Solar and Stellar Astrophysics · Cross-listed from physics.space-ph
Validation of Space Weather Forecasting at Leonid Space
Scott Shambaugh
We validate Leonid Space's space weather forecasts through comprehensive cross-validation of retroforecasts scored against the entire F10.7 and Ap historical record. We built a unified forecast model that jointly forecasts F10.7 and Ap on all timescales from 3 hours up to multi-decade chains of future solar cycles. This was used to generate an archive of historical 15-year retroforecasts, after performing a leave-one-out fit of the model on held-out data and conditioning only on historical data available at the time. The accuracy of this archive was scored against measured space weather indices at all lookahead horizons from 1 day to 15 years, using the continuous ranked probability score (CRPS) as the primary quality metric. All other publicly available F10.7 and Ap forecast archives were scored using the same approach, including NASA's MSAFE and Schatten forecasts, SWPC's 27-day, 45-day, and Solar Cycle predictions, SWPC/USAF's RSGA, SIDC's Ursigram, CLS, Athens, KSO, BGS, SEPC's 3-day and 27-day forecasts, AFRL/NSO's SIFT, and BoM. Taken together, these 15 flux forecasts and 12 Ap forecasts compared on common lookahead metrics make up the most comprehensive cross-comparison of space weather forecasts we are aware of. Over a common forecast interval since 2000, Leonid had the lowest CRPS prediction error of any F10.7 or Ap prediction model: strictly lowest for Ap at all lookaheads and for F10.7 up to 5 years, and parity with MSAFE after 5 years. Much of this performance comes from our well-calibrated uncertainty bands, and we urge space weather forecasters to include calibrated uncertainties with their predictions and to issue retroforecast archives that can be used to rigorously evaluate their generating models.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Cosmology & Astrophysics of the Dark Dimension with Bulk Majorana Neutrinos
Luis A. Anchordoqui and Cumrun Vafa
Recently, the possibility of having sterile Majorana
neutrinos charged under $B-L$ gauge
symmetry in the bulk of the dark dimension has been explored. We point out a cosmological restriction on the Majorana mass of bulk
neutrinos leading to mass $\gtrsim 100~{\rm GeV}$. This avoids the over-production of Kaluza-Klein
neutrino towers in the early universe thus resolving the cosmological
neutrino catastrophe of extra dimension scenarios. If the mass of the bulk
neutrino is at the lower end of this bound, it can potentially also explain the recently observed Fermi
halo excess on gamma rays through the evaporation of long-lived 5d (i.e. dark) black holes through Hawking radiation to bulk
neutrinos, which promptly decay into standard model particles.
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Astrophysics of Galaxies
The NIVARIA-Local Group simulations: Unveiling the origin of rotation curve diversity in dwarf galaxies and its connection to galaxy morphology
A. Contreras-Santos, A. Di Cintio, A. Negri et al. (+7 more)
Dwarf
galaxies exhibit a large diversity in rotation curve shapes, challenging
galaxy formation models within the $\Lambda$CDM paradigm. We present NIVARIA-LG, a new suite of cosmological simulations studying dwarf
galaxy evolution in realistic Local Group environments. This intermediate-resolution pilot lays the groundwork for the full-scale NIVARIA project. The simulations combine constrained Local Group initial conditions from HESTIA with the NIHAO
galaxy formation model. The simulated
galaxies reproduce observed stellar-to-
halo mass relations, match the Baryonic Tully-Fisher relation, and capture the distribution of stellar effective radii, including compact and diffuse
galaxies. We analyse the structural and kinematic properties of isolated dwarf
galaxies with $10^7 \lesssim M_\star/M_\odot \lesssim 10^{10}$, focusing on rotation curve diversity. NIVARIA-LG naturally produces a broad range of rotation curve shapes, including slowly rising systems underrepresented in previous simulations and steep rotation curves. We find that rotation curve diversity is primarily associated with gas extent and inner dark matter structure: more extended gas and shallower inner density profiles correspond to more slowly rising curves, while stellar effective radius shows little independent association. Individual
galaxies show that rotation curve shapes change rapidly as gas is redistributed during assembly. Recent
accretion events are also associated with more slowly rising curves in the most massive dwarfs. Together, these results suggest that rotation curve diversity is linked to the baryonic cycle, which shapes the inner dark matter distribution. The Local Group environment and its filaments influence this
evolution by regulating gas
accretion and redistribution, producing the observed diversity in rotation curve shapes.
