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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 18 June

Solar and Stellar Astrophysics

Once more: Leaky MHD waves in coronal magnetic flux tubes

Hans Goedbloed and Rony Keppens

By a detailed comparison of leaky magnetohydrodynamic waves in coronal magnetic flux tubes with leaky electromagnetic waves in dielectric media it is shown that the latter kind may be called quasi-normal modes, since they can be regularised by a normalisation which systematically cuts off the contribution of the external homogeneous region, whereas such a possibility is forbidden for the former kind by the conservation of magnetic flux. Consequently, leaky magnetohydrodynamic waves cannot be systematically applied to coronal seismology, i.e. to the inverse spectral problem of determining the different equilibrium distributions of the fields by comparing the spectra they produce with the observed ones.
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Astrophysics of Galaxies

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) XX. Star formation in the tidal tail of NGC 4254

A. Boselli, A. Lupi, P. Serra et al. (+26 more)

ALMA 12CO(1-0) observations of 42 star-forming regions located outside the disc of the Virgo Cluster galaxy NGC4254 within an HI gas tail produced during the galaxy's interaction with another cluster member have revealed the presence of ten giant molecular clouds (GMCs) in four of these regions. All of the GMCs were resolved at the angular resolution of the observations (~160 pc) and have molecular gas masses of M(H2)~(0.8-2.0)x10^6} Mo. These ten clouds are characterised by gas column densities [S(H2)~10 Mo pc^-2] and velocity dispersions [sigma_v(CO)~3-12 km s^-1] respectively lower and comparable to those encountered in similar GMCs in the Milky Way. They follow the relation between the gas column density and the star formation activity (Schmidt law) derived using similar data over the stellar disc of NGC4254 and other local and Virgo cluster galaxies. With analytic calculations and tuned simulations, we show that these clouds are unstable and thus expected to dissolve on relatively short timescales (~10-30 Myr). We show that they probably formed after the collapse of dense gas clouds in the HI gas tail stripped during the gravitational interaction that the galaxy suffered several hundreds millions of years ago. The clouds are short-lived and isolated given the low density of the surrounding intracluster medium, which cannot confine the gas expelled by stellar feedback. We discuss the implications of these results in the general context of the fate of stripped gas in hostile cluster environments.
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All authors A. Boselli, A. Lupi, P. Serra, P. Andreani, F. Calura, M-A. Miville-Deschenes, G. Hensler, M. Boquien, M. Fossati, S. Boissier, J. Braine, P. Cote, J.C. Cuillandre, F. de Gasperin, H. Edler, L. Ferrarese, G. Gavazzi, S. Gwyn, J. Hutchings, K. Kianfar, A. Longobardi, E.S. Mangola, S. Martocchia, E. Peng, H. Plana, J. Postma, J. Roediger, Y. Roehlly, M. Sun

Cosmology and Nongalactic Astrophysics

Finite-Core Signatures in LISA-Band Wave-Optics Lensing by Low-Mass Dark Matter Halos

Dejiang Li, Tonghua Liu, Kai Liao et al. (+3 more)

LISA-band gravitational waves from massive binary black holes can be diffractively lensed by low-mass dark matter halos and subhalos, so their frequency-dependent amplification can probe the inner density profile. We isolate the generic finite-core part of this signal by comparing fixed-mass Navarro-Frenk-White (NFW) and cored-NFW lenses and propagating both profiles to the complex wave-optics amplification factor. A finite core smooths the time-delay response and reshapes the diffraction peak; an NFW template with a lower concentration can mimic part of the effect, but structured complex residuals remain after time and phase alignment. The residual peaks for intermediate cores, $r_c/r_s\simeq0.25$–$0.3$. An SIDM-inspired isothermal-core profile gives the same qualitative response, showing that the signal is not an artifact of one cored parameterization. For a fiducial LISA source, an appreciable mismatch requires favorable near alignment and $M_{\rm vir}\gtrsim 10^7M_\odot$. The result is a finite-core baseline for isolated line-of-sight halos and for subhalos perturbing strongly lensed macro-images.
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All authors Dejiang Li, Tonghua Liu, Kai Liao, Beining Xia, Cuihong Wen, Jieci Wang

High Energy Astrophysical Phenomena

Supernova Remnants in the IXPE era: a review

Riccardo Ferrazzoli and IXPE Collaboration

The Imaging X-ray Polarimetry Explorer (IXPE) has opened a new observational window on the physics of supernova remnants (SNRs) by providing the first spatially resolved X-ray polarimetry measurements. These data directly probe the geometry and turbulence of magnetic fields in regions of efficient particle acceleration, thereby constraining models of diffusive shock acceleration and magnetic-field amplification. IXPE has so far observed six young SNRs (Cas A, Tycho, SN 1006, RX J1713.7-3946, Vela Jr., and RCW 86) with published results on the first five. The observations reveal significant polarization in all cases, with degrees of polarization ranging from 5% to over 30%, reflecting different turbulence levels and environmental conditions. Three remnants (Cas A, Tycho, and SN 1006) show predominantly radial magnetic fields, while RX J1713.7-3946 and Vela Jr. display tangential morphologies. This dual behavior, not simply correlated with evolutionary stage, challenges the long-standing dichotomy inferred from radio observations and suggests that both shock velocity and circumstellar medium density play key roles in shaping magnetic-field topology. IXPE's results mark a major step toward disentangling the processes governing cosmic-ray acceleration in young SNR shocks, with ongoing and future observations expected to further constrain the interplay between turbulence, shock dynamics, and particle acceleration.
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High Energy Astrophysical Phenomena

Accreting stellar-mass black holes

Greg Marcel, Bailey Tetarenko, Adam Ingram et al. (+3 more)

