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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 5 May

High Energy Astrophysical Phenomena

Searching For Fast Radio Transients And Radio Pulsars Using SPOTLIGHT

Kenil Ajudiya

Our initial impressions of astronomical objects was that they are inherently "static" over the course of any reasonably long observation. However, with the discovery of quasars and their scintillation in 1963-64, we learnt that there are transient phenomena even at the astronomical scales. The world of known transients has been expanding ever since then. Objects and phenomena like quasars, gamma ray bursts (GRBs), pulsars, rotating radio transients (RRATs), fast radio bursts (FRBs) and ultra long period transients (ULPTs) have answered several unanswered questions about the end states of stellar collapse, i.e, the formation and properties of back holes, neutron stars and white dwarfs. Even more interestingly, they have made us better realise how little we know about the universe. Even after more than 5 decades of research, many lurking questions about neutron stars await answers. In the current work, I explored the arena of FRB and radio pulsar astronomy by joining and contributing to the efforts of the SPOTLIGHT collaboration. The recent decades have witnessed huge leaps in radio instrumentation and high performance computing (HPC) technologies driven by the development of high throughput Graphics Processing Units (GPUs). These major technological advancements are conducive to probing extremely small time scales (up to microseconds) of astronomical events. Modern and next generation radio transients surveys at existing and upcoming radio telescopes worldwide are designed to make optimal use of the available resources to push the research frontiers with the sheer volume of data they produce (hence the terminology, data-driven astronomy). There is an urgent need to upgrade the existing time-domain radio astronomy software to keep up with the pace of the technological revolution on the hardware side. Although pulsar phenomena has been studied in great detail...
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High Energy Astrophysical Phenomena

Unveiling hidden millihertz quasi-periodic oscillations in 1A 0535+262

Zihan Yang, Ruican Ma, Mariano Méndez et al. (+9 more)

Be/X-ray binary pulsars show transient outbursts and complex timing behaviour, including millihertz quasi-periodic oscillations (QPOs), whose physical origin and energy dependence remain poorly understood. We aim to characterise the temporal evolution and energy-dependent properties of the mHz QPO during the 2020 giant outburst of 1A 0535+262. We use the multi-Lorentzian fitting framework to jointly model the power spectra and the real and imaginary parts of the cross-spectrum, incorporating simultaneous broadband X-ray observations from NICER and Insight-HXMT (0.2-120 keV). We report the first detection of weak, but significant, mHz QPOs at low X-ray energies (below 27 keV), extending their detection to a new energy regime. The centroid frequency evolves from 41 to 93 mHz, with the peak root-mean-square (rms) amplitude detected in the 50-65 keV. Throughout the outburst, the QPOs generally exhibit a hard lag between 0.12 pi rad and 0.9 pi rad. However, at the outburst peak, the higher-energy bands (above 35 keV) display a soft lag of up to -0.93 pi rad. We propose that interactions between soft seed photons and an extended outflow located outside the magnetosphere can account for the observed hard lags. Furthermore, we detect a double-peaked mHz QPO only at high energies (E above 35 keV) near peak luminosity. The two peaks maintain an approximately constant separation of 2*nu_spin and exhibit anti-correlated phase evolution. Our results indicate that the mHz QPOs in 1A 0535+262 are closely linked to the coupled evolution of a soft-photon source and a Comptonizing outflow or corona. The joint cross-spectral framework provides a complementary probe of mHz QPOs beyond traditional power-spectral analyses.
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All authors Zihan Yang, Ruican Ma, Mariano Méndez, Z.X. Li, Q.C. Zhao, Panping Li, Lian Tao, Shuang-Nan Zhang, Liang Zhang, Hua Feng, Xiang Ma, Yue Huang

Earth and Planetary Astrophysics

The ESO SupJup Survey. X. A carbon isotope contrast in the young ROXs 12 system

N. Grasser, I. A. G. Snellen, S. de Regt et al. (+7 more)

Emerging research suggests that elemental and isotopic ratios of exoplanet and brown dwarf atmospheres may serve as potential tracers of their formation pathways. The ESO SupJup Survey aims to shed light on this hypothesis, with a focus on the $^{12}$CO/$^{13}$CO ratio, by investigating the atmospheric composition of substellar companions and isolated brown dwarfs. In this work, we aim to characterize the atmospheres and determine the ratios of $^{12}$CO/$^{13}$CO of the Rho Ophiuchus X-ray source (ROXs) 12 system ($\sim$6Myrs), consisting of an M0 host with an L0 companion, as part of the ESO SupJup survey. Using high-resolution CRIRES+ K band spectra of these objects, we perform atmospheric retrieval analyses to derive their atmospheric properties, including the $^{12}$CO/$^{13}$CO ratio. Our retrieval framework is built on the radiative transfer code petitRADTRANS, with which we generate model spectra based on equilibrium chemistry tables computed with FastChem, coupled with the nested sampling algorithm PyMultiNest. We report the presence of H$_2$O, $^{12}$CO, $^{13}$CO, and HF in both the star and companion, with a tentative detection of H$_2^{18}$O in ROXs 12B. The $^{12}$CO/$^{13}$CO ratios of the two objects show a measurable, though not strongly significant, difference, namely $77\substack{+10 \\ -7}$ and $55\substack{+10 \\ -7}$ for ROXs 12A and B. We measure a C/O ratio of 0.54$\pm$0.01, while the C/O ratio of the star is not reliably constrained due to the absence of atomic oxygen lines in the K band. Furthermore, we retrieve moderate veiling in the host star of $r_k$=$0.17\substack{+0.02 \\ -0.03}$. Systems such as ROXs 12, in which both star and planet can be chemically and isotopically characterized, are crucial for constraining potential formation mechanisms of massive, wide-orbit super-Jupiters.
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All authors N. Grasser, I. A. G. Snellen, S. de Regt, D. González Picos, Y. Zhang, T. Stolker, S. Gandhi, R. Landman, P. Mollière, N. F. Allard

Astrophysics of Galaxies

Systematic underestimation of polarisation angle dispersion and its consequences for magnetic field strength estimates in star-forming regions

Seamus D. Clarke, Ya-Wen Tang, Patrick M. Koch et al. (+2 more)