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All authors A. Contreras-Santos, A. Di Cintio, A. Negri, J. Sarrato-Alós, S. Cardona-Barrero, G. García-Bethencourt, C. Brook, N. I. Libeskind, A. Knebe, A. Macciò
Astrophysics of Galaxies
Photometric Identification and Dynamical Purification of Blue Horizontal Branch Stars in DESI MWS DR1
Shuai Zhang, Xiaolong Wang, Kai Xiao et al. (+5 more)
Blue horizontal-branch (BHB)
stars are ideal tracers for mapping the structure of the Galactic stellar
halo. However, traditional spectroscopic identification is limited by data quality and sample size, while broad-band photometric methods often achieve only moderate completeness and purity. Building upon the color-space BHB identification method of \citet{2025ApJS..278...62H}, we synthesize SkyMapper $(u,v,g,z)$ photometry from DESI MWS DR1 spectroscopy and identify 9,237 BHB candidates in the $(g-z)_0$–$(u-v)_0$ color space using the HDBSCAN clustering
algorithm. We then construct a Kernel Density Estimation (KDE)
Bayesian probability model with capture-recapture (C-R) prior to assign posterior membership probabilities, achieving a probability-weighted purity of 88.9% and completeness of 94.2%. Applying an escape-velocity cut based on the Galactic gravitational potential, we remove 1,461 contaminants with unphysical kinematic parameters, yielding a clean photometric BHB sample $\mathcal{S}_c$ of 7,776
stars (retention rate $R_{\rm keep} = 84.2\%$). Systematic analysis of the contaminants reveals that they are predominantly faint sources ($g\sim20$~mag) with very low signal-to-noise ratios (median SNR~$<$~5). When the BHB color–luminosity relation is incorrectly applied to these objects, their space velocities are amplified beyond the Galactic escape limit, confirming that the escape-velocity filter essentially acts as a physical detector of low-SNR–driven distance inflation.
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All authors Shuai Zhang, Xiaolong Wang, Kai Xiao, Guozhen Hu, Wenyuan Cui, Ce Cai, Shuai Feng, Jie Ju
Astrophysics of Galaxies
The Galactic disk structure revealed by Gaia XP spectra
Zhenkang Tang, Jianhui Lian, Jialong Zhou et al. (+1 more)
The spatial structures of chemical populations constrain Galactic disk
evolution and its underlying physical processes. Gaia XP spectra provide one of the largest spectroscopic samples available. We use Gaia XP spectra to study Galactic disk mono-abundance populations (MAPs), measuring their scale heights as a function of radius and radial surface-mass-density profiles. We construct a red giant branch (RGB) sample and divide it into MAPs according to $[\alpha/{\rm M}]$ and $[{\rm M/H}]$. The sample covers a $6\times6$ kpc region centered on the Sun in the Galactic plane and extends to $|Z|<3.7$ kpc. We estimate XP completeness using a Gaia photometric parent sample and combine PARSEC isochrones with a Kroupa initial mass function (IMF) to calculate the selection function and convert observed stellar counts into intrinsic stellar mass densities. We fit vertical density profiles with an exponential model to derive scale heights and integrate the fitted profiles to obtain surface mass densities. The resulting profiles are generally consistent with those from APOGEE. All MAPs show flaring, with the high-$\alpha$ population exhibiting the strongest flaring and the metal-poor and sub-solar low-$\alpha$ populations showing the weakest. Surface-mass-density profiles differ significantly among MAPs: the high-$\alpha$ and metal-rich low-$\alpha$ populations show approximately exponential declines, whereas the other low-$\alpha$ populations exhibit plateau-like features, indicating that the Galactic disk cannot be described by a simple single-exponential profile. These differential structures suggest a complex Galactic disk assembly history likely regulated by birth conditions, secular dynamical heating, radial migration, and external perturbations.
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All authors Zhenkang Tang, Jianhui Lian, Jialong Zhou, Jiadong Li
Solar and Stellar Astrophysics
The $R$-Process Alliance: On J0010$-$1735, an Accreted, Chemically Unusual, Metal-poor Star with $R$-process Enhancement
Zoe Hackshaw, Rana Ezzeddine, Shivani P. Shah et al. (+11 more)
We present a detailed chemo-dynamical analysis of the chemically peculiar very metal-poor ([Fe/H]$=-2.22\pm 0.11$) Milky Way (MW)
halo star, 2MASS J00101758$-$1735387 (hereafter J0010-1735), discovered by the $R$-Process Alliance. We derive abundances for 45 elements, including 28
neutron-capture elements, and confirm that \thestar\ is highly $r$-process-enhanced, with [Eu/Fe]=$+1.30$. The light, $\alpha$, and Fe-peak element abundances ratios relative to Fe are all sub-solar, aside from C, Si, and most extremely, Ca. We investigate three possible formation scenarios based on the
star's chemical abundances and orbital kinematics: whether it formed in the in-situ MW
halo, in a MW dwarf
galaxy satellite, or in a satellite of the Magellanic Cloud system. Using the position of \thestar\ in the [Mg/Mn]–[Al/Fe] plane, the abundance pattern of both the light and heavy elements, and the kinematics, we conclude that J0010-1735 most plausibly originated in a now-disrupted ultra-faint dwarf
galaxy that was accreted into the MW
halo. We examine potential chemical enrichment scenarios of J0010-1735, including one similar to the $r$-process-enhanced UFD Reticulum II, or enrichment via a sub-Chandrasekhar Type Ia SNe, potentially supplemented by a Ca-rich gap transient and by a separate
neutron-rich site that facilitated $r$-process enrichment. A nuclear cosmochronometric age of $12.5\pm4.2$ Gyr is derived from the [Th/Eu] ratio, consistent with an ancient origin in one of the earliest
star-forming systems in the universe.
