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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 18 March

High Energy Astrophysical Phenomena

Optical transients from non-explosive double white-dwarf mergers: the case of a central neutron star remnant

M. M. Ridha Fathima, Alexandre M.R. Almeida, Mattia Bulla et al. (+3 more)

Discoveries of ultra-massive magnetic white dwarfs (WDs) and peculiar pulsars have been proposed to originate in double white dwarf (DWD) mergers. There are three possible post-merger central remnants of non-explosive mergers: 1) a stable sub-Chandrasekhar WD; 2) a rapidly rotating super-Chandrasekhar WD; 3) a neutron star (NS). In this work, we explore the thermal transient arising from non-explosive DWD mergers that leave an NS remnant from the prompt collapse of the merged core. The transient is powered by the cooling of the expanding dynamical ejecta, with energy injection from magnetic dipole radiation, which depends on the dipole factor $D = B_d^2/P_0^4$, with $B_d$ and $P_0$ being the surface magnetic field strength and initial rotation period of the newborn NS. We simulate lightcurves in the Legacy Survey of Space and Time (LSST) bands and estimate the horizon and detection rates for these transients across a range of model parameters. We find LSST detection horizons upper limits ranging $30$–$820$ Mpc and corresponding detection rates $10^2$–$10^6$ yr$^{-1}$ for $\log D = 24$–$40$. Accounting for the survey cadence, we find that only configurations with $\log D = 36$–$40$ are detectable within $240$–$760$ Mpc, with detection rates $10^4$–$10^5$ yr$^{-1}$. Combined searches across surveys can compensate for the low cadence and improve the detection rates of fast and less energetic sources. Multi-wavelength campaigns can aid in detecting the spindown radiation at higher energies observable after the optical transient. Observations of these transients will provide direct evidence of the non-explosive DWD mergers, characterise the remnants and progenitor parameters, and the fraction of explosive and non-explosive mergers.
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All authors M. M. Ridha Fathima, Alexandre M.R. Almeida, Mattia Bulla, Jaziel G. Coelho, Cristiano Guidorzi, Jorge A. Rueda

Cosmology and Nongalactic Astrophysics

Tightening Cosmological Constraints Within and Beyond $\Lambda$CDM Using Gamma-Ray Bursts Calibrated with Type Ia Supernovae

Wei Hong, Luca Izzo, Massimo Della Valle et al. (+3 more)

Context. Gamma-ray bursts (GRBs) reach redshifts beyond Type Ia supernovae (SNe Ia) and can extend distance measurements into the early Universe, but their use as distance indicators is limited by the circularity problem in calibrating empirical luminosity relations. Aims. We present a model-independent methodology to overcome this circularity by combining Pantheon$+$ SNe Ia, a distance reconstruction based on artificial neural networks (ANNs), and two GRB correlations (Amati and Combo) into a distance ladder from low to high redshift, with the goal of constraining cosmological parameters in $\Lambda \mathrm{CDM}$ and $w_0 w_a \mathrm{CDM}$. Methods. We use the ReFANN to reconstruct the luminosity distance $d_L(z)$ and distance modulus $\mu(z)$ from the Pantheon$+$ dataset, with hyperparameters optimized via approximate Bayesian computation rejection and a risk function. This model-independent reconstruction calibrates the Amati and Combo relations using a low-redshift ($z<1$) GRB sample from Fermi GBM and Swift-XRT. The calibrated relations then provide distance estimates for GRBs at $z \geq 1$. Finally, a joint Bayesian analysis simultaneously constrains the cosmological and GRB correlation parameters, ensuring self-consistent uncertainty propagation. Results. We obtain consistent cosmological constraints from two independent GRB correlations. The Hubble constant $H_0$ agrees with SNe Ia values, though potentially influenced by Pantheon$+$ dataset. High-redshift GRBs favour a higher matter density $\Omega_m$ than the Pantheon$+$ and hint at possible dark energy evolution.Conclusions. We present a framework that mitigates GRB cosmology's circularity problem, extending the distance ladder to $z \sim 9$ and establishing GRBs as a high-redshift probe.
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All authors Wei Hong, Luca Izzo, Massimo Della Valle, Orlando Luongo, Marco Muccino, Tong-Jie Zhang

Solar and Stellar Astrophysics

Magnetic field measurements in a sample of Class I and flat-spectrum protostars observed with SPIRou

L. Drouglazet, E. Alecian, A. Sousa et al. (+27 more)

Magnetic fields play a crucial role throughout stellar evolution, regulating angular momentum, channelling accretion, and launching jets and outflows. While the magnetic properties of Classical T Tauri Stars (CTTS) are well characterised, those of their progenitors, Class I and Flat-Spectrum (FS) protostars, remain poorly constrained due to observational challenges linked to their embedded nature. We aim to detect and characterise large-scale magnetic fields in a sample of Class I and FS protostars, which are expected to host strong dynamo-generated fields. Using SPIRou, a high-resolution near-infrared spectropolarimeter, we analysed polarised spectra and applied the Least Squares Deconvolution (LSD) technique to extract magnetic signatures and measure longitudinal fields from Stokes V profiles. We report new detections of large-scale magnetic fields in 5 FS protostars. Including the previously known magnetic FS protostar V347 Aur, 40% of our sample (15 objects) is confirmed to be magnetic. These stars exhibit clear Zeeman signatures, with longitudinal field strengths ranging from ~80 to ~200 G. The remaining targets show no detectable Stokes V signature, with upper limits on dipolar fields between 500 G and >5 kG. These results indicate that Class I and FS protostars can host large-scale magnetic fields, possibly weaker than in CTTS, supporting the idea that magnetic processes are already active during the main accretion phase and may influence star-disk interactions from the earliest stages.
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All authors L. Drouglazet, E. Alecian, A. Sousa, P.I. Cristofari, E. Artigau, J. Bouvier, A. Carmona, N.J. Cook, C. Dougados, G. Duchêne, C.P. Folsom, H. Nowacki, K. Perraut, S.H.P. Alencar, L. Amard, M. Audard, S. Cabrit, J.-F. Donati, K. Grankin, N. Grosso, O. Kochukhov, Á. Kóspál, V.J.M. Le Gouellec, L. Manchon, G. Pantolmos, P. Petit, L. Petitdemange, R. Devaraj, H. Shang, M. Takami