Accreting stellar-mass black holes exhibit dramatic variability across the electromagnetic spectrum, including spectral state transitions, outbursts, and jet production, making them unique laboratories for understanding accretion processes in strong gravitational fields. This review synthesizes recent progress in understanding these systems, focusing on their continuum emission, timing properties, emission lines, and X-ray polarization. A complex interplay between the accretion disk, the so-called corona, and jet underlies the observed spectral and timing behavior, with quasi-periodic oscillations and broadband noise providing windows into the dynamics of the innermost accretion flow. Emission lines across all wavelengths serve as critical diagnostics of disk structure, outflows, and reprocessing, while iron K lines in the X-ray band probe the properties of the inner disk through relativistic reflection. Polarization studies suggest that the corona is likely extended perpendicular to the jet axis in the hard state, while the soft state remains poorly understood, with observations that do not yet conform to simple theoretical expectations; a puzzle that continues to challenge our interpretation of accretion geometry. Despite significant advances, fundamental questions remain about the physical origins of state transitions, the role of magnetic fields in driving outflows and shaping the accretion flow, and the connection between disk instabilities and jet launching. This review underscores the need for future multi-wavelength, timing, and polarimetric studies to deepen our understanding of accretion physics in strong-gravity environments.
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All authors Greg Marcel, Bailey Tetarenko, Adam Ingram, Tom Maccarone, Alexandra Veledina, Phil Charles

Instrumentation and Methods for Astrophysics

NNNN: Neural Networks for Newtonian Noise Mitigation at the Einstein Telescope

Jan Kelleter, Patrick Schillings, Jonathan Kuckert et al. (+4 more)

The gravitational effects of seismic waves, so-called Newtonian noise, will likely limit the low-frequency sensitivity of future ground-based gravitational wave detectors, such as the Einstein Telescope. It has been proposed to mitigate this noise source by predicting it from measurements of the surrounding seismic displacement field using an array of seismometers. In this paper, we investigate the Newtonian noise prediction abilities of neural networks based on synthetic data from such seismometer arrays and compare the results with the Wiener filter as benchmark. We developed a simulation that generates density fluctuations of random plane waves and Gaussian wave packets, and that calculates the resulting Newtonian noise and displacement field. We investigate the performance on approximately stationary wave fields and single dominating long- and short-term events. For the first case, we observe comparable performance of neural networks and the Wiener filter with the networks performing slightly better. For the second case, however, we find that convolutional neural networks and graph neural networks can outperform the Wiener filter by factors of 15-80, depending on the frequency and the array configuration, and that they can reduce the corresponding Newtonian noise amplitude spectral density by factors of 10-30.
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All authors Jan Kelleter, Patrick Schillings, Jonathan Kuckert, David Bertram, Markus Bachlechner, Achim Stahl, Johannes Erdmann

Astrophysics of Galaxies

The SPHEREx View of Galaxy Clusters: A Simulation-based Validation of the Forced Photometry Pipeline for Extended Sources

Hyeonguk Bahk, Ho Seong Hwang, Lindsey Bleem et al. (+12 more)

We present a simulation-driven assessment of the performance of the SPHEREx pipeline for galaxy cluster science, focusing on photometry, source blending, survey depth, and photometric redshift accuracy. To do that, we compile a sample of eight galaxy clusters spanning a wide redshift range ($z \approx 0.02$-$1.1$) and develop an end-to-end pipeline. We use the ancillary data from the DESI Legacy Survey and COSMOS survey, and generate realistic mock SPHEREx observations with the SPHEREx Sky Simulator. By performing forced photometry on these images with The Tractor, we quantify the characteristic biases and uncertainties relevant to cluster science. We find that the photometry is generally unbiased, but source blending is the primary driver of catastrophic outliers, particularly when the combined flux of neighbors is comparable to the flux of targets. Measuring the effective survey depth, we find that SPHEREx detects members down to $K_{s}\approx 20$ AB ($5\sigma$), 7-9 mag fainter than the brightest cluster galaxy (BCG) in nearby clusters but only 1-2 mag for clusters at $z \sim 1$, where the BCG itself has faded close to this depth. Despite these challenges, we demonstrate that SPHEREx can achieve a photometric redshift precision of $\sigma_{\mathrm{NMAD}}\approx 0.003$-$0.01$ for cluster galaxies with an appropriate sample selection based on brightness or signal-to-noise. Combining the redshifts of quality-selected members, we recover cluster redshifts with a bias of $|\Delta z|/(1+z) < 0.002$ and a scatter of $\sigma \approx 0.002$ at $z \lesssim 0.5$, meeting the precision required for cluster cosmology.
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All authors Hyeonguk Bahk, Ho Seong Hwang, Lindsey Bleem, Yujin Yang, Yoonsoo P. Bach, Yun-Ting Cheng, Brendan P. Crill, Olivier Doré, Andreas L. Faisst, Zhaoyu Huai, Woong-Seob Jeong, Bomee Lee, Jeong Hwan Lee, Jeonghyun Pyo, Michael Zemcov

Astrophysics of Galaxies

Multi-band Structural Analysis of KiDS-selected Low Surface Brightness Galaxies with Hyper Suprime-Cam Imaging

