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Physics Astrophysics

astro-ph Watch Astrophysics

Sunday 3 May

Solar and Stellar Astrophysics

Probing the kinematics of FU Orionis objects through high-resolution near-infrared spectroscopy

Ellen Lee and Michael Connelley

FU Orionis (FUor) objects are thought to be described by a steady-state Keplerian disk. However, the characteristic double-peaked Keplerian line profile is not readily seen in most near-infrared spectra of FUors. In this paper, we measure the near-infrared line profiles of 15 FUors and FUor-like objects by convolving model cool atmosphere spectra with a linear combination of Gaussians. The models are fit to high-resolution spectra obtained with iSHELL on the NASA Infrared Telescope Facility (IRTF). Five of the targets are found to have double-peaked line profiles in K-band, which can also be fitted by a Keplerian line profile. For eight targets that were also observed in J-band, we find that the line profiles are well-correlated to what is observed in K-band, but the linewidth does not clearly appear to decrease with wavelength. We find that a double-peaked line profile can be difficult to see for several reasons, which include blending with extraneous molecular features and potential absorption from a disk wind or infalling material. The CO lines in M-band are morphologically different from their counterparts in K-band, so they are probably of a different origin.
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Astrophysics of Galaxies

Galaxy luminosity functions from far-UV to submillimetre at $z=0$ in the COLIBRE simulations

Shengdong Lu, Carlos S. Frenk, Cedric G. Lacey et al. (+15 more)

We present predictions from the COLIBRE cosmological hydrodynamical simulations of galaxy formation for the present-day galaxy luminosity functions (LFs) at wavelengths ranging from the far-ultraviolet (FUV) to the submillimetre. The simulations are post-processed with the radiative transfer code SKIRT, accounting for dust attenuation and emission using the distribution and properties of dust grains predicted directly by COLIBRE. Results from simulations varying in mass resolution by a factor of $\sim 10^2$ ($\sim 10^5 - 10^7\,\mathrm{M_{\odot}}$) show very good convergence over most luminosity ranges. The COLIBRE-SKIRT LFs match the data remarkably well from the FUV to $3.4\,\mu \rm m$ and also in the far-infrared and submillimetre wavelength range ($70-850\,\mu \rm m$). In the mid-infrared (MIR; $8-24\,\mu \rm m$), COLIBRE-SKIRT matches the data well at low luminosities but significantly underpredicts the luminosities of MIR-bright galaxies, with the discrepancy increasing towards longer wavelengths. The total infrared LF, obtained by integrating the spectral energy distributions over $8-1000\,\mu \rm m$, also matches observations well at the faint end but underpredicts the number of very bright galaxies. The unprecedented agreement at all other wavelengths indicates that COLIBRE, coupled with this calibration-free SKIRT post-processing framework, successfully predicts the properties of stellar populations at the present day and the amount and distribution of interstellar dust.
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All authors Shengdong Lu, Carlos S. Frenk, Cedric G. Lacey, Andrea Gebek, Joop Schaye, Shaun Cole, Sownak Bose, Nick Andreadis, Maarten Baes, Alejandro Benítez-Llambay, Evgenii Chaikin, Robert A. Crain, Anna Durrant, Filip Huško, Sylvia Ploeckinger, Alexander J. Richings, Matthieu Schaller, James W. Trayford

Cosmology and Nongalactic Astrophysics

Baryons in the Darkest Sites of the Universe

Kritti Sharma, Vikram Ravi, Dhayaa Anbajagane et al. (+9 more)

The pristine underdense patches of the Universe, cosmic voids, are powerful cosmological laboratories, uniquely sensitive to dark energy, modified gravity, and neutrino masses, yet their baryonic content remains uncharacterized. We present the first observational constraint on baryon underdensity in void interiors, exploiting the dispersion measures (DMs) of Fast Radio Bursts (FRBs) as tracers of the free electron column, independent of gas phase, temperature, and metallicity. By stacking 3,455 sightlines from CHIME/FRB on 1,288 SDSS BOSS voids over redshifts $0.2 < z < 0.7$, we measure a DM deficit toward void centers at $3.2\sigma$ significance, establishing that diffuse baryons inhabit the emptiest corners of the cosmic web at a suppressed level. The measured signal amplitude is consistent with an effective Universe model built directly from the observed galaxy underdensity in these voids, and a baryonic model calibrated to the FRB DM-redshift relation ($\alpha_v = 1.80 \pm 0.87$). A uniform-density void model yields an electron density contrast of $\delta_\mathrm{e,v} = -0.58 \pm 0.30$, implying a $\sim 60$% underdensity of baryons in void interiors relative to the cosmic mean. Jointly interpreting our FRB measurement with existing stacks of the thermal Sunyaev-Zel'dovich effect on voids further constrains the mean void gas temperature to $T_\mathrm{e} \lesssim (1.1 \pm 0.7) \times 10^6$ K, pointing to a warm-hot diffuse phase, consistent with hydrodynamical simulation predictions. With forthcoming FRB (CHORD, DSA, SKA) and galaxy (DESI, LSST, Euclid, PFS-Subaru, SPHEREx, Roman) surveys, set to expand both samples by orders of magnitude, this approach opens a new window onto tomographic baryon mapping, with direct implications for feedback models governing gas expulsion into low-density environments, and for the use of cosmic voids to extract cosmological constraints.
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All authors Kritti Sharma, Vikram Ravi, Dhayaa Anbajagane, William R. Coulton, Elisabeth Krause, Nico Schuster, Alice Pisani, Samuel McCarty, Liam Connor, Simone Ferraro, Nico Hamaus, Pranjal R. S

Solar and Stellar Astrophysics

The connection between solar coronal abundances and the underlying lower atmospheric properties

Paola Testa, Juan Martinez-Sykora, Bart De Pontieu et al. (+4 more)

