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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 10 March

Astrophysics of Galaxies

Obscured Star Formation in the Dwarf Galaxy DDO 43? A Comparative UV-IR Analysis

Áron Juhász and Enikő Pichler

We present a study of recent star formation in the dwarf irregular galaxy DDO 43 using GALEX FUV and WISE NIR imaging. We identify regions of elevated FUV flux, indicating unobscured star-forming activity across much of the galaxy. To further characterize the stellar content, we compare the FUV fluxes to archival WISE W1 and W2 infrared data across 56 regions of interest. A general correlation is found between the FUV and infrared fluxes, suggesting spatially coherent star formation throughout the galaxy. A few regions, however, show elevated infrared fluxes but little or no UV emission, potentially indicating localized, dust-obscured star formation.
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Solar and Stellar Astrophysics

Characterizing the 3D evolution of two successive CMEs heading for Mercury

Yanjie Zhang, Qingmin Zhang, Huadong Chen et al. (+3 more)

We studied two successive coronal mass ejections (CMEs) that erupted from the same active region (AR 12994) on 2022 April 15 and propagated toward Mercury. Using multi-view observations, we applied the revised cone model to determine the three-dimensional geometry and the early kinematics of the two CMEs. Our best fit parameters indicate large angular extents of 84 and 86 and propagation directions of 119.0 and 110.4 (measured from the Sun Earth line) for CME1 and CME2, respectively, while that of Mercury is 120.1. The derived axis inclinations are 28 for CME1 and 21 for CME2, consistent with the orientation of the erupting flux ropes in the source region. Height time analysis indicates approximately uniform motion speeds of 636 for CME1 and 696 for CME2, respectively. This paper provides valuable insights for predicting the impact of CMEs heading for Mercury as well as other solar planets in the future.
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All authors Yanjie Zhang, Qingmin Zhang, Huadong Chen, Zhentong Li, Dong Li, Haisheng Ji

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

Circumstellar Medium of Supernovae as New Probes for Feebly Interacting Particles

Yu Cheng, Chui-Fan Kong, Yen-Hsun Lin et al. (+2 more)

We propose a novel strategy to probe feebly interacting particles (FIPs) by exploiting the dense, confined circumstellar medium (CSM) surrounding core-collapse supernovae. FIPs produced in the protoneutron star can deposit substantial visible energy into the CSM via decay prior to the shock breakout from the progenitor star. This energy injection heats and ionizes the CSM, establishing an FIP-induced photosphere that generates distinctive precursor blackbody emission. Using early-time observations of supernova 2023ixf, we translate the nondetection of excessive precursor luminosity into stringent new constraints on MeV-scale dark photons as an exemplary model. Our results significantly extend existing core-collapse supernova bounds and exclude previously unexplored regions of parameter space. We further demonstrate that the FIP-induced dust sublimation offers key diagnostics for future Galactic supernovae, opening a new avenue to explore the dark sector.
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All authors Yu Cheng, Chui-Fan Kong, Yen-Hsun Lin, Meng-Ru Wu, Seokhoon Yun

High Energy Astrophysical Phenomena

The period clustering of magnetars and X-ray dim isolated neutron stars

Kaz{\i}m Yavuz Ekşi

The spin periods of magnetars and X-ray dim isolated neutron stars (XDINS) cluster within a remarkably narrow range. Using the current sample of 30 magnetars with measured periods (ranging from 0.33 to 11.78 s) and 8 XDINS (ranging from 3.45 to 12.76 s), we utilize the point-likelihood technique to constrain the birth and final periods of these sources, assuming a steady-state population. Employing a general braking law characterized by a constant braking index $n$, we find that for $n > 2$ the final (cut-off) period of magnetars is constrained to $P_f \simeq 11.8 - 12.0$ s and XDINS to $P_f \simeq 12.8 - 14.9$ s, at the 95 per cent confidence level, while the birth periods remains largely unconstrained for dipole spin-down ($n=3$) as in earlier work. The slight increase in the upper cutoff from $\sim$12 to $\sim$15 s over two decades of discoveries of new sources, yielding a threefold increase in the known magnetar population, and the extension of the minimum period to $\sim 0.33$ s strongly support a physical origin for this clustering. We discuss this result in the context of magnetic-field-decay models and fallback-disc torque-equilibrium scenarios. The combined magnetar and XDINS sample (38 sources) yields the tightest constraints on $P_f\simeq 12.8-12.9$ s, for $n=3$, suggesting possible evolutionary connections between these populations and pointing toward a common physical mechanism that terminates the observable phase of these neutron stars at periods near 14 s.
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High Energy Astrophysical Phenomena

CubeSats Reach the Millisecond X-Ray Domain: Crab Pulsar Timing with SpIRIT/HERMES

Wladimiro Leone, R. Mearns, T. Di Salvo et al. (+70 more)