Polarised dust emission observations are a valuable tool to infer the structure of the magnetic field and the dispersion of polarisation position angles may be used to estimate magnetic field strengths. A natural consequence of magneto-dynamic turbulence is for the angular dispersion to have a length-scale dependence, making the measurement of angular dispersion non-trivial. In this paper, we present a study of parametrised, scale dependent maps, focusing on the effect of pixel size and beam convolution on the measured angular dispersion when using the commonly employed unsharp-masking and structure function methods. We find that in all cases the measured angular dispersion is underestimated compared to the true value. The degree to which the measured angular dispersion is underestimated varies by factors of 1-10 when measured on scales of 1-3x the beam size, and depends on the underlying structure of the polarisation angle field. This suggests that currently derived magnetic field strengths using angular dispersions are chronically overestimated, potentially leading to an overly magnetically-dominated view of star formation. We present a method to estimate a correction factor to account for this and apply it to JCMT Orion A OMC-1 observations. We find that the magnetic field in OMC-1 is predominately found to vary on scales much larger than the JCMT's 14” beam and has a rather low degree of unresolved dispersion, leading to a correction factor of only $\sim$1.6 for angular dispersion measured at a scale of 14”/0.028 pc.
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All authors Seamus D. Clarke, Ya-Wen Tang, Patrick M. Koch, Gary A. Fuller, Dawei Xi

Solar and Stellar Astrophysics

Identification and characterization of 15265 super-Nyquist frequencies in 1309 {\delta} Scuti stars from Kepler photometry

Yanqi Mo, Weikai Zong, Xuan Wang et al. (+5 more)

The frequency of pressure (p) mode in $\delta$~Scuti stars can exceed the Nyquist limit of Kepler long-cadence photometry. {These 'super-Nyquist frequencies' (SNFs) are observed as 'reflected' peaks at lower frequencies, i.e., they are Nyquist aliases that pose} a threat to asteroseismic diagnostics. Their impact on $\delta$~Scuti p modes has yet to be comprehensively explored. We performed a systematic survey to search for SNFs in 1,838 Kepler $\delta$~Scuti stars through a novel technique based on sliding Lomb-Scargle periodogram, identifying 15,265 confirmed SNFs in 1,309 stars, from a total of 259,883 frequencies. We observe that the total number of detected frequencies per star remains featureless across the $\delta$~Scuti instability strip; however, young stars pulsate in higher frequencies and so have significantly more SNFs on average. Both the number and the rate of SNFs diminishes accordingly as $\delta$~Scuti stars become more evolved, which is consistent with both observation and stellar models. Furthermore, our method detects a greater fraction of modes as SNFs at higher frequencies, rising from approximately 1% at 20 \(\mu \)Hz to 23% at the Nyquist limit. The rate of underdetection is highest amongst low-amplitude modes. The SNF modulation patterns can be well distinguished from phase modulations induced by binarity or nonlinear mode interactions. We provide a frequency catalog for future asteroseismic studies of $\delta$~Scuti stars, wherein we identify each peak as being real or an alias, enabling further investigations into regular patterns of pulsation modes, linear combination frequencies, and theoretical modeling.
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All authors Yanqi Mo, Weikai Zong, Xuan Wang, Simon Murphy, Zilu Yang, Jian-Ning Fu, Stephane Charpinet, Xiao-Yu Ma

Astrophysics of Galaxies

Interpreting Galaxy Physical Properties Using Stellar Population Synthesis

Kenil Ajudiya

Galaxy formation and evolution is one of the most active areas of research in astronomy. In recent times there have been several developments on the observational fronts particularly with the discovery of several relations between galaxy physical properties. The exact details of how they come about still remains to be understood. Such a development has been primarily possible due to a deluge of multi-wavelength data ranging from the ultra-violet (UV) to the radio, mainly due to wide field surveys e.g., the Sloan Digital Sky Survey (SDSS) in the optical. Meanwhile, simultaneous theoretical developments like a better understanding of dust attenuation and emission led to the development of techniques to extract information from the SEDs of galaxies, exploiting information from the far-ultraviolet (FUV) to the far-infrared (FIR). The substantial progress made in stellar evolution theory in the 1980s and 1990s paved the way for the latter approach to become the de facto standard in modeling the SEDs of galaxies. It became possible to synthesise a population of stars with a certain distribution and evolve it in time, keeping track of the emission from the stars, new star formation activity, gas enrichment with elements heavier than hydrogen and helium, and the absorption and re-emission from the interstellar dust. This technique, known as the stellar population synthesis (SPS), makes use of these multi-wavelength (UV to IR) data to generate a library of model SEDs. The observed SEDs can then be compared with such a library using statistical fitting techniques like the Bayesian statistics to infer the physical properties of galaxies. The main focus of this thesis is on the reliability of stellar population synthesis modelling when only limited photometry of a small number of wavelength bands is available. It is divided in two parts: elaborate understanding of SPS modelling (Part I) and...
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Self-Interaction Bounds on Ultralight Dark Matter Couplings to Matter

Mohammad Aghaie and Shao-Ping Li

Ultralight dark matter (ULDM) couplings to matter fields and ULDM self-interactions are typically treated as independent probes. However, since the ULDM-matter couplings unavoidably induce self-interactions through quantum loop corrections, bounds on self-interacting ULDM from astrophysical and cosmological observations will also limit the coupling strength to matter. Applying this argument, we find that self-interaction bounds can impose strong constraints on the linear ULDM couplings to neutrinos, excluding a large portion of parameter space that is widely considered for probing ULDM via neutrino oscillation experiments. In addition, the self-interaction bounds also limit the quadratic ULDM couplings to electrons and light quarks, which can become stronger than from the stringent test of equivalence-principle violation. Our results demonstrate that the extreme observational sensitivity of cosmic microwave background and structure formations to repulsive self-interactions can robustly translate into powerful constraints on the ULDM interactions with fundamental particles.
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Cosmology and Nongalactic Astrophysics

Euclid preparation. Baryon acoustic oscillations extraction techniques: comparison and optimisation

Euclid Collaboration: E. Sarpa, A. Veropalumbo, M. Bonici et al. (+295 more)

