High Energy Astrophysical Phenomena
A Multi-Wavelength Picture of the Surprisingly Short 2024/25 Outburst from EXO 0748-676
Amy H. Knight, Lauren Rhodes, Noel Castro Segura et al. (+11 more)
After sixteen years in quiescence, EXO 0748-676 unexpectedly returned to outburst in March 2024. However, in stark contrast to its previous outburst (1985 - 2008), EXO 0748-676 returned to quiescence in January 2025, after ~ 10 months in outburst. Here, we collate data from nine observing facilities, covering wavelengths from
radio to X-ray, to provide the first multi-wavelength study of the 2024/25 outburst. Unlike the 1985 outburst, both the rise and decay are fully captured at X-ray and optical wavelengths. The light curves do not exhibit the hallmarks of a canonical transient low-mass X-ray binary outburst. Instead, the X-ray and optical fluxes remain reasonably stable during the 2024/25 outburst. The wealth of optical data of EXO 0748-676 reveals a skewed optical phase curve and an irradiation-dominated optical light curve which lasts until the onset of hydrogen recombination in the outer disc at ~11000K, triggering a rapid fade at the end of the outburst. X-ray observations by XMM-Newton and NICER revealed that EXO 0748-676 was heavily obscured early on, with spectra exhibiting a dampened soft X-ray contribution. We find that a spectral model including a clumpy, ionised absorber describes the obscuration, although the exact cause of the early-time obscuration remains uncertain. X-ray colour analysis indicates that EXO 0748-676 spent most of the ~10 month outburst in a faint, hard state. EXO 0748-676 increased marginally in brightness towards the end of the outburst, but never entered a soft spectral state. This behaviour is characteristic of a failed transition outburst.
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All authors Amy H. Knight, Lauren Rhodes, Noel Castro Segura, Douglas J. K. Buisson, Aru Beri, David M. Russell, Kevin Alabarta, Maria C. Baglio, Jakob van den Eijnden, Matthew J. Middleton, Payaswini Saikia, Chris Done, Rob Fender, Fraser Lewis
Cosmology and Nongalactic Astrophysics
Constraining Primordial Magnetic Fields with Weak Lensing
Anna D'Ambrosio and Matteo Viel
Introducing primordial
magnetic fields (PMFs) into the standard cosmological model, $\Lambda$CDM, has an impact on the matter power spectrum at the linear level, resulting in an increase of power on small scales. In this work, we use the enhanced spectrum as the initial condition for dark-matter-only N-body simulations and study its non-linear
evolution. From the resulting non-linear matter power spectrum, we calculate the convergence power spectrum of weak
lensing ($C_{\kappa}$) and show how the presence of PMFs causes an enhancement at high multipoles. We then construct an emulator for $C_{\kappa}$ that also includes intrinsic
alignment and baryon feedback. We perform MCMC analyses using mock data generated for different PMF models and for three values of the maximum multipole, $\ell_{\rm max}=5000$, $10000$, and $20000$. The PMFs models are characterized by the two parameters that define the power-law power spectrum of the
magnetic field $P_B(k)\propto B_{\rm 1Mpc}^2 k^{n_B}$, where $B_{\rm 1Mpc}$ is the amplitude at a scale of $1$ Mpc and $n_B$ is the power spectral index. For $\Lambda$CDM mocks, corresponding to $B_{\rm 1Mpc}=0$, we obtain approximate upper limits of $B_{\rm 1Mpc}<1.6$, $1.0$, and $0.8\,{\rm nG}$ at the $95\%$ confidence level for the three values of $\ell_{\rm max}$ respectively. For non-zero input
magnetic fields, the recovery of $B_{\rm 1Mpc}$ and $n_B$ depends strongly on the PMFs model and on the maximum multipole considered. Models with $n_B=-2.1$ are more easily constrained than models with $n_B=-2.7$, since they produce a stronger enhancement of the convergence power spectrum. We find no clear degeneracy between the PMFs parameters and the intrinsic
alignment or baryon feedback parameters, while $B_{\rm 1Mpc}$ and $n_B$ can be degenerate. We characterize this degeneracy through linear fits to selected $2$D posterior distributions.
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Astrophysics of Galaxies
The star formation history of Orion is structured and episodic
Alena Rottensteiner, João Alves, Stefan Meingast et al. (+6 more)
The propagation of
star formation throughout a molecular cloud complex can tell us much about its physical drivers and the importance of environmental versus intrinsic processes. We reconstruct the
star formation history (SFH) of the Orion
star-forming complex using the highest-resolution age map currently available. It comprises 47 co-spatial and co-moving groups identified by the SigMA clustering
algorithm, with homogeneously derived ages and group memberships. We find four periods of increased
star formation, separated by ~5 Myr each. The two periods of highest increase, at 6.4 and 11.3 Myr, can be statistically localized, together hold ca. 59% of all
stars, and are robust against resampling and changes to the age fitting. The two older, smaller increases at 16.2 and 21.4 Myr can be identified in the age distribution, but cannot be shown to be robust at this point. The ~5 Myr spacing between the episodes of increased
star formation is the same as found for the nearby Scorpius-Centaurus (Sco-Cen)
star-forming region. We find no methodological bias that could produce the SFH structure. We identify spatio-temporally connected structures, including three cluster-chain candidates. We conclude that
star formation in Orion seems to occur on the same timescales but with a different pattern than in Sco-Cen. The cause of the ~5 Myr separations remains a mystery, and its detection in two distinct
star-forming regions needs further investigation.