The High Energy Rapid Modular Ensemble of Satellites (HERMES) instrument is a compact X/$\gamma$-ray spectrometer operating on board the 6U (11 kg) SpIRIT CubeSat. The payload is particularly well suited for the observation of cosmic transients such as Gamma-Ray Bursts and bright pulsars thanks to its unique broadband sensitivity from a few keV to a few MeV and the temporal resolution down to half a microsecond. We report here the detection of the $\sim$33~ms Crab pulsar double-peaked pulse profile obtained by considering the canonical Crab ephemerides as provided by the Jodrell Bank catalog. We collected approximately 5.7$\cdot$10$^4$ photons from 730~s of observations, in the 3 keV – 2 MeV energy band, during a single operation, and achieved a 5$\sigma$ pulse profile significance in the 3–11.5 keV energy band with binning at the ms scale. The results demonstrate that SpIRIT/HERMES can achieve millisecond timing accuracy at high energies and, thanks to its wide field of view and broad energy band, has the potential to contribute to GRB monitoring in the near future. Such capabilities were previously the domain of flagship observatories, underscoring the performance of the HERMES instrument with its compact form factor.
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All authors Wladimiro Leone, R. Mearns, T. Di Salvo, L. Burderi, M. Thomas, M. Trenti, F. Fiore, E. J. Marchesini, R. Campana, G. Baroni, M. Dafcikova, A. Anitra, Y. Evangelista, A. Sanna, S. Puccetti, R. Iaria, S. Barraclough, M. Ortiz del Castillo, R. Bertacin, P. Bellutti, G. Bertuccio, A. Chapman, G. Cabras, F. Ceraudo, T. Chen, M. Citossi, R. Crupi, G. Della Casa, E. Demenev, G. Dilillo, M. Feroci, F. Ficorella, M. Fiorini, N. Gao, A. Guzman, P. Hedderman, A. Hudrap, C. Labanti, G. La Rosa, P. Malcovati, J. McRobbie, F. Mele, G. Molera Calves, J. Morgan, G. Morgante, B. Negri, D. Novel, P. Nogara, A. Nuti, E. O'Brien, G. Pepponi, M. Perri, A. Picciotto, R. Piazzolla, S. Pirrotta, S. Pliego Caballero, A. Rachevski, I. Rashevskaya, A. Riggio, F. Russo, A. Santangelo, G. Sottile, C. Tenzer, Y. Tao, S. Trevisan, A. Vacchi, G. Zampa, N. Zampa, S. Xiong, S. Yi, A. Woods, S. Zhang, N. Zorzi

High Energy Astrophysical Phenomena

Temporal Variation of the Coronal Radius Parameter in a Jetted Tidal Disruption Event: Swift J1644+57

Arka Chatterjee, Kimitake Hayasaki, Prantik Nandi et al. (+5 more)

Tidal Disruption Events are exotic astrophysical phenomena where matter from a star or the interstellar medium is captured by a supermassive black hole. The process liberates enormous energy, within a few months to a year timescale, enough to detect dormant black holes in near as well as the farthest galaxies. We revisit the long-term spectral variabilities associated with the jetted Tidal Disruption Event \source~by exploring the archival X-ray data obtained with Swift/XRT and XMM-Newton observatories. Our analysis reveals that the spectral indices decrease non-monotonically as \source~evolves with time. We also find that the soft (0.3-1.5 keV) and hard (1.5-10 keV) X-ray photon counts are highly correlated with a maximum correlation coefficient of 0.95 and peak at zero lag. Moreover, the soft and hard band variabilities obtained from XMM-Newton observations are highly correlated with a Pearson cross-correlation coefficient of 0.96. This indicates that the soft and hard X-ray photons are emitted from the same site, which is most likely a Compton cloud, i.e., the corona. Assuming the hard X-ray photons originate from the corona, we find that the coronal parameter undergoes rapid expansion during the early phases when accompanied by a relativistic jet launching and subsequently evolves toward a state of saturation with minor fluctuations in the latter stages. The temporal variation of the coronal radius parameter ($R_{cor}$) is consistent with a simple theoretical conjecture. We also discuss the application of our analytical outcomes to other jetted and non-jetted tidal disruption events.
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All authors Arka Chatterjee, Kimitake Hayasaki, Prantik Nandi, Neeraj Kumari, Skye R. Heiland, Arghajit Jana, Sachindra Naik, Samar Safi-Harb

Astrophysics of Galaxies

The statistics and structure of dissipation in subsonic and supersonic turbulence

Edward Troccoli and Christoph Federrath

Turbulence plays a critical role in the atmosphere, oceans, engineering, and astrophysics. The dissipation (heating) induced by turbulent flows is particularly important for the thermodynamics and chemistry of interstellar clouds, yet its structure and statistics remain poorly understood. Using high-resolution turbulence simulations with controlled explicit viscosity, we study the kinetic energy dissipation rate, $\varepsilon_{\mathrm{kin}}$, across subsonic and supersonic regimes. We find that dissipation lags large-scale kinetic energy injection events by $1.64\pm0.21$ and $0.48\pm0.07$ turbulent turnover times in subsonic and supersonic turbulence, respectively. Correlations show $\varepsilon_{\mathrm{kin}}\propto\vert\nabla\times\mathbf{v}\vert^2$ (vorticity squared) in the subsonic regime, where density fluctuations are negligible, while in the supersonic regime dissipation is primarily correlated with density, $\varepsilon_{\mathrm{kin}}\propto\rho^{3/2}$. A spectral analysis demonstrates that achieving numerical convergence of $\varepsilon_{\mathrm{kin}}$ across all scales is challenging, especially in the subsonic case, even at $2048^3$ resolution. Nonetheless, subsonic dissipation is clearly localised on small vorticity-dominated scales, while supersonic dissipation spans many scales, combining elongated, thin shocks with small-scale vorticity. Finally, we determine the fractal dimension of $\varepsilon_{\mathrm{kin}}$. In the subsonic regime, intense dissipation is predominantly organised in flattened vortex filaments embedded in thin shearing layers on small scales, becoming more volume-filling at larger scales. In the supersonic regime, $\varepsilon_{\mathrm{kin}}$ exhibits a fractal dimension between 1 and 2 across nearly all scales, likely reflecting shock surfaces and their intersections forming filaments.
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Astrophysics of Galaxies · Cross-listed from gr-qc

Relativistic Corrections to the Formation Rate of Extreme Mass-Ratio Inspirals

Chen Feng and Yong Tang

Extreme mass-ratio inspirals (EMRIs) are long-duration gravitational-wave sources in which a compact object gradually spirals into a massive black hole. Their formation is governed by the interplay between stochastic angular-momentum diffusion driven by two-body relaxation and the dissipative evolution caused by gravitational-wave emission, with the loss-cone boundary deciding whether an object undergoes an inspiral or a direct plunge. Building on this physical picture, we construct a relativistically self-consistent analytic framework for estimating EMRI event rates. In Schwarzschild spacetime, we generalize the standard loss-cone angular momentum to an energy-dependent quantity and revise the plunge pericenter by using the minimum stable radius derived from general relativity. Relative to the Newtonian treatment, we show that incorporating these relativistic effects increases the predicted EMRI rates by roughly a factor of 8. This enhancement becomes more pronounced for shallower stellar density profiles and is insensitive to the mass of the central massive black hole, which emphasizes that relativistic effects are essential for EMRI rate estimations that are relevant for space-based gravitational-wave detectors, such as LISA and Taiji.
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Astrophysics of Galaxies