Elemental abundances in the solar corona and solar wind are often observed to differ from those in the solar photosphere, most commonly showing an enhancement of low first ionization-potential (FIP) elements (the FIP effect). The observational evidence of the connection between the chemical fractionation in the solar atmosphere with FIP suggests that the mechanisms responsible for this effect take place in the chromosphere, where low-FIP elements are mostly ionized, while high-FIP elements remain mostly neutral. We discuss the findings of recent observational studies that have investigated the possible footprint of coronal abundance anomalies in the lower atmosphere. We also discuss the limitations of current observations, and future perspectives on addressing this important open issue in solar physics.
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All authors Paola Testa, Juan Martinez-Sykora, Bart De Pontieu, Alberto Sainz Dalda, David Long, Deborah Baker, David H. Brooks

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

Reviving Motivated Inflationary Potentials with $K$-inflation in the light of ACT

Milad Solbi, Daris Samart and Peera Simakachorn

Recent ACT data favor a higher scalar spectral index $n_s$, placing models such as $\alpha$-attractor T-models and natural Inflation in tension with current observations. We propose a K-inflation framework with a field-dependent non-canonical kinetic term $G(\phi)$ that reconciles these models with the latest Planck-ACT-LB-BK18 constraints. Our analysis includes a refined calculation of the reheating equation-of-state parameter $w_{\rm re}$, avoids standard power-law approximations, and tests consistency with the Swampland Distance and de Sitter Conjectures. We find that the additional friction from the non-minimal kinetic coupling shifts both models into the favored observational regions. For the $\alpha$-attractor T-model with $n=2$, viable solutions occur for $\beta\sim \mathcal{O}(10)$, with Swampland consistency favoring $\alpha\gtrsim \mathcal{O}(10^{-3})$. This case predicts matter-like reheating and a red-tilted gravitational-wave background that is unlikely to be detected soon. In contrast, natural Inflation with $n=4,5$ is compatible with CMB constraints for $\alpha\lesssim 7,8$ and $\beta\lesssim -1$, respectively, leading to stiff reheating and a blue-tilted gravitational-wave background potentially observable by LISA, Cosmic Explorer, Einstein Telescope, DECIGO, and BBO while satisfying BBN and $\Delta N_{\rm eff}$ bounds. Combining gravitational-wave probes with Swampland criteria may therefore help distinguish possible UV completions of inflation.
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Cosmology and Nongalactic Astrophysics

Constraints on the baryon density from fast radio bursts using a non-parametric reconstruction of the Hubble parameter

Lázaro L. Sales, Klecio E. L. de Farias, Amilcar R. Queiroz et al. (+3 more)

In this study, we use a sample of 130 well-localized fast radio bursts (FRBs) to constrain the physical baryon density $\Omega_{\rm b}h^2$, and the astrophysical contribution from host galaxies. The cosmological dependence entering the intergalactic dispersion measure is described through a non-parametric reconstruction of the Hubble parameter $H(z)$ obtained from cosmic chronometer data using the ReFANN neural-network framework, independently of the FRB sample. Within a Bayesian analysis, we jointly infer $\Omega_{\rm b}h^2$ and the parameters of a log-normal host-galaxy distribution, namely its median $e^\mu$ and logarithmic scatter $\sigma_{\rm host}$, using both real FRB data and a mock catalog. For the real sample, we obtain $\Omega_{\rm b}h^2=0.02236\pm0.00090$, $e^\mu=178.15^{+16.51}_{-16.97}~\mathrm{pc}\,\mathrm{cm}^{-3}$, and $\sigma_{\rm host}=0.794^{+0.064}_{-0.067}$. For the mock catalog, we find $\Omega_{\rm b}h^2=0.02248\pm0.00018$, $e^\mu=182.36^{+6.83}_{-6.48}~\mathrm{pc}\,\mathrm{cm}^{-3}$, and $\sigma_{\rm host}=0.711^{+0.024}_{-0.025}$. The baryon density constraint from the real FRB sample is in excellent agreement with both Big Bang Nucleosynthesis and Planck CMB determinations, differing from their central values by only $\simeq 0.05\%$. The mock analysis further illustrates the potential of future FRB samples, reducing the uncertainty on $\Omega_{\rm b}h^2$ to the sub-percent level while remaining statistically consistent with early-Universe constraints. Our findings show that combining FRB dispersion measures with a non-parametric reconstruction of the expansion history provides a robust pathway to constrain both cosmological and astrophysical parameters, establishing FRBs as a complementary low-redshift probe of the baryon density.
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All authors Lázaro L. Sales, Klecio E. L. de Farias, Amilcar R. Queiroz, Rafael A. Batista, Bruno W. Ribeiro, Raiff H. Santos

High Energy Astrophysical Phenomena

4HWC J2029$+$3641: a Pulsar Wind Nebula Powered by PSR J2030$+$3641?

Ziwei Ou, Jie Wang and Songpeng Pei

4HWC J2029+3641 is a newly discovered point source detected by HAWC, with no previously identified TeV counterpart. The gamma-ray pulsar PSR J2030+3641, located 0.1 degree from the source center, is a middle-aged pulsar showing spin parameters similar to Geminga. Using Fermni-LAT data spanning from August 2008 to February 2026, we performed binned maximum likelihood spectral analysis in the energy range from 300 MeV to 1 PeV. A phase-resolved analysis was conducted to separate the off-peak and on-peak emissions. No significant spatial extension was found for the off-peak component. The off-peak spectrum exhibits strong curvature and is best described by an exponentially cutoff power-law model. The observed radio-to-gamma phase lag and narrow peak separation favor an outer-gap model for the gamma-ray emission.
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Astrophysics of Galaxies

A Comprehensive Study of Morphology and Kinematics in Extended Nebulae Around UV Luminous Quasars at $z\approx1$

Zhuoqi Liu, Sean D. Johnson, Eric F. Bell et al. (+20 more)