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All authors Alena Rottensteiner, João Alves, Stefan Meingast, Sebastian Hutschenreuter, Núria Miret-Roig, Josefa Großschedl, Cameren Swiggum, Sebastian Ratzenböck, Monika G. Petr-Gotzens
Astrophysics of Galaxies
The impact of relativistic AGN jets on realistic galaxy cluster environments
K. Hervella-Seoane, M. Perucho, S. Planelles et al. (+2 more)
Context. Low-power FRI-like
radio jets dominate the AGN population, yet the main mechanism of heating the intracluster medium (ICM) and its efficiency remain a matter of debate. Aims. We investigate the impact of intermediate-power FRI-like relativistic jets on the inner region of realistic ICM, focusing on the role of weak shocks on heating and the environmental coupling in regulating energy deposition. Methods. We present six three-dimensional relativistic-hydrodynamic simulations of (1e44 - 1e45) erg/s FRI-like jets propagating through the central regions of realistic ICM environments extracted from cosmological GADGET-3 runs. Each simulation tracks 20 Myr of continuous jet activity with radiative cooling included. Results. Despite their intermediate power and mildly relativistic speed at injection, they decelerate rapidly to trans-sonic velocities (average Mach numbers ~ 2.3) and generate weak bow shocks that dominate the energy transfer. Approximately, 80% of the injected kinetic power is converted into internal energy of the ambient ICM, and bremsstrahlung cooling noticeably reduces the temperature of the shocked shells as they expand. Conclusions. Our results demonstrate that heating of the intergalactic and intracluster medium is highly efficient even in the case of weak shocks in FRI-like sources. This finding suggests low-power jets are a viable solution to the long-standing cooling-flow problem and likely regulate
star formation across diverse
galaxy cluster environments.
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All authors K. Hervella-Seoane, M. Perucho, S. Planelles, J.M. Martí, V. Quilis
Instrumentation and Methods for Astrophysics
NASA ASTRA White Paper : A Chandra Successor in the 2030s
C. S. Reynolds, E. Hodges-Kluck, E. A. Kara et al. (+19 more)
Chandra established that soft X-ray spectral imaging with approximately 1 arcsec angular resolution is an essential tool for almost every area of astrophysics, from the early Universe to ice chemistry in protoplanetary disks. While Chandra continues to deliver groundbreaking science, it lacks the sensitivity to be the counterpart to JWST, Roman, Rubin, LISA, ngVLA, ALMA, IceCube, NewAthena, ELT, and other upcoming large facilities. Here we highlight the scientific potential of a Chandra successor with >10x higher sensitivity and >50x survey speed. While the scientific reach of such a mission is very broad, we showcase four high-priority science questions that require these capabilities – How did supermassive black holes form?, How does stellar and AGN feedback work in
galaxies?, How does high-energy stellar activity affect
exoplanet atmospheres? and, How do black holes merge? A Chandra successor in the 2030s would also demonstrate the X-ray mirror technology for a future flagship and sustain the US high energy astrophysics workforce until that flagship launches. We outline the science-instrument trade space by sketching three missions based on the NASA Probe concept study report for the Advanced X-ray Imaging Satellite (AXIS): AXIS-Deep, AXIS-Classic, and AXIS-Fast, highlighting a breakthrough science case for each and listing others that drive the design.
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All authors C. S. Reynolds, E. Hodges-Kluck, E. A. Kara, M. Koss, K. Madsen, E. Miller, B. Williams, S. Allen, M. Bautz, K.Burdge, N. Cappelluti, B.Cenko, L. Corrales, A.Falcone, A. Foord, D. Haggard, L. Lopez, R. Mushotzky, A. Ptak, H.Russell, S. Safi-Harb, K.Stassun
Solar and Stellar Astrophysics
Eppur binaria non è esclusa: Pulsations in CZ Tuc appear to be tidally excited by its veiled companion
Piotr A. Kołaczek-Szymański, Patryk Iwanek, Jim Fuller et al. (+3 more)
Long secondary periods (LSPs), observed in about one-third of pulsating red giants, remain unexplained despite decades of study, with binarity and non-radial oscillations as the leading competing hypotheses. If LSP variables are indeed interacting, eccentric binary systems consisting of a red giant and a substellar object, tidally excited oscillations (TEOs) would be expected to appear in a fraction of them. Therefore, detection of TEOs offers an independent test of the binary scenario that has not previously been applied to LSP
stars. Using a combined, approximately 80-year light curve assembled from Digital Access to a Sky Century @ Harvard (DASCH), Hipparcos, and All Sky Automatic Survey (ASAS) photometry, we find that CZ Tucanae (CZ Tuc) exhibits a pulsation period of $55.4734\pm0.0074$ days along with its LSP of $443.62\pm0.12$ days, with a ratio of $7.9970\pm0.0024$ - consistent with a TEO. Theoretical models show the observed amplitude of the candidate TEO could be produced after adopting the estimated fundamental parameters of CZ Tuc. Our findings identify CZ Tuc as the first candidate LSP
star with a TEO, providing independent evidence for binarity among at least a subset of these enigmatic variables.
