Astrophysics of Galaxies
Optical Counterparts of MeerKLASS L-band and UHF-band surveys
M. Klein, S. Mangla, J. Mohr et al. (+7 more)
Context: Wide-area
radio continuum surveys require reliable optical and infrared counterpart identification, but high optical source densities and extended or multi-component
radio morphologies make this challenging. Aims: We present optical and infrared counterpart catalogs for MeerKLASS L-band and UHF-band on-the-fly continuum sources using KiDS DR5 and DESI Legacy Imaging Surveys DR10 (LS DR10), including counterpart probabilities,
redshifts, and host-
galaxy properties. Methods: We developed the
Stellar-mass Enhanced Density Association (SEDA) method, an empirical framework that compares candidate densities around
radio positions with those in a position-displaced control catalog. For
galaxies we use positional offset,
stellar mass, and
redshift;
quasar candidates are treated separately using offset and mid-infrared selection. A second-pass search associates multi-component
radio sources with common hosts. Results: In the L-band survey, we identify 20,400 KiDS-based counterparts with $P_{\rm true}>0.5$, corresponding to 66% of L-band sources within the KiDS footprint. In the UHF-band survey, we identify 61,633 LS DR10 counterparts, corresponding to 81% of the
radio sources. Spectroscopic
redshifts are available for 22% and 44% of the L-band and UHF-band counterparts, respectively. The
redshift distributions show low-
redshift star-forming
galaxies, intermediate-
redshift radio galaxies, and a high-
redshift tail dominated by
quasars. SEDA also recovers rare
radio-loud
quasars, including QSO J2318-3113 at $z=6.44$ and UHF_DR1 J+111111.8+053626.6 at $z=5.24$. Conclusions: SEDA provides a data-driven route to counterpart identification for wide-area
radio surveys with complex source morphologies. The catalogs enable future MeerKLASS studies of
radio source populations, host-
galaxy demographics, and rare high-
redshift radio quasars.
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All authors M. Klein, S. Mangla, J. Mohr, S. Chatterjee, K. Grainge, S. Paul, M. G. Santos, O. M. Smirnov, C. Tasse, L. Wolz
High Energy Astrophysical Phenomena
Phase-resolved QPO Analysis of GX 339-4: Improved Technique and Consistent Behaviors between QPOs and Broadband Noise
Jin Qin, Hua Feng, Liang Zhang et al. (+5 more)
The nature of low-frequency quasi-periodic oscillations (QPOs) in black hole X-ray binaries remains unclear, and their relationship with the accompanying broadband noise (BBN) is still under debate. Here, we propose an improved variational mode decomposition (VMD) technique. Compared with the original
algorithm that requires iterative, case-by-case parameter tuning, the new
algorithm automatically and consistently determines the relevant VMD parameters based on the QPO central frequency and width measured from the power spectral density (PSD). This enables a more robust phase determination for QPOs and can also be applied to the study of BBN. We found that, for low-frequency type-C QPOs without significant harmonics in the black hole X-ray binary GX 339-4, the spectral properties of the QPOs and BBN are statistically consistent with each other: (1) the
photon index is positively correlated with count rate as a function of phase, and (2) the PSD ratio spectra across different energy bands show no statistically significant QPO-like structures near the QPO frequencies, indicating that both components share the same energy dependence. These suggest that QPOs and BBN may be driven by the same physical processes. The QPO models based on
geometric modulation struggle to account for the results, while those invoking corona oscillations are favored.
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All authors Jin Qin, Hua Feng, Liang Zhang, Lian Tao, Qing-Cang Shui, Qing-Chang Zhao, Shu Zhang, Shuang-Nan Zhang
Earth and Planetary Astrophysics
Exploration of Exoplanet Atmospheres with the James Webb Space Telescope
Sasha Hinkley and David K. Sing
The James Webb Space
Telescope (JWST) is providing transformative characterization capabilities for the study of both transiting and directly imaged extrasolar
planets. Observations deep into the infrared in the form of both spectroscopy and coronagraphic imaging means that JWST is uniquely sensitive to most of the physical processes that dictate the properties of exoplanetary atmospheres. The observatory's thermal and pointing stability directly translates into the extreme photometric precision needed for exquisite transiting
exoplanet photometry, as well as highly sensitive coronagraphic observations. Over the mission's 20-25 year lifetime, roughly 10$^4$ hours will be dedicated to observations of
exoplanet atmospheres, providing a legacy data archive that will allow population-level characterization of
exoplanet atmospheres spanning terrestrial
planets, sub-Neptunes and gas
giants. This effort will also assess the prevalence of atmospheres of rocky
planets and thus the degree to which such
planets may have conditions conducive to habitability.
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Instrumentation and Methods for Astrophysics
NestyNet. I. Physics Functions Are Hard to Fit with Neural Networks: A Framework for Accurate Surrogates and Analytic Derivatives
Rodrigo Ibata, Wassim Tenachi, Foivos Diakogiannis et al. (+2 more)
Many of the smooth functions that matter most in physics are precisely the ones that standard neural network methods struggle to fit accurately. Here we present NestyNet, a coupled model-and-optimizer framework capable of fitting such targets to high accuracy while also delivering their gradients, Hessians,
Laplacians, and antiderivatives analytically and at low cost. This makes it a natural substrate for scientific machine learning tasks. The model is a deterministic segmented analytic surrogate, and its optimizer is a second-order Levenberg–Marquardt scheme whose damping and linear solves are tailored to the stiff, strongly correlated parameter geometries induced by multiscale and sharply structured targets typical in physics and other scientific applications. On the AI Feynman
benchmark of 120 physics equations, NestyNet achieves median improvement factors of $2\,100\times$ for function values, $1\,400\times$ for first derivatives, and $780\times$ for second derivatives relative to standard neural networks trained with first-order optimization (Adam). Even after refining those fits with quasi-Newton (L-BFGS) optimization, the corresponding improvements are $540\times$, $450\times$, and $250\times$. Owing to the analytic design it is up to $\approx 44\times$ faster than vectorized automatic-differentiation (autograd) baselines, with a margin growing with model size. The same analytic-derivative framework also supports vector- and complex-valued targets, measurement uncertainties in both inputs and outputs, and constraints, and its modules can be composed flexibly to build scientifically useful model architectures, all without reverting to autograd. Together, these components provide a practical modular framework for fitting difficult scientific surrogates while delivering accurate differential operators for subsequent analysis.