Gas flows between galaxies and the circumgalactic medium (CGM) play a central role in galaxy evolution and can become observable as giant nebulae when illuminated by the quasars. We present an ensemble study of nebulae around 30 UV-luminous quasars at z=0.4-1.4 from the CUBS and MUSEQuBES surveys, 27 of which are detected in extended [O II] and/or [O III] emission. Based on a joint analysis of nebular morphology and surrounding galaxy environments, we introduce three morpho-kinematic classifications. We identify eleven irregular, large-scale (>50 kpc) systems, many of which are likely interaction-related; twelve compact host-galaxy-scale nebula, likely tracing CGM/ISM gas; and four systems with complex morphologies of uncertain origin. We introduce a quantitative measure of the spatial and kinematic association between nebulae and quasar-host group galaxies, finding a statistically significant association for ten nebulae, most of which are irregular, large-scale nebulae, consistent with qualitative analysis. Radio jets are detected in six systems, with no strong correlation found between radio activity and nebular emission. The [O II] nebulae are more asymmetric than their Ly$\alpha$ counterparts at $z>2$, but bear more similarity to H I gas observed in 21 cm around local elliptical galaxies. Blueshifted-redshifted patterns, likely tracing gas rotation, are observed in roughly 30% of the systems, though disturbed kinematics suggest that feedback may also be important. These results show that giant quasar nebulae are not a uniform class of objects, but instead arise through multiple pathways shaped by host-galaxy gas, galaxy interactions, group environments, and quasar activity, with the most striking cases associated with galaxy interactions.
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All authors Zhuoqi Liu, Sean D. Johnson, Eric F. Bell, Zhijie Qu, Benoît Epinat, Hsiao-Wen Chen, Marc Rafelski, Jennifer I-Hsiu Li, Alexander Beckett, Mandy C. Chen, Sayak Dutta, David DePalma, Gwen C. Rudie, Joop Schaye, Patrick Petitjean, Sebastiano Cantalupo, Elise Fuller, Wolfram Kollatschny, Sebastián López, Nishant Mishra, Sowgat Muzahid, Andrea Travascio, Fakhri S. Zahedy

Cosmology and Nongalactic Astrophysics

Cosmology since the first Astro/Cosmo Moriond meeting// The emergence of the Big Bang 2.0

Alain Blanchard

This paper presents a necessarily incomplete review of the evolution of cosmology since the first Astro/Cosmo Moriond meeting in 1981. I trace the journey from the classical Big Bang model based on three pillars – universe expansion, primordial nucleosynthesis, and the cosmic microwave background – to the modern $\Lambda$CDM paradigm and the discovery of cosmic acceleration. I discuss major observational milestones: the COBE discovery of CMB fluctuations, the CMB measurements of the flat universe, the pivotal discovery of accelerated expansion through Type Ia supernovae and the emergence of precision cosmology with Planck. I review current tensions in cosmological parameters, particularly the Hubble tension and $\s8$ discrepancies, and discuss future prospects from large-scale structure surveys like DESI. The emergence of “Big Bang 2.0” reflects the profound paradigm shift from a model based on standard physics to a dynamical cosmos dominated by dark matter and dark energy, the description of which requires a physics that has yet to be developed and validated.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Pole structure of the Kerr Green's function

Hayato Motohashi and Yuto Suichi

We investigate the pole structure of Kerr black-hole perturbations in the frequency domain, focusing on the building blocks of the Green's function for the radial Teukolsky equation: the homogeneous radial solutions, the connection coefficients, and the Green's function itself. We show that the homogeneous solutions and the local connection coefficients develop simple poles at the Matsubara frequencies, thereby establishing the Matsubara pole structure explicitly within the Teukolsky formalism for asymptotically flat Kerr black holes. At the level of the local fixed-sector connection formula, the explicit Matsubara-pole factors cancel in the ratio of connection coefficients entering a decomposed Green's function contribution. We also identify higher-order zero-frequency singularities in the decomposed Green's function contributions, which scale as $\omega^{-2l-1}$ and cancel collectively in the total radial Green's function. These results clarify how Matsubara poles and sectoral zero-frequency singularities arise in the Teukolsky formalism and provide a frequency-domain foundation for understanding prompt response in time-domain ringdown waveforms in Kerr spacetime.
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Cosmology and Nongalactic Astrophysics

Constraints on Halo Gas Profiles from Joint kSZ and Galaxy Clustering Analysis of ACT DR6 and CMASS

Shaohong Li and Yi Zheng

We measure the kinetic Sunyaev-Zel'dovich (kSZ) signal through a joint analysis of the pairwise kSZ effect and galaxy clustering using CMASS galaxies and ACT DR6 maps. This approach breaks degeneracies between the optical depth and nuisance parameters, enabling a reconstruction of the halo optical depth profile as a function of aperture scale. The kSZ signal reaches its highest signal-to-noise ratio of 7.2 at an aperture radius of $\theta_{\rm AP} = 2$ arcmin, while the full profile rejects the no-kSZ hypothesis at $8.7\sigma$. Applying the same analysis pipeline to the Websky simulation, we find that the observed optical depth profile is somewhat more extended than the simulated one. This difference suggests that baryonic feedback in the real Universe may be stronger and redistribute gas to larger radii more efficiently than modeled in the simulation, although residual systematic effects and modeling uncertainties remain to be further investigated.
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Earth and Planetary Astrophysics

On the Dust Substructures Triggered by Two Super-Earths Migrating in Low-viscosity Disks

Zijia Cui and Ewa Szuszkiewicz

We investigate dust substructure formation induced by two super-Earths migrating in a low-viscosity disk with single-size dust grains selected from the submillimeter to centimeter range of sizes. The orbital evolution of planets takes place in the vicinity of the 2:1 commensurability, which allows to determine, in addition to the dust substructure properties, the dust impact on the rate of migration, the resonance capture, the libration overstability and the outcome of passage through the commensurability. Using two-dimensional two-fluid hydrodynamic simulations with dust feedback and dust diffusion taken into account, we identify two specific regions in the disk where the accumulation of dust particles is significant, leading to dust substructure formation with the dust-to-gas ratio values close to or even higher than 1 for large grains. The first region, with a narrow dust ring, is located between the planetary orbits and the second one, with a broad feature, evolving in time in a multiple ring substructure, is situated outside the orbit of the outer planet. Our results indicate that these two locations are favorable for planetesimal formation. We discuss the properties of the dust substructures formed in our simulations and outline possible consequences of their evolution for the observed architectures of multi-planetary systems.
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Solar and Stellar Astrophysics

Radio Signature of Higher Atmospheric Meridional Flow and Implications for Magnetic Trees in the Sun