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All authors Zoe Hackshaw, Rana Ezzeddine, Shivani P. Shah, Terese T. Hansen, Ruijie Shi, Yangyang Li, Timothy C. Beers, Anna Frebel, Erika Holmbeck, Alexander P. Ji, Jeremy Kowkabany, Vinicius M. Placco, Ian U. Roederer, Charli M. Sakari
High Energy Astrophysical Phenomena
A GeV Gamma-Ray Spectral Excess in the Fermi Blazar 4FGL J0136.5+3906
Shi-Ju Kang, Yue Yin, Yong-Gang Zheng et al. (+2 more)
We report the detection of a $\sim${{19}} GeV gamma-ray spectral excess (peak energy in observer frame) at $\sim$5.7$\sigma$ significance (3 degrees of freedom, without correction for trials and the look-elsewhere effect) in the Fermi-LAT data of the blazar 4FGL J0136.5$+$3906, based on $\sim${17} years of observations. The excess manifests as a distinct bump-like feature in the 100 MeV$-$1 TeV spectrum, with a flux of $\sim$3.6$\rm \times10^{-10}~ph~cm^{-2}~s^{-1}$. No similar feature is detected in nearby sources or background regions. The origin of this signal cannot be explained by standard blazar emission models and remains unknown. This Letter presents the observational finding without providing a definitive physical interpretation.
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All authors Shi-Ju Kang, Yue Yin, Yong-Gang Zheng, Qingwen Wu, Junhui Fan
Cosmology and Nongalactic Astrophysics
TDCOSMO 2026: new insights on the Hubble tension from strong lensing time delays
TDCOSMO Collaboration, Simon Birrer, Michele Cappellari et al. (+26 more)
We discuss the measurement of the Hubble constant ($H_0$) in flat $\Lambda$ cold dark matter cosmology based on the blind hierarchical analysis of 11 multiply-imaged
quasars (hereafter the TDCOSMO-2026 sample) and described in greater detail in a companion paper. In addition to the time delays, we use lens models based on high-resolution imaging from the Hubble Space
Telescope (HST) and from the James Webb Space
Telescope (JWST), analyzed jointly with axisymmetric dynamical models based on JWST-NIRSpec, VLT-MUSE, and Keck-KCWI spectroscopy. Our primary result $H_0=71.1^{+2.4}_{-2.3}$ km.s$^{-1}$.Mpc$^{-1}$ is based on the TDCOSMO-2026 sample, in combination with $\Omega_{\rm m}$ constraints from the DES-Dovekie
supernova (SN)
dataset. Our 3% precision accounts for the mass-sheet degeneracy. Importantly, our measurement is independent of the local distance ladder (LDL). Among individual late-universe probes, only the traditional LDL is more precise. We discuss our result in the context of the Hubble tension, the difference between $H_0$ measured in the late universe and the prediction based on early-universe probes such as the
cosmic microwave background (CMB). We construct combinations of independent late-universe probes and show that the tension with the Planck CMB prediction is robust to excluding any one of the methods based on Type-Ia
Supernovae, Cepheids, or the Tip of the Red Giant Branch. For example, we construct a 'no-SN' $H_0$ measurement, by replacing the DES-Dovekie constraint on $\Omega_{\rm m}$ with that from DESI baryon acoustic oscillations, and then combining TDCOSMO-2026 with independent non-SN late-universe probes. This 'no-SN' late-universe probe is in 3.7$\sigma$ tension with Planck. Even after completely excluding the LDL, the tension with Planck persists at the 2.7$\sigma$ level.