Dipanjan Mitra and Kanak Saha

We present a homogeneous multi-band structural analysis of 205 KiDS-selected low surface brightness galaxy (LSBG) candidates using deep Hyper Suprime-Cam (HSC) $G$, $R$, and $I$-band imaging. Structural parameters were derived using single-component Sérsic modeling with GALFIT. The sample is dominated by diffuse systems with low Sérsic indices, with the distributions consistently peaking near $n\approx0.7$ across all bands. The estimated $B$-band central surface brightness distribution has a median value of $\tilde{\mu}_{0,B}=24.55$ mag arcsec$^{-2}$, indicating that the galaxies lie firmly within the low surface brightness regime. The catalog is strongly dominated by red systems, comprising 178 red LSBGs (87.3$\%$) and 27 blue LSBGs (12.7$\%$). Despite this color bimodality, the red and blue subsamples show similar structural properties, with no statistically significant differences in Sérsic index, effective radius, axis ratio, or surface brightness distributions. The absence of a correlation between color and axis ratio further suggests that dust reddening is unlikely to be the primary driver of the red colors. Overall, the sample provides a well-characterized structural reference set of LSBGs in the HSC footprint and confirms that the KiDS selected candidates are predominantly genuine low surface brightness galaxies.
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High Energy Astrophysical Phenomena

On the braking index evolution of PSR B0540-69: wind braking of pulsars

H. Tong

The pulsar PSR B0540-69 has both a braking index measurement and spin-down state change. After its spin-down state change, it shows an increasing braking index with time. Previously, it is pointed out that the spin-down state change may be caused by an enhanced particle wind. The prediction is that its braking index will be smaller in the high spin-down state. The current measured braking index is approaching the previous prediction. The transient variation of braking index may be due to a small varying part of the particle density. The braking index evolution of PSR B0540-69 is found to be in an exponential form. Its braking index is expected to approach some steady value. Future braking index measurement may make clear the physics for the braking index evolution. It may also help to make test the particle acceleration mechanism in the pulsar magnetosphere. Finally, a phenomenological treatment of the wind braking model is presented in the appendix. It can simplify the applications of wind braking model to pulsar braking index, intermittent pulsars and PSR B0540-69.
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Solar and Stellar Astrophysics

The Curious Case of Dark Faculae on M Dwarf Stars

Alexander~I.~Shapiro, Sara~Seager, Sami~K.~Solanki et al. (+6 more)

The study of exoplanet atmospheres has brought a renewed interest in stellar astrophysics. Specifically, stellar magnetic activity from the host star contaminates exoplanet atmosphere transmission spectra, as evidenced by observations from the James Webb Space Telescope. The stellar surface magnetic features in the form of dark spots caused by large concentrations of surface magnetic fields and more diffuse and extended faculae caused by small-scale magnetic field concentrations change the apparent size of the star in a wavelength-dependent way. This spot and faculae contribution to the change in transit depth contaminates the planetary signal. Here we study the transition from bright faculae on G- and K-dwarfs to dark faculae on M-dwarfs. This dark appearance of faculae is in significant contrast to the conventional picture that faculae are brighter than the quiet star region as they are on the Sun. We use the 3D radiative magnetohydrodynamics code MURaM to simulate faculae, and calculate the faculae spectra with the MPS-ATLAS radiative transfer code. We present a qualitative explanation for the transition from dark to bright faculae attributing it to shallower flux tubes and reduced vertical temperature gradients at the surfaces of M dwarfs relative to the Sun.
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All authors Alexander~I.~Shapiro, Sara~Seager, Sami~K.~Solanki, Nadiia~Kostogryz, Veronika~Witzke, Krishnamurthy~Sowmya, Tanayveer~Bhatia, Yvonne~C.~Unruh, Robert~Cameron

Cosmology and Nongalactic Astrophysics

Is dark matter decaying ?

Jeremy Mould

An enduring signature of the decay of unstable dark matter constituents into other particles would manifest as a measurable discrepancy in the matter density parameter (Omega_m) between the recombination era (z ~ 1000) and the local Universe (z = 0). While precision measurements of the Cosmic Microwave Background tightly constrain the initial matter budget, evaluating this decay hypothesis requires an equally precise audit of the current epoch. We find that current local inventories of baryonic and dark matter are subject to systematic uncertainties - particularly in accounting for the warm-hot intergalactic medium, diffuse intra-cluster media, and the exact profiles of low-mass dark matter halos - rendering a definitive verdict on late-time dark matter decay currently hard to pin down. Furthermore, existing astrophysical bounds on cosmic rays, the diffuse gamma-ray background, and reionization history already heavily constrain potential decay channels during this epoch. However, next-generation observational technology is poised to resolve these local accounting gaps. Upcoming high-resolution spectroscopic surveys, next-decade X-ray missions, and advanced weak lensing campaigns will drastically reduce baryon and mass-mapping uncertainties, transforming the late-time matter audit into a cleaner, more definitive test.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Graviton Floor

Himeka Matsuo, Asuka Ito, Kazunori Kohri et al. (+2 more)

It has been observed that the Universe is permeated by the cosmic photon background, ranging from radio waves to gamma rays. We investigate the conversion of the photon background into gravitons in the presence of background magnetic fields in the Milky Way Galaxy and in blazar jets. We find that the resulting graviton background is dominated by the contribution generated in blazar jets. Importantly, this graviton background constitutes a graviton floor for high-frequency gravitational wave detectors searching for new physics, analogous to the neutrino floor.
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All authors Himeka Matsuo, Asuka Ito, Kazunori Kohri, Teruaki Suyama, Ryutaro Tomomatsu

Astrophysics of Galaxies

Evolution of starless cores in massive clumps seen by the ALMA ASHES and QUARKS surveys

Dongting Yang, Hong-li Liu, Sheng-li Qin et al. (+28 more)