We present the first end-to-end validation of the Euclid baryon acoustic oscillation (BAO) analysis pipeline, encompassing density-field reconstruction, two-point correlation function measurement, and cosmological-parameter inference. Using eight Euclid-like mock catalogues from each of four Flagship I snapshots, designed to reproduce the expected statistical properties of the first Euclid data release (DR1), we assess the two standard BAO reconstruction methods based on the Zel'dovich approximation, RecSym and RecIso, across $0.9 \leq z \leq 1.8$. The pipeline introduces several methodological advances: an emulator-based model evaluator (Bora.jl) combined with a Hamiltonian Monte Carlo sampler (NUTS), achieving more than a 500-fold speed-up relative to standard Markov chain Monte Carlo, and a semi-analytical covariance estimator (BeXiCov+WinCov) that enables robust error estimates from only eight mock realisations while remaining stable under fiducial-cosmology variations. These components ensure computational efficiency while reducing the risk of underestimating parameter uncertainties. Both reconstruction schemes yield unbiased BAO measurements across all redshifts and analysis choices, including smoothing scale and fiducial cosmology. In each snapshot, reconstruction enhances the figure of merit for $\{\Omega_m, H_0 r_s\}$ by $\sim3$, equivalent to tripling the effective survey volume. Combining the four redshift bins, the improvement remains substantial, with BAO-only constraints reaching $\sim10\%$ precision on $\Omega_m$ and $\sim3\%$ on $H_0 r_s$. Results from RecSym and RecIso are consistent within uncertainties, though we recommend RecSym during testing due to its lower sensitivity to covariance variations. These findings establish the accuracy, robustness, and scalability of the Euclid BAO pipeline for DR1, providing a solid foundation for future cosmological analyses.
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All authors Euclid Collaboration: E. Sarpa, A. Veropalumbo, M. Bonici, M. Kärcher, M. Crocce, E. Sefusatti, E. Maragliano, E. Branchini, C. Oliveri, G. Gambardella, B. Camacho Quevedo, C. Moretti, P. Monaco, J. Bautista, M. Viel, W. J. Percival, S. Nadathur, A. Pezzotta, A. Eggemeier, A. G. Sánchez, J. Bel, C. Carbone, A. Crespi, S. Radinović, G. Parimbelli, A. Farina, I. Risso, M. Guidi, G. Degni, D. Eisenstein, F. Beutler, C. García-García, G. Piccirilli, J. G. Sorce, B. Altieri, S. Andreon, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, J. Carretero, F. J. Castander, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, H. Degaudenzi, S. de la Torre, G. De Lucia, F. Dubath, X. Dupac, S. Escoffier, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, P. Fosalba, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, W. Gillard, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, C. Neissner, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, J. Rhodes, G. Riccio, F. Rizzo, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, D. Sapone, M. Schirmer, P. Schneider, T. Schrabback, M. Scodeggio, A. Secroun, E. Sihvola, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, D. Tavagnacco, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, Y. Wang, J. Weller, A. Zacchei, G. Zamorani, F. M. Zerbi, E. Zucca, M. Ballardini, A. Boucaud, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, T. Castro, J. A. Escartin Vigo, G. Fabbian, J. García-Bellido, J. Macias-Perez, R. Maoli, J. Martín-Fleitas, N. Mauri, R. B. Metcalf, M. Pöntinen, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Wiesmann, Y. Akrami, I. T. Andika, M. Archidiacono, F. Atrio-Barandela, E. Aubourg, L. Bazzanini, D. Bertacca, M. Bethermin, A. Blanchard, L. Blot, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, F. Caro, C. S. Carvalho, F. Cogato, S. Contarini, A. R. Cooray, O. Cucciati, S. Davini, T. de Boer, F. De Paolis, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, M. Y. Elkhashab, Y. Fang, P. G. Ferreira, A. Finoguenov, A. Franco, K. Ganga, T. Gasparetto, E. Gaztanaga, Z. Ghaffari, F. Giacomini, F. Gianotti, E. J. Gonzalez, G. Gozaliasl, A. Gruppuso, C. M. Gutierrez, A. Hall, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, K. Koyama, S. Kruk, M. C. Lam, F. Leclercq, L. Legrand, M. Lembo, F. Lepori, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, S. J. Liu, M. Magliocchetti, C. J. A. P. Martins, L. Maurin, M. Migliaccio, M. Miluzio, G. Morgante, K. Naidoo, A. Navarro-Alsina, S. Nesseris, F. Pace, D. Paoletti, K. Paterson, L. Patrizii, C. Pattison, A. Pisani, D. Potter, A. Pourtsidou, G. W. Pratt, S. Quai, M. Radovich, G. Rodighiero, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, A. Schneider, D. Sciotti, E. Sellentin, L. C. Smith, I. Szapudi, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, C. Uhlemann, C. Valieri, F. Vernizzi, G. Verza, S. Vinciguerra, M. von Wietersheim-Kramsta, N. A. Walton, A. H. Wright, H. W. Yeung

Instrumentation and Methods for Astrophysics

Mitigating effects of telescope jitter through differentiable forward-modeling

Max Charles, Louis Desdoigts, Benjamin Pope et al. (+3 more)

Instabilities in telescope pointing, commonly referred to as jitter, introduce image degradation that can compromise the accuracy of critical scientific observables. This work presents a differentiable forward-modeling approach to both understand and mitigate the impact of jitter. We apply dLux – a differentiable optical simulation framework built in the JAX numerical simulation framework – to model the blurring effects of jitter on the final image. We categorize jitter into low-, medium-, and high-frequency regimes with respect to the camera frame rate and build simple jitter models based on its manifestation on the detector. The forward-model approach proves effective for low- and high-frequency regimes, but the inherent unpredictability of medium-frequency jitter may lead to model misspecification. As a test case we apply these models to the TOLIMAN mission, a forthcoming CubeSat telescope dedicated to detecting nearby Earth-analogue exoplanets through high-precision astrometry. Using Fisher information analysis, we quantify the effect of jitter on TOLIMAN's primary science observable – the angular binary separation of the Alpha Centauri AB binary components. We find model misspecification does not introduce a systematic bias on the recovered binary separation except when fitting a one-dimensional jitter model to a two-dimensional motion, hence we recommend the use of a two-dimensional model. The forward-model approach offers a generalized method applicable to other telescope systems, including ongoing work with JWST's NIRISS instrument. This approach represents a significant step toward delivering higher accuracy measurements at modern observatories as demands on precision continue to rise.
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All authors Max Charles, Louis Desdoigts, Benjamin Pope, Connor Langford, David Sweeney, Peter Tuthill

Astrophysics of Galaxies

High-Redshift Gravitational Lens Discoveries in JWST NIRCam Using AnomalyMatch

Julia Dima, David O'Ryan, Sandor Kruk et al. (+2 more)