Cosmology and Nongalactic Astrophysics

Natura Non Facit Saltum: An Analytical Model of Smooth Slow-Roll to Ultra-Slow-Roll Transition

Diego Cruces, Minxi He, Shi Pi et al. (+3 more)

In this letter, we propose a single-field inflation model that realizes a slow-roll-to-ultra-slow-roll transition while keeping the second slow-roll parameter smoothly varying throughout. The model is built through a minimal modification by introducing a simple time dependence in the effective mass term of the Mukhanov-Sasaki equation. We obtain fully analytical solutions for both the background evolution and the curvature perturbations, which makes the parameter dependence of the curvature power spectrum easy to track. To the best of our knowledge, this is the first analytical model that describes a smooth transition of this kind. We also compare its signatures with those of the corresponding sharp-transition counterpart.
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All authors Diego Cruces, Minxi He, Shi Pi, Jianing Wang, Masahide Yamaguchi, Yuhang Zhu

High Energy Astrophysical Phenomena

Revealing the Spectral Properties of Galactic Interstellar Medium by Survey Observations

Ya-Wen Xiao, Jian-Fu Zhang and Alex Lazarian

Based on multi-frequency radio polarization survey datasets, we investigate the spectral characteristics of the Galactic interstellar medium (ISM) using the polarization frequency analysis (PFA) method, referred to as polarization variance. By comparing this novel PFA technique with the traditional power spectrum approach, and by cross-examining data from two distinct surveys, we aim to reinforce the robustness of our findings. Our analysis reveals that the ISM scaling slope in the Galactic disk is steeper than the classic Kolmogorov slope, whereas the ISM scaling slope in the Galactic halo aligns with the Kolmogorov slope. We suggest a distinct turbulence cascade process operating in the Galactic halo compared to the Galactic disk.
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Instrumentation and Methods for Astrophysics

KMTNet Synoptic Survey of Southern Sky II: Data Reduction and Real-Time Transient Detection Pipeline

Mankeun Jeong, Myungshin Im, Joonho Kim et al. (+9 more)

We present a comprehensive pipeline developed for the image processing of the KMTNet Synoptic Survey of the Southern Sky (KS4) Data Release 1. This pipeline encompasses several key processes, including data quality assurance, astrometry, photometric zero-point (ZP) calibration, bad pixel masking, image stacking, and difference image analysis (DIA). The astrometric solutions were validated by cross-matching with the Gaia EDR3 catalog, achieving sub-pixel astrometric accuracy (< 0.4 arcsec). To ensure spatial consistency, we divided each image into multiple subsections and confirmed that astrometric accuracy was maintained even at the edges. We performed a two-stage photometric calibration. Initial ZP solutions were computed for each individual image frame using the APASS DR9 and SkyMapper DR3 catalogs. Subsequently, we corrected residual spatial variations in the stacked images using Gaia XP photometry. This procedure yielded a 5-sigma depth of 22-23 AB mag across the BVRI bands, with root-mean-square errors of approximately 0.03 mag when referenced to Gaia stars in the magnitude range of 14-19 mag. The processed KS4 images span over 4,000 deg^2 of the southern sky, providing reference images suitable for DIA. This publicly available pipeline also supports real-time processing of newly acquired images, enabling prompt transient detection. We demonstrate its effectiveness through successful applications in gravitational-wave follow-up observations.
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All authors Mankeun Jeong, Myungshin Im, Joonho Kim, Seo-Won Chang, Sungho Jung, Chung-Uk Lee, Dong-Jin Kim, Bomi Park, Jaewon Lee, Jiseop Shin, Changwan Kim, Gregory S. H. Paek

Astrophysics of Galaxies

EMU/GAMA: Refining Dust Extinction Corrections for H{\alpha} Luminosity Functions Using Radio-Based Calibration

J. Willingham, A. Hopkins, T. Zafar et al. (+17 more)

We present a novel approach to correcting H$\alpha$ luminosity functions for dust extinction by calibrating against radio-based star formation rates (SFRs), using data from the Evolutionary Map of the Universe (EMU) and Galaxy and Mass Assembly (GAMA) surveys. Accurate dust correction is essential for deriving SFRs from rest-frame UV-optical emission lines, particularly as the James Webb Space Telescope extends such measurements to galaxies at $z>5$. While a luminosity dependence of dust obscuration has long been recognised, our method exploits the empirical relationship between obscured (H$\alpha$) and unobscured (radio) SFRs to provide a dust correction that can be applied where traditional spectroscopic techniques, e.g. Balmer line based approaches, are unavailable. We apply the SFR based dust correction to 25 published H$\alpha$ luminosity functions spanning $0<z<8$, and derive corresponding star formation rate densities (SFRDs). Adopting the locally calibrated H$\alpha$–radio relation ends up with an overestimate of the cosmic SFRD by more than two orders of magnitude at $z\gtrsim1$. Motivated by the luminosity dependent relation in the local Universe, we introduce a new model where the luminosity dependence of the dust obscuration decreases with increasing redshift. This approach can reproduce observed SFRDs across cosmic time. These results highlight the potential of a radio-based calibration for dust correction, where a luminosity dependent correction would need to decline in strength with increasing redshift. This implies that the dust content or distribution in galaxies at early epochs differs substantially from that in the local Universe.
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All authors J. Willingham, A. Hopkins, T. Zafar, J. Afonso, U.T. Ahmed, A. Ahmad, A. Battisti, D. Bomans, M. J. I. Brown, M. Cowley, D. Farrah, T.J. Galvin, B. Holwerda, D. Leahy, U. Maio, T. Mukherjee, J. Prathap, N. Seymour, J.Th. van Loon, E. Ward

Astrophysics of Galaxies

Modeling supernova feedback in galaxy formation simulations with energy-conserving momentum injection