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All authors Rodrigo Ibata, Wassim Tenachi, Foivos Diakogiannis, Neil Ibata, Anirudh Shankar
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
A Novel Kerr-like Black Hole in a General Double Power Law Dark Matter Environment: Geometry, Spectroscopy, and Energy Extraction
Supakchai Ponglertsakul and David Senjaya
We construct a novel Kerr-like black hole solution embedded in a general double power law dark matter environment by applying the Newman–Janis
algorithm to a Schwarzschild-like seed geometry. This framework provides a unified rotating spacetime for arbitrary double power law density profiles and reveals how dark matter modifies the horizon structure, extremal
spin, and
curvature properties of rotating black holes. Remarkably, we find that the rotation–
halo interplay can eliminate essential
curvature singularities for Dehnen-type profiles with $\gamma\leq2$, despite the singular nature of the corresponding static configurations. We then investigate the spectroscopic signatures of the dark matter environment through massive scalar perturbations in the Dehnen $(1,4,\gamma)$
halo. Using an analytical low-frequency matching method, we derive the quasibound state spectrum, the onset condition for scalar cloud formation, and superradiant amplification factor, showing that the
halo parameters $\rho_0 r_0^3$ and $\gamma$ leave characteristic imprints on the scalar spectrum. Increasing the
halo density or the cusp strengthens the binding of quasibound states and enhances their decay, shifts the scalar cloud threshold, and suppresses superradiant amplification effectivity by narrowing the allowed frequency window and lowering the amplification factor peak. Finally, we analyze rotational energy extraction from thermal scalar fields and demonstrate that the efficiency is controlled by the interplay between the thermal spectrum and the superradiant instability, with lower temperatures and less cuspy density profiles yielding more efficient energy extraction.
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Astrophysics of Galaxies
Cosmological Distance Measurements of High Redshift Blazars: OJ 248 (z=0.939) and 4C +38.41 (z=1.814)
Young-Bin Shin, Sang-Sung Lee, Sincheol Kang et al. (+3 more)
In this study, we estimated the angular diameter distances to two high-
redshift active
galactic nuclei (AGNs), OJ 248 (z = 0.939) and 4C +38.41 (z = 1.814), using 43 GHz
radio light curves. The aim of this work is to extend AGN variability-based distance measurement methods to the high-
redshift regime. The distance estimates were analyzed under two assumptions for the maximum intrinsic brightness temperature TB,int: (1) the equipartition temperature, and (2) the sample-averaged TB,int. As a representative result, when adopting the equipartition temperature, the angular diameter distances to OJ 248 and 4C +38.41 are estimated to be 7592.7 +/- 396.7 Mpc and 11069.8 +/- 1216.9 Mpc, respectively. In addition, Doppler factors were calculated using the inverse-Compton method, and additional distance estimates were obtained based on these values. Our error budget analysis shows that the most significant systematic uncertainty arises from epoch selection. These results indicate that systematic effects have a substantial impact on the derived distance estimates and limit their reliability, particularly in the high-
redshift regime. Reducing these uncertainties will require improved observational cadence and reduced post-fit noise. AGN variability provides an alternative approach to distance estimation. However, our results reveal significant limitations in the current methodology and indicate that further methodological and observational improvements are required before its cosmological applicability can be reliably assessed.
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All authors Young-Bin Shin, Sang-Sung Lee, Sincheol Kang, Whee Yeon Cheong, Chanwoo Song, Jeffrey A. Hodgson
Astrophysics of Galaxies
Investigating radio source population and spatial characteristics of diffuse Galactic synchrotron emission in the GAMA-23 field with uGMRT Band-3
Rashmi Sagar, Abhirup Datta and Aishrila Mazumder
We present upgraded
Giant Meterwave
Radio Telescope (uGMRT) Band-3 observations of the
Galaxy and Mass Assembly (GAMA)-23 field. The observations consist of a total of 33 hours spread over 50 pointings, corresponding to $\sim$56 minutes per pointing at the central frequency of 325 MHz. The final image mosaicked from these pointings has a central off-source RMS noise of $109\,\mu\mathrm{Jy}/\mathrm{beam}$ and covers an area $65.31\,\text{deg}^2$ with a resolution of $15.8''$. This wide-area deep-field observation provides a
radio source catalog of 5741 sources with flux densities ${\geq}5{\sigma}$. We present complementary uGMRT observations overlapping with the high-frequency Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe survey. We derived the spectral index from the matched sources in the GAMA-23 field for the first time. We have studied the statistical properties of diffuse
Galactic synchrotron emission (DGSE) in the GAMA-23 field using six different latitude target pointings. We fitted DGSE in the form of power law $C_{\ell} = A(1000/{\ell})^{{\beta}}$. Our DGSE amplitude range of $A = 1-20\,{\text{mK}}^2$ and $\beta$ varies between $1.5$ and $2.4$. This work presents one of the first characterizations of DGSE in the southern sky at 325 MHz, setting a precedent for foreground modeling required for sensitive
radio observations with the upcoming SKA.
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High Energy Astrophysical Phenomena
A broadband outburst of the compact steep-spectrum quasar 3C 138 in 2024-2026
T. V. Mufakharov, Yu. V. Sotnikova, V. V. Vlasyuk et al. (+20 more)
After several decades of relative quiescence, the compact steep-spectrum
quasar 3C 138 entered an active phase in 2024-2026, exhibiting strong broadband flaring. We investigate its multiwavelength behaviour using dense multifrequency
radio monitoring at 1-22 GHz with RATAN-600 and RT-32, optical R-band observations with Zeiss-1000 and AS-500/2, X-ray measurements with Swift/XRT and SRG/ART-XC, and the
Fermi-LAT $\gamma$-ray light curve. The
radio brightening accelerated after 2022 and was strongest at the highest frequencies. The
radio spectra hardened markedly, with the 11-22 GHz spectral index evolving from steep to flat or inverted during the active phase. The X-ray flux increased by more than a factor of three during 2025-2026, while the
photon index hardened from $\Gamma_{\rm X}\simeq 1.6$ to $\Gamma_{\rm X}\simeq 0.9$ and softened back after the peak.