Context. Strong gravitational lenses provide a unique tool to probe cosmology and astrophysics at high redshift, offering constraints on the mass distribution of background source populations. Despite their scientific value, their rarity and subtle visual features make them challenging to identify in the wealth of data delivered by facilities such as the James Webb Space Telescope (JWST), whose unmatched resolution and near-infrared coverage make it particularly well-suited to detecting lensing systems in this regime. Aims. We make use of the specialised open-source software AnomalyMatch, a semi-supervised learning method to trawl the ASTRODEEP and COSMOS-Web surveys for gravitational lenses. Methods. Building on a training dataset of eleven previously identified gravitational lenses, we use AnomalyMatch and its iterative human-in-the-loop method to train a neural network to identify gravitational lenses in JWST Level 3 products using ESA Datalabs. Results. In total we identify 58 unique gravitational lenses. These are graded by four experts into 16 Grade A, 16 Grade B, and 26 Grade C lenses. Of all lenses identified, 37 were previously uncatalogued. We analyse their properties such as photometric redshift measurements and spectroscopic redshift, when the latter is available. The lenses previously identified span spectroscopic redshifts to zspec < 1.39 and photometric redshifts to zphot < 2.21. The uncatalogued lens system with the highest redshift is at zphot = 2.1. Conclusions. Overall, we demonstrate the potential of AnomalyMatch for large-scale searches for gravitational lenses and other rare high-redshift objects in JWST archives.
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All authors Julia Dima, David O'Ryan, Sandor Kruk, Laslo E. Ruhberg, Pablo Gómez

Instrumentation and Methods for Astrophysics

StreakMind: AI detection and analysis of satellite streaks in astronomical images with automated database integration

Rafael Carrillo Navarro, René Duffard, Pablo García-Martín et al. (+3 more)

Artificial satellites and space debris increasingly contaminate astronomical images, affecting scientific surveys and producing large volumes of streaked exposures. Manual inspection is no longer feasible at scale, and reliable detection and characterisation of streaks has become essential for both data-quality control and the monitoring of objects in Earth orbit. We present StreakMind, an automated pipeline designed to detect Near-Earth Objects and satellite streaks in astronomical images, characterise their geometry, and cross-identify them with known orbital objects. The system integrates all inference results into a structured database suitable for large surveys. A YOLO OBB model was trained on a hybrid dataset of 2335 images and applied to processed FITS frames. Geometric refinement, inter-frame association, satellite cross-identification, and Gaussian-based confidence scoring were then used to produce final identifications stored in a relational database. Observations from La Sagra Observatory were used to develop and test the method. On the test set, the model achieved a precision of 94 percent and a recall of 97 percent. It reliably detected faint streaks, delivered consistent geometric reconstructions, and performed robust satellite cross-identification. StreakMind demonstrates strong potential for large-scale automated analysis of linear streaks produced by both Near-Earth Objects and artificial satellites, contributing to space situational awareness.
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All authors Rafael Carrillo Navarro, René Duffard, Pablo García-Martín, Javier Romero, Nicolás Morales, Luis Gonçalves

Solar and Stellar Astrophysics

Data-Constrained Modeling of Electron Transport and Asymmetric Precipitation in the 2011 August 4 Solar Flare

Feiyu Yu, Xiangliang Kong, Ze Zhong et al. (+6 more)

Energetic electrons accelerated at coronal reconnection sites during solar flares precipitate into the lower solar atmosphere, generating nonthermal emissions and regulating energy deposition. However, how their transport and precipitation are jointly governed by the three-dimensional (3D) magnetic topology, turbulent scattering, and Coulomb collisions remains unclear. Here, we aim to disentangle these physical processes by using a data-constrained 3D particle transport model for the 2011 August 4 flare. The simulated distribution of precipitated electrons aligns closely with photospheric quasi-separatrix layers and reproduces the observed two-ribbon morphology in 1700~Å. We reveal a strong polarity asymmetry, with the 10~s precipitation fraction about six times higher in the weak positive polarity. This arises primarily from distinct mirror ratios of different polarities under the 3D magnetic configuration and can be understood via a modified escape probability for an asymmetric magnetic bottle. Varying strengths of turbulent scattering lead to a rise-then-fall trend and a pronounced energy dependence in the precipitation fraction. Coulomb collisions globally suppress precipitation, especially at low energies, and further amplify the polarity asymmetry. This integrated modeling framework bridges detailed transport physics to observable flare emissions and advances the development of quantitative models for realistic solar flare events.
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All authors Feiyu Yu, Xiangliang Kong, Ze Zhong, Zhentong Li, Zelong Jiang, Yingli Cui, Zhao Wu, Yao Chen, Gang Li

Solar and Stellar Astrophysics

COCONUT: Toward practical time-evolving Sun-to-Earth magnetohydrodynamic modeling

Haopeng Wang, Stefaan Poedts, Andrea Lani et al. (+16 more)

Due to computational efficiency and numerical stability limitations, coronal simulations constrained by static magnetograms are typically performed first and then used to drive inner-heliosphere (IH) models. In this paper, we calculate the Sun-to-Earth coronal and wind evolutions using a single time-evolving MHD model, showing that implicit MHD models have the potential to meaningfully simplify and improve the overall Sun-to-Earth modelling pipeline. We extend the implicit time-evolving coronal MHD model COCONUT out to 1 AU, and utilise it to investigate solar coronal and wind evolutions around a solar maximum Carrington rotation (CR). We compare quasi-steady-state and time-evolving Sun-to-Earth simulations to evaluate the impact of the inner-boundary magnetic field evolution, which is neglected in steady-state simulations, on background plasma parameters. Comparisons with commonly used coupled Sun-to-Earth simulations are also conducted to further validate and assess the Sun-to-Earth model COCONUT. The results show that the time-evolving implicit MHD modelling approach yields noticeable differences compared to oversimplified steady-state simulations, and is efficient enough for practical applications. Modelling the solar corona and wind using a single MHD model simplifies the modelling pipeline and avoids uncertainties associated with coupling different coronal and IH models. The noticeable differences in the temporal evolution of plasma parameters at the L1 and L5 points highlight the need to use continuously evolving, synchronised magnetic field observations to improve global coronal and solar wind simulations, whereas the overall consistent evolutionary trend reveals the reliability of using L5 observations to forecast solar wind conditions near Earth about four days in advance.
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All authors Haopeng Wang, Stefaan Poedts, Andrea Lani, Rayan Dhib, Luis Linan, Tinatin Baratashvili, Fan Zhang, Quentin Noraz, Hyun-Jin Jeong, Nicolas Wijsen, Martina Condoluci, Lingyu Dong, Junyan Liu, Rui Zhuo, Mahdi Najafi-Ziyazi, Ketevan Arabuli, Myrthe Flossie, Jasmina M. Magdalenić Zhukov, Brigitte Schmieder