Takashi Okamoto

Accurate modeling of supernova (SN) feedback in galaxy formation simulations is complicated by energy conservation violations arising from the vector nature of momentum injection. We present a mechanical feedback scheme addressing two key sources: the relative motion between gas elements and the SN-hosting star particle, and multiple momentum injections into a single gas element within one timestep. Computing the kinetic energy increment in the rest frame of the gas element ensures energy conservation while avoiding the momentum inversion that can occur when this calculation is instead performed in the lab frame. This correction inherently violates momentum conservation, disturbing the angular momentum distribution and hindering disk formation when momentum is coupled on galactic scales. To prevent unphysical large-scale momentum coupling without an ad hoc maximum coupling radius, we switch to purely thermal feedback when the cooling radius is resolved by the local inter-element separation. Our scheme is designed for high- to intermediate-resolution zoom-in simulations with star particle masses up to $\sim 10^5\,M_\odot$. Through cosmological zoom-in simulations of dwarf galaxies ($M_\mathrm{vir} \sim 10^{11}\,M_\odot$) at two mass resolutions, we demonstrate good convergence in star formation histories; without the momentum correction, stellar mass in low-resolution runs falls to as low as 59% of that in high-resolution counterparts. At the feedback strength reproducing dwarf galaxy stellar masses, a Milky Way-mass simulation overproduces stellar mass, suggesting additional processes, such as active galactic nuclei feedback, are required at this mass scale.
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Instrumentation and Methods for Astrophysics

An Analysis of Large Astronomical Detector Controller Systems and Implications for Future ESO Detector Systems

Mathias Richerzhagen, Naidu Bezawada, Sebastian Elias Egner et al. (+11 more)

Large astronomical instruments using tens to hundreds of optical or infrared science detectors pose specific challenges for detector control, where, in addition to performance, other engineering aspects like scalability, power consumption, size, weight and programmatic aspects such as cost and sustainability need to be considered. In this paper we analyze the approach existing instruments have taken for detector control. We focus this analysis on recent ground based astronomical instruments using 10 or more detectors for science imaging or spectrography. From this analysis we identify key technologies, like cryogenic electronics, Ethernet based interfaces and fully-digital detectors, for implementing efficient control of many detectors. We also propose a concept joining all identified technologies that could be considered for future large ESO instruments as a complement of ESO's general detector controller, NGCII.
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All authors Mathias Richerzhagen, Naidu Bezawada, Sebastian Elias Egner, Elizabeth George, Alessandro Meoli, Alexander Rüde, Matthias Seidel, Domingo Álvarez Méndez, Olaf Iwert, Leander Mehrgan, Javier Reyes, Benoît Serra, Omar Sqalli, Derek Ives

Astrophysics of Galaxies

Bar-Informed Kinematic-Distance Mapping of Molecular Gas in the Inner Milky Way

Junichi Baba

We present a bar-informed kinematic-distance (BIKD) method to reconstruct face-on molecular-gas maps of the inner Milky Way from PPV data, relaxing the standard assumption of axisymmetric circular rotation that can generate severe artifacts in barred regions. BIKD replaces the rotation curve with a non-axisymmetric streaming field extracted from hydrodynamical simulations in an observationally constrained barred Galactic potential, and infers a discrete distance posterior along each sightline using a Gaussian likelihood in line-of-sight velocity. To mitigate multi-modality, we adopt posterior-weighted map making via posterior sampling. We validate the full pipeline in closed-loop tests on the simulations, showing that the recovered large-scale morphology is only weakly sensitive to simple distance priors and remains stable across plausible variations in bar angle, snapshot time, and pattern speed. We then apply BIKD to a Galactic CO survey to obtain a face-on $\Sigma$ map. Compared to a standard axisymmetric kinematic-distance (KD) reconstruction, BIKD strongly suppresses line-of-sight–elongated finger-of-God features and robustly recovers a bar-aligned, quadrant-asymmetric inner-Galaxy morphology under model marginalization. The model-marginalized radial profiles show an approximately exponential decline beyond $\sim4$ kpc, a pronounced deficit at $R\sim0.5$–$3.5$ kpc, and a central concentration consistent with Central Molecular Zone surface densities. Finally, we compare prominent ridge-shaped overdensities in the BIKD map with independent spiral-arm loci traced by high-mass star-forming region masers with VLBI trigonometric parallaxes and by classical Cepheids with period–luminosity distances. Several maser-parallax segments are qualitatively consistent with the dominant BIKD ridges, whereas the Cepheid loci do not coincide with them within their recommended azimuth range.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.HC

Scale-Aware Navigation of Astronomical Survey Imagery Data on High Resolution Immersive Displays

Ava Nederlander, Zainab Aamir and Arie E. Kaufman

Upcoming astronomical surveys produce imagery that spans many orders of magnitude in spatial scale, requiring scientists to reason fluidly between global structure and local detail. Data from the Vera C. Rubin Observatory exemplifies this challenge, as traditional desktop-based workflows often rely on discrete views or static cutouts that fragment context during exploration. This paper presents a design-oriented framework for scale-aware navigation of astronomical survey imagery in high-resolution immersive display environments. We illustrate these principles through representative usage scenarios using Vera Rubin Observatory and Milky Way survey imagery deployed in room-scale immersive environments, including tiled high-resolution displays and curved immersive systems. Our goal is to contribute design insights that inform the development of immersive interaction paradigms for exploratory analysis of extreme-scale scientific imagery.
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Solar and Stellar Astrophysics

On the shape of the ascending branch of the light curves of Long Period Variables

Do Thi Hoai Pham Tuyet Nhung and Pierre Darriulat

The present article is written in the wake of a recently published study of the relation between the light curves of Long Period Variables and their evolution along the Asymptotic Giant Branch (AGB). It introduces a pair of new parameters that describe the shape of the ascending branches of such light curves. This parameterization reveals strong correlations with other parameters describing the evolution of the star on the AGB: periods, regularity and amplitudes of the oscillations, effective temperatures, mass loss rates, carbon and oxygen isotopic ratios, colour indices. It sheds new light on the occasional presence of humps on the ascending branches and on the distinction between stars that have not experienced strong Third Dredge Up (TDU) events and those that have as well as between oxygen-rich and carbon-rich stars. One of the new parameters, referred to as q, is particularly efficient at tracking the evolution of the star along the AGB. Globally, a simple picture can be drawn in the plane spanned by the period and by q. Yet, many details remain unexplained when looking at this picture in finer details. Overall, the results presented in the article help significantly with clarifying the complex set of observations that have been made in this domain and should inspire new considerations on their relation with the underlying physical mechanisms at stake inside the stars.
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Astrophysics of Galaxies