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All authors TDCOSMO Collaboration, Simon Birrer, Michele Cappellari, Frédéric Courbin, Christopher D. Fassnacht, Pierre Fleury, Joshua A. Frieman, Aymeric Galan, Xiang-Yu Huang, Daniel P. Johnson, Sanjana Khanolkar, Shawn Knabel, Hrvoje Krizic, Martin Millon, Takahiro Morishita, Veronica Motta, Pritom Mozumdar, Eric Paic, Hadrien Paugnat, Allan G. Schweinfurth, Anowar J. Shajib, William Sheu, Dominique Sluse, Massimo Stiavelli, Sherry H. Suyu, Tommaso Treu, Felipe Urcelay, Devon M. Williams, Kenneth C. Wong
Instrumentation and Methods for Astrophysics
From Sky to Science: Time Domain Astronomy with the ILMT Survey
Kuntal Misra, Bhavya Ailawadhi, Talat Akhunov et al. (+10 more)
The PyLMT transient detection pipeline has been operational since November 2023 and has detected $\sim$10,000 transients and variable objects in ILMT images in near real time. The survey has enabled the discovery and characterisation of a range of bright and faint optical transients. The detected population spans a broad diversity of astrophysical phenomena, including
supernovae, variable
stars, active galactic
nuclei (AGN) variability, and Solar System objects such as asteroids and comets. We provide a concise overview of the detection of a variety of transient and variable classes identified with the ILMT, emphasising the survey's potential contributions to a broad class of astrophysical sources. We highlight representative science cases, including
supernovae, AGNs, variable
stars, and asteroids, to demonstrate the scientific potential of the ILMT survey.
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All authors Kuntal Misra, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Naveen Dukiya, Sara Filali, Paul Hickson, Priyanshi Kumari, Gokul Singh Mehra, Vibhore Negi, Kumar Pranshu, Jean Surdej, Sarvesh Kumar Yadav
Instrumentation and Methods for Astrophysics
Modelling the Point Spread Function of ILMT images
Naveen Dukiya, Bhavya Ailawadhi, Talat Akhunov et al. (+11 more)
We have devised an approach to model the empirical Point Spread Function (PSF) of the images taken with the 4-meter International
Liquid Mirror
Telescope (ILMT). The characteristics of the ILMT PSF are influenced by the nature of the
Liquid Mirror, as well as by instrument specific and atmospheric factors. As the
telescope uses Time Delay Integration (TDI) mode for tracking the passing objects, the PSF varies along the declination axis due to differential motion and
star-trail
curvature. The 5-element optical corrector homogenizes the PSF to some degree, but does not completely eliminate the disturbing effects mentioned above. The PSF in the RA direction is changing due to the sky conditions. We show that we can successfully model the PSF of 4k$\times$4k chunks using PSFEx, accounting for second-order X-Y variability. Our software robustly reproduces the PSF and its variation across the field.
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All authors Naveen Dukiya, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Sara Filali, Paul Hickson, Priyanshi Kumari, Gokul Singh Mehra, Kuntal Misra, Vibhore Negi, Kumar Pranshu, Jean Surdej, Sarvesh Kumar Yadav, Archana Gupta
Cosmology and Nongalactic Astrophysics
Gravitational waves from strong first-order phase transitions in an expanding Universe
Jintao Zou, Zizhuo Zhao, Yongtao Jia et al. (+1 more)
We investigate the gravitational waves generated by first-order phase transitions (PTs) in an expanding Universe. Using a scalar field-fluid coupled model, we perform three-dimensional
lattice numerical simulations of slow first-order PTs with strong strength. We observe that the contribution from sound waves to the gravitational wave (GW) signal significantly dominates over that from bubble collisions. The sound wave spectra exhibit two peaks located at the mean bubble separation and the sound-shell width. Rotational modes are generated in the fluid during the bubble collisions, and their magnitude grows with the PT strength. The lifetime of the sound wave source increases with decreasing $\alpha$: for weaker transitions the source can persist for longer than a Hubble time, while for stronger transitions it decays within a Hubble time. When the walls propagate as deflagrations, the GW spectral shape changes drastically, with steeper ultraviolet tails and a shorter-lived sound wave source. We also observe that the magnitude of the normalized GWs is roughly an order of magnitude smaller than obtained in the Minkowski spacetime simulations.
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All authors Jintao Zou, Zizhuo Zhao, Yongtao Jia, Ligong Bian
Instrumentation and Methods for Astrophysics
Mid-IR Water-Vapor Seeing: Implications for ELT/METIS High-Contrast Imaging from VLTI Data
Abhirami S Raghu, Prashant Pathak, Olivier Absil et al. (+7 more)
Direct imaging and characterization of rocky
exoplanets remains one of the central challenges in exoplanetary science. The mid-infrared (mid-IR) offers a favorable high-contrast imaging (HCI) regime, as the
planet-
star contrast is more moderate than at shorter wavelengths. However, mid-IR observations with extremely large ground-based
telescopes (ELTs) are strongly affected by spatio-temporal fluctuations in atmospheric water vapor (WV), which introduce chromatic wavefront errors that are largely invisible to adaptive optics systems operating at shorter wavelengths. This poses a significant challenge for mid-IR HCI instruments such as METIS, which aims to detect thermal emission from rocky
exoplanets in the $N$-band (8–13 $\mu$ m). To quantify WV-induced wavefront errors, we analyze $K$-band fringe-tracker data from the
GRAVITY instrument at the VLTI and derive the optical path difference between group-delay and phase-delay measurements. This difference provides a direct measure of the differential WV column density ($\Sigma$) above the
telescopes. We examine the dependence of the RMS differential WV column density ($\sigma_{\Sigma}$) on precipitable water vapor (PWV), airmass, seeing, and wind speed across multiple VLTI configurations. Among these parameters, PWV shows the strongest correlation with $\sigma_{\Sigma}$. We further explore the influence of the vertical PWV distribution on this relationship. Next, we use power-spectral-density analysis to quantify how increasing PWV modulates $\Sigma$ variability. The wavefront error associated with this phenomenon on ELT scale is approximately 15~nm RMS in the $L$-band and 175~nm RMS in the $N$-band, relative to the $K$-band. These results provide a quantitative framework for assessing and mitigating atmospheric WV effects in next-generation mid-IR HCI instruments.