Solar and Stellar Astrophysics

A Search for High Frequency Oscillations in TESS Cycle 7

Guanda Huang, Xiaodian Chen, Shu Wang et al. (+2 more)

High-quality, short-cadence photometry from TESS enables the detection of rapid oscillators with unprecedented sensitivity. In this work, we conduct a homogeneous search for high-frequency variability using 20-second cadence light curves from TESS Cycle 7 (Sectors 84–96). From $\sim 3.9\times10^{4}$ light curves, we compute Lomb-Scargle periodograms and select candidates exhibiting at least one significant signal with $\mathrm{FAP}\le 10^{-4}$ at frequencies $f\ge 50~\mathrm{d^{-1}}$. After excluding previously reported objects and performing pixel-level and light-curve vetting to mitigate contamination, we identify 73 rapid oscillators, including 24 pulsating white dwarfs, 31 hot subdwarfs, and 18 A-F stars. Using an iterative prewhitening procedure, we carry out a detailed frequency analysis for each target and derive the oscillation frequencies and amplitudes. We further investigate the physical origins of the detected frequency content and present statistical characterizations of the rapid-oscillator sample. We highlight one white dwarf and one subdwarf that exhibit clear frequency multiplets consistent with rotational splitting. This work enlarges the sample of rapid oscillators accessible with TESS data and provides a uniformly measured frequency-amplitude catalog, establishing a consistent basis for future asteroseismic and population studies.
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All authors Guanda Huang, Xiaodian Chen, Shu Wang, Xiaobin Zhang, Licai Deng

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

Non-radial pulsations of gravitationally coupled two-fluid neutron stars in general relativity

Ankit Kumar, Daniel A. Caballero, Hajime Sotani et al. (+1 more)

Non-radial oscillations of neutron stars provide a powerful probe of stellar structure and relativistic gravity, but a fully general relativistic treatment for gravitationally coupled two-fluid stars with independently conserved currents has so far been lacking. In this work, we develop a fully relativistic framework for polar perturbations of gravitationally coupled two-fluid neutron stars, assuming that the two fluids interact only through the common spacetime and are not coupled by entrainment or direct microphysical interactions. We derive the coupled linear perturbation equations governing the metric and both fluid components, and complete the formulation by establishing the regularity, surface, and exterior matching conditions required for a well-posed oscillation eigenvalue problem. We then implement the resulting system numerically and compute representative polar mode spectra for gravitationally coupled two-fluid stellar models. This implementation provides a practical way to address mode identification in gravitationally coupled two-fluid stars, allowing the fundamental ($\mathsf{f}$) and pressure ($\mathsf{p}$) mode branches of the spectrum to be classified according to their dominant inner- or outer-fluid character through the associated eigenfunctions and their node structure. The formalism developed here provides a foundation for extending relativistic asteroseismology to multi-fluid compact stars and for exploring their potential gravitational-wave signatures in a fully general relativistic setting.
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All authors Ankit Kumar, Daniel A. Caballero, Hajime Sotani, Nicolás Yunes

High Energy Astrophysical Phenomena

Utilizing Dispersion Measure of Fast Radio Bursts to Probe the Intergalactic Medium Turbulence

Rui-Nan Li, Zhao Joseph Zhang, Kentaro Nagamine et al. (+3 more)

Extragalactic fast radio bursts (FRBs) have emerged as powerful probes of turbulence within the intergalactic medium (IGM), a phenomenon that plays a crucial role in various cosmological and astrophysical processes. In this study, we employ the structure function (SF) analysis on the dispersion measures (DMs) of over 3,000 FRBs, leveraging the recently released CHIME/FRB Catalog 2 alongside previously observed sources. By comparing our results with mock datasets generated from cosmological simulations, we find excellent agreement at large angular separations. At small angular scales, our findings reveal a potential scaling behavior consistent with a two-dimensional (2D) Kolmogorov power spectrum. From this scaling, we constrain the turbulence outer scale to be on the order of several Mpc, which aligns with theoretical expectations, independent observations of the low-redshift IGM, and cosmological simulations. Ultimately, to conclusively confirm this Kolmogorov-like turbulent cascade and overcome current small-sample statistical limitations, a larger sample of FRBs with sub-arcsecond localization is required.
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All authors Rui-Nan Li, Zhao Joseph Zhang, Kentaro Nagamine, Yuri Oku, Qin Wu, F. Y. Wang

Monday 4 May

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

High-Power AM-CW Lunar Laser Ranging as a $\mu$Hz SGWB Detector

Slava G. Turyshev

High-power amplitude-modulated continuous-wave lunar laser ranging (AM-CW LLR) is a stochastic-gravitational-wave-background (SGWB) experiment that measures GW-driven drift and diffusion of the Earth–Moon orbit. Its observable is the coherent phase of a GHz modulation envelope returned by an individually resolved single hollow corner-cube retroreflector (HCCR), converted to absolute range and analyzed through its time-dependent mean and covariance. The response occurs at lunar orbital harmonics; the dominant low-eccentricity channel is centered at $f_2=0.847245\,\mu{\rm Hz}$, and a five-year broadband forecast applies to spectra smooth over the resolution scale $T_{\rm obs}^{-1}=6.34\,$nHz about that resonance. A scalar 1-kW, 1064-nm link yields $5.893\times10^3$ detected photons s$^{-1}$ and an $88.8$–$124.3\,\mu$m photon contribution in 100 s, while the forecasts adopt projected total range precisions of $80$ and $50\,\mu$m. In the covariance-dominated weak-signal regime, $\Omega_{\rm gw}^{95}\propto\sigma_R^2\nuEff^{-1}T_{\rm obs}^{-4}$. Using the published Earth–Moon response normalization, the five-year 95% thresholds are $1.86\times10^{-7}\Dtot$ for $80\,\mu$m and $500\,{\rm yr}^{-1}$ and $2.42\times10^{-8}\Dtot$ for $50\,\mu$m and $1500\,{\rm yr}^{-1}$, where $\Dtot$ is the full-analysis threshold divided by the unit-factor response-anchored forecast. If end-to-end calibration, sampling, and marginalization give $\Dtot\le1.15$, the higher-performance campaign reaches nominal source-statistic equality for $\Omega_{\rm gw}=7.08\times10^{-8}$ in five years. These measurable performance and information-retention requirements define high-power AM-CW LLR as a standalone quantitative SGWB experiment at the $0.85\,\mu{\rm Hz}$ Earth–Moon resonance.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Constraining Tsallis Corrections to Photon Reheating from Electron-Positron Annihilation: A Phenomenological Approach