Timescale-dependent Optical Variability of Turn-on Changing-look Active Galactic Nuclei

Yu Tao, Jie Tang and Xuan Wei

Changing-look active galactic nuclei (CL AGNs) provide a valuable opportunity to study optical variability associated with changes in accretion state. We investigate the optical variability of turn-on CL AGNs, selected through the emergence or strengthening of broad emission lines, using g-band light curves from the Zwicky Transient Facility. For a final sample of 106 objects, we measure structure-function amplitudes at three fixed rest-frame timescales, SF30, SF150 and SF300, and examine their dependence on optical luminosity, Eddington ratio, black-hole mass and rest-frame wavelength using Spearman-rank correlations and multivariate regressions. The strongest trends are found on monthly timescales. SF30 is significantly anti-correlated with both optical luminosity and Eddington ratio, with Spearman coefficients of rho = -0.39 and rho = -0.33, respectively. These negative trends remain in multivariate regressions after accounting for black-hole mass and rest-frame wavelength. The dependence weakens at longer timescales: SF150 shows only weak evidence for luminosity or Eddington-ratio dependence, while SF300 shows no robust dependence. Black-hole mass shows no robust single-parameter correlation, and its multivariate coefficients depend on the model form, indicating that its apparent role is affected by covariance with luminosity and Eddington ratio. The rest-frame wavelength term is generally negative, but cannot be separated from redshift in this single-band analysis. These results suggest that monthly optical variability in turn-on CL AGNs is more closely linked to bright-state accretion properties than variability on half-year to year-long timescales.
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High Energy Astrophysical Phenomena

State-dependent broadband X-ray Timing Reconfiguration in the Changing-look AGN NGC 1566

Yu Tao, Jie Tang, Xuan Wei et al. (+1 more)

NGC 1566 has shown dramatic X-ray spectral changes during its recent changing-look outburst, but the evolution of its broadband X-ray timing properties remains poorly constrained. We combine long-term Swift/XRT monitoring with high-time-resolution XMM-Newton observations to construct one pre-outburst Dim broadband PSD and two outburst broadband reconstructions associated with the O1 peak and O2 decay observations. In the outburst reconstructions, the same Swift/XRT up-state monitoring segment provides the low-frequency constraint, while the O1 and O2 XMM-Newton observations provide phase-specific high-frequency constraints. Using PSRESP forward modelling with the observed sampling windows, we test bending-power-law PSD models in the soft (0.3-2 keV) and hard (2-10 keV) bands. The Dim and O2-associated reconstructions are acceptably described by bending-power-law solutions, whereas the O1 peak observation does not yield a robust bend-frequency measurement. For the accepted Dim and O2-associated solutions, the preferred bend frequency shifts from about 2.0 x 10^-5 to about 2.7 x 10^-7 Hz in the soft band, and from about 2.1 x 10^-5 to about 2.7 x 10^-7 Hz in the hard band, implying a substantially longer characteristic variability timescale in the O2-associated reconstruction. This consistent shift in both energy bands suggests that the timing evolution is not confined to the soft-excess component alone, but reflects a broader change in the X-ray variability structure. Together with previous spectral studies, these results point to a transient reconfiguration of the disc-corona variability timescale during the changing-look transition in NGC 1566.
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All authors Yu Tao, Jie Tang, Xuan Wei, Xiaohan Zhang

Astrophysics of Galaxies

The dominance of turbulence over magnetism in the formation of massive star cluster seeds

Junhao Liu, Patricio Sanhueza, Piyali Saha et al. (+32 more)

High-mass stars form in protoclusters, where gravo-magnetic processes shape collapsing clouds and clumps to be elongated preferentially perpendicular to magnetic (B) fields. Yet it remains unclear whether gravo-magnetic processes still govern the formation of smaller-scale condensations in massive-star-forming protoclusters, which are crucial for understanding the stellar initial mass function and multiplicity. Here we report the first statistical evidence that the condensation elongations are preferentially aligned with local B fields, based on high-resolution data from the largest dust polarization survey toward 30 massive star-forming regions with the Atacama Large Millimeter/submillimeter Array (ALMA). Our clustered massive star formation simulations reveal that this more parallel alignment is exclusively observed in models where initial turbulence dominates B fields. In contrast, models with initial B fields dominating turbulence distinctly exhibit a more perpendicular alignment. The comparison between observations and simulations suggests that turbulence could play a more important role than B fields in the formation of condensations in the context of clustered massive star formation, contradicting the prediction of classical magnetically regulated models. Moreover, we find a possibly turbulence-induced preferential misalignment between the B field and rotation axis of condensations, which may potentially reduce the magnetic braking efficiency and facilitate the formation of large protostellar disks. Our findings indicate that turbulence could be critical in determining the initial stellar properties.
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All authors Junhao Liu, Patricio Sanhueza, Piyali Saha, Kaho Morii, Josep Miquel Girart, Qizhou Zhang, Fumitaka Nakamura, Paulo C. Cortes, Valeska Valdivia, Benoit Commercon, Patrick M. Koch, Kate Pattle, Xing Lu, Janik Karoly, Manuel Fernandez-Lopez, Ian W. Stephens, Huei-Ru Vivien Chen, Chi-Yan Law, Keping Qiu, Shanghuo Li, Henrik Beuther, Eun Jung Chung, Jia-Wei Wang, Fernando A. Olguin, Yu Cheng, Jihye Hwang, Sandhyarani Panigrahy, Chakali Eswaraiah, Maria T. Beltran, Qiuyi Luo, Spandan Choudhury, Ji-hyun Kang, Wenyu Jiao, Luis A. Zapata, A. -Ran Lyo

Solar and Stellar Astrophysics

Stereoscopic Observation of Recurrent Streamer Waves Driven by Successive Slow Coronal Mass Ejections