We present a systematic comparative analysis of 324 starless cores in early-phase infrared-dark clouds (IRDCs; ASHES survey) and evolved-phase infrared-bright clouds (IRBCs; QUARKS survey) using 1.3 mm continuum and line data by the Atacama Large Millimeter/submillimeter Array (ALMA). Despite having comparable sizes ($\sim$2500 au),starless cores in IRBCs exhibit systematically higher median mass ($1.5\,M_{\odot}$ vs. $0.6\,M_{\odot}$), number density, and surface density–enhancements of approximately a factor of two relative to starless cores in IRDCs. Starless cores in IRBCs also display relatively stronger non-thermal motions ($\rm\sigma \sim 0.5\,km\,s^{-1}$ vs. $\rm0.3\,km\,s^{-1}$), higher total virial parameters (median $\alpha_{\mathrm{vir,tot}} \sim$ 2.3 vs. 1.0), and steeper density profiles, indicating more centrally concentrated structures in feedback-driven, turbulence-enhanced environments. These findings support a dual evolutionary origin: (i) new core formation in evolved IRBCs under altered initial conditions, and (ii) subsequent dynamical mass growth via accretion from extended reservoirs. The prevalence of low-mass starless cores–even in late-stage IRBC environments–challenges models requiring massive prestellar cores and instead favors competitive-like dynamical mass accretion scenarios for high-mass star formation.
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All authors Dongting Yang, Hong-li Liu, Sheng-li Qin, Tie Liu, Wenyu Jiao, Guido Garay, Patricio Sanhueza, Fengwei Xu, Lei Zhu, Sami Dib, Xindi Tang, Amelia Stutz, Xiaofeng Mai, Siju Zhang, A.Y. Yang, Anandmayee Tej, Shanghuo Li, Xunchuan Liu, Pablo Garc{\i}a, Mika Juvela, James O. Chibueze, Prasanta Gorai, kee-tae Kim, Chang Won Lee, Tapas Baug, Swagat Ranjan Das, Shivani Gupta, Jihye Hwang, Leonardo Bronfman, Archana Soam, L. K. Dewangan

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Charged Lepton Flavor Violation at Neutrino Telescopes

Writasree Maitra, Carlos A. Argüelles, P. S. Bhupal Dev et al. (+2 more)

Any observation of charged lepton flavor violation (CLFV) would be a clear signal of beyond-the-Standard-Model physics. Here, we propose a novel CLFV search using neutrino telescopes with their large cosmic-ray muon samples. Specifically, we use a recent IceCube cosmic-ray muon dataset and propose a new search for muon-to-tau conversion inside the IceCube detector. We illustrate our idea with CLFV interactions described by model-independent Effective Field Theory (EFT) operators and present the IceCube sensitivity on the relevant EFT scale. We also consider a specific realization of the EFT operator in terms of an axial-vector $Z'$ interaction and show sensitivities in the $Z'$ mass-coupling plane. We compare our sensitivities with those from low-energy CLFV searches, as well as from current and future collider experiments. We also show projections from next-generation neutrino telescopes, such as IceCube-Gen2 and HUNT, and demonstrate how neutrino telescopes can provide a powerful complementary probe of CLFV.
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All authors Writasree Maitra, Carlos A. Argüelles, P. S. Bhupal Dev, Ivan Martinez-Soler, Manibrata Sen

Cosmology and Nongalactic Astrophysics

The stability of voids in the Local Universe: The role of the cosmological constant

V.G.Gurzadyan, N.N.Fimin and V.M.Chechetkin

The Vlasov kinetic formalism is employed to study the evolution and stability of cosmic voids in the Local Universe, taking into account not only the gravitational attraction, but also the repulsive effect of the cosmological constant (i.e., local dark energy). In accordance with the theorem on the general function of the identity between the gravitational fields of a sphere and a point mass, the cosmological constant provides a natural explanation for the Hubble tension, attributing it to local and global flows characterized by different Hubble parameters. The crucial role of the \Lambda-repulsion in maintaining the stability of voids at the present epoch is demonstrated when Landau damping suppresses discrete collapse modes and prevents random local density perturbations inside the voids from growing and incorporating new galaxies into the walls. Inside the voids, the \Lambda-repulsion exceeds the attractive force of the residual matter, driving matter outward and accelerating its migration toward the void boundaries. In the Local (late) Universe, cosmic voids have entered a stage characterized by stable and more pronounced walls, as studied via observational surveys across different redshift ranges.
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Cosmology and Nongalactic Astrophysics

Enhancing the Detection Sensitivity of Primordial Parity Violation using Galaxy Spins

Byoungjo Yu, Junsup Shim and Hyunmi Song

It has been recently demonstrated that the signature of primordial parity violation could be imprinted in halo spins, indicating its potential detectability through the late-time galaxy spin field (Shim et al. 2025). In this study, we develop an optimized halo selection strategy to enhance the detection significance of such a signal, focusing on halo mass and local density. Using N-body simulations with parity-asymmetric initial conditions, we show that the optimized halo sample allows for a higher detection sensitivity than the full halo sample, despite its reduced sample size. Finally, we assess the observational feasibility of our strategy and show that future spectroscopic surveys can provide sufficient data to realize this enhanced sensitivity.
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High Energy Astrophysical Phenomena

On the Contribution of Local Sources to the Galactic Cosmic-Ray Spectrum: An Exact Series Solution for Two-Zone Diffusion

Zi-Hang Liu, Yiwei Bao and Ruo-Yu Liu

Measurements of cosmic-ray proton and helium spectra below the knee show deviations from simple power laws, including multi-TeV structures. A possible explanation is that one or a few nearby sources contribute an additional component to the local spectrum. However, previous study shows that a dominant local contribution is statistically unlikely under a homogeneous diffusion model. In this work, we investigate how this probability changes if cosmic rays experience inefficient transport near their sources, motivated by observations of extended gamma-ray emission around Galactic accelerators. We derive a series Green's function that enables fast calculation of the particle distribution in this scenario, making Monte Carlo calculations for Galactic source populations feasible. The inner slow-diffusion region delays escape and redistributes the arriving particles in time and energy. In Monte Carlo realizations, the probability that the strongest local source becomes comparable to the background at $10\,\rm{TeV}$ increases from about $0.4\%$ in homogeneous diffusion to $1.7$–$2.2\%$ in the two-zone models. Thus inhibited near-source transport weakens, but does not remove, the statistical difficulty. We then examine cataloged nearby candidate supernova remnants and show that a $10\,\rm{TeV}$ feature can be reproduced only with additional assumptions, especially a harder local injection spectrum and a favorable diffusion coefficient. The predicted contribution of a given source changes strongly among different particle transport model. Therefore, the local source interpretations are plausible but highly model dependent, and require independent constraints on source injection history, particle transport mechanisms, and local interstellar turbulence.
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Astrophysics of Galaxies

PMO Polaris CO survey. II. Where is the dust?