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All authors Abhirami S Raghu, Prashant Pathak, Olivier Absil, Benjamin Courtney-Barrer, Gilles Orban de Xivry, Julien Woillez, Alexis Matter, Philippe Bério, Roy van Boekel, Bernhard Brandl
Earth and Planetary Astrophysics
Milani and Juventas Optical Navigation Images in Support of the Hera Radio Science Experiment
Edoardo Gramigna, Ozgur Karatekin, Birgit Ritter et al. (+7 more)
The European Space Agency's Hera mission aims to advance planetary defense by investigating the Didymos binary asteroid system following NASA's DART impact on Dimorphos. Incorporating simulated CubeSat images into Hera's orbit determination framework significantly improves positional accuracy, reducing uncertainties by up to three orders of magnitude for Milani and one for Juventas. This data enable more precise estimation of key parameters such as asteroid masses, rotational states, and moments of inertia, with up to 90% uncertainty reduction in Dimorphos' dynamical state under chaotic scenarios. Sensitivity analysis reveals the influence of pointing accuracy, image noise, and imaging frequency. Additionally, dedicated scientific investigations using Dimorphos-focused CubeSat images further advance understanding of the system. These findings underscore the critical role of CubeSat images in refining navigation and advancing science, offering valuable insights for future small-body missions.
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All authors Edoardo Gramigna, Ozgur Karatekin, Birgit Ritter, Iosto Fodde, Fabio Ferrari, Felice Piccolo, Paolo Tortora, Riccardo Lasagni Manghi, Marco Zannoni, Ryan S. Park
Earth and Planetary Astrophysics
Hera Orbit Determination Covariance Analysis of Didymos Binary Asteroid with the Full Two-Body Problem
Edoardo Gramigna, Riccardo Lasagni Manghi, Marco Zannoni et al. (+7 more)
Standard planetary
radio science analyses may be inadequate for accurately interpreting data from the Hera mission at the Didymos system due to the anticipated challenge posed by the coupling between the translational and rotational motions of the asteroids. A more precise dynamical model, the full two-body problem model, which includes a mutual gravitational potential, may be required to fit the Hera data properly. This work presents a covariance analysis of the Hera
radio science experiment using this advanced model. The tested dynamical scenarios are based on recent lightcurve observations indicating that Dimorphos is in an excited non-principal axis
spin state that is, on average, tidally locked. Three non-principal axis scenarios are analyzed using a multi-arc local estimation approach instead of the global one adopted in previous investigations involving non-chaotic states. The results show that tumbling or chaotic cases significantly improve the recovery of the bodies' moments of inertia due to the enhanced observability of the system's dynamics from the excited
spin state. However, the local estimation approach slightly degrades the accuracy of the mass estimation by a factor of 1.3-3 and Dimorphos' relative orbit by about one order of magnitude. Developing a dedicated constrained multi-arc filter is thus required to improve the estimation accuracy of the Didymos system's dynamical state further. Nevertheless, these results still meet the Hera
radio science requirements.