Matias P. Gonzalez

In this work we generalize the entropy transfer from electron-positron annihilation to photons in the early Universe. The generalization is implemented within the Tsallis formalism by using generalized distribution functions derived from Curado-Tsallis constraints. Through this deformation, the entropy density of the electromagnetic sector is modified, while the photon component is kept extensive. Therefore, the nonextensive correction is introduced only in the $e^-e^+$ pairs. This affects the entropic degrees of freedom before electron-positron annihilation and consequently modifies the temperature ratio $T_\nu/T_\gamma$. The resulting correction is then mapped into an effective value of \(N_{\rm eff}\) within the instantaneous decoupling approximation. Comparing this effective thermodynamic estimate with CMB$+$BAO data, and using BBN only as an illustrative Gaussian comparison, we obtain an order-of-magnitude phenomenological interval for the nonextensive parameter. The result should not be interpreted as a precision neutrino decoupling constraint, since a full treatment would require solving the kinetic evolution of the neutrino sector, including non-instantaneous decoupling, finite-temperature QED effects and possible spectral distortions.
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Cosmology and Nongalactic Astrophysics

Primordial black hole contribution to the stochastic background of gravitational waves

D. Martín-González

The amplitude of the detected stochastic gravitational-wave background (SGWB) measured by pulsar timing arrays (PTAs) and the discovery of early and over-massive central black holes at high redshift by the James Webb Space Telescope (JWST) challenge current models of supermassive black hole (SMBH) formation. We aim to study if halos containing a significant population of primordial black holes (PBHs) would increase the amplitude of the PTA signal. PBHs add an iso-curvature component to the matter power spectrum, accelerating the formation and merger of dark-matter halos at all redshifts. We propose that black holes in the halo sink to the center via dynamical friction. The central black hole grows through hierarchical merging in addition to the gas-accretion channel. We computed the resulting GW amplitude and performed a Bayesian inference analysis using the NANOGrav 15-year dataset. We show that the predicted amplitude of the gravitational-wave background agrees with the observations. Our model only requires $0.09\%-0.12\%$ of the total mass of the halo to fall to the center; this is compatible with a fraction of $f_{\rm pbh}\sim 0.1$ PBHs being dark matter if the in-falling PBHs in the stellar mass range represent about $1\%$ of the total population, as was found in our previous estimation of the formation of SMBHs at $z\sim 6-10$. The PBH model that explains the JWST new found populations of SMBHs also explain the amplitude of the stochastic background of gravitational waves.
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Astrophysics of Galaxies

ArkenstoneBH. A model for high-specific energy black hole feedback in cosmological simulations

James M. Sullivan, Greg L. Bryan, Matthew C. Smith et al. (+6 more)

AGN feedback is a key piece of galaxy evolution but is difficult to model due to its high specific energies, multiphase nature, and limited simulation resolutions. Arkenstone is a subgrid framework for representing multiphase flows in coarse resolution simulations that has been used to model stellar feedback driven galactic winds. It ensures the correct treatment of high specific energy feedback that would otherwise be challenging to model accurately in Lagrangian simulations. We introduce the new Arkenstone BH model, which extends the Arkenstone framework to model black hole feedback. We focus on describing the first piece of this framework, which follows the hot, high specific energy phase of these outflows. The second piece, which treats their multiphase structure with a scheme for modeling unresolved cold clouds, will be implemented and described in a later paper. We present Arkenstone BH in simulations of an isolated galaxy to demonstrate the framework and its ability to capture high specific energy feedback that interacts only weakly with cold, dense gas. We show how these energetic outflows suppress star formation in our isolated galaxy by counteracting the inflow of gas from the circumgalactic medium into the interstellar medium. This work is part of the "Learning the Universe" collaboration, which aims to understand the Universe's underlying physics and initial conditions.
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All authors James M. Sullivan, Greg L. Bryan, Matthew C. Smith, Jake S. Bennett, Drummond B. Fielding, Bryan A. Terrazas, Sophie Koudmani, Rachel S. Somerville, Michaela Hirschmann

Solar and Stellar Astrophysics

Double Neutron Star Delay Times Across Cosmic Metallicities: The Role of Helium Star Progenitors

Abhishek Chattaraj, Jeff J. Andrews, Max Briel et al. (+5 more)

Metallicity can play a significant role in massive binary evolution through its impact on the opacity within stellar interiors and wind-driven mass loss. In this work, we investigate how the double neutron star (DNS) delay time distribution (DTD) is shaped by the metallicity-dependent evolution of the helium star$-$NS progenitor system. Drawing from insights rooted in single and binary star physics, we argue that at a given metallicity, the stellar radius during the helium main-sequence sets a lower limit on the size of the DNS orbit at birth. We then perform population synthesis with the detailed binary evolution code POSYDON to illustrate the resulting DTD across a range of metallicities. Our results indicate that, independent of the common envelope efficiency and reasonable natal kicks, the majority of DNS mergers across metallicities occur typically no earlier than $\simeq 40\,\rm{Myr}$ after star formation and peaks strongly between $80-250\,\rm{Myr}$. Roughly $15\%$ of DNSs merge within 80 Myr, which may explain $r$-process enrichment in environments with brief star formation histories, while $\gtrsim 20\%$ merge on delay times $>1$Gyr, providing an explanation for short gamma-ray bursts in old, metal-poor galaxies. The shape of the DTD can be complex, with a metallicity-dependent split in the dominant formation channel imprinting a characteristic double-peaked structure. Although ideally oriented natal kicks can produce very short merging DNS, we find that the required kick magnitudes are inconsistent with observations. Our work has implications for assessing the contribution of DNS mergers to $r$-process enrichment and gamma-ray bursts/kilonovae transients across cosmic time.
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All authors Abhishek Chattaraj, Jeff J. Andrews, Max Briel, Tassos Fragos, Seth Gossage, Vicky Kalogera, Philipp M. Srivastava, Elizabeth Teng

Astrophysics of Galaxies

Nowhere Left to Hide: Uncovering All of the Massive Young Embedded Star Clusters in the Antennae with JWST

Rupali Chandar, Miranda Caputo, Paul Goudfrooij et al. (+15 more)