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All authors Piotr A. Kołaczek-Szymański, Patryk Iwanek, Jim Fuller, Dorota M. Skowron, Grzegorz Pojmański, Igor Soszyński
Instrumentation and Methods for Astrophysics
Inferring radio beams from sparse sampling patterns: a case study with the Murchison Widefield Array
Michael J. Wilensky and Aman Chokshi
Accurate primary-beam models are essential for high-dynamic-range
radio experiments, particularly searches for the redshifted 21-cm signal from the Epoch of Reionisation, where beam errors can couple bright foreground emission into the faint cosmological measurement. Using reprocessed satellite observations we infer the 137-MHz, zenith-pointed power beams of Murchison Widefield Array receiving elements. We develop two complementary
Bayesian approaches for quantifying departures from nominal electromagnetic simulations: a physically motivated model of complex variations among individual dipoles and a hierarchical spline model for flexible direction-dependent structure. The measurements reveal shallower and displaced nulls together with coherent sidelobe deformations. The dipole model captures much of this broad structure, whereas the spline recovers additional localised features while remaining largely robust to isolated pass-shaped artefacts. Despite their sparse and distinct sampling patterns, four independent 20-day subsets, each containing approximately 20% of the full
dataset, recover consistent null and sidelobe morphology across the visible hemisphere. These results demonstrate that opportunistic satellite transmissions can support practical, repeatable beam reconstruction, while motivating future chromatic, phase-referenced measurements of the full Jones response.
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Astrophysics of Galaxies
LIGHTS. Limitations of Far-Infrared Tracers for Galactic Cirrus Mitigation in the Era of Ultra-Deep Imaging
Ouldouz Kaboud, Ignacio Trujillo, Ignacio Ruiz Cejudo et al. (+18 more)
Current and forthcoming deep optical imaging surveys are reaching surface brightness levels fainter than 30 mag/arcsec$^2$, where Galactic cirrus emission becomes a significant contaminant. This poses a major challenge for the study of extremely low-surface-brightness extragalactic structures. We investigate the relationship between far-infrared emission, as traced by the Herschel 250 $\mu$m band, and optical surface brightness in the Sloan g- and r-bands. We find that, for Galactic cirrus with $\mu_g\gtrsim$~27 mag/arcsec$^2$, a linear relation is consistent with the data, assuming optically thin dust, with optical cirrus emission amounting to $\sim$0.1% of the far-infrared flux. Using Herschel far-infrared data to trace Galactic cirrus enables its identification over wide areas, but at the cost of significantly reducing spatial resolution. This limitation introduces source confusion and restricts the effective surface brightness depth that can be robustly probed in optical data. We show that, when cirrus emission is modeled using Herschel 250 $\mu$m data, the limiting surface brightness is $\mu_V\sim$~28 mag/arcsec$^2$, substantially shallower than the nominal depth of surveys such as LIGHTS or the 10-year coadd LSST ($\mu_V\sim$~30.5 mag/arcsec$^2$). These results highlight a fundamental limitation in the use of currently available far-infrared data for cirrus mitigation in ultra-deep optical imaging, and emphasize the need for higher-resolution cirrus tracers to fully exploit the depth of upcoming surveys.
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All authors Ouldouz Kaboud, Ignacio Trujillo, Ignacio Ruiz Cejudo, S. Zahra Hosseini-ShahiSavandi, Mireia Montes, Sergio Guerra Arencibia, Mauro D'Onofrio, Dennis Zaritsky, Javier Roman, Nushkia Chamba, Giulia Golini, Chen-Yu Chuang, Minh Ngoc Le, Carlos Marrero-de la Rosa, Zahra Sharbaf, Richard Donnerstein, Sepideh Eskandarlou, Raul Infante-Sainz, Garreth Martin, Samane Raji, Nafise Sedighi
Earth and Planetary Astrophysics
How eccentric is the debris disk of epsilon Eridani? ALMA reveals a near-circular belt
Oto Ulrich, Joshua B. Lovell, David J. Wilner et al. (+2 more)
The nearby (3.2 pc) K2V
star $\epsilon$ Eridani hosts the closest detected debris disk and an exo-Jupiter analog ($\epsilon$ Eridani b). In this work, we reanalyse ALMA Band 6 (1.29 mm) observations of $\epsilon$ Eridani to assess whether its outer debris belt exhibits a non-zero eccentricity, potentially induced by
planet-disk interactions. Considering two models, one that accounts for the disk's forced eccentricity ($e_\mathrm{f}$) and another that accounts for a proper eccentricity ($e_\mathrm{p}$), we place stringent (99.7th-percentile) upper limits of $e_\mathrm{f} < 2.6\%$ and $e_\mathrm{p} < 6.8\%$, respectively, and find tentative evidence for a non-zero forced eccentricity of $e_\mathrm{f} = 1.62^{+0.39}_{-0.40}\%$ at the $4\sigma$ level. This corresponds to the lowest millimeter-derived upper limit on the forced eccentricity of any debris disk to date, which, together with the low upper limit on the proper eccentricity, suggests that the outer belt is nearly circular and dynamically cold. We further explore planetary system architectures that are consistent with these ALMA-based results in combination with Spitzer/IRAC, JWST/NIRCam F444W, and JWST/MIRI F2550W data. Together, these analyses provide insight into potential
planet-disk interactions in this nearby system, constraining any additional
planet beyond $\epsilon$ Eridani b to masses ranging from $\sim 2\times10^{-4}$ to $0.3\,M_\mathrm{Jup}$ at orbital separations of $\sim 6$-$60$ au.