Srinjana Routh, Anshu Kumari, Rohan Bose et al. (+4 more)

The coupling between plasma flows and magnetic fields in the solar atmosphere governs the transport of angular momentum and the redistribution of magnetic flux, yet its manifestation in the magnetically dominated upper chromosphere remains uncertain. Using 27 years of 17 GHz full-disk solar radio imaging observations from the Nobeyama Radioheliograph, we report the first detection of a poleward flow signature at heights of $3000\pm500$ km, an altitude where plasma magnetohydrodynamics expects magnetic dominance ($\beta<1$). The derived latitudinal velocity profile ($5-15$ m/s) mirrors the established photospheric meridional circulation, displaying modulation with solar cycle parameters. Comparison with long-term synoptic magnetograms reveals that the motion of 17 GHz brightness features closely tracks poleward magnetic flux transport, implying a deep magnetic anchoring of these structures. This finding provides the first observational evidence that chromospheric flows at radio wavelengths reflect subsurface meridional dynamics, consistent with the "magnetic tree" hypothesis, which links high-altitude motion to deep-seated magnetic connectivity.
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All authors Srinjana Routh, Anshu Kumari, Rohan Bose, Vaibhav Pant, Divya Paliwal, Dipankar Banerjee, Nat Gopalswamy

Cosmology and Nongalactic Astrophysics

Constraints on Phenomenological Amplitudes of CMB Anisotropy with Multi-Datasets

Yang Han, Lu Chen, Guo-Hao Li et al. (+1 more)

Cosmic microwave background anisotropies encode crucial information about the early Universe and fundamental cosmological physics. Although the standard $\Lambda$CDM model provides a successful description of cosmic evolution, persistent cosmological tensions and subtle small-scale anomalies still challenge its internal consistency. In this paper, we investigate six phenomenological amplitude parameters $A_{\rm{new}}$ (new=L, SW, Dop, eISW, lISW, Pol) corresponding to the key effects related to CMB anisotropy: the Lensing, Sachs-Wolfe, Doppler, early Integrated Sachs-Wolfe, late Integrated Sachs-Wolfe, and Polarization effects, respectively. Using modified CAMB and Cobaya packages, we constrain the $\Lambda$CDM$+A_{\rm{new}}$ models with two data combinations: Planck+DESI+PantheonPlus (PDP) and Planck+ACT+DESI+PantheonPlus (PADP). Only the $\Lambda$CDM+$A_{\rm{L}}$ is favored by AIC, with $A_{\rm{L}}=1.0656_{-0.0303}^{+0.0304}$ from PDP and $A_{\rm{L}}=1.0795_{-0.0289}^{+0.0260}$ from PADP, which implies 2.16$\sigma$ and 3.06$\sigma$ deviation from the $\Lambda$CDM model; values of $A_{\rm{SW}}$ show 1.21$\sigma$ and 1.96$\sigma$ deviations to 1; $A_{\rm{lISW}}$ is poorly constrained because the lISW effect has negligible influence at $\ell \geq 30$; and others are consistent with the $\Lambda$CDM model. Moreover, no noticeable improvement on the Hubble and $\sigma_8$ tensions is found within these one-parameter extended scenarios. ACT DR6 high-$\ell$ data strengthens the $\Lambda$CDM$+A_{\rm{L}}$ preference over the $\Lambda$CDM model, and reduces $A_{\rm Pol}$ uncertainty by more than one order of magnitude, highlighting the importance of ground-based high-$\ell$ observations for future CMB analyses.
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All authors Yang Han, Lu Chen, Guo-Hao Li, Pei-Yuan Xu

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

Scalar-Electromagnetic Couplings as Source of Deformed Black Hole: From Shadows to Thermodynamic Topology

Ednaldo L. B. Junior, José Tarciso S. S. Junior, Francisco S. N. Lobo et al. (+5 more)

We reconstruct a static and spherically symmetric black hole geometry originally proposed as an effective metric by identifying a consistent matter source derived from a fundamental action. The space-time is supported by a magnetically charged nonlinear electrodynamics (NED) field non-minimally coupled to a scalar field. Dimensional consistency reduces the parameter space to a single magnetic charge, and the inverse construction formalism yields a one-parameter family of electromagnetic Lagrangians $\mathcal{L}(F)=F^{n+1}/(n+1)$, encompassing both linear and nonlinear electrodynamics. We analyze the horizon structure and determine the critical magnetic charge separating black hole and horizonless configurations. The photon sphere and the corresponding shadow radius are computed, and observational bounds from the Event Horizon Telescope for Sagittarius A* constrain the allowed range of the magnetic charge. In the extended phase space thermodynamics, the solution satisfies the first law and the Smarr relation, exhibits a Hawking-Page phase transition, and presents a single change in stability without van der Waals-type critical behavior. We also investigate the topological properties of both the photon sphere and the thermodynamic parameter space. The photon sphere carries a total topological charge $Q_{\text{tot}}=-1$, while the thermodynamic vector field yields a global winding number $W=0$, placing the solution in the same topological class as the one of the Reissner-Nordström black hole. We finally discuss the versatility of this non-minimal coupling framework in both providing theoretical support to previously introduced solution and also to connect them to observational settings within strong-field gravity.
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All authors Ednaldo L. B. Junior, José Tarciso S. S. Junior, Francisco S. N. Lobo, Jorde A. A. Ramos, Manuel E. Rodrigues, Diego Rubiera-Garcia, Luís F. Dias da Silva, Henrique A. Vieira

Solar and Stellar Astrophysics

Formation of Suprathermal Electron Populations in the Expanding, Turbulent Solar Wind

Maximilien Péters de Bonhome, Fabio Bacchini, Luca Pezzini et al. (+1 more)