Xunchuan Liu, Bing Gang Ju, Fujun Du et al. (+10 more)

Dust plays critical chemical and dynamical roles in the interstellar medium (ISM), but its specific association with molecular and atomic gas remains difficult to isolate. Combining the PMO Polaris CO Survey (PPCOS), EBHIS \ion{H}{I} data, and Planck dust maps, this study investigates dust distributions across multiple gas components in the Polaris Flare. We employ multi-technique linear decomposition – including full-spectrum fitting and a regularization approach – to reconstruct the dust distribution from multi-component gas emissions. This framework quantifies dust contributions from CO-associated, \ion{H}{I}-associated, and CO-dark molecular gas phases. CO-associated dust accounts for 20–40% of the total dust mass, whereas dust in the broad \ion{H}{I} (warm neutral medium, WNM) component is negligible. Instead, \ion{H}{I}-associated dust concentrates primarily within the narrow cold neutral medium (CNM) and a distinct, ultra-narrow component with a velocity width comparable to the \ion{H}{I} spectral resolution. Residual dust at atomic-to-molecular (\ion{H}{I}–CO) interfaces contributes 4–10% to the global dust mass, but exceeds 25% at molecular cloud boundaries, confirming a substantial presence of CO-dark molecular gas. Furthermore, the velocity fields of dust-associated \ion{H}{I} closely match those of CO, indicating active dynamical coupling between CO-emitting gas and the surrounding CNM. Guided by these results, we present a stepwise schematic cartoon illustrating the coupling between multi-phase gas structures, molecular formation, and dust growth.
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All authors Xunchuan Liu, Bing Gang Ju, Fujun Du, Paul F Goldsmith, Tianwei Zhang, Lixia Yuan, Lianghao Lin, Zhihong He, Chao Zhang, Ping Yan, Shengyu Jin, Yongxing Zhang, Dengrong Lu

Earth and Planetary Astrophysics

Following up the Kepler field with PLATO: Transit Timing Performance

Morgan A. Mitchell, James McCormac, Don Pollacco et al. (+11 more)

The European Space Agency is set to launch PLATO, the third medium-class mission of its Cosmic Vision programme, in early 2027. Using the transit method, PLATO is expected to detect thousands of exoplanets orbiting bright, nearby stars of spectral types F5-K7. Although the mission is primarily designed to enable mass measurements via radial velocities, its precise photometry and long observational baselines may also permit the detection of transit timing variations (TTVs), which can provide complementary dynamical constraints in multi-planet systems. One possible PLATO observing scenario involves a two-year-long observation of a Northern field that may partially or fully overlap with the original Kepler field, creating an opportunity to revisit known multi-planet systems with a photometric baseline exceeding 20 years. We simulate PLATO observations of 152 Kepler host stars containing at least one planet with previously detected TTVs, yielding a sample of 361 transiting planets. Our CCD-level simulations incorporate realistic stellar variability and employ both aperture and point spread function (PSF)-fitting photometry, accounting for each target's real photometric contaminants. While the extended temporal baseline offers the potential for improved dynamical constraints in favourable cases, our simulations show that this potential is strongest for carefully selected systems, as PLATO's smaller collecting area and larger pixel scale limit the achievable per-transit precision relative to Kepler. We identify a subset of systems most likely to benefit from complementary dynamical constraints through PLATO observations.
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All authors Morgan A. Mitchell, James McCormac, Don Pollacco, Emmanuel Grolleau, Nicholas Jannsen, Daniel R. Reese, Réza Samadi, Yoshi Nike Emilia Eschen, Ioannis Apergis, James A. Blake, David J. A. Brown, Lauren Doyle, Isobel S. Lockley, Lixian Shen

Earth and Planetary Astrophysics

Upper Limits on Planet-Induced GHz Radio Emission from Inactive M Dwarfs

Jackie Villadsen, Carter Russell, Luna Guerrero et al. (+9 more)

Nearby short-period exoplanet systems may produce detectable stellar radio emission due to sub-Alfvénic star-planet interaction (SPI), but there are no confirmed cases yet. We targeted five slowly-rotating M dwarfs with transiting terrestrial planets, observing at GHz frequencies throughout their sub-day orbital periods. We did not detect any bursty SPI-like emission, but detected two stars in quiescence: LHS 3844 (unpolarized) and LHS 1678 (circularly polarized). These detections imply persistent magnetic activity at Gyr ages, especially notable for LHS 1678 given its low photometric variability, and can serve as targets for radio transit experiments. Our SPI non-detections may be due to radio beaming geometry, a sub-GHz maximum emission frequency, or undetectable flux density. If the last case applies, then flux density upper limits constrain the exoplanet magnetosphere. GJ 367 b has the tightest constraints – no extended magnetosphere and an exoplanet field <0.8 G – although these results depend strongly on unknown stellar wind parameters inferred from stellar rotation period. Due to their small orbital distance, our non-detection systems a priori appear to have more favorable conditions for SPI than most radio-detected SPI candidate systems in the literature, a tension that can either be resolved by favorable wind/geometry conditions on the detected candidates or by a non-SPI (stellar activity) explanation for those candidate detections. Our results favor the approach of sub-GHz searches for radio SPI, especially with the sensitivity of new/upcoming facilities such as MeerKAT, and underscore the need for observational and theoretical work to constrain the magnetized stellar wind parameters.
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All authors Jackie Villadsen, Carter Russell, Luna Guerrero, Ethan Harvie, Ariana Watson, Arjun Anand, John Sebastian Pineda, Vanessa Moss, Daniele d'Antonio, Louisa Canepa, E. Cappellazzo, Andrew Zic