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All authors Oto Ulrich, Joshua B. Lovell, David J. Wilner, Antranik A. Sefilian, Mark Booth
High Energy Astrophysical Phenomena
XClass: An Automated Multiwavelength Machine-Learning Pipeline for Classification of Extragalactic X-ray Sources. I. Pipeline Description
Blagoy Rangelov, Nicholas Moore, Haley Dutton et al. (+1 more)
Most X-ray sources detected in nearby
galaxies by the Chandra X-ray Observatory lack astrophysical classifications. We present XClass (X-ray Classifier for extragalactic sources), an end-to-end machine-learning pipeline that classifies extragalactic X-ray point sources into seven classes: AGN, LMXBs, HMXBs, CVs, low-mass and high-mass foreground
stars, and
supernova remnants. The key challenge is photometric heterogeneity: training sources are predominantly Galactic with photometry from wide-field surveys (PanSTARRS and 2MASS), while extragalactic targets require Hubble Space
Telescope (HST) imaging in a disjoint filter system. We address this through a spectral energy distribution (SED) translation that fits class-appropriate spectral models to each training source and convolves the best-fit model through HST filter curves, producing synthetic magnitudes in a common feature space. The classifier uses an asymmetric two-stage Random Forest: Stage 1 separates broad categories (AGN, X-ray binaries, SNRs,
stars) and Stage 2 resolves X-ray binaries into LMXBs and HMXBs using an augmented feature vector that includes Stage 1 probabilities. The training set is assembled from ten Galactic catalogs and extragalactic SNR catalogs, cross-matched with the Chandra Source Catalog v2.1. Features include X-ray hardness ratios, SED-translated HST colors, and X-ray-to-optical flux ratios. We restrict the training set to sources with at least one optical magnitude, avoiding imputation artifacts; the pipeline achieves 99.6% accuracy and balanced accuracy of 0.90 on the resulting 11,374-source optical baseline, with excellent calibration (ECE = 0.002). XClass is modular, generalizable to any HST filter configuration, and will be applied to M31 and M33 in a companion paper.
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All authors Blagoy Rangelov, Nicholas Moore, Haley Dutton, Erika Marentes
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
QCD axion misalignment during reheating
Disha Bandyopadhyay, Debasish Borah and Nayan Das
We study the production of QCD
axion dark matter (DM) via
vacuum and kinetic misalignment mechanisms during an extended reheating period after the end of slow-roll inflation. With pre-inflationary Peccei-Quinn breaking and considering a monomial inflaton potential during reheating, we classify our study into three different perturbative reheating scenarios in which the inflaton decays into (i) a pair of Standard Model (SM)-like
bosons, (ii) a pair of SM-like
fermions, or (iii) exclusively into a pair of heavy right-handed
neutrinos, which eventually decays into the SM final states after dominating the energy density of the Universe for an intermediate epoch. For each of these reheating scenarios, we study the details of QCD
axion relic separately via
vacuum and kinetic misalignment mechanisms. For different combinations of reheating, monomial inflaton potential and misalignment mechanisms, we identify the parameter space consistent with the observed DM relic density while satisfying other cosmological and laboratory constraints. We also check the scope of probing the currently allowed parameter space at
axion-detection and gravitational wave (GW) experiments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Primordial Black Hole and Gravitational Wave by Peaked Cosmic Perturbations from Axion Curvaton
Keisuke Harigaya, Lian-Tao Wang and Jiangyi Yi
We demonstrate that an
axion field can develop perturbations peaked at an intermediate wavenumber through its inflationary dynamics. We compute the resultant spectrum of gravitational waves (GWs) and primordial black holes (PBHs) generated through the curvaton mechanism. The GW spectrum exhibits a triangular shape, with UV and IR slopes determined by the
axion's inflationary
evolution and treatable as free parameters. In computing the PBH abundance, we properly account for the nonlinear relation between
curvature and density perturbations and the primordial non-Gaussianity generated by the curvaton. The PBHs can account for all of dark matter, accompanied by blue-tilted isocurvature perturbations at small scales. The IR slope of the GW spectrum is anti-correlated with the magnitude of the dark matter isocurvature perturbations, offering a multi-messenger test of the model.
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Astrophysics of Galaxies
Which Milky Way Streams Make the Best Dark Matter Detectors?