Nonthermal features are ubiquitously observed in electron velocity distribution functions in the solar wind, yet their origin in the collisionless, turbulent, expanding solar-wind plasma remains unclear. We investigate how solar-wind expansion and Alfvénic turbulence jointly generate and regulate these features using the first fully kinetic particle-in-cell simulation of an expanding turbulent plasma under heliospheric conditions. In our setup, expansion-driven weakening of the magnetic field adiabatically cools the plasma perpendicularly to the mean field while leaving the parallel temperature largely unchanged, driving the system toward the firehose-instability threshold. Concurrently, strongly anisotropic turbulence leads to perpendicular heating and the development of nonthermal features. Subsequently, we find that suprathermal electron populations preferentially develop in the parallel direction, forming pronounced power-law tails even under weakly compressive, highly Alfvénic conditions, and persist despite anisotropy regulation by the firehose instability. The preferentially parallel energization suggests the involvement of parallel electric fields or resonant wave–particle interactions, rather than simple velocity-space redistribution. These results provide the first direct evidence of the emergence of nonthermal-electron features in a unified kinetic framework linking expansion, turbulence, and instabilities in the solar wind.
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All authors Maximilien Péters de Bonhome, Fabio Bacchini, Luca Pezzini, Viviane Pierrard

Astrophysics of Galaxies

A Short-timescale Negative Optical Continuum Lag in SDSS J083717.88+191647

Chen MuLin, Cheng PeiZhen, Chen XingQian et al. (+4 more)

Continuum reverberation mapping (RM) is a powerful technique for constraining the accretion disk structure in active galactic nuclei (AGNs). In typical cases, the shorter-wavelength emission is used as the reference, and a positive time lag is observed since the inner, hotter regions of the accretion disk respond earlier than the cooler outer regions at longer wavelengths. However, we detect a short-timescale negative inter-band lag in SDSS~J083717.88+191647 using RM techniques, where the g-band lags behind the r-band emission. The light curves from the Zwicky Transient Facility reveal two distinct phases, a stabilizing and a declining phase, in which the time lags show opposite signs. Using JAVELIN with the $g$-band as the reference, we obtain time lags of $3.68^{+1.94}_{-2.78}$~days during the stabilizing phase and $-1.60^{+0.69}_{-0.54}$~days during the declining phase. Although negative continuum lags have been reported in a few previous studies, the present case is distinguished by its clear phase dependence and the accompanying color evolution. We attribute the observed lag reversal to a moving dust-cloud obscuration scenario, in which the cloud crossing the line of sight preferentially obscures emission from the outer longer-wavelength regions of the disk, causing the $r$-band to decline earlier than the $g$-band and thus producing the observed negative inter-band lag. Our results indicate that AGN variability may be more complex than previously thought. Future high-cadence, multi-band observations will be essential to test this dust-obscuration model and to further explore the interplay between the accretion disk emission and dust in AGNs.
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All authors Chen MuLin, Cheng PeiZhen, Chen XingQian, Gu Ying, Zheng Qi, Liao GuiLin, Zhang XueGuang

Saturday 2 May

Earth and Planetary Astrophysics · Cross-listed from physics.geo-ph

Stochastic Resonance in a Thermally Driven Low-Dimensional Geodynamo Model

Giuseppina Nigro, Edoardo Cascio, Giuseppe Consolini et al. (+1 more)

Geomagnetic field reversal sequences exhibit persistence times spanning a broad range, from a few $10^4$ years to superchrons lasting more than $10^7$ years. Despite extensive observational and theoretical work, the physical mechanisms governing how such reversals occur and how their broad temporal variability is organized are still not fully understood. Here we investigate the temporal variability of geomagnetic polarity in a thermally driven low-dimensional geodynamo model subject to a slow periodic modulation of the control parameter governing the large-scale induction, namely the $\alpha$-effect parameter. We find that the modulation generates a multipeaked probability density function of magnetic persistence times, with local maxima occurring at approximately integer multiples of the modulation timescale, as expected in a stochastic-resonance-like regime. The peak positions follow an approximately linear dependence on their index, showing that the characteristic timescales selected by the system are set by the imposed modulation period. These results provide a physically motivated numerical framework in which slow modulation of a geodynamo control parameter can organize reversal statistics through stochastic-resonance-like dynamics.
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All authors Giuseppina Nigro, Edoardo Cascio, Giuseppe Consolini, Francesco Berrilli

Solar and Stellar Astrophysics

MHD simulations on the large-scale propagation of high-speed solar wind streams

Stefan J. Hofmeister

We investigate the propagation of high-speed solar wind streams from their origin near the Sun to 1 AU using three-dimensional magnetohydrodynamic simulations. By tracking both global stream structure and individual plasma parcels, we assess how local in-situ measurements relate to the underlying plasma evolution. We find that high-speed streams are not parcel-preserving structures: commonly used diagnostics such as peak velocity, density, or temperature do not trace fixed plasma elements, and feature-based radial trends can therefore misrepresent the true evolution. Instead, velocity-based relationships provide a more robust framework for linking plasma parcels across heliocentric distances. Stream evolution is dominated by interaction regions, where compression leads to deceleration of fast wind, acceleration of slow wind, and significant heating. A boundary layer forms close to the Sun and can dominate narrow streams, biasing in-situ measurements toward lower apparent velocities. We show that three-dimensional transport, in particular latitudinal flows, redistributes mass and magnetic flux and reduces center-to-flank contrasts. While radial magnetic flux is conserved, the total field strength is not in spherical sampling geometries due to non-radial components. Finally, observed stream properties and geoeffectivity depend strongly on sampling location, stream geometry, and latitudinal magnetic deflection, introducing systematic variability and asymmetries in geomagnetic response.
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Solar and Stellar Astrophysics

A Point-Spread Function for the Extreme Ultraviolet High-Resolution Imager on board Solar Orbiter

Stefan J. Hofmeister, Emil Kraaikamp, Sergei Shestov et al. (+7 more)