Stellar age determination using deep neural networks: Isochrone ages for 1.3 million stars, based on BaSTI, MIST, PARSEC, Dartmouth and SYCLIST evolutionary grids

T. Boin, L. Casamiquela, M. Haywood et al. (+4 more)

We aim to develop a model-driven deep learning approach to age determination, by training neural networks on stellar evolutionary grids. Contrary to the usual data-driven deep learning approach of using prior age estimates as training data, our method has the potential for a wider and less biased range of application. The low computational cost of deep learning methods compared to bayesian isochrone-fitting allows for a broad analysis of large spectroscopic catalogues. We train multilayer perceptrons on different stellar evolutionary grids to map [M/H], MG, (GBP - GRP) to stellar age ${\tau}$. We combine Gaia photometry and parallaxes, metallicities and ${\alpha}$ elements from spectroscopic surveys and extinction maps, which are passed through the neural networks to estimate stellar ages. We apply our method to the LAMOST DR10, GALAH DR3 & DR4 and APOGEE DR17 spectroscopic surveys, for which we estimate the ages using the BaSTI tracks, along with other stellar evolutionary models. We leverage this novel technique to study, for the first time, differences in age estimates from several evolutionary grids applied on very large datasets. In addition, we date 13 open clusters and one globular cluster and find a median absolute deviation with literature ages of 0.20 Gyr. Along with the stellar ages catalogues from our estimates, we release NEST (Neural Estimator of Stellar Times), a python package to estimate stellar age based on this work, as well as a web interface. We show that, when using the same evolutionary grid, our method retrieves the same ages as a bayesian approach like SPInS, for only a fraction of the computational cost, with a 60,000 speedup factor for a typical star. This model-driven deep learning technique thus opens up the way for broad galactic archeology studies on the largest datasets available today and in the near future with upcoming surveys such as 4MOST.
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All authors T. Boin, L. Casamiquela, M. Haywood, P. Di Matteo, Y. Lebreton, M. Uddin, D.R. Reese

Astrophysics of Galaxies

The Salamander: A case study of the magnetic field and peculiar morphology of G309.8-2.6 through radio polarimetry

Wenhui Jing, Jennifer L. West, Xiaohui Sun et al. (+17 more)

Studying the interaction between core-collapse supernova remnants (SNRs) and their surrounding environments is essential to understanding the mechanism for energy transfer to the interstellar medium (ISM) and the intrinsic physical properties of these remnants. In this paper, we focus on G309.8-2.6. Our new observations reveal that this object includes an SNR shell with a relic pulsar wind nebula (PWN) that extends well beyond the emission that has been previously observed in X-rays. We present new radio continuum and polarization images of G309.8-2.6 from the Evolutionary Map of the Universe (EMU) and Polarization Sky Survey of the Universe's Magnetism (POSSUM) surveys with the Australian Square Kilometre Array Pathfinder (ASKAP). The images reveal the complex and peculiar morphology of G309.8-2.6. The linear polarization displays an atypical S-shaped morphology and a highly ordered magnetic field. The rotation measure (RM) map shows a large-scale gradient or possible sign reversal, depending on the foreground RM. We reprocessed archival X-ray observations from Chandra and eROSITA, and retrieved archival H$\alpha$ and infrared observations. We performed a joint analysis of the multiwavelength data and proposed scenarios to explain the unusual shape. Our results place new constraints on the magnetic field of G309.8-2.6, including its environment, and demonstrate the power of polarization observations in probing the properties of SNRs.
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All authors Wenhui Jing, Jennifer L. West, Xiaohui Sun, Roland Kothes, Isabel Sander, Samar Safi-Harb, Denis Leahy, B. M. Gaensler, Xianghua Li, Brianna Ball, Craig Anderson, W. Becker, Miroslav D. Filipović, Andrew M. Hopkins, Yik Ki Ma, Naomi McClure-Griffiths, Syed Faisal ur Rahman, Cameron L. van Eck, Jacco Th. van Loon, Jayde Willingham

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Optical calibration systems of the Pacific Ocean Neutrino Experiment

M. Agostini, A. Alexander Wight, M. Altomare et al. (+89 more)

This work presents the design and performance characterization of the optical calibration systems produced for the Pacific Ocean Neutrino Experiment (P-ONE), which target gain, energy and time calibration in the detector. These systems include novel light-pulse driver circuitry based on gallium nitride field-effect transistor technology and its application to directional and isotropic, self-monitoring optical calibration instruments. A total of 330 directional light pulsers and two isotropic, 17-inch calibration modules (P-CALs) were produced for the first P-ONE line. We present the designs and performance of both the directional and isotropic calibration devices and perform detailed optical characterizations of both full-production batches. In a wavelength range of $365 - 520\,$nm, our developed driver circuits achieve emission intensities up to $10^{11}\,$photons and pulse widths as small as $1.4\,$ns, respectively. Light-pulse drivers and self-monitoring electronics in the P-CAL were characterized using the same experimental setup, and the instrument's optical-isotropy design was optimized in combination with a dedicated GEANT4-based simulation framework. The optimized P-CAL achieves a simulated isotropy grade of $1.00 \pm 0.01$ across the entire $4\pi\,$solid angle range. These simulation investigations were explicitly confirmed by dedicated measurements in both air and water using two independent experimental setups, and we report the results. With this, a detailed performance estimate for deployed P-CAL modules in P-ONE was possible.
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All authors M. Agostini, A. Alexander Wight, M. Altomare, K. Baş, N. Baily, P. S. Barbeau, A. J. Baron, S. Bash, C. Bellenghi, M. Boehmer, M. Brandenburg, P. Bunton, N. Cedarblade-Jones, B. Crudele, M. Danninger, T. DeYoung, A. Gärtner, J. Garriz, D. Ghuman, L. Ginzkey, T. Glukler, V. Gousy-Leblanc, D. Grant, A. Grimes, C. Haack, R. Hall, R. Halliday, D. Hembroff, F. Henningsen, M. Herle, O. Janik, H. Johnson, W. Kang, S. Karanth, T. Kerscher, S. Kerschtien, K. Kopański, C. Kopper, P. Krause, C. B. Krauss, N. Kurahashi, C. Lagunas Gualda, A. Lam, T. Lavallee, K. Leismüller, R. Li, S. Loipolder, C. Magee, S. Magel, P. Malecki, T. Martin, A. Maunder, C. Miller, N. Molberg, R. Moore, B. Nührenbörger, B. Nichol, W. Noga, R. Ørsøe, L. Papp, V. Parrish, P. Pfahler, J. Pflanz, B. Pirenne, E. Price, A. Rahlin, M. Rangen, E. Resconi, S. Robertson, M. F. Rodriguez-Pilco, D. Salazar-Gallegos, A. Scholz, L. Schumacher, S. Sharma, B. R. Smithers, C. Spannfellner, J. Stacho, I. Taboada, K. Tchiorniy, J. P. Twagirayezu, M. Un Nisa, B. Veenstra, M. Velazquez, L. von der Werth, C. Weaver, N. Whitehorn, B. Winnicky-Lewis, L. Winter, R. Wroński, J. P. Yañez, S. Yun-Cárcamo, A. Zaalishvili