Vedant Chandra, Charlie Conroy, Risa Wechsler et al. (+7 more)
The abundance and properties of low-mass dark matter subhalos can be inferred by measuring the density and velocity structure of stellar streams, testing physical models of dark matter. Which streams make the most promising dark matter detectors, and which subhalos would they encounter? We use the semi-analytic model galacticus to simulate the Milky Way's dark subhalos, including tidal stripping under the influence of the galactic disk. Deriving stream initial conditions that best match present-day observations, we forecast subhalo encounters for 24 globular cluster streams around the Milky Way. Over their lifetimes, the 10 most perturbed streams are predicted to each experience $\approx 2$-$12$ significant subhalo encounters with velocity kicks $v_\mathrm{kick} > 0.1$ km s$^{-1}$. Jet, AAU, GD-1, and Palomar 5 lead the list, with Jet encountering twice the subhalos of any other stream. The subhalos that encounter streams have been tidally stripped to $1$-$20\%$ of their peak mass and are twice as compact as previous works have assumed. A spectroscopic survey of streams with sub-km s$^{-1}$ precision could reveal the influence of dark subhalos below the threshold of
galaxy formation. Predicting the abundance and scatter of low-mass subhalos that reach the inner
galaxy remains a dominant uncertainty in connecting stellar streams to models of dark matter.
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All authors Vedant Chandra, Charlie Conroy, Risa Wechsler, Ana Bonaca, Andrew Benson, Jacob Nibauer, Tara Dacunha, Philip Mansfield, Paul Menker, Anya Phillips
High Energy Astrophysical Phenomena
Three New Likely Spider Millisecond Pulsar Binaries and Optical Kinematic Tracers of Intrabinary Shocks
Jay Strader, Rebecca Kyer, Laura Chomiuk et al. (+9 more)
We report the discovery of three candidate spider millisecond
pulsars via multi-wavelength follow-up of unassociated Fermi Large Area
Telescope gamma-ray sources. All have optical spectroscopy from the SOAR 4.1-m
telescope and X-ray data from Swift. Two optical/X-ray sources are exceptionally strong redback candidates, sitting close to the centres of the localization ellipses of the gamma-ray sources 4FGL J1020.4-5314 and 4FGL J1408.7-3747. We show that both optical sources are spectroscopic binaries with orbital periods (0.15-0.3 d) and mass functions (0.6-0.9 Msun) typical for redbacks. 4FGL J1020.4-5314 shows bright, very broad (full width at half maximum 2100 km/s) H-alpha emission in all spectra obtained over two years. Remarkably, the H-alpha radial velocities are offset in phase from the absorption-line velocities of the secondary, and match the signal expected for an emission source near the primary. This demonstrates, for the first time for any spider, that the H-alpha emission can be associated with an intrabinary shock that wraps around the
pulsar, opening up the possibility of using optical emission lines as kinematic tracers of the intrabinary shock in some redbacks. A third candidate spider is less secure in its association with the gamma-ray source 4FGL J1429.8-0739, but has unusual properties, including a 30.5-hour orbital period, a potential subgiant secondary, and a high X-ray luminosity, making it worthy of further investigation.
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All authors Jay Strader, Rebecca Kyer, Laura Chomiuk, Elias Aydi, Peter Craig, Thomas M. Do, Isabella Molina, Teresa Panurach, Subhroja Roy, Kirill V. Sokolovsky, Samuel J. Swihart, Ryan Urquhart
Solar and Stellar Astrophysics
Gaia neutron stars: demographics, birth rates, and connections to other neutron star populations
Cheyanne Shariat, Natsuko Yamaguchi, Kareem El-Badry et al. (+1 more)
Gaia DR3 revealed a new class of
neutron stars (NSs) in au-scale orbits with solar-type companions. How these 'Gaia NSs' form remains unclear, and constraining their intrinsic population properties is a necessary step toward understanding their origin. However, the current sample of 27 Gaia NS candidates is strongly biased by Gaia's astrometric sensitivity. In this work, we carefully model the Gaia selection function and incorporate it into a hierarchical
Bayesian framework to infer the intrinsic demographics of the Gaia NS population. We find that the population favors a decreasing period distribution with power-law slope $\alpha_P=-0.75 \pm 0.35$, a visible-
star mass distribution peaked near $M_1\approx 0.85~{\rm M_\odot}$ ($\sigma_{M_1} \approx 0.2~{\rm M_\odot}$), an NS mass distribution peaked near $M_{\rm NS}\approx 1.3~{\rm M_\odot}$ with a tail towards higher masses, and an eccentricity distribution weighted toward moderate-to-large eccentricities. The intrinsic space density is $n\approx120~{\rm kpc^{-3}}$ within 2 kpc, implying that only $\sim3\%$ of the local Gaia NS population has been discovered so far. Our forecasts predict that Gaia DR4 will increase the sample to $\sim300$-650 NS candidates, including access to longer orbital periods that will provide direct tests of formation models. Finally, we place Gaia NSs in the context of the broader Galactic NS population by comparing their intrinsic birth rate, lifetime, and size to other classes of isolated and binary NSs. Only 0.01% - 1% of all NSs are born into au-scale orbits with solar-type companions, making the birth rate of Gaia NSs 10 - 100 times smaller than that of high-mass X-ray binaries and broadly comparable to symbiotic X-ray binaries.