Solar and Stellar Astrophysics

The Effects of Energy Conservation in Simulating Solar Eruptions

Xianyu Liu, Spiro K. Antiochos, Nishtha Sachdeva et al. (+6 more)

Strict energy conservation is, perhaps, the most basic principle in all physics, but has proven to be difficult to satisfy in numerical simulations of solar eruptions. The Alfvén Wave Solar atmosphere Model (AWSoM) is used to perform a rigorous comparison of CME simulations whose only difference is the use of a conservative vs. non-conservative scheme for the energy equation. A simple, symmetric active region is assumed for the initial magnetic field. As expected, the different numerical schemes result in very different plasma thermal energy, but surprisingly, we also find a factor $>2$ difference in the final kinetic energy, with the energy substantially larger in the energy-conservative scheme. The increase in thermal energy is comparable to the increase in kinetic energy in the conservative simulation. Our analysis reveals that the flare reconnection and increase of kinetic energy terminate earlier with the non-conservative scheme. We conclude that the plasma thermodynamics plays a critical role in the flare reconnection, with the thermal pressure gradient in the current sheet slowing down the reconnection. Our results imply that using strict energy-conservative numerics is critical for space weather modeling of CMEs and for understanding the CME energy budget partitioning.
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All authors Xianyu Liu, Spiro K. Antiochos, Nishtha Sachdeva, Gábor Tóth, Ward B. Manchester IV, Bart van der Holst, Igor V. Sokolov, Tamas I. Gombosi, Lulu Zhao

Wednesday 17 June

High Energy Astrophysical Phenomena

Circumstellar Disc and X-ray Variability in the Be/X-ray Binary SXP 5.05 During its 2024 Outburst

Chintan Patel, Sayantan Bhattacharya, Karan Akbari et al. (+3 more)

Be/X-ray binaries provide a unique opportunity to study the interaction between neutron stars and circumstellar discs. SXP 5.05 is a particularly rare system, exhibiting eclipse-like X-ray variability attributed to obscuration by the Be star disc rather than a simple stellar eclipse. Motivated by its unusual geometry and the well-studied 2013 outburst, we present a multiwavelength analysis of its 2024 outburst using NICER X-ray observations and long-term optical monitoring from OGLE. The X-ray light curve shows a declining outburst with lower peak intensity and shorter duration compared to 2013, indicating a reduced accretion episode. The spectral evolution, characterized through hardness ratios, reveals a transition from a soft, high-intensity state to a harder, low-intensity state. Coherent pulsations near 5.05 s are detected throughout the observations, with properties consistent with previous measurements. The optical light curves show a reduced variability amplitude relative to 2013, possibly from a less extended or less dense circumstellar disc. Orbital-phase-folded optical profiles reveal a persistent, phase-locked dip structure, indicating a stable non-axisymmetric disc component that evolves across outburst phases. Together, these results support a picture in which the observed variability is driven by changes in disc structure and viewing geometry. SXP 5.05 thus remains a key system for probing the time-dependent properties of Be star discs through combined X-ray and optical observations.
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All authors Chintan Patel, Sayantan Bhattacharya, Karan Akbari, Rajapandi Nadar, Sudip Bhattacharyya, Manojendu Choudhury

Earth and Planetary Astrophysics

The fate of Earth during the Sun's giant phases: New constraints from ab initio tidal modelling and AGB mass loss

M. Esseldeurs, S. Mathis and L. Decin

The long-term evolution of planetary systems around solar-type stars is governed by the interplay between stellar expansion, tidal interactions, and mass loss during the red giant branch (RGB) and asymptotic giant branch (AGB) phases. However, tidal dissipation efficiencies and AGB mass-loss rates both remain poorly constrained, leading to significant uncertainty in predicting the fate of planetary systems, in particular, that of the Earth orbiting the ageing Sun. We reassess the survival of the Earth and the inner Solar System planets during the entire evolution of the Sun, focusing on the impact of updated tidal dissipation prescriptions and varying AGB mass-loss rates. We modelled the orbital evolution of the Earth using stellar evolution tracks for a solar-mass star. We compared these results with outcomes obtained using previously published and commonly adopted tidal prescriptions, and we explored a range of AGB mass-loss rates. We find that the predicted fate of the Earth is highly sensitive to the tidal model and the assumed mass-loss rate. Based on updated tidal dissipation prescriptions, Earth survives the RGB and AGB phases of the Sun. In contrast, the use of earlier tidal dissipation prescriptions leads to engulfment during the AGB phase. Furthermore, low AGB mass-loss rates result in engulfment, and vice versa. Using the observed mass-loss rates of the AGB star L2 Pup as a proxy for the Sun's future AGB mass-loss rate results in the survival of the Earth during the AGB phase when combined with our tidal dissipation evaluation. Given the current observational uncertainties in AGB mass-loss rates, the ultimate fate of the Earth remains uncertain, highlighting the need for improved constraints on the late-stages of stellar evolution. However, considering observational proxies for the Sun during the AGB phase, it is likely that the Earth will survive the Sun's giant phases.
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Solar and Stellar Astrophysics

Effects of the Background Magnetic Field on Flux Rope Eruptions

Xianyu Liu, Spiro K. Antiochos, Igor V. Sokolov et al. (+5 more)