Solar and Stellar Astrophysics

Detection and Astrometry of the Ba-Bb Subsystem in $\alpha$ Piscium: First Dual-Field Interferometry at the CHARA Array

Narsireddy Anugu, Robert Klement, John D. Monnier et al. (+14 more)

We present the first on-sky demonstration of dual-field interferometry at the CHARA Array and the first direct resolution of the inner Ba–Bb subsystem in the bright hierarchical triple $\alpha$ Piscium. Using $H$-band fringe tracking on component A with MIRC-X to stabilize $K$-band science fringes on component B with MYSTIC, we detected a companion at a projected separation of 7 mas, confirming a long-suspected but previously unresolved short-period subsystem within the B component. The nearly equal $H/K$-band flux ratio indicates that Ba and Bb are near-twin F-type stars, consistent with the two narrow-lined components seen in optical spectra of B. By combining CHARA interferometry with archival VLTI/GRAVITY astrometry and radial velocities from archival and new spectroscopy (NARVAL and ARCES), we derive a well-constrained orbit with a period of $P = 25$ d, eccentricity $e \simeq 0.6$, and inclination $i \simeq 65^\circ$, yielding precise dynamical masses of $1.668\pm0.033\,M_\odot$ and $1.646\pm0.029\,M_\odot$. No additional companion is detected down to $\Delta H \approx 5$ at separations of 0.2–2 AU. We also obtained dual-field differential astrometry of the wide A–B pair with a precision of ~0.234 mas at a separation of $1.85''$, with an error budget dominated by internal delay-line actuators, fringe-tracking performance and chromatic dispersion. While the long-period outer orbit is not refined by these measurements, their agreement with the published astrometric orbit provides an on-sky validation of the CHARA dual-field mode. These results establish $\alpha$ Psc as a well-characterized hierarchical system suitable for future benchmark studies and demonstrate CHARA's new capability for off-axis interferometry and sub-mas astrometry on arcsecond-scale binaries.
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All authors Narsireddy Anugu, Robert Klement, John D. Monnier, Douglas R. Gies, Gail H. Schaefer, Stefan Kraus, Sebastián Carrazco-Gaxiola, Akshat S. Chaturvedi, Mayra Gutierrez, Becky Flores, Jeremy Jones, Colin Kane, Rainer Köhler, Karolina Kubiak, Olli W. Majoinen, Nicholas J. Scott, Kayvon Sharifi

Solar and Stellar Astrophysics

Empirical flare energy limits for the largest historical sunspots

N.A. Krivova, T. Chatzistergos, M. Kazachenko et al. (+1 more)

Extreme solar particle events reveal that the Sun can occasionally produce eruptions significantly more energetic than those observed in the modern era. These events are thought to originate from powerful coronal mass ejections, typically associated with large solar flares triggered by magnetic field reconnection in complex active regions. Stellar observations indicate that Sun-like stars can host superflares exceeding 10^34 erg roughly once per century, yet it remains uncertain whether the Sun can reach such flare energies. We empirically estimate the upper limit of solar flare energies using statistical relations between flare - ribbon areas and released energy derived from modern observations. By extrapolating these upper-envelope relations to the largest sunspot group recorded since 1859 - the Great Sunspot of 8 April 1947 - we find that exceptionally large and complex solar active regions could, in principle, produce flares with bolometric energies of a few 10^34 erg.
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All authors N.A. Krivova, T. Chatzistergos, M. Kazachenko, E. Isik

Cosmology and Nongalactic Astrophysics

Exploring the $S_8$ Tension: Insights from the CatNorth 1.5-Million Quasar Candidates

Jin Qin, Xue-Bing Wu, Yuming Fu et al. (+4 more)

The parameter $S_8$, a key probe of cosmic structure growth, exhibits a persistent $\sim3\sigma$ tension between high-redshift measurements from cosmic microwave background (CMB) anisotropies and low-redshift weak gravitational lensing observations. This discrepancy may indicate either unaccounted systematic effects or new physics beyond the standard $\Lambda$CDM cosmology. In this work, we constrain $S_8$ using the high purity CatNorth 1.5 million quasar candidate catalog and the Planck DR4 CMB lensing data across the broad redshift ranges through auto-correlation and cross-correlation analyses. To address the spatial incompleteness, we develop a machine-learning-based selection function that effectively suppresses the systematics-induced power spectrum excess on large scales. Our robust low-redshift measurements at $z<1.5$ yield $S_8 = 0.844^{+0.058}_{-0.056}$, consistent with the Planck 2018 CMB anisotropies constraints of $S_8=0.834\pm0.016$ but lower than the $0.879^{+0.055}_{-0.055}$ reported by a previous work using the Quaia quasar candidate catalog. However, for high-redshift faint quasars at $z>1.5$, we find a lower value of $S_8=0.724^{+0.058}_{-0.054}$, likely due to the sample incompleteness and/or the foreground contamination. Further tests on the volume-limited samples exhibit a consistent trend: $S_8 = 0.835^{+0.053}_{-0.049}$ for $z < 2$, $0.824^{+0.061}_{-0.062}$ for $0.4 < z < 1.5$, and a lower value of $0.789^{+0.062}_{-0.062}$ for the higher redshift range of $1.5 < z < 2.5$. While future data may refine these results, our current measurements based on a large sample of quasar candidates show less evidence of the $S_8$ tension.
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All authors Jin Qin, Xue-Bing Wu, Yuming Fu, Haojie Xu, Yuxuan Pang, Yun-Hao Zhang, Pengjie Zhang