Yuandeng Shen and Reetika Tiwari

We report the stereoscopic observations of two recurrent streamer waves in a single streamer structure, utilizing coordinated observations from the SOHO, STEREO, and SDO missions. Contrary to the long-held view that fast coronal mass ejections (CMEs) are necessary drivers, we demonstrate that these recurrent waves were excited by two consecutive slow CMEs (<500 km/s} accompanied by only modest flare activity. Three-dimensional reconstruction reveals that the first and second waves propagated with significant decelerations of - 7.93 and - 10.26 m s^-2, respectively. Their average amplitudes were 0.41 and 0.77 solar radii, wavelengths were 4.02 and 6.17, and periods were 2.66 and 2.53 hours, respectively. While the amplitude of the first wave declined with heliocentric distance (consistent with conventional energy convection), the second wave exhibited an intriguing increasing trend in amplitude. Both waves showed a linear increase in wavelength and period with distance, indicating a non-stationary and dispersive medium. Crucially, despite the disparity in driver energy and wave scales, the periods and their change rates remained nearly identical for both events. This provides compelling case-specific evidence that the streamer wave period is primarily determined by the inherent eigenmodes of the streamer plasma slab rather than the specific characteristics of the trigger. We conclude that the generation of observable streamer waves is a combined consequence of the streamer's structural stability and the energy transfer efficiency of the triggering disturbance.
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Tuesday 17 March

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

Climate and ocean circulation changes toward a modern snowball Earth

Takashi Obase, Takanori Kodama, Takao Kawasaki et al. (+4 more)

It has been hypothesized that the Earth may have experienced snowball events in the past, during which its surface became completely covered with ice. Previous studies used general circulation models to investigate the onset and climate of such snowball events. Using the MIROC4m coupled atmosphere–ocean climate model, this study examined the changes in the oceanic circulation during the onset of a modern snowball Earth and elucidated their evolution to steady states under the snowball climate. Abruptly changing the solar constant to 94% of its present-day value caused the modern Earth climate to turn into a snowball state after ~1300 years and initiated rapid increase in sea ice thickness. During onset of the snowball, extensive sea ice formation and melting of sea ice in the mid-latitudes caused substantial freshening of surface waters and salinity stratification. By contrast, such salinity stratification was absent if the duration between the change in the solar flux and the snowball onset was short. After snowball onset, the global sea ice cover and the buildup of salinity stratification caused drastic weakening in the deep ocean circulation. However, the meridional overturning circulation resumed within several hundred years after the snowball onset because the density flux by sea ice production weakens the salinity stratification. While the evolution of the oceanic circulation would depend on the continental distribution and the evolution of continental ice sheets, our results highlight the gradual growth of sea ice and associated brine rejection are essential factors for the transient evolution of the oceanic circulation in the snowball events.
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All authors Takashi Obase, Takanori Kodama, Takao Kawasaki, Sam Sherriff-Tadano, Daisuke Takasuka, Ayako Abe-Ouchi, Masakazu Fujii

Solar and Stellar Astrophysics

Probing the magnetic field of a coronal mass ejection with PSR J1022+1001

El Mehdi Zahraoui, Hannah T. Rüdisser, Golam M. Shaifullah et al. (+24 more)

We investigate whether low-frequency pulsar observations can provide LoS magnetic field estimates and whether these are consistent with synthetic LoS signatures extracted from a three-dimensional CME reconstruction constrained by Solar Orbiter data. We analyze a CME occultation of the LoS to PSR J1022+1001 on 20 August 2021 at a projected heliocentric distance of 24.6 R_sun, observed simultaneously with LOFAR and NenuFAR. From LOFAR, we derive time-resolved dispersion measure (DM) and rotation measure (RM) and isolate the CME contributions using background estimates for interstellar, solar wind and ionospheric components. We then infer the density-weighted LoS-averaged magnetic field component <B||>_PSR from the ratio delta-RM/delta-DM. In parallel, we reconstruct the CME using a semi-empirical 3DCORE model fitted to Solar Orbiter in-situ magnetic field observations at 0.65 au. We sample the modeled magnetic field along the pulsar LoS using fixed spatial sampling points and compute synthetic LoS-averaged signatures <B||>_3D for different flux rope configurations. The derived <B||>_PSR increases from approximately -9 nT to a peak near 63 nT during the observed interval. Comparison with synthetic signatures shows that the polarity and temporal evolution of the LoS signal are strongly dependent on the flux rope configuration and only a South-West-North (SWN) configuration (confirmed by Solar Orbiter in-situ data) reproduces the observed sign and overall evolution, whereas alternative configurations are incompatible. The modeled amplitudes, however, are systematically larger than the pulsar-derived values by roughly a factor of five. We show that simultaneous low-frequency pulsar DM and RM measurements can provide LoS magnetic field estimates for a CME and can be used to test CME magnetic structure against data-constrained three-dimensional reconstructions.
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All authors El Mehdi Zahraoui, Hannah T. Rüdisser, Golam M. Shaifullah, Caterina Tiburzi, Jean-Mathias Grießmeier, Ute V. Amerstorfer, Christian Möstl, Mateja Dumbovic, Emma E. Davies, Pietro Zucca, Joris P.W. Verbiest, Andreas J. Weiss, Louis Bondonneau, Baptiste Cecconi, Benedetta Ciardi, Christian Vocks, Gilles Theureau, Julien Girard, Oleksandr Konovalenko, Vyacheslav Zakharenko, Oleg Ulyanov, Peter Tokarsky, Stéphane Corbel, Philippe Zarka, Cyril Tasse, Ralf-Jürgen Dettmar, Ihor P. Kravtsov

High Energy Astrophysical Phenomena

Diffuse X-ray Emission in the Sagittarius C Complex

Zhenlin Zhu, Mark R. Morris, Gabriele Ponti et al. (+1 more)

The Sagittarius C (Sgr C) complex, located on the western edge of the Central Molecular Zone (CMZ), hosts a mixture of star-forming and non-thermal activity whose X-ray properties remain poorly understood. Using deep archival Chandra and XMM-Newton observations, we resolve the diffuse X-ray emission in Sgr C into two components: an H II region coincident with the radio peak and a brighter diffuse feature located to its southwest. Spatially resolved spectroscopy reveals the presence of a soft (kT <= 1 keV) plasma with metal abundances consistent with the elevated metallicity expected in the CMZ in both regions, along with a harder (~ 8 keV) thermal component within the H II region. The observed diffuse X-ray emission and its association with an expanding [C II] shell suggest that the hot gas may originate from a young supernova remnant (SNR) embedded in the H II region. Under this interpretation, the inferred shock velocity (~ 800 km/s) and SNR age (>= 1.7 kyr) are consistent with a core-collapse SNR in the Galactic Center. These results reveal Sgr C as a potential host of a SNR and highlight the complex interplay between massive-star feedback, magnetic fields, and molecular gas in the CMZ.
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All authors Zhenlin Zhu, Mark R. Morris, Gabriele Ponti, Ping Zhou