Flare decomposition revealed five $\gamma$-ray
flares and a sequence of optical subflares during the later stages of the activity. The $\gamma$-ray, X-ray, and optical maxima occur within a $\simeq 13$-day interval, suggesting a common activity episode, whereas the
radio brightens more gradually and in a frequency-dependent manner. Under the adopted compact-zone geometries, the sparse two-state spectral energy distributions (SEDs) can be represented by one-zone synchrotron self-Compton (SSC) solutions, while the relative contribution of external Compton (EC) remains geometry dependent. The
flare shifts the modelled energy partition towards relativistic electrons. These results favour a longer-lived, core-dominated activity phase, with later high-energy and optical
flares superposed on the opacity-driven
radio evolution of an emerging synchrotron component.
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All authors T. V. Mufakharov, Yu. V. Sotnikova, V. V. Vlasyuk, S. Yu. Sazonov, M. L. Khabibullina, A. G. Mikhailov, A. B. Pushkarev, T. An, Y. A. Kovalev, Y. Y. Kovalev, A. V. Popkov, M. A. Kharinov, G. S. Uskov, I. Yu. Lapshov, E. V. Filippova, A. Yu. Tkachenko, K. V. Iuzhanina, A. K. Erkenov, R. Yu. Udovitskiy, O. I. Spiridonova, I. A. Rakhimov, T. S. Andreeva, A. A. Ogloblin
High Energy Astrophysical Phenomena
Prospects for characterizing Population III remnants with next-generation gravitational-wave observatories
N. V. Krishnendu, Patricia Schmidt and Geraint Pratten
The most distant gravitational-wave (GW) detection by LIGO, Virgo and KAGRA so far is a binary black hole (BBH) merger at a
redshift of $z\sim 1.1$, corresponding to a luminosity distance of $D_L \sim 8 \, \rm Gpc$. The next-generation GW detectors, the Einstein
Telescope (ET) and
Cosmic Explorer (CE), will detect mergers beyond the peak of
star formation at $z_{\rm peak}\sim 2$, enabling the direct detection of the remnants of the first
stars in the early Universe. Realising this science potential requires accurate inference of the
redshift, sky localization and intrinsic properties of the most distant mergers. In this work, using a fully
Bayesian framework and an astrophysically motivated model, we study Population III remnants with an ET-CE detector network and quantify the measurement uncertainties in
redshift, sky localisation, intrinsic masses and
spins for BBHs at $z \geq 15$. Considering an optimistic ($5\, \rm Hz$) and pessimistic ($10\,\rm Hz$) lower cutoff frequency for the detectors' sensitivity, we show that the $5\, \rm Hz$ configuration consistently improves the
redshift inference for
spin-precessing binaries. We also find that the source-frame component masses can be measured to within $\sim 12\%$ on average, and that the highest-
redshift sources in the population can be reliably characterised. In contrast, we find only modest constraints on the BH
spins. The improved low-frequency sensitivity also extends the
redshift reach of the detector network, enabling events injected at $z_{\rm true}\simeq19.8$ to be confidently identified as originating beyond $z\simeq18.5$ at $90\%$ credibility, compared to a maximum lower-bound
redshift of $z\simeq17.5$ for the $10\,\rm Hz$ configuration. Improved detector sensitivity below $10\, \rm Hz$ also reduces the sky-localisation uncertainties, which are essential for cosmological cross-correlation.
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Astrophysics of Galaxies
Ruffled Feathers: Merger-driven galaxy size growth and structural transformation in EAGLE
Kai Wang, Carlton Baugh, Sownak Bose et al. (+9 more)
Galaxy mergers drive both the size growth and the transformation from discs to spheroids, yet the prescriptions used to model these processes in semi-analytic frameworks have not been tested against the realistic merger population in cosmological hydrodynamical simulations. Using $\approx 4{,}500$ mergers identified in the EAGLE simulation, we test an energy-conservation
estimator for post-merger
galaxy sizes and quantify merger-driven morphological transformation. The predicted remnant half-
stellar-mass radius matches the simulated descendant size with a scatter of $\approx 0.12$-$0.15$ dex and no significant systematic dependence on progenitor properties, while a commonly used dissipation correction applied to gas-rich mergers under-predicts the post-merger size by up to $\approx 0.4$ dex in a cosmological context and increases the overall scatter. The per-merger size growth increases monotonically with the
stellar mass ratio of the merging pair, from $\lesssim 0.03$ dex for minor mergers to $\approx 0.10$ dex for equal-mass mergers. From the energy-conservation
estimator, we analytically derive the size growth efficiency per unit accreted
stellar mass, $\eta \equiv \mathrm{d}\log_{10} r_{\star}/\mathrm{d}\log_{10} M_{\star}$, and show that $\eta$ reaches $\approx 2$ only in the idealised limit of collisionless minor mergers with zero orbital energy; as $\eta$ is highly sensitive to the orbital energy at the time of merging, the minor merger channel cannot be established as the driver of the rapid size growth of massive
galaxies without better constraints on this quantity. Beyond the size growth, mergers systematically reduce rotational support and increase triaxiality in proportion to mass ratio, but even the most nearly equal-mass mergers do not always fully destroy the disc, in tension with the complete disc destruction assumed in several semi-analytic models.
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All authors Kai Wang, Carlton Baugh, Sownak Bose, Shaun Cole, Carlos S. Frenk, Cedric Lacey, Shengdong Lu, Peder Norberg, Isabel Santos-Santos, Francesco Shankar, Tom Theuns, Tao Wang
Solar and Stellar Astrophysics
Photometric Distances for Metal-poor Giants and a Search for Hypervelocity Stars with LAMOST DR13 and Gaia DR3
Shuai Xu, Haibo Yuan, Bowen Huang et al. (+2 more)
Hypervelocity
stars (HVSs) are
stars with velocities high enough to escape the Milky Way, but their identification depends sensitively on distance estimates, particularly for distant
giants. In this work, we search for metal-poor HVS candidates by combining LAMOST DR13 spectroscopy with
Gaia DR3 astrometry. We calibrate a
metallicity-dependent color–absolute-magnitude relation for normal metal-poor
giants using a high-quality reference sample, and apply it to derive photometric distances for 41{,}331
stars. The relation reproduces the reference absolute magnitudes with a scatter of 0.24\,mag, corresponding to an intrinsic distance uncertainty of $\sim$9.7%. Combining these distances with
Gaia proper motions and LAMOST radial velocities, we identify 13 initially unbound candidates under the
Galactic potential from \citet{McMillan2017}. Spectral inspection indicates that several are chromospherically active binaries or other non-standard systems for which a
giant-
star calibration is unreliable; removing these contaminants leaves nine metal-poor HVS candidates. Backward orbit integrations suggest that one candidate is most consistent with a disk origin, while three have trajectories suggestive of an association with the Sagittarius stream.