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

Renormalisation and matching of massless scalar correlation functions in Soft de Sitter Effective Theory

Martin Beneke, Patrick Hager and Andrea F. Sanfilippo

For light and massless scalar fields, cosmological correlation functions suffer from infrared divergences and secular logarithms. Soft de Sitter Effective Theory (SdSET) has been proposed by Cohen and Green as the effective description of the non-trivial dynamics of long-wavelength modes $k_{\rm phys} < H$ in de Sitter space, which is responsible for the infrared and late-time logarithms, and as a systematic extension of the stochastic approach. In this article, we construct SdSET in dimensional regularisation, including an initial-condition functional. We demonstrate by examples that renormalisation and matching works as for flat-space effective field theories. Adopting massless $\kappa \phi^4$ theory as the UV theory, we match the tree-level trispectrum and six-point function, and the one-loop power spectrum to SdSET, verifying explicitly that SdSET is the appropriate effective field theory for the quantum dynamics of superhorizon modes.
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Cosmology and Nongalactic Astrophysics

Pure Natural Inflation Passes the ACT

Cristóbal Zenteno Gatica, Alexandros Papageorgiou and Matteo Fasiello

Pure natural inflation is a compelling effectively single-field model of inflation stemming from a top-down approach to the acceleration mechanism. In this short letter we show that such model is compatible with the latest CMB constraints obtained from the Atacama Cosmology Telescope combined with baryon acoustic oscillation data from the Dark Energy Spectroscopic Instrument. Under both the instantaneous reheating hypothesis and standard assumptions for reheating, we rule in a non-trivial fraction of the parameter space. We apply our analysis also to a phenomenological extension of the model and chart its viable parameter space.
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High Energy Astrophysical Phenomena

Beyond Fermi-II: Intermittent Particle Acceleration by Relativistic Turbulence in Astrophysical Plasmas

Anton Dmytriiev, Frans van der Merwe and Markus Böttcher

Stochastic particle acceleration in turbulent plasmas plays a key role in shaping high-energy emission from relativistic outflows, such as those in Active Galactic Nuclei (AGN) and microquasars. While traditional Fermi-II models provide a foundational framework, they often oversimplify the complex nature of realistic magnetohydrodynamic (MHD) turbulence, especially in high-amplitude ($\delta B/B_0 \sim 1$) and relativistic regimes. Recent plasma simulations for these conditions have revealed highly non-linear energization effects, such as sudden, large momentum jumps, that remain largely unexplored in astrophysical applications. We present a novel Monte Carlo framework STRIPE that models particle acceleration as a continuous-time random walk (CTRW), capturing both intermittent energy gains and radiative losses. The stochastic evolution of particle momenta is driven by jumps with random magnitudes determined by a distribution of magnetic-field-line velocity gradients, with synchrotron and inverse Compton cooling incorporated self-consistently. Using STRIPE, we explore particle acceleration under physical conditions characteristic of TeV-PeV $\gamma$-ray emitting microquasars recently identified by Large High Altitude Air Shower Observatory (LHAASO). We find that relativistic, high-amplitude turbulence naturally produces particle spectra with steep low-energy cutoffs, and hard extended power-law high-energy tails reaching tens of PeV. These features differ markedly from standard quasi-linear theory and are well suited to explaining the unexpectedly hard TeV-PeV spectra of LHAASO-detected microquasars. These results highlight turbulent acceleration in the relativistic regime as a promising mechanism for particle energization in microquasar systems, as well as potentially other extreme astrophysical environments.
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Instrumentation and Methods for Astrophysics

Accurate spectroscopic redshift estimation using non-negative matrix factorization: application to MUSE spectra

Masten Bourahma, Nicolas F. Bouché, Roland Bacon et al. (+5 more)

Accurate and automated galaxy redshift determination is essential for maximizing the scientific return of spectroscopic surveys. In this paper, we propose a data-driven method to address this challenge. The method first learns a rest-frame representation of galaxy spectra using Non-negative Matrix Factorization (NMF). The method then reconstructs new spectra using this representation at different trial redshifts, and identifies the correct redshift by selecting the one that minimizes the reconstruction error. We apply our method to galaxy spectra from the Multi Unit Spectroscopic Explorer (MUSE), covering redshifts from 0 to 6.7. Our method achieves an overall success rate of 93.7%. We further demonstrate two applications: (i) the separation between true and false sources, and (ii) the detection of blended sources from one-dimensional spectra. Our results demonstrate that NMF-based representations provide a powerful and physically motivated framework for redshift estimation in current and future large spectroscopic surveys.
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All authors Masten Bourahma, Nicolas F. Bouché, Roland Bacon, Johan Richard, Tanya Urrutia, Afonso Vale, Martin Wendt, T. T. Thai

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Deep Learning Search for Gravitational Waves from Compact Binary Coalescence