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All authors Edoardo Gramigna, Riccardo Lasagni Manghi, Marco Zannoni, Paolo Tortora, Michalis Gaitanas, Ioannis Gkolias, Kleomenis Tsiganis, Ryan S. Park, Alex Meyer, Petr Pravec
Cosmology and Nongalactic Astrophysics
TDCOSMO 2026: A 3% measurement of the Hubble constant from strong lensing and stellar kinematics
TDCOSMO Collaboration, Simon Birrer, Michele Cappellari et al. (+26 more)
We present cosmological constraints from 11 strongly lensed
quasars with measured time delays (hereafter, the TDCOSMO-2026 sample). In addition to expanding the sample, we improve many aspects of our blind analysis with respect to our 2025 analysis. Among other improvements, spatially resolved kinematics are available for nine systems, including six with JWST-NIRSpec, compared to one in 2025; for three lens models, JWST-NIRCam images now replace HST; axisymmetric dynamical modeling is applied directly to the spatially resolved data, instead of an axisymmetric correction factor applied to spherical models; and the line-of-sight convergence is now based on the Euclid Flagship simulations instead of the Millennium Simulation. Our baseline and primary result is based on the TDCOSMO-2026 sample, in combination with a prior on $\Omega_{\rm m}$ from the DES-Dovekie
supernova sample. In the flat $\Lambda$ cold dark matter ($\Lambda$CDM) cosmology, we find $H_0=71.1^{+2.4}_{-2.3}$ km.s$^{-1}$.Mpc$^{-1}$, a 3.3% uncertainty that accounts for the mass-sheet degeneracy. The SLACS and SL2S samples are in excellent agreement with the TDCOSMO-2026 sample, improving the precision on $H_0$ in flat $\Lambda$CDM to 3.0%. Using the DESI-DR2 baryon acoustic oscillations (BAO) likelihood instead of DES-Dovekie yields fully consistent results. We also present constraints in the open $\Lambda$CDM, $w$CDM, $w_0w_a$CDM, and $w_{\phi}$CDM cosmologies; the TDCOSMO $H_0$ inference is robust and consistent across all of them. The combination of the TDCOSMO+SLACS+SL2S likelihood with those from DESI-DR2 and DES-Dovekie disfavors $w=-1$ at the $2.3$-$2.5\sigma$ level in all three dark energy extensions that we tested. We find, e.g., $w_0=-0.88^{+0.04}_{-0.05}$ in $w_{\phi}$CDM and $w_0 = -0.85^{+0.07}_{-0.06}$ in $w_0w_a$CDM, while $w_a = -0.48^{+0.46}_{-0.44}$ remains consistent with zero.
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All authors TDCOSMO Collaboration, Simon Birrer, Michele Cappellari, Frédéric Courbin, Christopher D. Fassnacht, Pierre Fleury, Joshua A. Frieman, Aymeric Galan, Xiang-Yu Huang, Daniel P. Johnson, Sanjana Khanolkar, Shawn Knabel, Hrvoje Krizic, Martin Millon, Takahiro Morishita, Veronica Motta, Pritom Mozumdar, Eric Paic, Hadrien Paugnat, Allan G. Schweinfurth, Anowar J. Shajib, William Sheu, Dominique Sluse, Massimo Stiavelli, Sherry H. Suyu, Tommaso Treu, Felipe Urcelay, Devon M. Williams, Kenneth C. Wong
Astrophysics of Galaxies
Multiphase Analysis of (U)LIRG Nuclear Activity (MAUNA). I. Spatially Resolved Optical Emission-Line Diagnostics
Justin A. Kader, Vivian U, Marina Bianchin et al. (+33 more)
We present resolved optical integral-field spectroscopy of the 32 luminous and ultraluminous infrared
galaxy systems of the Multiphase Analysis of (U)LIRG Nuclear Activity (MAUNA) sample, drawn from the GOALS survey and selected to have JWST/MIRI medium-resolution spectrometer (MRS) observations. The data set combines new Keck/KCWI observations of 10 systems with archival VLT/MUSE cubes for 22 systems, covering H$\beta$ to [S II] at ~1 arcsecond spatial resolution (~0.9 kpc at the sample median distance). Using the optical [N II]/H$\alpha$ BPT diagram, we find that composite and LINER-like excitation together account for most of the classified area (median fractions 0.44 and 0.26), while Seyfert-like gas covers a median fraction of 0.02 but carries a far larger proportion of the line luminosity where it is present. Both the projected size of the Seyfert-classified region, $R_{\rm Sy}=0.08$-$7.5$ kpc, and its [O III] luminosity increase with the bolometric AGN luminosity, with $R_{\rm Sy}\propto L_{\rm AGN,bol}^{0.54\pm0.18}$, as expected for gas photoionized at a constant ionization parameter. The scatter about the luminosity relation depends on dust opacity: the [O III] luminosity per unit AGN luminosity falls by $1.09\pm0.25$ dex per unit depth of the 9.7 $\mu$m silicate absorption feature (Spearman $\rho=-0.60$, $p=0.001$). Optical excitation diagnostics therefore locate AGN-excited gas reliably but systematically underestimate the luminosity the AGN supplies to the host in the most obscured (U)LIRGs.