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All authors Shuai Xu, Haibo Yuan, Bowen Huang, Xiao Kai, Wuming Yang
High Energy Astrophysical Phenomena
GeV {\gamma}-ray emission in the star-forming region S140
Li-Nuo Yang and Pak-Hin Thomas Tam
We report the detection of a GeV {\gamma}-ray source in the S140 HII region using 17.75 years of
Fermi-LAT data, with a source-detection significance of ~32.1{\sigma} in the 0.1-500 GeV energy band. The emission is significantly extended (AIC evidence ratio above 1 GeV is 2x10^9) and is therefore designated as 4FGL J2220.8+6319e. The {\gamma}-ray emission coincides spatially with a molecular cloud that hosts the massive young
stellar object S140 IRS1. Its spectrum is best fitted by a log-
parabolic spectrum (TS_cur(LP) = 104.1) and can be reproduced by both hadronic and leptonic models. The jet driven by S140 IRS1 offers a viable particle acceleration site, yielding injection timescales and maximum particle energies consistent with theoretical expectations, whereas
stellar winds are energetically disfavored.
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Instrumentation and Methods for Astrophysics
GRAVITY+: reducing non-common-path aberrations for sub-10 {\mu}as astrometric accuracy
Quentin Fournier, Guillaume Bourdarot, Frank Eisenhauer et al. (+26 more)
GRAVITY is a state-of-the-art instrument for near-infrared astrometric interferometry that routinely achieves astrometric accuracy of 30-100 microarcsecond in its phase-referenced dual-field mode. However, its fundamental limit is not yet reached, and can still be improved by several factors. In this paper, we focus on the effect of systematics, and in particular the effect of non-common path aberrations between the science channel and the metrology signal in the
GRAVITY Fiber Coupler. Through comprehensive laboratory measurements using a dedicated fiber coupler replica and phase-shifting interferometry at 1908 nm, we have characterized these high-order wavefront errors with nanometer precision in the laboratory. We characterized on-sky the effect of these high-order wavefront imperfections on narrow-angle astrometry, using observations of the binary system GJ65. As part of the
GRAVITY+ project, high-precision mirrors designed for nanometer-level surface quality, bringing an order of magnitude improvement over existing
GRAVITY injection optics, are currently in production and will be installed in the fiber coupler units by the end of 2027. This upgrade is expected to enable astrometric accuracy at the sub-10 microarcsecond level in dual-field mode with integration times of just a few minutes.
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All authors Quentin Fournier, Guillaume Bourdarot, Frank Eisenhauer, Helmut Feuchtgruber, Dieter Lutz, Etienne Rosin, Stefan Gillessen, Reinhard Genzel, Taro Shimizu, Oliver Pfuhl, Felix Mang, Michael Hartl, Thomas Ott, Ekkehard Wieprecht, Vishaal Gopinath, Françoise Delplancke-Stroebele, Luis Esteras Otal, Felix Widmann, Sebastiano von Fellenberg, Pierre Bourget, Guy Perrin, Julien Woillez, Paulo Garcia, Sebastian Hönig, Laura Kreidberg, Jean-Baptiste Le Bouquin, Thibaut Paumard, Christian Straubmeier, for the GRAVITY+ Collaboration
High Energy Astrophysical Phenomena
Kinematically Resolving the Fe K Complex in Her X-1: The Accretion Disk and Ionized Wind Across X-ray Eclipses
Koh Sakamoto, Teruaki Enoto, Peter Kosec et al. (+8 more)
We present XRISM/Resolve spectroscopy of Her X-1 across three X-ray eclipses observed in September 2024, resolving its iron K complex through the ingress, mid-eclipse, and egress phases. The 5 eV high energy resolution of Resolve enabled us to disentangle and detect all primary components of the iron K complex: neutral iron fluorescence (Fe K$\alpha$ and K$\beta$), highly ionized emission lines (Fe XXV He$\alpha$ and Fe XXVI Ly$\alpha$). The neutral Fe K$\alpha$ emission is not significantly detected during mid-eclipse, indicating a compact origin near the
neutron star. At ingress and egress, the line centroid exhibits red- and blue-shifts of $\sim 200$ km s$^{-1}$ after correcting for the systemic velocity and the
neutron star's orbital motion. This residual shift corresponds to Keplerian rotation at a characteristic radius of $r_{\rm disk} \sim 6.6\times10^{6}$ km, suggesting an association with the outer
accretion disk. In contrast, the highly ionized Fe XXV He$\alpha$ and Fe XXVI Ly$\alpha$ lines remain visible during eclipses, indicating an extended origin. Photoionization modeling (SPEX pion model) yields $\log_{10}(\xi/{\rm erg\,cm\,s^{-1}}) \sim 3.4$ and $N_{\rm H} \sim 3.1\times10^{22}$ cm$^{-2}$ consistent with the ionized disk wind of Her X-1. Flux-ratio diagnostics constrain the
geometric inner boundary of the clumpy disk wind to $R_{\rm in} = 3^{+5}_{-2} \times 10^{10}$ cm ($1\sigma$), consistent with the Compton-heated thermal winds. The inferred mass
outflow rate is $\dot{M}_{\rm out} \approx 3.2 \times 10^{-9}\,M_{\odot}$ yr$^{-1}$ (half the supplied mass), consistent with absorption line measurements of the disk wind obtained out of eclipse.