Lorenzo Mobilia, Tito Dal Canton and Gianluca Maria Guidi

Gravitational-wave searches rely on a combination of methods, including matched filtering, coherent analyses, and more recent machine-learning-based pipelines. For compact binary coalescences — where signals originate from the relativistic dynamics of compact objects — matched filtering remains a central element, but its computational cost will increase substantially with the data volumes and parameter-space coverage required by next-generation interferometers such as the Einstein Telescope. Developing complementary strategies that reduce computational load while preserving detection performance is therefore essential. We investigate a hybrid approach that combines matched-filtering concepts with Convolutional Neural Networks, enabling efficient signal searches without relying on the usual $\chi^2$ rejection test. Using simulated data sets that include injected signals in Gaussian noise, transient noise, and physical effects not represented in the template bank — such as eccentricity, precession and higher-order modes — we show that the method achieves a detection efficiency comparable to or better than a standard matched-filtering search while offering a more resource-efficient pipeline in all the cases where the physics included in the signals were not represented in the template bank or when glitches were affecting the data. Conversely, the analysis also reveals some loss of detection capability for standard BNS/BBH searches in pure Gaussian noise. These results indicate that deep-learning-assisted searches can support sustainable gravitational-wave data analysis in future detector eras.
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Earth and Planetary Astrophysics

From planetesimals to planets with N-body simulations in the giant-planet formation region

Sebastian Lorek and Michiel Lambrechts

The cores of wide-orbit giant planets can form via pebble accretion if large planetesimals form in the outer regions of protoplanetary discs at sufficiently early times. Streaming instability simulations support mass distributions consistent with Solar System minor body constraints, but when and where planetesimal formation took place remains uncertain. Here, we report on our N-body simulations of core formation through pebble and planetesimal accretion starting from streaming-instability inspired planetesimal mass distributions. We explore two initial radial planetesimal distributions, a ring-like and a spatially more uniform distribution, between 10 and 50 AU. To address the numerical challenge of simulating realistic planetesimal numbers, corresponding to one to ten Earth masses of planetesimals, we made use of GPU acceleration for the N-body interactions (with GENGA) and a newly developed pebble accretion module. We find that the top of the planetesimal mass distribution provides the seeds for core formation through pebble accretion, leading to the formation of multiple giant planets. This is consistent with previous studies not including N-body interactions. Planetesimal surface densities, crudely corresponding to an initial 10% formation efficiency, imply low mean collision rates (around unity) in the gas disc phase. Our simulations show that giant planet formation depends only weakly on the initial locations where planetesimals form, because of rapid dynamical scattering, and on their total mass budget, due to filtering of the pebble flux between embryos. After disc dissipation, giant planet systems stir the remnant primordial planetesimals, making a scattered disc an inherent outcome of giant planet formation. Giant impacts between planetary cores generally appear to be rare in the first 100 Myr.
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Astrophysics of Galaxies

Testing Screened Modified Gravity with Strongly Lensed Gravitational Waves

Chengsheng Mu, Shuo Cao, Shuxun Tian et al. (+3 more)

Screening mechanisms are essential components in many modified gravity theories, which satisfy local tests of General Relativity (GR) and address cosmic acceleration on cosmological scales. The strong gravitational lensing of gravitational waves (GWs) offers a unique observational probe into cosmology and fundamental physics. In this paper, we investigate the possibility of testing screened modified gravity theories with strongly lensed gravitational waves. Specially, we develop the refined theoretical and statistical framework, in order to measure the post-Newtonian parameter $\gamma_{\text{PN}}$ in the presence of screening effects. Specially, the mass-truncated power-law and Navarro-Frenk-White (NFW) models are introduced to quantify the modified lensing potential. Our analysis also addresses the mass-sheet degeneracy (MSD) problem, by incorporating the absolute magnification and time delay measurements accessible through strongly lensed GW systems. We find that individual lensed GW system detected by next-generation GW detectors can provide stringent constraints on the PPN parameter ($\gamma_{\text{PN}}$) across different screening scales ($\Lambda$). Therefore, future measurements of strongly lensed GWs have great promise to seek departures from GR on kpc-Mpc scales, due to more precise time delay from lensed GW signals.
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All authors Chengsheng Mu, Shuo Cao, Shuxun Tian, Xinyue Jiang, Chenfa Zheng, Dadian Cheng

Cosmology and Nongalactic Astrophysics

Hidden Vela Supercluster Revealed by First Hybrid Redshift & Peculiar Velocity Reconstruction

A.M. Hollinger, H.M. Courtois, R.C. Kraan-Korteweg et al. (+2 more)

A large fraction of the extragalactic sky is obscured by foreground dust and stars along the plane of the Milky Way, leaving a major gap (~ 20%) in whole-sky maps of large-scale structures – an incompleteness that is even more severe for peculiar velocity samples. This has long limited an unambiguous interpretation of observed cosmic flows and their connection to the underlying mass-density field. We present a new hybrid reconstruction methodology which combines 65,518 galaxy peculiar velocity distances from the CF4++ catalogue (Courtois2025) with 8283 new galaxy redshifts observed near the southern Galactic plane (|b| <= 10 degrees) Zone of Avoidance. A major advance is the inclusion of 2176 high-sensitivity, interferometric HI redshifts obtained with the SARAO MeerKAT telescope which for the first time provide coverage of the innermost 3degrees-wide strip of the southern ZOA and to unprecedented depth. This hybrid redshifts & peculiar velocities approach yields a substantially revised view of the inferred overdensities in and around the ZOA. In particular, the Vela supercluster emerges as a dominant mass concentration, rivaling the Shapley concentration and exceeding the mass associated with Laniakea and the Great Attractor region. With a total mass of 33.8 10^16 Msol, a characteristic radius of 70 hmpc, and a double core morphology at a distance of 189 hmpc, Vela dominates the mass budget and gravitational influence of the southern Zone of Avoidance. These results provide the most complete and dynamically consistent picture to date of the southern Zone of Avoidance and demonstrate the transformative potential of hybrid reconstruction techniques tailored for the next generation of large-scale surveys.
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All authors A.M. Hollinger, H.M. Courtois, R.C. Kraan-Korteweg, J. Mould, S.H.A. Rajohnson

High Energy Astrophysical Phenomena

Low-energy atmospheric neutrino flux calculation with accelerator-data-driven tuning

Kazufumi Sato, Hiroaki Menjo, Yoshitaka Itow et al. (+1 more)