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All authors Justin A. Kader, Vivian U, Marina Bianchin, Yiqing Song, George C. Privon, Sabrina Stierwalt, Tanio Diaz-Santos, Lee Armus, Vassilis Charmandaris, Ezequiel Treister, Rosalie McGurk, Hanae Inami, Jeffrey A. Rich, Sean T. Linden, Anne M. Medling, Loreto Barcos-Muñoz, Gabriela Canalizo, Aaron S. Evans, Kirsten L. Larson, Tianmu Gao, Thomas Lai, Laura Lenkic, Jaya Nagarajan-Swenson, Justin Howell, Cristina M. Lofaro, Matthew A. Malkan, María Sánchez-García, Christopher D. Martin, Mateusz Matuszewski, Claire E. Max, Joseph M. Mazzarella, James D. Neill, Nikolaus Z. Prusinski, Raymond Remigio, David Sanders, Jason Surace
Astrophysics of Galaxies
Beyond the Damped Random Walk: Multiband AGN Variability from SDSS to Rubin LSST
Izak Schmidlkofer, Zhirui Hu, Weixiang Yu et al. (+1 more)
The flux variability of Active Galactic
Nuclei (AGNs) is commonly modeled using the damped random walk (DRW), but increasingly rich multiband time-domain surveys motivate more flexible
stochastic models that characterize variability beyond a single timescale and exploit dependence across bands. Multivariate continuous-time autoregressive moving average (MCARMA) processes extend the multivariate DRW to higher-order
stochastic dynamics and provide a
matrix-valued power spectral density for characterizing marginal variability and cross-band dependence. In a carefully selected Sloan Digital Sky Survey (SDSS) Stripe~82 sample, higher-order models are selected for 109 of 134 AGNs (81.3%), with substantial rather than marginal support in most objects; convergence diagnostics indicate that this fraction is conservative. The fitted models also reveal strong cross-band dependence that generally decreases with wavelength separation. Motivated by this richer structure, we investigate its recoverability under Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) observing conditions. Model-order recovery depends strongly on the underlying
stochastic behavior as well as source brightness and observing cadence. Recovery is high across many of the simulated settings, but deteriorates when the characteristic features of higher-order variability become difficult to distinguish from the multivariate DRW. Additional simulations show that this loss of distinguishability can persist over a range of underlying variability behaviors. These results show that
stochastic structure beyond the multivariate DRW is prevalent in our selected SDSS sample, while its recoverability with LSST depends on both observational conditions and the form of the underlying
stochastic variability. The methodology is implemented in the Python package mcarma.
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All authors Izak Schmidlkofer, Zhirui Hu, Weixiang Yu, Hyungsuk Tak
Instrumentation and Methods for Astrophysics
ELISA: A Bayesian X/$\gamma$-ray Spectral Analysis Toolkit
Wang-Chen Xue, Sheng-Lun Xie, Chao Zheng et al. (+11 more)
Forward-folded X/$\gamma$-ray spectral fitting increasingly benefits from
Bayesian workflows to better capture counting statistics, background uncertainties, and complex parameter degeneracies, while fully reproducible end-to-end implementations are still not always straightforward to deploy in routine analyses. We present ELISA (Efficient Library for Spectral Analysis), an open-source Python toolkit that streamlines the full spectral analysis loop for X/$\gamma$-ray astronomy: data loading, model construction, inference, and model validation and comparison. ELISA couples a JAX-accelerated forward model with a unified fitting interface, supporting both rapid optimization and modern
Bayesian sampling. Built-in diagnostics make convergence checks and predictive assessment a standard part of the workflow, motivating principled model refinement when needed. Using a spectral fitting example of the Insight-HXMT Crab observation, we find substantial improvements in sampling efficiency compared with XSPEC's default MCMC implementation. ELISA is available at https://github.com/wcxve/elisa and on PyPI at https://pypi.org/project/astro-elisa.
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All authors Wang-Chen Xue, Sheng-Lun Xie, Chao Zheng, Shao-Lin Xiong, Xiao-Bo Li, Yong Chen, Peng Zhang, Yan-Qiu Zhang, Jia-Cong Liu, Chen-Wei Wang, Wen-Jun Tan, Yue Wang, Jin-Peng Zhang, Zheng-Hang Yu
High Energy Astrophysical Phenomena
Magnetar X-ray flares as elementary reconnection events in a self-organized critical magnetosphere
Sheng-Lun Xie, Yi Zhao, Wen-Long Zhang et al. (+3 more)
Magnetar bursts are commonly attributed to
magnetic energy release, yet the physically relevant dissipation unit has remained uncertain. Here we argue that this unit is not the burst as conventionally defined, but the short substructures within bursts, namely magnetar X-ray
flares (MXFs). Using 789 MXFs from SGR~J1935+2154, we show that their waiting times separate into two components, interpreted as reflecting clustered intra-episode events and longer inter-episode intervals, that their proxy emission measure and temperature exhibit distinct rising and declining trends, and that their energy release scale (ERS) proxy distribution has a high-end slope in the same statistical regime as solar and stellar
flares. Combined with the previously measured MXF duration slope, these results identify MXFs as a three-dimensional fractal-diffusive self-organized critical (FD-SOC) system with $\beta_{\rm diff}\simeq2$, implying reconnection avalanches that expand linearly through an active magnetosphere. We infer that magnetar active episodes are global unloading states assembled from many elementary
flares. Magnetar X-ray
flares are therefore the physically relevant units for magnetar outburst statistics and for connecting magnetar high-energy activity to other impulsive phenomena.