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All authors Koh Sakamoto, Teruaki Enoto, Peter Kosec, Takeshi GO Tsuru, Takuto Narita, Daijiro Hitotsuyanagi, Laura Brenneman, Ruediger Staubert, Jon M. Miller, Andrew Fabian, Daniele Rogantini
Solar and Stellar Astrophysics
Identification of a superbright nova in our Galaxy: revisiting the light curve analyses of the candidate novae CP Lac, CP Pup, V838 Her, V597 Pup, V5583 Sgr, and V5589 Sgr
Izumi Hachisu and Mariko Kato
The two very fast novae in our
Galaxy, V1500 Cyg and V1674 Her, reached the absolute $V$ magnitude of $M_{V,\rm max}\approx -10.4$. These brightest novae are identified as superbright novae. Such superbrightnesses are realized if an optically thick shocked shell forms far outside the nova (white
dwarf) photosphere and expands at the velocity of a few thousands km s$^{-1}$. We have analyzed $V$ light curves of six candidates novae, CP Lac, CP Pup, V838 Her, V597 Pup, V5583 Sgr, and V5589 Sgr by comparing with our model nova light curves of 1.25 $M_\odot$ and 1.35 $M_\odot$ white
dwarfs calculated with the free-free emission from a nova wind. Analyzing the data with our method, we obtain $M_{V, \rm max}=-10$ for V838 Her, and we suggest that its large peak optical luminosity is due to the ejection of an optically thick shell like we suggested for the case of V1674 Her. The light curves of the other five novae, CP Lac, CP Pup, V597 Pup, V5583 Sgr, and V5589 Sgr are reproduced only with the free-free emission model $V$ light curves without an optically thick shocked shell. Their $M_{V,\rm max}$ are fainter than $-10$ mag. We conclude that these five are not superbright novae.
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Earth and Planetary Astrophysics
Dust transport in envelopes of disk-embedded planets: II. Fully convective envelopes
Ayumu Kuwahara and Michiel Lambrechts
We perform 3D multifluid simulations of gas and
dust to quantify how convection reshapes the spatial distribution of
dust grains inside the envelopes of disk-embedded
planets. Building on the first paper of this series, which explored convectively stable envelopes, we here consider envelopes in which convection is sustained by the
accretion luminosity. The
dust-to-gas ratio inside the planetary envelope is set primarily by the degree of dynamical isolation from the surrounding disk. When convection extends beyond the Bondi radius, the envelope remains connected to the disk flow and maintains a
dust-rich state through continuous material exchange. Conversely, when an inner convective layer is separated from an outer recycling layer, the recycling flow filters incoming solids. The
dust distribution inside the convective layer is then controlled by the competition between convective stirring and gravitational settling. This yields two regimes: a settling-dominated regime, in which large grains (typically $s\gtrsim0.1$ cm) fall at the terminal velocity and the envelope becomes
dust depleted, and a convection-dominated regime, in which smaller grains are trapped in convective circulation and the envelope retains its
dust. The delivery and release of volatile species from accreting solids at the envelope sublimation front, together with the efficiency of convective mixing, determine how this material is distributed between the core and envelope. Our findings imply that super-Earths and mini-Neptunes inside the water snowline have volatile-depleted cores and volatile-rich envelopes, while
planets at wider orbits can have a wide diversity of envelope compositions from depleted to enriched. This compositional diversity for planetary envelopes appears to be consistent with the large diversity in observed atmospheric compositions of mini-Neptunes.
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Earth and Planetary Astrophysics
Dust transport in envelopes of disk-embedded planets: I. Convectively stable envelopes
Ayumu Kuwahara and Michiel Lambrechts
Planets embedded in protoplanetary disks accrete solids through their gaseous envelopes. The spatial distribution of these
dust particles inside the envelopes of disk-embedded
planets is poorly known. We present high-resolution two- and three-dimensional multifluid simulations that follow the dynamics of gas and
dust around
planets similar in mass to Earth. Our simulations resolve an outer recycling flow and an inner convectively stable envelope that is shielded from the recycling flow. We identify strongly
dust-depleted envelopes: the
dust-to-gas ratio decreases radially inward and is reduced by more than two to four orders of magnitude in the deep interior ($<0.1\,R_{\rm B}$; Bondi radius) compared to its value at the outer edge of the envelope. Small grains, with a dimensionless stopping time ${\rm St}\lesssim10^{-3}$, remain entrained in the recycling flow and do not enter the envelope, whereas large grains (${\rm St}\gtrsim10^{-2}$) penetrate the envelope but settle rapidly onto the core along the midplane. The resulting
dust depletion in convectively-stable envelopes implies a substantial reduction in
dust opacity throughout much of the envelope, facilitating cooling and a more rapid transition to runaway gas
accretion. These results further suggest that enriching the deep envelope ($<0.1\,R_{\rm B}$) with
dust or volatiles requires their delivery through large pebbles that then subsequently disintegrate, or sublimate, from their host grains in the deep envelope interior.
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Astrophysics of Galaxies
An ALMA study of hub-filament systems II.Quiescent filaments converging towards highly dynamic hubs
Michael Anderson, Nicolas Peretto, Sarah E. Ragan et al. (+7 more)
Hub-filament systems are networks of converging interstellar filaments, often with active
star formation at their centres, that may play an important role in high-mass
star formation. In the first paper of this series, we found that the mass fraction that ends up in a clump's most massive core is significantly higher in IR-dark hubs than in IR-bright clumps, suggesting that the most-massive cores form early on. Such early massive core formation requires large inflow rates and dynamically active IR-dark clumps. We now present N$_2$H$^+$(J=1-0) observations of six IR-dark hub-filament systems mapped with ALMA 12m, 7m, and total power at 3” resolution, to trace the kinematics of the dense gas. The data show intricate emission structures and complex spectra. To characterise their kinematics, we have developed mwydyn, a fully-automated, multiple velocity component, hyperfine line-fitting code. Our results reveal that the emission invariably consists of quiescent individual filaments in the outskirts that converge towards the hub centres where a systematic increase in velocity dispersion and number of components is observed. We also find that the distribution of centroid velocities is remarkably similar between clumps, despite spanning more than one order of magnitude in mass. We propose that our results are best explained by the mixing of gravitationally-driven multi-directional inflows, resulting in highly complex and dynamic hub centres. We also discuss the implications of the observed differentiated filament and hub gas kinematics in the context of the 3D morphology of hub-filament systems.