We have incorporated a hadron interaction tuning based on accelerator data into our atmospheric neutrino flux calculation, which has been used to analyze atmospheric neutrino oscillations at Super-Kamiokande. This new approach enables a more direct evaluation of the flux uncertainty than a conventional tuning using atmospheric muons. The neutrino flux calculated with this new tuning is 5%–10% smaller but still consistent with our previously published prediction within its uncertainty. The flavor ratio $(\nu_{\mu}+\bar{\nu}_{\mu})/(\nu_e+\bar{\nu}_e)$ and $\bar{\nu}/\nu$ ratios were consistent with the previous prediction. Based on the measurement errors of the accelerator data, we evaluated the flux uncertainty associated with the new tuning to be 7%–9% in the $E_{\nu} <$ 1 GeV region, which was difficult to assess with the conventional tuning. The flux uncertainty in the $1<E_{\nu}<10$ GeV region was evaluated to be 5%–7%, which is an improvement over the conventional tuning.
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All authors Kazufumi Sato, Hiroaki Menjo, Yoshitaka Itow, Morihiro Honda

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

Non-perturbative determination of the QCD Equation of State up to the electroweak scale

Michele Pepe

The QCD Equation of State with $N_f=3$ massless quark flavours is determined non-perturbatively over a broad range of temperatures, extending from the electroweak scale down to 3 GeV, and smoothly connecting to the low-temperature regime. The comparison with perturbative predictions shows that, even at temperatures approaching the electroweak scale, the Equation of State can be accurately described only by adding terms beyond the known perturbative series, including non-perturbative contributions. The strategy that allows this investigation in the previously unexplored high-temperature regime combines shifted boundary conditions with a determination of the lines of constant physics based on the running of a non-perturbatively defined renormalized coupling. This methodology is general and can be applied to QCD with four or five massive quark flavours.
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Solar and Stellar Astrophysics

$\Lambda$ effect in rotating hydrodynamic convection

P. J. Käpylä

Context: Rotating anisotropic convection generates differential rotation in stellar convection zones. Aims: The main aim is to compute the non-diffusive contribution ($\Lambda$ effect) to angular momentum transport, described by Reynolds stress, from rotating turbulent convection. Methods: Rotating hydrodynamic convection is simulated in Cartesian geometry at different latitudes and rotation rates. Large-scale flows are suppressed such that the Reynolds stress is due to non-diffusive effects. Results: The radial angular momentum flux is downward (outward) for slow (fast) rotation. This is in contrast in prevailing theories in mean-field hydrodynamics where the radial transport is always downward. The outward transport at rapid rotation is due to thermal Rossby waves that manifest as elongated large-scale convection cells near the equator. The horizontal angular momentum flux is always equatorward, with increasing concentration toward the equator as in earlier Cartesian studies. The magnitudes of the $\Lambda$ effect coefficients are roughly an order of magnitude lower than in the case of anisotropically forced turbulence or in analytic theories. Conclusions: The current results highlight the tension between numerical simulations, widely used mean-field models, and solar observations. The mean-fields models have been remarkably successful in reproducing solar differential rotation but underlying assumptions regarding turbulence in these models seem to be at odds with 3D simulations. The current simulation results for the vertical (radial) angular momentum transport are in accordance with spherical shell simulations, where thermal Rossby waves are responsible for the generation of equatorial acceleration or solar-like differential rotation. Thermal Rossby waves are absent in the turbulence models of current mean-field theories and they have not been unambiguously detected in the Sun.
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Instrumentation and Methods for Astrophysics

The Key to Unlocking Exoplanet Biosignatures: a UK-led IR Spectrograph for the Habitable Worlds Observatory Coronagraph

Beth Biller, Dan Dicken, Olivier Absil et al. (+13 more)

The detection of life on rocky exoplanets in the habitable zones of nearby stars would be a paradigm-shifting advance, and it is one of the greatest scientific challenges of our time. There is no single spectral feature that is an unambiguous sign of life on a given exoplanet. Instead, the current state-of-the-art approach involves detecting multiple molecular atmospheric features that should not exist together in equilibrium, e.g. simultaneous detection of O$_2$ and CH$_4$. Spectra across a wide wavelength (0.3-1.7 $\mu$m) range are necessary to cover multiple spectral features per molecule of interest and to contextualise the suite of molecular features detected. While the US will lead the optical arm of the Habitable Worlds Observatory (HWO) coronagraph, a UK-led contribution of a near-infrared Integral Field Spectrograph (IFS) for the infrared arm will ensure UK leadership in the flagship scientific goal of HWO - to search for signatures of life on potentially habitable exoplanets.
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All authors Beth Biller, Dan Dicken, Olivier Absil, Raziye Artan, Jo Barstow, Jayne Birkby, Christophe Dumas, Sasha Hinkley, Tad Komacek, Katherine Morris, Lorenzo Pino, Sarah Rugheimer, Colin Snodgrass, Stephen Todd, Vinooja Thurairethinam, Amaury Triaud

Cosmology and Nongalactic Astrophysics

Reliable Tests of Faint-end UV Luminosity Functions in Strong Lensing Fields

Jiashuo Zhang

Dark matter comprises ~85% of the entire mass of the Universe, but the fundamental nature of its constituent particles remains elusive. In this thesis, I test for two competitive dark matter models: the conventional heavy particle paradigm, and dark matter being ultralight bosons of mass $\sim 10^{-22}$eV ($\psi$DM). More specifically, I test for the faint-end turnover induced by $\psi$DM models, exploiting the strong lensing power by massive galaxy clusters to probe intrinsically fainter magnitudes. A key challenge for such an analysis would be contamination by low-z galaxies sharing similar observed SEDs as high-z galaxies. As I will demonstrate, such a contamination issue is generally severe and may wash out the faint-end turnover signatures. I also show that $\sim 50\%$ of the purported $3.5\leq z\leq 5.5$ galaxies within existing photometric redshift catalogs constructed for Hubble Frontier Fields (HFF) are in fact low-z interlopers. Luckily, individual mitigation of interlopers can be achieved with the combination of deep HST and JWST observations. For fields without supplementary data, machine learning methods will be shown useful in preserving the mitigating power. Cleaner $3.5\leq z\leq 5.5$ and $6\leq z\leq 10$ samples are derived for a more reliable test in strong lensing field of MACS J0416, with which I found no evidence for faint-end turnovers, leading to a constraint on the $\psi$DM mass of $>2.97\times10^{-22}$eV at 95% confidence. This constraint will also be interpreted in an scheme where dark matter is composed of multiple particle copies, where I argue the derived mass bound is likely on an effective de Broglie scale governing the collective behavior of the entire $\psi$DM budget under gravitational equilibrium established.
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Astrophysics of Galaxies