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All authors Cheyanne Shariat, Natsuko Yamaguchi, Kareem El-Badry, Thomas J. Maccarone
Astrophysics of Galaxies
Water enhances the formation of refractory sulfur in interstellar ices
Carlos del Burgo Olivares, Hector Carrascosa, Guillermo M. Muñoz Caro et al. (+3 more)
Sulfur is the tenth most abundant element in space, yet it is strongly depleted in the gas phase of dense interstellar regions, suggesting sequestration in dust grain components that are difficult to detect. We study whether UV irradiation and thermal processing of H2S-containing interstellar-ice analogues can produce refractory sulfur species, and whether water-dominated ice enhances their formation. We performed UV irradiation and warm-up experiments on H2S-containing ice analogues with and without water, and the resulting refractory residues were analysed ex situ. Refractory sulfur species, including the sulfur allotropes S6-S8, are formed during UV irradiation and thermal processing of H2S-containing interstellar-ice analogues. Water enhances the formation of these sulfur allotropes by two orders of magnitude. We propose a formation mechanism in which ionic intermediates stabilised by the water-ice
matrix promote chain growth and cyclisation, yielding predominantly S8. The combined detection in our residues of sulfur allotropes and polythionic species, also reported in meteorites and samples returned from asteroids, supports their formation in pre-cometary ice mantles covering dust grains. Because these species can incorporate multiple sulfur atoms per molecule, they constitute an efficient solid-phase reservoir for the missing sulfur in dense cloud environments where young
stars are born. Refractory sulfur can therefore serve as a tracer of water-ice environments in space.
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All authors Carlos del Burgo Olivares, Hector Carrascosa, Guillermo M. Muñoz Caro, Rafael Lebron-Aguilar, Jose E. Quintanilla-Lopez, Yao-Jen Chen
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
From the Old to the New Starobinsky Inflation
Shinji Hirano
Starobinsky's original model of inflation, driven by the trace anomaly of conformal fields, and its $R+R^2$ (scalaron) formulation are often treated separately. The original anomaly-driven
evolution connects an early de Sitter phase supported by the Euler anomaly to a scalaron regime, where the observable modes leave the horizon. Building on this known background connection, we compute the scalar and tensor spectra on the exact background and find that the anomaly corrections are controlled by $aN_*/(18b)$, where $a$ and $b$ are the Euler-anomaly and $R^2$ coefficients and $N_*$ the number of e-folds after the pivot exits the horizon; scalaron inflation is recovered as this parameter vanishes. The observed tilt at $N_*=60$ then requires only $b/a\simeq35$, rather than the $b/a\gtrsim10^9$ of early realizations. At this
benchmark the scalar spectrum is redder than in scalaron inflation at fixed $N_*$, and the tensor-to-scalar ratio is about 17% lower at fixed tilt, a quantitative signature of the anomaly. For minimal gravitational reheating, $N_*\simeq53$, the tilt remains within $1\sigma$ of the Planck value for $b/a\gtrsim35$. In the de Sitter analysis, a finite range of the Weyl coupling excludes an extra real
spin-two pole and keeps the causal response decaying. A companion paper gives the full analysis.
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Astrophysics of Galaxies
Probing the Reionization History and Bubble Sizes with JWST Lyman-$\alpha$ Fraction Measurements
Aritra Kundu, Adam Lidz and Guochao Sun
Recent James Webb Space
Telescope (JWST) measurements quantify the fraction of ultraviolet-selected
galaxies showing detectable Lyman-alpha (Ly-$\alpha$) lines at $z \sim 6-14$. These Ly-$\alpha$ fractions are partly shaped by Ly-$\alpha$ scattering from neutral hydrogen in the surrounding intergalactic medium (IGM), and so the observed Ly-$\alpha$ fraction
evolution can inform our understanding of the reionization history and the size distribution of ionized bubbles during reionization. We compare the JWST measurements with Ly-$\alpha$ transmission calculations based on both the THESAN reionization simulations and a flexible semi-analytic model. In each case, we calibrate a sub-grid model for the intrinsic Ly-$\alpha$ emission lines emerging from the interstellar medium (ISM) and circumgalactic medium (CGM) of the host
galaxies using empirical estimates of the Ly-$\alpha$ equivalent width (EW) distributions at $z \sim 6$. We find that the reionization history and bubble sizes in THESAN yield good agreement with current JWST Ly-$\alpha$ fraction observations, with a reduced $\chi^2_\nu = 0.4-1.2$. Our semi-analytic models and THESAN Ly-$\alpha$ transmission calculations agree well, allowing us to explore a wide range of reionization models. We derive $1\sigma$ bounds on the average mass-weighted neutral fractions of: $\langle x_{\mathrm{HI}} \rangle$ = $0.38^{+0.14}_{-0.38}$ ($0.52^{+0.09}_{-0.21}$), $0.57^{+0.23}_{-0.57}$ ($0.68^{+0.12}_{-0.39}$), and $0.93^{+0.05}_{-0.17}$ ($0.89^{+0.11}_{-0.15}$) at $z \sim$ 7, 8, and 11, based on the Ly-$\alpha$ fraction measurements with EW $>25\,\mathring{\rm A}$ ($>10\,\mathring{\rm A}$).