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All authors Michael Anderson, Nicolas Peretto, Sarah E. Ragan, Andrew J. Rigby, Adam Avison, Ana Duarte-Cabral, Gary A. Fuller, Yancy L. Shirley, Alessio Traficante, Gwenllian M. Williams
Solar and Stellar Astrophysics
Reconnection Jets Detected during the Footpoint Drift of a CME Flux Rope: New Signatures of Ongoing 3D Arcade-Flux Rope Reconnection
Renjie Liu, Hechao Chen and Chun Xia
Utilizing multi-wavelength data from the
Solar Dynamics Observatory, we report the first imaging detection of reconnection jets driven by the footpoint drift of an erupting hot-channel flux rope (HFR) during an X1.6-class
solar flare. Our results demonstrate that these jets are inherent byproducts of the HFR eruption, exhibiting strong spatiotemporal coupling with the HFR footpoint drift and the morphological
evolution of the associated
flare ribbon hooks. Unlike standard coronal jets, these ejections lack an inverted-Y morphology and show no association with underlying photospheric flux cancellation or emergence. They manifest as clusters of small-scale, collimated ejecta (180-200 km s$^{-1}$) featuring co-existing cool and hot emission components visible in both cool (304 and 171 Angstrom) and hot (94 Angstrom) EUV channels. The imaging observations reveal that these jets are triggered by successive 3D arcade-flux rope (ar-rf) reconnection as the expanding HFR interacts with the ambient coronal side arcades. The morphological and dynamic complexity of these observed jets implies that the ongoing ar-rf reconnection in
solar eruptions is episodic and bursty in nature. Our estimates show that a decrease of approximately 9 G in localized
magnetic field strength is required to power these individual jets. As direct signatures of 3D
magnetic reconnection, these observed jets pinpoint the exact site and characterize the nature of the process, providing new observational insight into 3D numerical simulation extensions of the standard
flare model. Further observational case studies of these jets are required to fully understand their prevalence across
solar eruptions.
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Solar and Stellar Astrophysics
New Statistical Topology Theory Predicts Turbulent Magnetic Emergence from the Sun's Interior
Anda Xiong, Hongyan Li, Shangbin Yang et al. (+6 more)
We propose and verify a new statistical
topology framework to study the complex
magnetic field
evolution of Sun-like
stars. The Sun, as the
star we are most familiar with, exhibits chaotic behaviors such as
solar flares and mass ejections that are crucial to the Earth. While these phenomena are mainly driven by the
magnetic field, it has been challenging to understand the complex
magnetic field. In this paper, we propose a new model to understand the helicity behavior of
magnetic loops before their emergence from the interior by advancing the loop ensemble theory from statistical physics. We derive several new power-law scalings that are essential to the Sun's
magnetic field, including
magnetic flux,
magnetic helicity, and linking number. We examine our prediction by a large data analysis through long-term continuous observation over 32 yr. These results not only provide evidence for the new statistical
topology framework but also systematically explain the intrinsic unpredictability on the emergence of extreme
solar activities. This new discovery on the critical structure of loop ensemble can also be applied to a wide range of
turbulence systems.
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All authors Anda Xiong, Hongyan Li, Shangbin Yang, Haiqing Xu, Quan Wang, Haisheng Ji, Xin Liu, Yuanyong Deng, Hongqi Zhang
Astrophysics of Galaxies · Cross-listed from physics.chem-ph
X-ray Driven Trihydrogen Formation on Silica Nanosurfaces
Samuel Sahel-Schackis, Adam Summers, Ritika Dagar et al. (+29 more)
The trihydrogen cation ($\mathrm{H_3^+}$) initiates the ion-molecule reactions that build molecular complexity in interstellar space. Whether its canonical formation reaction, $\mathrm{H_2^+ + H_2 \rightarrow H_3^+ + H}$, proceeds on inorganic surfaces under radiation-driven ionization has remained untested. Here we drive $\mathrm{H_3^+}$ formation on hydrated silica nanoparticles using intense 1.88 keV X-ray pulses, combining ion velocity map imaging, electron time-of-flight spectroscopy, and single-particle coherent diffractive imaging to resolve this chemistry on individual particles. The self-induced surface electric field on the V/nm scale drives interfacial charge transfer and water fragmentation. This field is the dominant parameter governing the relative yields of $\mathrm{H^+}$, $\mathrm{H_2^+}$, and $\mathrm{H_3^+}$ across particle size, composition, and aggregation. Density functional theory and nonadiabatic
quantum molecular dynamics simulations trace this field-driven charge transfer, directly analogous to band bending at
semiconductor photoelectrodes. These results establish surface-field-driven charge transfer as a unifying mechanism between radiation dominated astrophysical environments and field-driven surface catalysis.
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All authors Samuel Sahel-Schackis, Adam Summers, Ritika Dagar, Alexandra Feinberg, Martin Grassl, Simon Dold, Rebecca Boll, Yevheniy Ovcharenko, Chris Aikens, Cesar Costa Vera, Alberto De Fanis, Avijit Duley, Felix Gerke, Daniel Jost, Regina Leiner, Michael Meyer, Ilana J. P. Molesky, Razib Obaid, Jeffrey Powell, Nils Rennhack, Björn Senfftleben, Hendrik Tackenberg, Paul Tuemmler, Sergey Usenko, Christian Peltz, Thomas Fennel, Markus Gallei, Eckart Rühl, Artem Rudenko, Daniel Rolles, Thomas Linker, Matthias F. Kling
High Energy Astrophysical Phenomena
Influence of effective mass of the relativistic mean field theory on core collapse supernovae and compact objects
Kohsuke Sumiyoshi, Hajime Togashi, Shun Furusawa et al. (+4 more)
We study the influence of the effective mass in the relativistic mean field (RMF) theory on the properties of the central core of collapse-driven
supernovae and the formation of compact objects. Influence of the effective mass has been so far studied within the non-relativistic frameworks. In order to clarify the role of the effective mass in the relativistic frameworks, which is different from non-relativistic ones, we adopt the set of equation of state (EOS) tables using the parameterizations TM1e and TM1m, which have different effective masses but with the same saturation properties, in the RMF theory. We show that choices of the effective mass in
supernova matter affect both the stiffness of the EOS through pressure and the thermodynamical behavior through temperature under the RMF frameworks. We explore differences in matter
evolution with
neutrino emissions by performing a set of numerical simulations of the gravitational collapse and bounce of massive
stars and the cooling of the proto-
neutron stars. The EOS with large effective mass leads to compact proto-
neutron stars and early collapse to black holes with high densities and temperatures due to the softness. It leads to high energy
neutrinos in long emission from the proto-
neutron star cooling and in short burst from the black hole formation.