We present the point-spread function (PSF) of the Extreme Ultraviolet High-Resolution Imager (HRIEUV) onboard Solar Orbiter, which observes the Sun at 174 Angstrom. This PSF provides a quantitative description of light diffracted by the mesh and mounting supporting the entrance filter, light diffracted by the mesh supporting the filter-wheel filter, as well as light that is diffusely scattered by the microroughness of the mirrors. Deconvolution with this PSF corrects the images for instrumental scattered light, substantially improving image quality and photometric accuracy. First, we determine the diffraction component of the PSF from mechanical drawings of the instrument. We find that 26% of the incoming light is diffracted, predominantly by the entrance-filter mounting and mesh. Second, we fit the diffuse scattered light using partial image occultations during the 2023-Jan-03 Mercury transit. We find that the diffuse scattered light is well described by a softened power law, which scatters 42% of light over the detector. Combined, 57% of the incoming light is redistributed over the detector by diffraction and scattering. Correcting for these effects markedly enhances the dynamic range and contrast of the observations. The intensity in bright structures intensifies by up to 40% and the intensity in dark structures decreases by up to 85 %. All images features become much clearer, facilitating a more precise scientific analysis of HRIEUV observations.
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All authors Stefan J. Hofmeister, Emil Kraaikamp, Sergei Shestov, Luca Teriaca, Alexandros Koukras, Cis Verbeeck, Frederic Auchere, Daniel W. Savin, Michael Hahn, David Berghmans

High Energy Astrophysical Phenomena

Zooming in on the GeV $\gamma$-ray flare of the blazar PKS 1725+123 with a multimessenger lens

Suvas Chandra Chaudhary, Saikat Das, Raj Prince et al. (+1 more)

Blazars are promising sources of extragalactic high-energy astrophysical neutrinos, detected at energies $\gtrsim 10$ TeV by the IceCube neutrino observatory. Here, we report the first-ever broadband timing and spectral study of the flat-spectrum radio quasar PKS 1725+123, which has recently emerged as a compelling multimessenger target following its spatial association with the IceCube event IC-201021A. This triggered extensive follow-up observations from radio to VHE $\gamma$-rays, and a multi-episode flare was identified at a later time. During this period, the source exhibited high flux variability across all wavelengths. The Fermi-LAT analysis suggests rapid variability on timescales of less than 6 hours, implying a compact emission region with a radius of $\sim10^{16}$ cm. Our one-zone leptohadronic model shows that the high-energy $\gamma$-ray flux is produced by a combination of inverse-Compton scattering of external photons from the hot accretion disk and the broad-line region, while the X-ray emission is dominated by synchrotron self-Compton radiation from relativistic electrons. The secondary radiation from the hadronic cascade is found to be sub-dominant in the $\gamma$-ray regime, and the X-ray data constrain the maximum proton energy to $\sim 20$ PeV in the observer frame. Photopion production occurs predominantly with accretion-disk photons, resulting in an estimated muon-neutrino event rate of $\approx 0.3~\mathrm{yr}^{-1}$ during the flaring state with the flux peaking at $\sim1$ PeV. Future observations of TeV $\gamma$-rays by CTA and LHAASO will further constrain cosmic-ray production in this source.
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All authors Suvas Chandra Chaudhary, Saikat Das, Raj Prince, Brian van Soelen

Earth and Planetary Astrophysics

The Days Drag On on WASP-121 b: Interpreting its NIRISS Spectroscopic Phase Curve with General Circulation Models

Robert C. Frazier, Emily Rauscher, Jared Splinter et al. (+18 more)

Ultra-hot Jupiters present extreme atmospheric phenomena not found in the Solar System. These planets' daysides experience strong temperature inversions, molecular species (including H2) dissociate, and magnetism disrupts their atmospheric circulation. On their nightsides H2 can recombine and clouds may form. Spectroscopic phase curves let us measure these spatially inhomogeneous conditions, which can then be interpreted with three-dimensional (3-D) models. In this work we compare the JWST/NIRISS spectroscopic phase curve of the ultra-hot Jupiter WASP-121 b to state-of-the-art 3-D models with varying modeling assumptions, including the aforementioned physical phenomena. We demonstrate the importance of accurately accounting for the planet's radius in comparison between data and models, as it changes the implied overall planetary emission. We find that the 3-D models predict planet emission $\sim$12% higher than observed, contributing to a continued tension between measured and predicted hot Jupiter albedos. We identify multiple pieces of evidence that confirm a strong source of drag operating in this planet's atmosphere. In addition, the nightside emission spectrum is devoid of strong absorption features, which may be best explained by nightside clouds. One feature of the dataset that is not matched by the 3-D models is a trend of increasing eastward phase offset with decreasing wavelength, for wavelengths shorter than $\sim$1.4 \textmu m. This result is not consistent with reflection from dayside clouds, nor can it be explained by removing atmospheric opacity sources. Our analysis highlights the complexities in generating 3-D models and interpreting observations of ultra-hot Jupiters in the JWST era.
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All authors Robert C. Frazier, Emily Rauscher, Jared Splinter, Thomas D. Kennedy, Xianyu Tan, Vivien Parmentier, Isaac Malsky, Louis-Philippe Coulombe, Romain Allart, Nicolas B. Cowan, David Lafrenière, Ryan MacDonald, Stefan Pelletier, Lisa Dang, René Doyon, Doug Johnstone, Lisa Kaltenegger, Michael R. Meyer, Caroline Piaulet-Ghorayeb, Michael Radica, Jake D. Turner

Solar and Stellar Astrophysics

On the Radial Evolution of the Solar Wind : The Source Alignment Method Applied to Parker Solar Probe and Solar Orbiter Observations

Jean-Baptiste Dakeyo, Tamar Ervin, Stuart Bale et al. (+10 more)

The properties of the solar wind, as measured in situ throughout the heliosphere, depend both on the characteristics of its coronal source and on the intrinsic processes governing its interplanetary evolution. Recently, radial and Parker spiral alignment techniques have been applied to Parker Solar Probe (PSP) and Solar Orbiter (SO) observations to investigate the radial evolution of the same solar wind parcel. These studies have shown that the solar wind can undergo significant acceleration even beyond its primary acceleration region (i.e., above 15 solar radii). However, such radial and Parker spiral alignments are rare in practice, which limits the statistical significance and general applicability of the results. We introduce a new source alignment technique designed to overcome these limitations. Using magnetic backmapping, we associate similar solar wind streams observed by the two spacecraft based on the proximity of their photospheric footpoints, combined with additional in-situ stream similarity criteria. Applying the source alignment method to PSP and SO observations, we identify a total of 548 alignment intervals, each lasting 30 minutes. By constructing statistics over all alignments, we find that the solar wind speed increases by an average of 45% per radial decade (approximately 147 km/s) between the two probes. This result demonstrates that solar wind acceleration in the inner heliosphere remains significant compared to that occurring below 15 solar radii. Among the different studied plasma parameters, the radial evolution of the electron temperature and plasma density, show the strongest anti-correlation with the increase in bulk velocity.
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All authors Jean-Baptiste Dakeyo, Tamar Ervin, Stuart Bale, Pascal Démoulin, Nikos Sioulas, Victor Réville, Mingzhe Liu, Alexis Rouillard, Milan Maksimovic, Davin Larson, Orlando Romeo, Philippe Louarn, Roberto Livi