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Instrumentation and Methods for Astrophysics
Two bits about lossy compression: On the limits of compression in cosmology
Hurum Maksora Tohfa and Matthew McQuinn
Astronomy is in an era of enormous sky surveys and of the large simulation suites needed to interpret them, both costly to store and slow to share. Simulation outputs are stored as 32-bit floats, yet numerical noise and astrophysical uncertainties make better than percent-level pixel accuracy unnecessary. Because cosmological fields are statistically homogeneous with nearly Gaussian mode amplitudes, classic rate-distortion results apply directly, and non-Gaussian structure permits further compression. We use the scientific compression package SZ3, and a neural compressor that fixes the quantization and learns the probability of each quantization bin with an autoregressive
transformer. SZ3 beats the Gaussian approach only where the field is smooth on the pixel scale or its values pile up at a single point, while the neural approach matches or beats SZ3 on every field we consider and is 9 to 27% below the Gaussian-optimal coder at fixed distortion, with the largest margin where the field is most non-Gaussian. Because the quantizer, not the network, sets the error, a poorly trained model can waste bits but never cost accuracy. A model trained only on weak
lensing convergence maps transfers to $N$-body density fields without retraining, suggesting it has learned generic properties of cosmological structure rather than features of one
dataset. Eulerian grids need only 1-4 bits per pixel (bpp) at percent-level accuracy, and particle displacements and velocities 5-6 at the precisions they require. The approach carries over to observational data: on Rubin Observatory Data Preview 1 coadds, with the quantization step set to a quarter of the background noise, the fine-tuned
transformer needs 4.0 bpp, 27% fewer than the Gaussian coder.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Interpreting the High-Recoil LUX-ZEPLIN Event with Bino-/Singlino-like and Higgsino Dark Matter
Subhojit Roy, Pedro Schwaller and Carlos E. M. Wagner
The LUX-ZEPLIN (LZ) experiment has recently reported a nuclear-recoil candidate at $E_R\simeq248$ keV. We study two supersymmetric interpretations based on distinct neutralino couplings to the $Z$
boson. In the elastic case, a bino- or singlino-like neutralino scatters through a diagonal axial $Z$ coupling set by the Higgsino asymmetry $X=|N_{13}|^2-|N_{14}|^2$ rather than by the total Higgsino fraction. Since the
spin-dependent blind spot does not coincide with the
spin-independent one,
Higgs-mediated scattering can be suppressed while retaining $X\sim10^{-2}$. In the MSSM this favors low $\tan\beta$, in tension with the observed
Higgs mass for a few-TeV squark spectrum, a tension relieved by the tree-level quartic of the NMSSM. An explicit NMSSM
benchmark with $m_\chi\simeq500$ GeV and $X\simeq0.007$, below current LZ limits, obtains its relic abundance from a singlet-like pseudoscalar resonance just above threshold, which also suppresses present-day annihilation. In the inelastic case, a pseudo-Dirac Higgsino scatters endothermically, with a splitting of a few hundred keV generated by gauginos at the PeV scale which can be lowered by opposite-sign bino-wino cancellation, or by weak singlino mixing; the minimal thermal realization is strongly constrained by solar-
neutrino searches. The two mechanisms predict distinct recoil spectra away from the candidate.
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Astrophysics of Galaxies
Sub-kiloparsec Test of the Kennicutt-Schmidt Relation in a Strongly Lensed Dusty Star-Forming Galaxy at z~2.78
C. Cornil-Baïotto, J. Molina, G. Mahler et al. (+9 more)
[abridged]
Star formation is a key process driving
galaxy evolution, but understanding how it proceeds within the interstellar medium (ISM) requires resolving cold molecular gas and dust on sub-kpc scales. At z~2-3, near the peak of
cosmic star formation, such resolution can generally only be achieved through strong gravitational
lensing. We present an ALMA study of SMMJ0658, a 20x-magnified main-sequence
star-forming
galaxy at z=2.7768 +/- 0.0002, lensed by the Bullet Cluster (z=0.296) into three images. We use 0.2" and 0.6" ALMA Band-3 observations to test the Kennicutt-Schmidt (KS) relation at sub-kpc scales at
cosmic noon. Using a JWST-based strong-
lensing model of the Bullet Cluster, we reconstruct source-plane CO(3-2) and rest-frame 803um dust-continuum maps down to ~200pc scales. We derive spatially resolved molecular gas and
star formation rate surface densities, depletion times, and the scale dependence of the CO-to-dust flux ratio over 200pc-3.2kpc apertures. The 0.2" ALMA data reveal massive, dense
star-forming clumps, with Sigma_mol ~1.3-2.3 x 10^3 M_sun pc^-2, Sigma_SFR ~0.5-2.3 M_sun yr^-1 kpc^-2, and tau_dep ~0.82-2.56 Gyr. CO-dust spatial decorrelation produces a strong scale dependence in tau_dep. We find a KS-relation breakdown scale of 0.8 +/- 0.1 kpc, consistent with individual regions tracing distinct stages of the
star-formation cycle. The ALMA and JWST data also reveal evidence for a lensed
galaxy pair at z~2.78, although whether SMMJ0658 is undergoing an early-stage interaction remains uncertain. Our results show that the apparent universality of the KS relation breaks down once individual
star-forming regions are spatially resolved, in line with observations from the local universe to z~1. We extend this picture to z~2.78, providing new insight into the resolved properties of the clumpy cold ISM and the
star-formation cycle at
cosmic noon.