The Antennae galaxies merger produces the brightest infrared emission of any galaxy within ~20 Mpc, mostly from intense star formation taking place in supergiant molecular cloud complexes in the overlap region. Here, we present new, high-resolution NIRCam and MIRI images of the Antennae galaxies taken with the F150W, F187N, F335M, F360M, F410M, and F770W filters on JWST to search for the predicted but as-yet-undiscovered population of deeply embedded, optically obscured star clusters. We identify a population of 45 sources, 40 previously unknown, with high Bralpha/Halpha and Paalpha/Halpha flux ratios which are likely very young clusters still embedded or just emerging from their natal cocoons, and estimate their age, extinction (A_V), and mass. We find that all are extremely young (< 2.5 Myr), have A_V between 2 and 10 mag, and masses between ~ 10^4 and several x 10^6~Msun. We believe we have now uncovered all clusters with M > 3 x 10^4 Msun and A_V > 2 mag in the Antennae. While our sample represents a small fraction(~15%) of clusters younger than 3~Myr by number, it dominates the ionizing photon luminosity across the galaxy pair (~60%). We find elevated H_2/PAH ratios of the ISM surrounding the most massive pair of embedded clusters, supporting the idea that merger-induced shock-heated gas play an important role in the formation of extremely massive clusters.
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All authors Rupali Chandar, Miranda Caputo, Paul Goudfrooij, Sean T. Linden, Angus Mok, Cory Whitcomb, Grant Donnelly, Florent Renaud, John-David T. Smith, Alberto Bolatto, Danny A. Dale, Sara Duval, Lindsey Hands, Ralf Klessen, Caroline Kuczek, Karin Sandstrom, Eva Schinnerer, Fabian Walter

Astrophysics of Galaxies

A Multi-Survey Machine-Readable Corpus of Milky Way Globular Cluster Parameters for Retrieval-Augmented Generation Applications

David C. Flynn

We present the Milky Way Globular Cluster Corpus v1.3.1, a unified machine-readable database of fundamental parameters for 174 Milky Way globular clusters assembled from four independent published surveys. Each cluster record integrates photometric, structural, and spectroscopically-calibrated metallicity parameters from Harris (1996) (2010 revision), Gaia EDR3 proper motions from Vasiliev & Baumgardt (2021), N-body dynamical masses and orbital parameters from Baumgardt et al. (2023), and mean chemical abundances from the APOGEE DR17 globular cluster Value Added Catalog of Schiavon et al. (2024). The corpus contains 17,438 non-null data points across 174 clusters stored in JSONL, JSON, and flat CSV formats with consistent native-typed fields (float, int, bool, null), embedded provenance blocks, and fully documented schema. Survey coverage is 157/174 clusters for Harris photometry, 170/174 for Gaia EDR3 proper motions, 154/174 for Baumgardt N-body dynamics, and 72/174 for APOGEE DR17 chemistry. The corpus was designed as a Retrieval-Augmented Generation (RAG) knowledge base for large language model applications in astrophysics research, following the same multi-survey integration methodology as the Unified Galaxy HI Rotation Curve Corpus (Flynn 2026), and has been validated for structured context injection with instruction-following language models. It is equally suitable for traditional quantitative analyses including orbit modeling, cluster classification, chemical tagging, and multi-survey cross-validation. The dataset is available at Zenodo DOI: 10.5281/zenodo.19907766.
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Solar and Stellar Astrophysics

Evidence for anisotropic non-Maxwellian velocity distributions in the solar transition region

Paola Testa, Bart De Pontieu, Kyuhyoun Cho et al. (+2 more)

Spectroscopic observations of the solar transition region have long shown excess line broadening and non-Gaussian profiles, but their spatial distribution and prevalence are not well established, and their physical origin remains the subject of debate. Here we analyze SiIV line profiles in full-disk mosaics of observations with Interface Region Imaging Spectrograph (IRIS; De Pontieu et al. 2014), and find that non-Gaussian k-like profiles, indicative of suprathermal velocity distributions, are pervasive (comprising ~60% of the observed profiles). In addition, we find that their occurrence depends strongly on the angle between the line of sight and the magnetic field as inferred from NLFFF extrapolations. k-like profiles become increasingly prevalent when the magnetic field is oriented transverse to the observer, whereas Gaussian profiles become more prevalent when the field is aligned with the line of sight. This geometric dependence provides evidence that the observed velocity distributions in the transition region are non-Maxwellian and anisotropic. Our findings provide evidence for the importance, in the solar transition region, of kinetic processes, and the key role the magnetic field plays in the superposition of signals, and/or the generation or relaxation of non-Maxwellian particle distributions, likely caused by magnetic energy release through reconnection. These effects are not captured by the magnetohydrodynamic approaches that are typically invoked to study the solar atmosphere. Our results highlight the need and provide constraints for more advanced multi-fluid and/or kinetic modeling of the solar transition region.
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All authors Paola Testa, Bart De Pontieu, Kyuhyoun Cho, Thomas Ayres, Alexander Russell

Solar and Stellar Astrophysics

On the cool nature of coronal nanojets

Gabriele Cozzo, Paola Testa, Juan Martinez-Sykora et al. (+5 more)

Reconnection-driven nanoflares are widely considered a leading mechanism for coronal-loop heating, but their direct fingerprints in the tenuous coronal plasma remain elusive. The recently discovered coronal nanojets offer a potential probe of reconnection dynamics, but their extreme collimation, directionality and multi-wavelength visibility are not fully understood. Here we present a 3D rMHD simulation that unprecedentedly reproduces the key properties of nanojets, offering a viable model to explain their nature. These results provide a unified picture in which nanojet morphology, dynamics and detectability are contingent on the thermodynamic environment of reconnection. Together, our results point to a cool origin of coronal nanojets, where cool and dense material permits narrow, multi-band jet signatures to emerge from reconnection.
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All authors Gabriele Cozzo, Paola Testa, Juan Martinez-Sykora, Paolo Pagano, Fabio Reale, Bart De Pontieu, Viggo Hansteen, Alberto Sainz-Dalda

High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph

On The Nonthermal Power Laws In Magnetized Turbulent Plasmas

Rostom Mbarek, Daniel Grošelj and Alexander Philippov

Building on recent progress in the understanding of particle transport in magnetized plasmas, we derive a scaling law for the formation of nonthermal spectral tails in mildly and strongly magnetized turbulent environments. We validate this scaling using driven-turbulence particle-in-cell simulations that incorporate particle escape, allowing the system to reach a steady state. The simulation results show good agreement with our theoretical predictions. We then discuss the astrophysical implications of these findings, focusing on proton acceleration in the coronae of supermassive black holes and the resulting high-energy neutrino emission.
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Astrophysics of Galaxies · Cross-listed from gr-qc

Can wormholes have vanishing Love numbers?