Earth and Planetary Astrophysics

Conditions for planetesimal formation via the streaming instability persist under turbulence driven by magnetorotational instability

Linn E.J.Eriksson, Ziyan Xu, Jeonghoon Lim et al. (+3 more)

Strong dust clumping by streaming instability (SI) is the leading proposed mechanism for forming planetesimals, the building blocks of terrestrial planets and giant-planet cores. The critical dust-to-gas density ratio above which the SI leads to dust concentration strong enough to result in gravitational collapse depends on local dust properties and disk conditions, such as particle Stokes number, pressure gradient, and turbulence. The role of turbulence has recently drawn attention because simulations have shown that even modest levels of istropically forced turbulence can significantly increase the critical dust-to-gas ratio. However, we show that this does not hold for turbulence self-consistently generated by the magnetorotational instability (MRI). We present the first parameter study of the SI in three-dimensional shearing-box simulations including non-ideal magnetohydrodynamics with ambipolar diffusion. Modest turbulence yields a clumping boundary as low as pure hydrodynamical cases, while stronger turbulence does increase the critical dust-to-gas density ratio, though appreciably less than in the models where turbulence is isotropically forced. Particle concentration occurs inside zonal flows, large-scale structures generated by the MRI. Our results suggest that self-consistent, MRI-driven turbulence does not necessarily inhibit planetesimal formation.
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All authors Linn E.J.Eriksson, Ziyan Xu, Jeonghoon Lim, Chao-Chin Yang, Pinghui Huang, Mordecai-Mark Mac Low

Cosmology and Nongalactic Astrophysics

Reconstructing the Type Ia Supernova Absolute Magnitude with Two-Probe Physics-Informed Neural Networks

Denitsa Staicova

We apply two variants of Physics-Informed Neural Networks (PINNs) to reconstruct the Type~Ia supernova absolute magnitude $M_B(z)$ from joint BAO and supernova data under four cosmological models ($\Lambda$CDM, CPL, GEDE, $\Lambda_s$CDM) and two DESI~DR2 fiducial sets. A heteroscedastic single-network method tested across four constraint configurations establishes that the Etherington distance duality relation is a more fundamental constraint than cosmological model priors, reducing internal inconsistencies by up to an order of magnitude. Under full constraints all models recover $M_B \approx -19.3$~mag with biases below 0.05~mag. A Fisher information-weighted two-network variant trains independent networks on BAO and SN data, providing clean probe separation; it finds no significant pointwise $M_B$ evolution in $z \in [0.3, 1.5]$, but reveals a systematic separation of redshift-binned $M_B$ distributions. The heteroscedastic method identifies a persistent $2$–$3\sigma$ residual at $z \sim 0.4$–$0.5$ that is consistent across all four models and both fiducials, implying the same underlying tension. While the origin of this feature remains ambiguous, its model-independence and cross-method consistency warrant further investigation with forthcoming data.
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Cosmology and Nongalactic Astrophysics

Fast partial-sky spherical harmonic transforms

Julien Carron and Martin Reinecke

We discuss in some details a novel algorithm for performing partial-sky spherical harmonic transforms (SHT), building on the Fourier-sphere method of Reinecke et al (2023) handling efficiently high numbers of arbitrary locations on the sphere. Our main motivations are Cosmic Microwave Background lensing from the South Pole Telescope, and the South Pole Observatory program targeting primordial gravitational waves from inflation, requiring high-resolution, numerically intensive work on small sky fractions. We achieve speed-up factors ranging from 3 to 10 on SPT-3G main field and BICEP3 deep footprint, and much more on smaller patches. More generally, the algorithm eliminates in our case study the usual disadvantages of arbitrary pixelisations in comparison to isolatitude pixelisations or flat-sky approximations, making it ideal for ambitious workflows that require repeated SHTs on limited sky regions.
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Cosmology and Nongalactic Astrophysics

SLSim: a strong lensing population simulation package

Narayan Khadka, Simon Birrer, Henry Best et al. (+45 more)

Gravitational lensing offers unique insights into cosmology by bending light around massive objects. Strong gravitational lensing, in particular, produces magnified and often multiple images of distant sources, crucial for precise cosmological measurements and understanding the distribution of dark matter in the universe. Current studies are limited by the number of strong gravitational lenses. From upcoming cosmological surveys, we anticipate observing a several orders of magnitude increase in the number of lenses, for both static and transient phenomena. However, detecting and analyzing these events from vast surveys like Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) presents significant challenges. To prepare for these challenges, we introduce SLSim, a versatile simulation tool tailored for the Vera C. Rubin Observatory. SLSim integrates advanced astrophysical models with computational efficiency to generate synthetic strong lens populations under realistic observational conditions. SLSim simulates static and variable lensing scenarios, essential for cosmological studies, training and testing lens search and data analysis pipelines. This paper details SLSim,'s design and implementation, emphasizing its modularity and capabilities across various astrophysical regimes. Validation against observational data and existing simulations confirms SLSim's accuracy in reproducing observed lensing phenomena. SLSim is publicly available at https://github.com/LSST-strong-lensing/slsim, and we anticipate continued development and expansion of its capabilities. Users are encouraged to check the repository for updates and to contribute to ongoing community efforts in strong lensing simulations.
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All authors Narayan Khadka, Simon Birrer, Henry Best, Paras Sharma, Katsuya T. Abe, Xianzhe Tang, Carly Mistick, Felipe Urcelay, Emrecan M. Sonmez, Nikki Arendse, Sydney Erickson, Jacob O. Hjortlund, Phil Holloway, Alan Huang, Rahul Karthik, Mia Lamontagne, Vibhore Negi, Justin R. Pierel, Bruno Sanchez, Aysu Ece Saricaoglu, Anowar Shajib, Yixuan Shao, Padma Venkatraman, Bryce Wedig, Aadya Agrawal, Timo Anguita, Pedro Bessa, Clecio R. Bom, Sofia Castillo, Thomas Collett, Tansu Daylan, Steven Dillmann, Margherita Grespan, Erin E. Hayes, Remy Joseph, Richard Kessler, Tian Li, Phil Marshall, Anupreeta More, Veronica Motta, Gautham Narayan, Matt O'Dowd, Masamune Oguri, Graham Smith, Aprajita Verma, Giorgos Vernardos, the Strong Lensing Science Collaboration, the LSST Dark Energy Science Collaboration