Solar eruptive events are generally believed to involve magnetic flux ropes (MFR), formed either in the pre-eruptive phase of the event or during the eruption itself. These MFR eruptions exhibit significant complexity and variations due to the interplay of the physical mechanisms involved, in particular magnetic reconnection and ideal instabilities. This work considers the effect of the background magnetic field on the nature of eruptions with pre-existing MFRs. We used a new MHD model to simulate the whole MFR eruption process, including the pre-eruptive stage and the initiation. Three simulations were performed, all of which used an identical bipolar active region, but with different background magnetic fields in the three cases. The simulations resulted in two successful eruptions (CMEs) and one failed eruption (a confined flare). We analyzed the energetics and the acceleration of the MFR in detail, and found a transition to a rapid exponential rise phase in two of the simulations. We also calculated the criterion for the torus instability and the timing of the breakout and flare reconnections. Our results show that the rapid exponential rise phase is likely due to breakout reconnection. We conclude that a background field antiparallel to the active-region field lowers the magnetic free-energy threshold for eruption; but, does not guarantee a successful eruption. We also found that an antiparallel background field leads to faster flare reconnection, but of shorter duration. Our findings underscore the importance of the background magnetic field in understanding CMEs.
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All authors Xianyu Liu, Spiro K. Antiochos, Igor V. Sokolov, Tamas I. Gombosi, Bart van der Holst, Gábor Tóth, Nishtha Sachdeva, Lulu Zhao

Solar and Stellar Astrophysics

Review of Machine Learning Models for Solar Energetic Particle Prediction

Spiridon Kasapis, Pouya Hosseinzadeh, Kathryn Whitman et al. (+73 more)

Solar energetic particle (SEP) events have attracted increasing attention due to their significant radiation hazards for aviation, spacecraft electronics, and human missions beyond Earth's magnetosphere. From a scientific perspective, SEP events are intriguing because they arise from a set of physical processes extending from the solar surface and corona through the heliosphere, offering insight into particle acceleration and transport mechanisms that are widely applicable across astrophysics. Therefore, advancing our ability to understand and predict SEP events is essential both for deepening our knowledge of such mechanisms and for safeguarding space technologies and exploration. Traditionally, researchers have modeled SEPs using physics-based simulations and empirical methods. More recently, machine learning (ML) has emerged as a new tool for understanding and predicting SEP events. The purpose of this manuscript is to review the currently available ML models for SEP prediction, identify the datasets used for training, compare their architectures, inputs, and outputs, and, based on these insights, outline good practices and recommendations for future research.
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All authors Spiridon Kasapis, Pouya Hosseinzadeh, Kathryn Whitman, Ricky Egeland, Manolis Georgoulis, Angelos Vourlidas, Athanasios Papaioannou, Eleni Lavasa, Anastasios Anastasiadis, Giorgos Giannopoulos, Andres Munoz-Jaramillo, Bala Poduval, Irina N. Kitiashvili, Alexander G. Kosovichev, Viacheslav Sadykov, Soukaina Filali Boubrahimi, Tate T. Hutchins, Hameedullah A. Farooki, Manuel E. Cuesta, Leng Y. Khoo, Sungmin Pak, Robert Czarnota, Jamie S. Rankin, Jamey Szalay, Mitchell M. Shen, Georgios Livadiotis, Zigong Xu, David J. McComas, Nikolaos Sarlis, Dionissios Hristopulos, Arik Posner, Alec J. Engell, Mohammed AbuBakr Ali, Ali G. A. Abdelkawy, Abdelrazek M. K. Shaltout, M. M. Beheary, Christina O. Lee, Sigiava Aminalragia-Giamini, Constantinos Papadimitriou, Ingmar Sandberg, Savvas Raptis, Shah Muhammad Hamdi, Monica Laurenza, Mirko Stumpo, Sumanth A. Rotti, India Jackson, Aatiya Ali, Atilim Gunes Baydin, Nathan Schwadron, Subhamoy Chatterjee, Maher A. Dayeh, Gelu M. Nita, Patrick M. O'Keefe, Chun Jie Chong, Paul Kosovich, Russell D. Marroquin, Berkay Aydin, Petrus C. Martens, Lulu Zhao, Yang Chen, Yian Yu, Monica G. Bobra, Ward Manchester, Tamas Gombosi, Ming Zhang, Jesse Torres, Philip K. Chan, Mohamed Nedal, Kamen Kozarev, Peijin Zhang, Kimberly Moreland, Hazel M. Bain, Samuel Hart, Michael J. Starkey, Alan G. Ling, Simone Benella

Cosmology and Nongalactic Astrophysics

Increasing the sensitivity of full-shape galaxy clustering measurements in configuration-space with three-point statistics

Zachery Brown and Lado Samushia

We investigate the cosmological constraining power of a compressed line of sight dependent three point correlation function (3PCF) estimator on small scales (<80 Mpc/h) in configuration space, with a particular focus on emission line galaxies (ELGs) targeted by the Nancy Grace Roman Space Telescope's Galaxy Redshift Survey (GRS), and complementary luminous red galaxy (LRG) samples observed by the Dark Energy Spectroscopic Instrument (DESI). These scales avoid the baryon acoustic oscillation (BAO) feature and are therefore expected to provide information that is largely complementary to standard BAO measurements, while retaining partial overlap with full shape clustering analyses. Our forecasts are based on AbacusSummit simulations at z = 1.1 and z = 0.8, populated with galaxies using halo occupation distribution (HOD) models matched to Roman ELG and DESI LRG samples respectively. The three point measurements are computed with TriCo, a fast configuration space triangle counting code developed for this analysis. After marginalizing over uncertainties in the galaxy halo connection, we find that incorporating the 3PCF yields a substantial improvement over two point statistics alone, tightening the constraint on sigma_8 by a factor of 5 in our fiducial forecast. This gain arises not from a localized feature or specific scale range, but from the cumulative information content across triangle configurations. Restricting to the monopole of the 3PCF captures only part of this information, with the full line of sight dependent measurement providing an additional factor of 2 to 3 improvement over the monopole. Adding line of sight dependent three point information substantially increases the constraining power of small scale configuration space galaxy clustering.
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Cosmology and Nongalactic Astrophysics