Shauvik Biswas

Wormholes are fascinating alternatives to black hole geometries. In this paper, we have studied a special case of wormhole solution in the context of $R=0$ spacetime. Our approximate analytical calculations show that under a strictly static axial gravitational perturbation of this spacetime, the magnetic-type tidal Love number (for $\ell=2$) vanishes if we keep the solution of the master equation up to linear order in the regularisation parameter of the geometry. Moreover, imposing physically viable boundary conditions on the master variable we have corroborated our result with the numerical solutions. We have further extended our analysis towards the case of Damour-Solodukhin wormhole, which also yields similar conclusion.
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Astrophysics of Galaxies

Uncovering the multi-scale structure of dust distribution in nearby galaxies

E. Tanchon, M. Boquien, J. Chastenet et al. (+18 more)

High-resolution JWST-MIRI images now allow us to resolve in great detail the multi-scale nature of the emission in nearby star-forming galaxies, from compact star-forming regions to large-scale diffuse emission, giving new insights into dust emission, its composition, and the surrounding interstellar medium (ISM). We aim to understand at which scale the different processes driving dust emission in mid-infrared (7.7-21 um) wavelengths take place and if we can disentangle dense regions' emission from emission linked to a more diffuse component. We use and enhance the constrained diffusion decomposition (CDD) algorithm, an alternative to the wavelet transform decomposition, to disentangle the emission coming from compact regions from the emission originating from diffuse sources. This allows us to cleanly quantify the mid-IR spectral properties of the ISM at intervals within a continuum of physical scales. We find a transition scale of PAH emission around 300 pc, with weaker PAH fraction at smaller scales, highlighting the destruction of PAHs in HII regions. We also show variations in the PAH fraction in different morphological environments, with a smaller fraction in bright and star-forming environments. Studying and comparing the probability distribution functions (PDFs) of HII regions and diffuse ISM with the PDFs at different scales, we find a similar separation scale around 200 pc at which we observe a transition from a power-law PDF for dense structures to a log-normal one for the diffuse ISM.
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All authors E. Tanchon, M. Boquien, J. Chastenet, D. A. Dale, O. V. Egorov, R. Indebetouw, R. S. Klessen, S. E. Meidt, D. Pathak, J. Sutter, D. A. Thilker, A. Amiri, A. T. Barnes, F. Bigiel, I. S. Gerasimov, S. C. O. Glover, K. Grasha, K. L. Larson, J. C. Lee, H.-A. Pan, T. G. Williams

Solar and Stellar Astrophysics

Chromosphere of the quiet sun: II. Atmospheric response to small-scale magnetic flux emergence

Quentin Noraz, Mats Carlsson and Guillaume Aulanier

Coupling between the photosphere, chromosphere and corona in the quiet Sun (QS) is governed by a complex interplay between magnetic structuring, heating, mass loading, and radiative cooling. Constraining how this balance responds to variations in small-scale magnetic flux remains limited. We investigate how chromospheric heating and its thermodynamic coupling to higher atmospheric layers vary as a function of small-scale magnetic flux emergence. We performed a parametric set of 3D radiative-MHD simulations with the Bifrost code, starting from a weakly magnetised QS reference model and injecting horizontal magnetic flux of increasing amplitude into the sub-surface convection zone. The resulting chromospheric dynamics, heating, mass loading, and coronal response were analysed. Chromospheric temperatures and mechanical heating rise monotonically with increasing magnetic-field strength. Although the fractional contribution of shocks decreases, reconnecting current sheets keeps maintaining about 50%. In contrast, the temperature at the base of the corona exhibits a non-monotonic response, reaching a maximum at intermediate magnetic amplitudes and decreasing for the strongest-field case. We show that stronger magnetic-field strength increases chromospheric heating, which increases the coronal-base density through efficient mass loading, and amplifies radiative losses. These density-driven radiative losses dominate the coronal energy balance and thus lead to reduced coronal-base temperatures despite increased heating. Our results demonstrate the sensitivity of chromospheric structure and dynamics to small-scale flux emergence, and its key role in regulating coronal thermodynamics. This result illustrates the chromosphere-s role as a thermodynamic gatekeeper, and further warrants future investigations of atmospheric models relevant to global solar-wind models and space-weather forecasts.
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Astrophysics of Galaxies

Resolving the Multiphase Outflow, Shock Signatures, and PAHs in the AGN-Starburst Composite ULIRG F10565+2448 with JWST MIRI/MRS

Kylie Yui Dan, Jerome Seebeck, Sylvain Veilleux et al. (+9 more)

We present new James Webb Space Telescope Mid-Infrared Instrument (MIRI) Medium-Resolution Spectrometer (MRS) observations of the nearby ultra-luminous infrared galaxy F10565+2448. These integral field spectroscopic data reveal an unresolved nuclear outflow in both warm-ionized and warm-molecular gas phases as well as a resolved blueshifted kpc-scale warm-molecular outflow. The unresolved warm-ionized outflow has a mean projected velocity up to $-520$ km/s, while the unresolved warm-molecular outflow is slower at $-150$ km/s. For the resolved warm-molecular outflow, the projected mean velocity ($-280 < v_{50} < -110$ km/s) is only slightly faster than the velocity of the disk ($-70 < v_{50} < 120$ km/s) and as such likely does not exceed the estimated escape velocity of $\gtrsim 300$ km/s. The warm-molecular outflow is slightly hotter ($507 \pm 25$K) than the disk ($329 \pm 5$K), and displays areas of higher temperature and lower column density that may indicate a shock front, which we explore using the [Fe II] 5.34 $\mu$m/Pf$\alpha$ shock diagnostic. Analysis of the polycyclic aromatic hydrocarbon features reveal trends of ionization and grain size that first decrease with radius up to 1 kpc before increasing up to 3 kpc. These results bolster the picture of F10565+2448 being an AGN-starburst composite where both star formation and AGN-powered phenomena are required to explain the outflow energetics.
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All authors Kylie Yui Dan, Jerome Seebeck, Sylvain Veilleux, David Rupke, Eduardo Gonzalez-Alfonso, Ismael Garcia-Bernete, Weizhe Liu, Dieter Lutz, Marcio Melendez, Miguel Pereira Santaella, Eckhard Sturm, Francesco Tombesi