Earth and Planetary Astrophysics · Cross-listed from cond-mat.mtrl-sci

Spin crossover in FeO under shock compression

Lélia Libon, Alessandra Ravasio, Silvia Pandolfi et al. (+17 more)

FeO (wüstite), which exhibits complex electronic and structural properties with increasing pressure and temperature, is a key mineralogical phase for understanding deep planetary interiors. However, direct measurements of its spin state at high-pressure and temperature remain challenging in static compression experiments. Here, we employ laser-driven shock compression to extend the FeO principal Hugoniot up to $\sim$900 GPa and perform in situ X-ray diffraction and X-ray emission spectroscopy up to 250 GPa, probing FeO's crystal structure and spin state. We demonstrate a continuous spin crossover of iron in FeO over a broad pressure range, with the high-spin state persisting beyond Earth's core-mantle boundary (CMB) conditions. These observations provide new experimental constraints on iron spin state at extreme conditions essential for geophysical models of (exo)planetary interiors.
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All authors Lélia Libon, Alessandra Ravasio, Silvia Pandolfi, Yanyao Zhang, Xuehui Wei, Jean-Alexis Hernandez, Hong Yang, Amanda J. Chen, Tommaso Vinci, Alessandra Benuzzi-Mounaix, Clemens Prescher, François Soubiran, Hae Ja Lee, Eric Galtier, Nick Czapla, Wendy L. Mao, Arianna E. Gleason, Sang Heon Shim, Roberto Alonso-Mori, Guillaume Morard

Earth and Planetary Astrophysics

Long-term outburst activity of comet 17P/Holmes and constraints on ejecta size distributions

Maria Gritsevich, Marcin Wesołowski, Josep M. Trigo-Rodríguez et al. (+4 more)

A quantitative understanding of cometary outbursts requires robust constraints on the size distribution of ejected particles, which governs outburst dynamics and underpins estimates of released gas and dust. In the absence of direct measurements of particle sizes, assumptions about the size distribution play a central role in modelling dust-trail formation, their dynamical evolution and observability, and the potential production of meteor showers following encounters with Earth. We analyse brightness amplitude variations associated with outbursts of comet 17P/Holmes from 1892 to 2021, with particular emphasis on the exceptional 2007 mega-outburst. During this event the comet underwent a rapid and substantial brightening: at its peak, the expanding coma reached a diameter exceeding that of the Sun and briefly became the largest object in the Solar System visible to the naked eye. We constrain the size distribution and total mass of porous agglomerates composed of ice, organics, and dust ejected during the outburst. The inferred particle size distribution is consistent with a power law of index q, yielding effective particle sizes between 10^-6 m for q = 4 and 5 x 10^-3 m for q = 2. Accounting for effective particle size, sublimation flux, and bulk density, we find that the total number of ejected particles increases with both q and sublimation flux. These results place constraints on the physical properties of outburst ejecta and provide physically motivated initial conditions for long-term dust-trail evolution modelling. They further indicate that cometary outburst brightness is determined primarily by the number of particles and their size distribution, rather than by the total ejected mass alone, with direct implications for the origin and evolution of meteoroid streams and the interplanetary dust population.
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All authors Maria Gritsevich, Marcin Wesołowski, Josep M. Trigo-Rodríguez, Alberto J. Castro-Tirado, Jorma Ryske, Markku Nissinen, Peter Carson

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

Multi-Component Dark Matter as a Solution to the Galactic Center GeV Excess

Farinaldo S. Queiroz, Clarissa Siqueira and Carlos E. Yaguna

The Galactic Center Excess (GCE) is a compelling signature of dark matter annihilation, but its spectral morphology is difficult to reconcile with the traditional paradigm of a single particle species. In this work, we perform a systematic investigation of multi-component dark matter sectors, exploring scenarios with two ($N=2$) and three ($N=3$) distinct particle species while considering both exclusive and mixed annihilation channels. Using the Akaike Information Criterion (AIC) to rigorously penalize model complexity, we find that the GCE data statistically favors an $N=2$ scenario where each dark matter component annihilates exclusively into a single final state. Our results reveal that the preferred solutions naturally follow a light-plus-heavy mass hierarchy, and that specific final states such as $t\bar{t}$, $ZZ$, and $hh$, which are individually unable to explain the excess are effectively “resurrected” by the improved morphological fit provided by the multi-component framework. Furthermore, we show that these scenarios may mitigate the tension with current constraints, reaching compatibility within existing uncertainties. Our results suggest that the GCE may be the first evidence of a diverse dark sector, favoring a multi-scale solution over the minimal WIMP paradigm.
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Solar and Stellar Astrophysics

Stellar characterization with photometric colors from J-PLUS and 2MASS surveys

J. F. Aguilar, P. Cruz, E. Solano et al. (+18 more)

Aims. We aim at deriving stellar atmospheric parameters based on the photometric data from the Javalambre Photometric Local Universe Survey (J-PLUS) in addition to near-infrared photometry from the Two Micron All-Sky Survey (2MASS). Methods. Our method consists of a semi-supervised machine learning approach based on the k-means method combined with a modified k-nearest neighbors algorithm. This method compares the observed photometry to a set of reference data to estimate the stellar effective temperature ($T_{\rm eff}$), surface gravity ($\log{g}$), and metallicity ([Fe/H]) of stars from J-PLUS Data Release 3 (DR3). Results. We estimated $T_{\rm eff}$, $\log{g}$, and [Fe/H], for approximately 5.6 million stars from J-PLUS DR3, along with their errors.Our results were in agreement with spectroscopic estimates from LAMOST and APOGEE.We also applied a dimension reduction method, seeking greater efficiency by reducing the computation time and minimizing the needed information for calculating the stellar parameters, resulting in a subset of 11 colors. From this approach, stellar parameters were obtained for approximately six million stars. Conclusions. Our results demonstrated the potential of using a method built from machine learning algorithms that do not require prior training. Additionally, it was shown that the proposed method allowed estimating reliable atmospheric parameters even when the available photometry did not fulfill all photometric quality criteria. We defined a neighborhood parameter, which assesses the reliability of our estimations and indicates that objects with smaller neighborhoods values have lower uncertainties.
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All authors J. F. Aguilar, P. Cruz, E. Solano, P. R. T. Coelho, A.Ederoclite, V. M. Placco, P. Mas-Buitrago, A. Alvarez-Candal, F. Jiménez-Esteban, A.J. Cenarro, D. Cristóbal-Hornillos, C. Hernández-Monteagudo, C. López-Sanjuan, A. Marín-Franch, M. Moles, J. Varela, H. Vázquez Ramió, J. Alcaniz, R.A. Dupke, L. Sodré Jr, R.E. Angulo