Astrophysics of Galaxies

Non-Equilibrium Ionisation in Photoionised Haloes: Implications for Shock Stability and Absorption-Line Signatures

Itai Bromberg, Kartick C. Sarkar, Orly Gnat et al. (+1 more)

We investigate the impact of nonequilibrium ionisation (NEI) and the metagalactic radiation-field on the thermal evolution, virial shock stability, and absorption signatures of gas surrounding galaxies. Using 1D, spherically symmetric hydrodynamical simulations with an extended version of the hydra code, we follow dark-matter growth, gas dynamics, time-dependent ionisation and cooling in the presence of the UV background. We explicitly track all ions of H, He, C, N, O, Ne, Mg, Si, S, and Fe in haloes of mass 1e11-1e13Msun from z=100 to z=0. Without a UV background, NEI enhances post-shock cooling due to underionised gas, reducing pressure support and raising the minimum mass for stable shock formation. Including the UV background pre-ionises the IGM, suppressing NEI, and restoring the CIE threshold. The IGM temperatures deviate from thermal equilibrium due to adiabatic expansion and collapse, while ionisation remains close to equilibrium in the presence of a UV background, except in transient rapidly cooling regions where NEI occurs. We compute absorption columns of OVI, CIV, and HI, showing that a photoionised IGM may produce substantial warm-ion columns extending beyond Rvir, including OVI column densities comparable to observed values. Our models indicate weak halo-mass dependence and extended distributions. We also find that z>~3 haloes can produce CIV (NCIV~1e13-15cm^-2) and HI (NHI~1e15-17cm^-2) columns out to ~10Rvir. Our results highlight the role of the UV background in regulating the thermal state and observable signatures of the gas surrounding galaxies, and emphasize the importance of accounting for IGM contributions when interpreting CGM absorption-line observations.
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All authors Itai Bromberg, Kartick C. Sarkar, Orly Gnat, Yuval Birnboim

Solar and Stellar Astrophysics

Speckle Interferometry at SOAR in 2024 and 2025

Andrei Tokovinin, Brian D. Mason, Rene A. Mendez et al. (+1 more)

Results of speckle interferometry observations at the 4.1 m SOuthern Astrophysical Research (SOAR) telescope obtained during 2024-2025 are presented. We present 5316 measurements of relative positions and magnitude differences in 3532 pairs (including 524 unpublished measures made before 2024) with median and minimum separations of 0.19" and 12 mas, respectively; non-resolutions of 1723 stars are documented as well. More than 400 pairs have been resolved here for the first time and not resolved by Gaia; among those are 222 TESS objects of interest, 46 inner subsystems in known wider binaries within 100 pc, and 43 subdwarfs. Positional measurements are used to compute or improve binary orbits; elements of 202 orbits with meaningful errors are given here, while preliminary and tentative orbits are published elsewhere. Of special note are orbits with large and accurately measured eccentricties (e.g. e=0.9866+/-0.0014 for J13038-2035) and orbits of pre-main sequence binaries. Appendix contains parameters of 86 binaries used for calibration of pixel scale and orientation.
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All authors Andrei Tokovinin, Brian D. Mason, Rene A. Mendez, Edgardo Costa

High Energy Astrophysical Phenomena

Powerful parametric instability of Alfven waves in astrophysical pair plasma

Maxim Lyutikov

We demonstrate that in highly magnetized pair plasmas, nonlinear Alfven waves with wave-number $k \leq k_0 = \omega_p^2 /(\delta \omega_B)$ ($\delta =( \delta B)/B_0$ are relative fluctuations of the magnetic field) experience powerful modulational instability. In the two-fluid approximation, we develop an analytic set-up for circularly polarized (CP) Alfven mode in its frame (where the initial configuration is stationary; it is moving with relativistic, amplitude-dependent Alfven velocity $v_A (\sigma, \delta ) $, while both charges experience different, amplitude-dependent, synchrotron gyration). PIC simulations using EPOCH code demonstrate that for Alfven waves with $k$ near $k_0$, large, parametrically-driven density fluctuations develop, and lead to fast modulational instability. Charge separation effects, for a CP wave in magnetized pair plasma, might be temporarily important; on longer time-scales the density fluctuations are charge neutral and in symmetric pair plasma quickly grow to large amplitudes. In highly magnetized plasma, $\sigma \gg 1$, high frequency modes $k / k_0 \sim (2-3 ) \times \sigma \gg 1 $ are quickly generated; for smaller plasma magnetization, the dominant mode is at the Bragg's condition $k = 2 k_0$. Long term behavior of CP and LP modes is similar. We discuss application of the results to the physics of Fast Radio Bursts generated/propagating in the magnetospheres of magnetars.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Constraints on Einstein-aether gravity from the precision timing of PSR J1738+0333

Massimo Vaglio, Amodio Carleo, Abhimanyu Susobhanan et al. (+5 more)