Epicyclic Density Variations in the Indus Stellar Stream

Yong Yang, Geraint F. Lewis, Ting S. Li et al. (+12 more)

Longitudinal density fluctuations observed in stellar streams can result from gravitational interactions with massive perturbers in the Milky Way, such as dark matter subhalos. Analysing these density variations provides a powerful probe of properties (motion, mass, size, etc.) of the perturbing objects. However, caution is needed because density variations may arise naturally from internal dynamics of streams, namely epicycles. In this work, we focus on the Indus stellar stream, a remnant of an ancient dwarf satellite of the Galaxy. An Indus stream spanning $\sim 90^\circ$ is revealed in the southern Galactic sky using a comprehensive matched-filter analysis utilizing data from the Gaia mission. A spatial density model is fitted to the filtered map to quantitatively characterize the morphology, which demonstrates episodic density peaks and gaps in the stream. Through N-body simulations, we show that there are strong epicyclic motions of stars happening during tidal disruptions. The present-day longitudinal densities from simulations are comparable to the measurement from data, with similar numbers and locations of peaks and gaps, suggesting that the observed density should mainly be caused by epicycles. We also find that a cuspy dark matter halo for the Indus dwarf is likely to produce milder stellar epicyclic peaks compared to a cored halo which results in steeper peaks. This arises from different instantaneous mass loss due to distinct central mass distributions of halos, where a cored halo usually leads to severer tidal stripping. The observed density exhibits moderate peak sharpness, implying that Indus may have originally possessed a cuspy halo.
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All authors Yong Yang, Geraint F. Lewis, Ting S. Li, Sarah L. Martell, Denis Erkal, Alexander P. Ji, Sergey E. Koposov, Daniel B. Zucker, Andrew B. Pace, Lara R. Cullinane, Gary S. Da Costa, Kyler Kuehn, Guilherme Limberg, Gustavo E. Medina, S5 Collaboration

Cosmology and Nongalactic Astrophysics

Mock Catalogs of Strongly Lensed Gravitational Waves via A Halo Model Approach with Ground-based Detectors

Youkai Li, Kai Liao, Mingqi Sun et al. (+4 more)

As plans for the construction of third-generation gravitational wave (GW) detectors advance, research into strongly lensed GWs has become increasingly critical. It is anticipated that hundreds of multi-image lensed GWs will be detected annually. We present a comprehensive suite of lensed GW mock catalog derived from a composite lens mass model incorporating dark matter halos, galaxies, and subhalos. We analyze three source populations with four detector network configurations considering the earth rotation. Our simulations encompass not only conventional doublets and quadruplets but also subhalo-lensed events, highly magnified systems, and complete three or five image systems with a detectable central image, a feature distinct from optical lensing. For the joint ET+CE network, we forecast an annual detection rate of approximately 400 doublets and 36 quadruplets. Notably, this population includes roughly 107 events lensed by subhalos and 20 complete systems with detectable central images. Furthermore, we analyze high-magnification events ($\mu > 3$), predicting approximately 360 such cases. Under a more relaxed selection criterion that requires only at least one lensed signal to exceed the detection threshold, we estimate a total of approximately 617 lensed events. We also investigate the impact of variations in lens mass models and stellar evolution models on event rates, as well as the distributions of SNR pairs and time delays. These results establish a more physically grounded statistical prior for the future identification and authentication of lensed GW signals. The Gravitational Waves-Lensing Mock Catalog (GW-LMC) have been made publicly available.
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All authors Youkai Li, Kai Liao, Mingqi Sun, Lilan Yang, Xuheng Ding, Marek Biesiada, Tonghua Liu

Cosmology and Nongalactic Astrophysics

Constraining Neutrino Mass with the Void Weak Lensing Effect

Wenshuo Xu, Cheng Zhao, Chen Su et al. (+2 more)

Cosmic voids, the underdense regions of the Large Scale Structure (LSS), provide cosmological information highly complementary to that obtained from overdense regions. In this work, we investigate the constraining power of the void-shear cross-correlation (void lensing effect) on the total neutrino mass. Based on cosmological $N$-body simulations with varying neutrino masses, we populate BOSS LOW-Z-like galaxies at $0.2<z<0.4$ using HOD fitting, identify voids with the DIVE void finder and obtain their density profiles from the underlying dark matter and neutrino distributions. We then generate mock shear catalogues through ray-tracing and measure the corresponding void lensing signals, assuming a source number density of $10/{\rm arcmin}^{2}$ and sky area of around $8400\,{\rm deg}^2$. Under this setup, void lensing independently yields a constraint on total neutrino mass as $\sigma(M_{\nu})=0.096\,{\rm eV}$ ($M_{\nu}<0.232\,{\rm eV}$, 95% C.L.) in the absence of shape noise, and $\sigma(M_{\nu})=0.340\,{\rm eV}$ ($M_{\nu}<0.707\,{\rm eV}$, 95% C.L.) when adopting a Stage-III-like shape noise. Moreover, we find a clear linear relationship between the void lensing signal and neutrino mass. We further validate the forward modelling of the void lensing signal from the void density profiles across different cosmologies, demonstrating its accuracy and potential for future applications. These findings highlight void lensing as a promising probe of massive neutrinos and motivate its applications to galaxy survey data as well as the combination with other cosmological observables.
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All authors Wenshuo Xu, Cheng Zhao, Chen Su, Huanyuan Shan, Yu Liu