Reheating as a variational probe of cosmological observables

Jinn-Ouk Gong

We formulate reheating as a constrained variational problem in the space of equation-of-state histories, rather than attempting to describe it through microscopic models. We introduce a regularized functional framework that identifies reheating histories which extremize a given cosmological observable under minimal physical assumptions. As illustrative applications, we consider prompt gravitational waves, induced gravitational waves, and primordial black holes. We find that different observables select qualitatively different regions of reheating-history space. These examples demonstrate that cosmological observables define distinct extremal directions in reheating-history space and can therefore be used to systematically explore the space of post-inflationary expansion histories.
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Solar and Stellar Astrophysics

Simulation to a Newborn Supernova Remnant from a Low-mass Iron Core Star

Sudarshan Neopane, Michael A. Sandoval, W. Raphael Hix et al. (+3 more)

Supernova remnant observations show a high degree of asymmetry, mixing, and inhomogeneity. These asymmetries are seeded during the early seconds of the explosion and are further enhanced and modified as the shock and ejecta move through the stellar progenitor and into the circumstellar medium. We present simulations of a 9.6 solar mass zero-metallicity progenitor initialized after shock revival and evolved for several years when the ejecta is in the circumstellar medium. A suite of 1D and 2D simulations examines the effects of neutron-star wind and radioactive decay heating. In 1D, decay heating forms a low-density bubble that suppresses the reverse shock. While in 2D, the heating is localized to metal-rich pockets, inflating them and compressing the surrounding material into dense shells. In 3D the neutron-star wind and decay heating modify the plume morphology, producing more large-scale structures. The extended plume morphology leads to an asymmetrical shock breakout. After breakout, the leading plumes cannot keep up with the shock front, resulting in deceleration and fragmentation by the reverse shock while retaining the large-scale asymmetry. The projected ejecta morphology and velocities are strongly viewing angle dependent. The relatively uniform metal-rich distribution does not resemble the strongly inhomogeneous ejecta structure of Cas A. The 160-isotope decay network shows that 24.4% of the radioactive heating comes from decay chains other than the canonical Ni-56 chain. The low explosion energy, low Ni-56 yield, and Ni/Fe ratio greater than unity suggest an observational signature similar to an electron capture supernova.
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All authors Sudarshan Neopane, Michael A. Sandoval, W. Raphael Hix, J. Austin Harris, O. E. Bronson Messer, Eric J. Lentz

Earth and Planetary Astrophysics

Atmospheric asymmetries in WASP-121 b revealed by rotational transits detected with JWST

Cyril Gapp, Aurélien Falco, Thomas M. Evans-Soma et al. (+6 more)

Close-in exoplanets are tidally locked to their host star and thus exhibit extreme atmospheric temperature gradients. It has been theorized that the fraction of star light absorbed by such planets during transit changes as a function of orbital phase as progressively hotter or colder atmospheric gas rotates into view, but this effect has not been observed so far. Here, we show that two transits of the ultra-hot Jupiter WASP-121 b, acquired with JWST/NIRSpec and NIRISS, exhibit asymmetric transit light curves caused by the planet's rotation during transit. We observe increasing CO absorption and slightly decreasing H$_2$O absorption in the transmission spectrum, as the planet rotates. These results are indicative of a stronger longitudinal temperature gradient across the evening than across the morning terminator, consistent with higher temperatures in the eastern half than in the western half of the dayside. The observed changes of the transmission spectrum with orbital phase are in line with the temperature increase causing thermal dissociation of H$_2$O, while CO remains abundant. The observation of longitudinal gradients of atmospheric temperature and chemistry from the planet's rotational transit provides a new probe for constraining atmospheric heterogeneity using JWST beyond differences between morning and evening terminators from limb asymmetries.
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All authors Cyril Gapp, Aurélien Falco, Thomas M. Evans-Soma, David K. Sing, Shashank Dholakia, Vivien Parmentier, Jérémy Leconte, Eva-Maria Ahrer, Guangwei Fu

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

sft-wick: A formalism and package for Feynman-diagram expansion and evaluation in stochastic field theories

Zheng Zhang

When stochastic field dynamics are cast into a path-integral formulation, perturbation theory becomes systematic but the resulting expansion quickly grows combinatorially large. The setting targeted here includes multi-component, multi-dimensional fields with matrix propagators, tensor-valued couplings, and non-Gaussian driving noise specified by arbitrary $n$-point cumulants. Wick pairings grow factorially, and component indices must be routed through the tensor-valued vertices. The useful output is not a raw contraction list, but a diagram table: one entry per topology, with multiplicities, coupling sums, signs, and causal constraints resolved. We present sft-wick, an open-source Python package that constructs these diagram tables and computes their integrals numerically. Given an action and an observable, it enumerates topologically distinct Feynman diagrams, derives their algebraic coefficients, and evaluates the resulting diagram integrals from user-supplied response and cumulant functions. The core algorithm enumerates spatial topologies before routing component indices, avoiding contraction-by-contraction Wick expansion. Response-field constraints, including vanishing response-response contractions, the ito prescription, and the absence of causal response loops, are enforced during enumeration. Predictions are validated against direct Langevin simulation, agreeing to within the simulation's statistical noise.
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