We constrain Einstein-aether gravity – a Lorentz-violating extension of General Relativity in which a dynamical, unit timelike vector field selects a preferred frame – using updated high-precision pulsar timing observations of PSR J1738+0333 from EPTA second Data Release and the NANOGrav 9-year release, in combination with ToAs from Arecibo, Green Bank, Nancay, Parkes, and Westerbork. Our method accounts for both conservative and dissipative first post-Newtonian corrections arising from Lorentz violation; here we apply it to PSR J1738+0333 using the Bayesian timing pipeline Vela to process the full ToA dataset. We sample the joint posterior over binary component masses, post-Keplerian parameters and center-of-mass velocity components, and then apply a resampling scheme to propagate posteriors into robust constraints on the fundamental theory parameters, obtaining the most stringent strong-field bounds on the Einstein-aether coupling constants from a single binary pulsar system to date.
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All authors Massimo Vaglio, Amodio Carleo, Abhimanyu Susobhanan, Enrico Barausse, Bilel Ben Salem, Alessandro Corongiu, Paulo C. C. Freire, Delphine Perrodin

High Energy Astrophysical Phenomena

Black Hole Supernovae Outcomes Across a Wide Progenitor Range

Oliver Eggenberger Andersen, Evan O'Connor, Liubov Kovalenko et al. (+2 more)

Black hole supernovae (BHSNe), the term we use for core-collapse events in which black hole (BH) formation occurs after shock revival but before the explosion is complete, have emerged as a natural outcome of multidimensional simulations as these calculations have been extended to seconds after bounce. Yet they remain one of the least studied outcomes of core collapse. Here, we assess whether they are confined to the most compact and massive progenitors, whose birth rates are low, or whether they arise systematically across a wider range of progenitor structures. We perform 23 long-term axisymmetric core-collapse simulations of progenitors spanning 19.51-60$\,M_\odot$ and compactnesses $0.31 \lesssim \xi_{2.5} \lesssim 0.63$. We find 18 BHSN outcomes across nearly the full ZAMS mass range considered, corresponding to progenitors with $0.40 \lesssim \xi_{2.5} \lesssim 0.63$. BH formation occurs between $\sim0.7$ s and $\sim4.4$ s after bounce. After BH formation, we continue the evolution with an excision treatment to at least 5000 s. The final explosion energies span $\sim2\times10^{49}$-$3\times10^{51}$ erg, while the final BH gravitational masses span $\sim3$-$26\,M_\odot$. We find a clear remnant-mass trend with CO-core mass, but show that the CO core alone is not an adequate proxy for the final BH mass, especially for progenitors at the low- and high-mass ends of the CO-core distribution. Except for the highest CO-core mass models, no single spherical mass coordinate cleanly separates ejecta from remnant material. Finally, a 2D axisymmetric and a 3D model are compared as we discuss differences between the two geometries.
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All authors Oliver Eggenberger Andersen, Evan O'Connor, Liubov Kovalenko, Haakon Andresen, Sean M. Couch

Earth and Planetary Astrophysics

The atmosphere of the warm Neptune GJ 436 b probed with ESPRESSO

E. Herrero-Cisneros, M. R. Zapatero Osorio, J. Sanz-Forcada et al. (+21 more)

Aims. We aim to identify the presence of atomic and molecular species in the upper atmosphere of the warm Neptune-sized transiting planet GJ 436 b, which has a radiative equilibrium temperature of 690 K and a mass of 25.4 Earth masses. Methods. Using transmission spectroscopy, we observed two full transits of GJ 436 b with the ESPRESSO spectrograph, covering the wavelength range from 3800 to 7880 Angstrom. We searched for traces of atomic (H I, Li I, Na I, Mg I, V I, Cr I, Fe I, and Fe II) and molecular (TiO, VO) species by directly detecting planetary absorption features and by cross-correlating the planetary spectrum with theoretical spectra computed for each investigated species. Results. Our analysis reveals no strong planetary detection for any of the species, consistent with a featureless optical spectrum. We derived upper limits by combining all ESPRESSO observations. Post-transit stellar flares were detected on both nights, primarily affecting chromospheric lines. A tentative Fe I signal appears in the first transit (S/N = 3.4 +/- 0.2) at a wind velocity of about -18.6 km/s, which is unexpectedly large for a cool planet. This weak signal is not present in the second transit and, combined with its low significance, suggests an origin in noise. In the less probable scenario where the feature is suppressed during the second transit by the higher stellar activity state, the T1 tentative signal peaks at 1300 K, which is above the equilibrium temperature of GJ 436 b. Ultimately, this result would imply a neutral iron abundance comparable to or exceeding that of the host star.
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All authors E. Herrero-Cisneros, M. R. Zapatero Osorio, J. Sanz-Forcada, R. Allart, T. Azevedo Silva, S. Cristiani, A. R. Costa Silva, Y. C. Damasceno, P. Di Marcantonio, P. Figueira, J. I. González Hernández, B. Lavie, M. Lendl, G. Lo Curto, C. J. A. P. Martins, E. Pallé, F. Pepe, A. Psaridi, R. Rebolo, J. Rodrigues, N. C. Santos, J. V. Seidel, A. Sozzetti, A. Suárez Mascareño

Cosmology and Nongalactic Astrophysics

A structural degeneracy explains reionization tensions and limits dark matter constraints

Zihan Wang and Huanyuan Shan

Over the past decade, reionization studies have yielded persistent factor-of-two-to-five disagreements in the inferred ionizing escape fraction $f_{\mathrm{esc}}$ and peak star formation efficiency $f_{*,0}$, compounded by JWST's discovery of unexpectedly bright $z>10$ galaxies. We show that this discrepancy arises from an algebraically exact structural degeneracy: the ionizing photon rate $\dot{n}_{\mathrm{ion}} \propto f_{\mathrm{esc}} \times f_{*,0}$ renders all reionization-history probes, including Thomson optical depth, neutral hydrogen fraction, UV luminosity function, and quasar proximity zones, sensitive only to their product, leading to an intrinsically non-invertible mapping between model parameters and observations. We demonstrate the robustness of this degeneracy using a large suite of N-body simulations of self-interacting dark matter haloes spanning $10^9$-$10^{11} M_\odot$. Despite substantial changes to galaxy-scale structure, observables remain indistinguishable once the effective ionizing emissivity is matched, severely limiting reionization-based dark matter probes. We identify that only observables sensitive to the spatial topology of ionized regions can break this degeneracy. Our results provide a unified explanation for the scatter among published constraints and establish a framework for interpreting reionization observations and their implications for early galaxy formation and dark matter.
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