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All authors Sheng-Lun Xie, Yi Zhao, Wen-Long Zhang, Chen-Wei Wang, Yun-Wei Yu, Shao-Lin Xiong
High Energy Astrophysical Phenomena
Impact of Decay-Chain Feeding by Long-Lived Heavy Nuclei on Nuclear Cosmochronology
Qiu-Hong Chen, Meng-Hua Chen, Xianlin Yang et al. (+1 more)
Nuclear cosmochronology provides an independent method for determining the ages of astrophysical objects without relying on Galactic chemical
evolution models. Long-lived radioactive actinides synthesized via the rapid
neutron-capture process ($r$-process) particularly thorium and uranium serve as ideal chronometric
nuclei. However, predicting the initial abundances of these
nuclei and their subsequent long-term
evolution remains a major source of uncertainty in nuclear cosmochronology. In this work, we investigate the impact of decay-chain feeding from long-lived progenitor
nuclei on nuclear cosmochronology and estimate the corresponding age corrections. We develop a self-consistent radioactive decay network that includes all relevant decay pathways and couple it to $r$-process nucleosynthesis calculations. By tracking the long-term
evolution of $r$-process nucleosynthesis based on
neutron star merger trajectories, the dominant long-lived
nuclei shaping the
evolution of the chronometric elements Th and U are identified as $^{232}$Th, $^{235}$U, $^{236}$U, $^{238}$U, and $^{244}$Pu. It is found that delayed feeding substantially modifies the long-term
evolution of actinides particularly for $^{232}$Th, which receives significant late-time contributions from heavier progenitor
nuclei such as $^{244}$Pu and $^{236}$U. As a consequence, the U/Th and Th/X chronometers exhibit significant sensitivity to delayed feeding from the progenitor
nuclei $^{244}$Pu and $^{236}$U, with age corrections reaching $\sim5$~Gyr. These results suggest that decay-chain feeding from long-lived progenitor
nuclei plays a crucial role in nuclear cosmochronology and should be properly accounted for in age determinations based on actinide chronometers.
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All authors Qiu-Hong Chen, Meng-Hua Chen, Xianlin Yang, En-Wei Liang
High Energy Astrophysical Phenomena
Reawakening of GS 1843+00: A Multiwavelength Study of its 2026 Giant X-ray Outburst
Gaurava K. Jaisawal, Georgios Vasilopoulos, Francesco Carotenuto et al. (+1 more)
GS 1843+00 (Ginga 1843+009) is a poorly studied Be/X-ray binary system that underwent a major X-ray outburst in 2026 February-May after nearly sixteen years of quiescence. We present an X-ray, optical, and
radio study of GS 1843+00 during this outburst, focusing on the
evolution of the
neutron star emission geometry, Be-disk connection, and possible outflow activity. We analyse three NuSTAR observations obtained at different stages of the outburst, complemented by archival RXTE and Chandra data, optical spectroscopy and imaging with the Nordic Optical
Telescope, and a MeerKAT
radio observation. NuSTAR observations reveal coherent X-ray pulsations around 29.7 s with a
spin-up rate of $(-5.1\pm0.1)\times10^{-8}$ s s$^{-1}$ during the outburst. The pulse profiles show strong
evolution with energy and outburst phase, with distinct morphologies even at comparable luminosities. The pulsed fraction varies between 1 and 16% and exhibits a complex reversal in energy dependence above 7 keV, increasing with energy during the first two observations and decreasing during the third. The 3-79 keV broadband spectra are described by thermal Comptonization with a blackbody and an Fe K$\alpha$ emission line, with no evidence for a cyclotron absorption feature. Phase-resolved spectroscopy reveals variations in the Comptonization and blackbody parameters, indicating changes in the
accretion-column structure. Optical spectroscopy confirms the presence of a Be-circumstellar disk through H$\alpha$ and Paschen-series emission lines. No
radio counterpart is detected, with a $3\sigma$ upper limit of 36 $\mu$Jy beam$^{-1}$ at 1.28 GHz. Weaker H$\alpha$ emission compared with previous epochs indicates that the Be-circumstellar disk was in a different state during the current episode, while the
radio non-detection suggests that any associated outflow activity was faint or below the detection limit.
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All authors Gaurava K. Jaisawal, Georgios Vasilopoulos, Francesco Carotenuto, Hannah C. I. Wichern