Astrophysics of Galaxies

Compton-thick AGN in the NuSTAR Era. XI. Analyzing 11 CT-AGN Candidates Selected with Machine Learning

Ross Silver, Nuria Torres-Alba, Stefano Marchesi et al. (+8 more)

This work discusses the broadband X-ray spectral analysis of 11 candidate heavily-obscured active galactic nuclei (AGN) selected based on their infrared and X-ray properties by a recently published machine learning algorithm. This paper is part of a larger work to identify and characterize all AGN in the local universe (z < 0.1) with the largest line-of-sight (los) column densities (NH), the so-called Compton-thick (CT-, NH,los >= 1024 cm-2) AGN. We modeled the X-ray spectra using two physically- motivated models, UXClumpy and RXTorusD. Of the 11 AGN in our sample, we found three to be obscured with 22.7 < LogNH,los <= 23.0, five have 23.0 < LogNH,los <= 23.25, and three have 23.4 < LogNH,los <= 23.9, according to UXClumpy. Meanwhile, according to RXTorusD, we found three AGN to be obscured with 22.7 < LogNH,los <= 23.0, four with 23.0 < LogNH,los <= 23.4, and four with 23.85 < LogNH,los <= 23.96. Additionally, this work served as a comparison between UXClumpy and RXTorusD. We found broad agreement between the two, with 8/11 sources agreeing on the value of the photon index Gamma, while only 5/11 sources agreeing on the NH,los value within the 90% confidence level.
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All authors Ross Silver, Nuria Torres-Alba, Stefano Marchesi, Vittoria Gianolli, Isaiah Cox, Dhrubojyoti Sengupta, Indrani Pal, Marco Ajello, Xiurui Zhao, Kouser Imam, Anuvab Banerjee

Instrumentation and Methods for Astrophysics

Quantifying the Scientific Potential of Intermediate and Extreme Mass Ratio Inspirals with the Laser Interferometer Space Antenna

Lorenzo Speri, Francisco Duque, Susanna Barsanti et al. (+4 more)

The Laser Interferometer Space Antenna (LISA) will enable precision studies of Extreme and Intermediate Mass Ratio Inspirals (EMRIs/IMRIs), providing unique probes of astrophysical environments of galactic nuclei and strong-field gravity. Using a fully relativistic pipeline across primary masses $m_1 \in [5\times10^4, 10^7]\,M_\odot$ and secondary masses $m_2 \in [1, 10^4]\,M_\odot$, we map instrumental performance directly to detection horizons and parameter measurement precision. EMRIs with $m_1 = 10^7\,M_\odot$ and $m_2 \sim 1\,M_\odot$ are the most sensitive to instrument degradation, with redshift horizons at $z \sim 0.01$, while IMRIs are the least sensitive to degradation and reach redshifts $z \sim 1-3$. All prograde systems considered achieve sub-percent spin precision within three months of observation. The full 4.5-year mission increases the horizon of systems with $m_1 = 10^7\,M_\odot$ and $m_2 \sim 1\,M_\odot$ by a factor of $\sim 4$ and improves sky localization by one to two orders of magnitude reaching $ < 10\,\mathrm{deg}^2$. IMRI detection is robust against degradation, but their parameter estimation is more vulnerable due to fewer cycles in band. With the full baseline, EMRI observations constrain scalar dipole emission and Kerr quadrupole deviations below ground-based bounds by one to two orders of magnitude. We release the accompanying software and an interactive website to enable the community to rapidly quantify the scientific potential of EMRIs and IMRIs.
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All authors Lorenzo Speri, Francisco Duque, Susanna Barsanti, Alessandro Santini, Shubham Kejriwal, Ollie Burke, Christian E. A. Chapman-Bird

Astrophysics of Galaxies

Ultraviolet variability in Radio-Loud Active Galactic Nuclei observed by UVIT onboard AstroSat

M. Reshma, C. S. Stalin, Amit Kumar Mandal et al. (+3 more)

Radio-loud active galactic nuclei (AGN) are among the most luminous objects in the Universe, emitting radiation from low-energy radio waves to high energy $\gamma$-rays. They are well known to exhibit flux variations at nearly all accessible wavelengths. However, their variability properties in the ultraviolet (UV) band remain relatively less explored compared to other wavebands. Here, we present the results of a systematic investigation of the UV flux and spectral variability characteristics of 24 radio-loud AGN spanning the redshift range 0.018 $\le$ $z$ $\le$ 2.218. The sample comprises 17 BL Lac objects, 6 flat spectrum radio quasars (FSRQs) and one radio-loud narrow line Seyfert 1 galaxy. We used observations obtained with the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat during its first ten years of operation, covering both the far-UV (FUV; 1300$-$1800 Å) and near-UV (NUV; 2000$-$3000 Å) bands. Of the 24 sources analysed, 18 showed significant UV variability on hour timescales. We found a bluer when brighter (BWB) spectral trend in two sources: the FSRQ CTA 102 and the BL Lac PKS 0447$-$439. The observed UV variability in our sample of radio-loud AGN, together with the BWB trend detected in these two sources, supports a scenario in which the hour timescale UV variations are driven by intrinsic processes within their relativistic jets.
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All authors M. Reshma, C. S. Stalin, Amit Kumar Mandal, S. B. Gudennavar, Senorita Benedict, Prajwel Joseph