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All authors Kohsuke Sumiyoshi, Hajime Togashi, Shun Furusawa, Shuying Li, Hong Shen, Ken'ichiro Nakazato, Hideyuki Suzuki
Solar and Stellar Astrophysics
Distribution of magnetic helicity and energy with height in solar atmosphere
Hongyan Li, Shangbin Yang, Haiqing Xu et al. (+3 more)
Magnetic helicity and
magnetic energy are key to understanding the
solar dynamo and eruptions, and their three-dimensional distributions are of great significance. However, how these quantities vary with height remains poorly understood. Moreover, because the three-dimensional distribution depends on
magnetic field extrapolation, determining the optimal extrapolation height from physical rather than empirical criteria remains an open problem. To address this issue, this work investigates the vertical distributions of
magnetic helicity and
magnetic energy in the
solar corona within active regions. We analyze 150 active regions observed by the
Solar Magnetic Field
Telescope (SMFT) from 1988 to 2019, grouped by absolute
magnetic flux, perform nonlinear force-free field (NLFFF) extrapolations, and compute the relative
magnetic helicity with a finite volume method. It is found that an extrapolation height of at least 81 Mm retains 97% of the total
magnetic helicity and energy while reducing computational costs by approximately 38% under the adopted configuration. This work provides important parameter constraints for the long-term statistical study of
magnetic helicity in
solar active regions.
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All authors Hongyan Li, Shangbin Yang, Haiqing Xu, Quan Wang, Anda Xiong, PeiXin Luo
Instrumentation and Methods for Astrophysics
MARS: A Lightweight Morphology-Aware RFI Segmentation Network for Mask-Guided Mitigation in Radio Astronomy
Zhaocheng Gong, Jack White, Jayanta Roy et al. (+1 more)
Next-generation
radio telescopes generate filterbank data at rates that make storing all observations for later offline mitigation impractical. Mitigation must therefore operate in real or near-real time within the search pipeline while preserving dispersed astrophysical signals. CPU tools fit GPU-centred search pipelines poorly, while neural alternatives can be computationally heavy. We present MARS, a GPU-based RFI mitigation pipeline centred on a lightweight Morphology-Aware RFI
Segmentation Network. The model is a reduced-width, full-resolution U-Net with a bottleneck containing local, horizontal, and vertical filters to capture compact and elongated RFI structures in the frequency-time plane. Normalisation, patch construction, mask reconstruction, replacement, baseline removal, and output rescaling are also implemented on GPU. Training includes an astronomical-signal preservation loss that discourages false flagging of dispersed pulses. In controlled patch-level tests, MARS achieves an RFI-mask F1 score of $0.978$ and a precision of $0.995$. It retains $97.6\%$ of the injected dispersed-signal fluence in clean patches and $96.4\%$ of the non-overlapping signal fluence in patches containing mixed injected RFI. Ablation experiments show that the astronomical-signal preservation loss particularly improves the protection of compact, low-DM, high-S/N pulses. At filterbank level, period-matched PRESTO candidates recovered after MARS mitigation have median significance ratios of $0.90$–$0.99$ relative to filtool. Both methods also recover the known
pulsars in two real GMRT observations. On an NVIDIA GH200 GPU, MARS achieves a compute-only speedup of $6.2\times$–$7.0\times$ over the fastest tested multi-threaded filtool configurations on an AMD EPYC 9825 CPU.
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All authors Zhaocheng Gong, Jack White, Jayanta Roy, Wesley Armour
High Energy Astrophysical Phenomena
No evidence for a supermassive black hole binary in GSN 069
Yuhe Zeng, Zhen Pan, Bin Liu et al. (+1 more)
Quasi-periodic eruptions (QPEs) are recurrent soft X-ray
flares from
galactic nuclei and provide a new time-domain probe of
stellar-mass objects (SMOs) orbiting supermassive black holes (SMBHs). In an extreme-mass-ratio inspiral (EMRI) system interacting with an
accretion disk, QPEs are produced when the SMO repeatedly crosses an
accretion disk, so that the eruption times trace the orbital motion of the EMRI. We investigate whether such timing information can be used to probe a more distant SMBH companion. We develop two complementary diagnostics: (1) the motion of the EMRI host SMBH around the SMBH-binary (SMBHB) center of mass induces a light-travel-time modulation in the observed QPE arrival times, specifically an in-phase modulation in arrival times of even and odd eruptions; (2) if the QPE source contains a surviving
stellar orbiter, the external SMBH must not drive the SMO into
tidal disruption through eccentricity excitation by the von Zeipel–Lidov–Kozai (ZLK) mechanism. Using GSN 069 as an example, we find no in-phase modulation in the QPE timing (i.e., no evidence for a SMBHB) and constrain the excluded parameter space of the companion SMBH. These results demonstrate that QPE timing and
stellar survival offer complementary routes for constraining otherwise hidden SMBH companions in nearby
galactic nuclei.
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All authors Yuhe Zeng, Zhen Pan, Bin Liu, Cong Zhou
High Energy Astrophysical Phenomena
A Roadmap for Transient Hunters: Mapping Stellar Mass and Star Formation Rate Anisotropies in the Local Universe
Ye-Hao Cheng, Yuan-Pei Yang and Ye Li
Over the past few decades, an increasing number of transients in nearby
galaxies have been discovered through various survey projects. Unlike astrophysical phenomena at cosmological distances, transients in the local universe exhibit a pronounced anisotropy in their sky distribution. Consequently, adopting an appropriate survey strategy is essential to improve the efficiency of transient searches in the local universe. In this work, we utilized a large
galaxy catalog to map the sky distributions of
stellar mass and
star formation rate (SFR) across different luminosity distance thresholds and angular resolutions of the grid on the celestial sphere. These maps can further serve to characterize the anisotropic spatial distribution of nearby extragalactic transients. For different angular resolutions of the celestial sphere, we find that the sky distributions of
stellar mass of
galaxies are similar to those of the SFR in the main anisotropic structures. As the luminosity distance threshold increases, the anisotropic structures of the sky distributions become more isotropic. We calculate the angular power spectra and fluctuations of the sky distribution of
stellar mass and SFR at a given angular resolution and find that the angular power spectra and fluctuations decrease rapidly as the luminosity distance threshold increases. Finally, by qualitatively comparing the sky distribution of core-collapse
supernovae with our SFR sky distribution, we find that the two exhibit consistent patterns in several prominent structures. The mapped sky distributions of
stellar mass and SFR can serve as valuable references for future surveys in searching for extragalactic transients.
