$ more magnetized, $\approx30\%$ faster, $\approx2.6$ times hotter, $\approx34\%$ denser, and $\approx2.8$ times more over-pressured, while expanding $\approx96\%$ faster and maintaining low plasma $\beta$. Expansion speed also scales strongly with ICME size and bulk speed, suggesting that sheath dynamics regulate ejecta expansion. For the 32 ICMEs with Heavy Ion Sensor (HIS) observations, $\approx30\%$ exhibit $\mathrm{O}^{7+}/\mathrm{O}^{6+}\approx1$, whereas Fe-based composition signatures ($\langle Q_{\mathrm{Fe}}\rangle$, $\mathrm{Fe}^{\ge16+}/\mathrm{Fe}$, and $\mathrm{Fe}/\mathrm{O}$) identify $\approx50$–$65\%$ of events, consistent with lower charge-state enhancements during solar minimum. Superposed epoch analysis reveals enhanced heavy-ion signatures within magnetic-cloud intervals, linking in-situ composition to coronal heating. This catalog provides a robust benchmark for multi-mission studies, machine-learning applications, CME evolution models, and space-weather investigations.
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All authors Felix N. Minta, Stefano A. Livi, George C. Ho, Susan T. Lepri, Heather A. Elliott

Earth and Planetary Astrophysics

Dynamical analysis of the 5:1 mean-motion resonance of the HD 202206 system

Yingyi Cao, Man Hoi Lee, Sabine Reffert et al. (+2 more)

The HD 202206 system, which features two substellar companions with a 5:1 period ratio around a solar-type star, offers a rare opportunity to study high-order mean-motion resonances and provides new insights into the formation and evolution of substellar companions in extrasolar planetary systems. We revisited the HD 202206 system, aiming to conduct a more comprehensive analysis of orbital inclinations, companion masses, resonance dynamics, and potential formation mechanisms. Our analysis of the astrometric jitter around the best fit in the Gaia DR3 catalog and the proper motion anomalies between Hipparcos and Gaia places robust constraints on the orbital inclinations. We performed a new dynamical fit to all available radial velocity data from the CORALIE and HARPS spectrographs. We assessed the dynamical configuration and long-term stability of the system using samples generated by nested sampling. Our analysis shows that the orbital inclinations are strongly constrained to about $51^\circ$. Consequently, the best-fit dynamical solution, assuming a coplanar and inclined ($i = 51^\circ$) configuration, yields an inner brown dwarf of $21.56 M_\mathrm{J}$ and an outer giant planet of $3.12 M_\mathrm{J}$. The corresponding orbital periods are 256.26 days and 1298.87 days, with eccentricities of 0.426 and 0.180. An investigation of the five relevant resonance angles shows that only one is librating with a large amplitude. Our stability analysis confirms that the system is dynamically stable. Our results provide new constraints on the masses and inclination of the system, challenging earlier claims of a face-on configuration and shedding light on the formation and evolution of substellar companions in extrasolar planetary systems.
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All authors Yingyi Cao, Man Hoi Lee, Sabine Reffert, Trifon Trifonov, Stefan Stefanov

Instrumentation and Methods for Astrophysics

Progress report on the integration of the IRTF adaptive secondary mirror

Ellen Lee, Mark Chun, Ruihan Zhang et al. (+13 more)

IRTF-ASM-1 is the first on-sky adaptive secondary mirror using the hybrid variable reluctance (HVR) actuators developed by the Netherlands Organization for Applied Scientific Research (TNO). Since its first light in April 2024, the ASM has continued to work consistently well with no hardware issues. The primary purpose of IRTF-ASM-1 is to serve as a demonstration of the HVR actuator technology, both in terms of verifying its robustness and testing calibration methods that are relevant to larger ASMs. However, as the ASM has proven to be easy to handle and reliable in its performance, we are moving toward integrating the ASM for long-term use at IRTF. We present closed loop results with the ASM and IRTF's off-axis facility wavefront sensor FELIX. Correcting the first seven Zernike modes through coma at 90-180 Hz, we are able to enhance the seeing by a factor of 1.8 in FWHM under 0."5 seeing conditions. We also performed the first science observations with the ASM in "static" mode and demonstrated that we can improve the throughput of IRTF's slit spectrograph by approximately a factor of 2, although this requires good reference slopes in FELIX. In the near future, we plan to optimize the calibration of reference slopes in FELIX and streamline the software so that the system can be operated by a non-AO expert.
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All authors Ellen Lee, Mark Chun, Ruihan Zhang, Olivier Lai, Michael Connelley, Tony Denault, Jacob Taylor, John Rayner, Max Baeten, Arjo Bos, Matias Kidron, Fred Kamphues, Stefan Kuiper, Wouter Jonker, Alan Ryan, Philip Hinz