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Cosmology and Nongalactic Astrophysics
photo-3x2-pt: Cosmology from cosmic shear and galaxy clustering with a single photometric galaxy catalog
Takashi Hamana
We perform a joint cosmological analysis using angular power spectra of
galaxy clustering,
galaxy-shear cross correlation, and
cosmic shear (hereafter referred to as photo-3x2-pt) measured from the Hyper Suprime-Cam year-3 (HSC-Y3) weak
lensing shape catalog. We employ the pseudo-$C_\ell$ method to measure these power spectra and use the template deprojection method to mitigate systematics in the
galaxy density maps. We perform a standard
Bayesian likelihood analysis for cosmological inference based on the measured photo-3x2-pt, including contributions from intrinsic
alignments of
galaxies,
galaxy clustering bias,
lensing magnification effect, baryonic feedback effect, and source
redshift distribution errors. For a flat cold dark matter model, we find a 68% credible interval of $0.76 \le S_8 \le 0.81$. This result is consistent with those of the HSC-Y3
cosmic shear analyses (Dalal et al. 2023, Li et al. 2023), but is $\sim 25$% tighter than theirs. We also perform a performance test using mock catalogs that mimic the HSC-Y3 data to validate our photo-3x2-pt analysis. Through
Bayesian parameter inference of mock data, we verify that unbiased estimates can be obtained for the key cosmological and nuisance parameters, including $S_8$, model parameters of intrinsic
alignment,
galaxy clustering bias, and shift parameters of the source
redshift distributions.
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Solar and Stellar Astrophysics
Hot molecular cores in the W49A molecular cloud complex
Ryosuke Miyawaki, Masahiko Hayashi and Tetsuo Hasegawa
We present a comprehensive
dataset of hot molecular cores (HMCs) in the W49A molecular cloud complex based on high-resolution ALMA observations, including the 1.3~mm continuum, 12 molecular lines, and the H30alpha recombination line. In total, 18 HMCs are identified in the CH$_{3}$CN ($J_K=12_3-11_3$) map, together with 20 continuum sources in the 1.3~mm map. Ten HMCs have peaks coincident within 0\farcs1 of the 1.3~mm continuum peaks, indicating that thermal
dust emission dominates the 1.3~mm emission for these sources. Correlation analyses of the line luminosities suggest a common structural picture for HMCs, in which five distinct regions with different physical and chemical properties coexist: hot and dense gas (CH$_3$CN, HC$_3$N, HNCO, OCS, H$_2$CO),
outflow gas (SiO, SO), envelope gas (SO$_2$, CH$_3$OH), extended gas ($^{13}$CS, DCN, C$^{18}$O), and ionized gas (H30alpha). We find an empirical relation $X(\mathrm{CH_3CN})=2.5\times10^{-7}\exp[-490/T_\mathrm{rot}]$ between the fractional abundance and rotation temperature of CH$_{3}$CN, suggesting that $T\gtrsim200$–300~K is required to achieve high abundances of $\sim10^{-7}$. We find that HMCs without embedded H/UCHII regions are more numerous than, or at least comparable in number to, HMCs with such regions, suggesting that the former may have longer lifetimes ($\sim$10$^{5}$~yr) than the latter ($\sim$10$^{4}$~yr). We discuss the implications of these results for the core
accretion and competitive
accretion models.
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Earth and Planetary Astrophysics
Beyond Point Masses. VI. Spin-Orbit Evolution of the Centaur Binary Typhon-Echidna
Benjamin Proudfoot, Will Grundy and Darin Ragozzine
Only three binaries have been identified among the Centaur population. Because their perihelia are significantly closer than those of other trans-Neptunian binaries (TNBs), these systems allow a detailed look at tight binaries in the broader TNO population and provide critical insight into the disruption of binaries as they enter the Centaur population. Using recent and archival Hubble Space
Telescope (HST) observations, along with Keck data, we present a
spin-orbit study of Typhon-Echidna. We find that the binary's mutual orbit is inconsistent with a Keplerian orbit; more detailed non-Keplerian fits show that the mutual orbit is rapidly precessing. We measure Typhon's dynamical oblateness, $J_2$, at $\sim10\sigma$ confidence and find that Typhon's rotation pole is $\gtrsim20^\circ$ misaligned with the binary's mutual orbit. Assuming Typhon has a triaxial shape, our results, combined with rotational light curves and thermal measurements from the literature, suggest ellipsoidal semi-axes of $a=93^{+8}_{-6}$ km, $b=84^{+6}_{-6}$ km, and $c=65^{+9}_{-8}$ km. We further investigate the observational consequences of the complex
spin-orbit dynamics, including light curve alteration by axial precession of Typhon and substantial changes to the system's mutual event season. Based on the system's dynamically excited state, we suggest a recent encounter with a
giant planet may have substantially altered the system, potentially consistent with a binary in an early stage of disruption. This hypothesis can be tested with resolved photometric observations of the system. Our investigation highlights how non-Keplerian dynamics enhances our understanding of TNB systems and motivates ongoing observations of TNBs with astrometry, photometry, and
stellar occultations.
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Cosmology and Nongalactic Astrophysics
A Gaussian Covariance Matrix for Joint Pre- and Post-Reconstruction Full-Shape Power Spectrum Analysis
Yuting Wang, Ruiyang Zhao, Gong-Bo Zhao et al. (+1 more)
We apply the Gaussian covariance formalism to develop a semi-analytical covariance model for the joint analysis of pre-reconstruction, post-reconstruction, and cross full-shape
galaxy power spectra. We model the reconstruction-reduced, scale-dependent cross shot noise using displacement-field statistics and introduce a new
estimator that directly measures this term. Using the measured power spectra and the modeled shot-noise predictions as inputs, we construct the Gaussian covariance while accounting for correlations between the pre- and post-reconstruction density fields. We validate the resulting semi-analytical Gaussian covariance against mock catalogues. Using emulator-based parameter inference, we demonstrate that the semi-analytical Gaussian covariance adequately captures the dominant contribution to the covariance structure of the full data vector ($P_{\ell}^{\rm pre}, P_{\ell}^{\rm post}, P_{\ell}^{\rm cross}$). For the joint fit to these three power spectra, it yields cosmological constraints consistent with those obtained using the mock-based numerical covariance over the adopted fitting ranges: $k_{\rm max}=0.18\,h\,{\rm Mpc}^{-1}$ for $P_{\rm pre}$ and $P_{\rm post}$, and $k_{\rm max}=0.12\,h\,{\rm Mpc}^{-1}$ for $P_{\rm cross}$.
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All authors Yuting Wang, Ruiyang Zhao, Gong-Bo Zhao, Kazuya Koyama