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All authors C. Cornil-Baïotto, J. Molina, G. Mahler, G. Rihtaršič, M. Boquien, M. Bradač, E. Ibar, A. H. Gonzalez, T. Verdugo, O. López-Cruz, J. Magaña, V. Motta
Cosmology and Nongalactic Astrophysics
Is DESI Seeing Dynamical Dark Energy, or a Cosmic Glitch in Gravity?
Robin Y. Wen, Lukas Tobias Hergt, Niayesh Afshordi et al. (+1 more)
Combined baryon acoustic oscillation and
cosmic microwave background data have begun to mildly favor departures from $\Lambda\mathrm{CDM}$. This is usually framed as 2-parameter dynamical dark energy. However, a 1-parameter "
cosmic glitch in
gravity" model, whose cosmological gravitational coupling differs from Newton's constant as in Hořava
gravity, fits at least as well. $\textit{Planck}$+ACT+SPT and DESI~DR2 give $G_\mathrm{cosmo}/G_\mathrm{N}=0.9920\pm0.0025$, a $3.3\,\sigma$ preference for weaker cosmological
gravity, robust to adding CMB
lensing and
supernovae. Fitted to the CMB alone, the glitch predicts DESI distances; $w_0w_a$CDM does not.
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All authors Robin Y. Wen, Lukas Tobias Hergt, Niayesh Afshordi, Douglas Scott
High Energy Astrophysical Phenomena
A new method for inspiral-to-ringdown waveforms of compact binaries: Helmholtz orbits and spherical-Bessel flux
Hong-Bo Jin
The waveform is obtained from one balance of energy and radiation on Helmholtz orbits of the retarded mass kernel, with a spherical-Bessel flux. That balance follows from the Dirac–Maxwell equation with a modified vertex, the single $U(1)$ coupling being replaced by the eight operators of the source interaction. After contact that balance is the energy loss of one packet: a bounded well for a black-hole remnant and the Coulomb ladder of one
star for a
neutron-
star remnant. Ringdown starts from the spherical projection of that end state, which contains its
spin. The comparisons use model waveforms at the published parameters. For GW250114, at the Coulomb-radius contact and after a shift of $-16\,\mathrm{ms}$, the noise-weighted norm ratio against the NRSur7dq4 median in $100$–$200\,\mathrm{Hz}$ stays between $1.36$ and $1.94$ across the published distance interval. Stopping at $2.4$ times that radius lowers the ratio to $1.11$, which the same interval moves from $0.94$ to $1.35$. With contact placed on the published merger time and with no time shift, that ratio is $3.32$ at the Coulomb radius and $2.30$ at $2.4$ times that radius. At the larger radius, the unretarded limit of this balance, with unit spherical-Bessel weights, reaches contact at $94\,\mathrm{Hz}$, and in $20$–$100\,\mathrm{Hz}$ the norm ratio to the Helmholtz balance is $1.12$ after a shift of $+27\,\mathrm{ms}$. For GW170817, $|h_{+}|$ near $100\,\mathrm{Hz}$ is $8.0\times10^{-23}$, and the mismatch against the $2.5$PN inspiral is a difference in phasing.
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Astrophysics of Galaxies
The assembly history of NGC 1365 through chemical archaeology
Lisa J. Kewley, Kathryn Grasha, Alex Garcia et al. (+8 more)
Galaxies build through infalling gas and
galaxy mergers. Tracking the dynamical history of a
galaxy from a single snapshot in time is notoriously difficult. We show that the dynamical history of a
galaxy can be tracked using oxygen abundances as archeological tracers. We derive the gas-phase oxygen abundances for 4546 spaxels across the face-on spiral
galaxy NGC~1365 at a spatial resolution of 175 pc, providing one of the most detailed chemical fossil records of a spiral
galaxy outside our Milky Way. We apply IllustrisTNG cosmological simulations to analyse the chemical abundance distribution in a theoretical model for NGC~1365. In the model, the main disk oxygen abundance gradient formed earliest, 11.9-12.5 billion years ago via mergers with multiple dwarf
galaxies. A steep inner bar gradient formed slowly over the last 12 billion years through enrichment from
star formation triggered by the infall of gas into the nuclear regions. An extended ionized gas disk with flat oxygen abundances was assembled more recently (5.9-8.6 billion years ago) through a minor merger. This work indicates that cosmological simulations and ultra-high spatial resolution oxygen abundances together can provide an archaeological probe of the
star formation and merger histories of spiral
galaxies.
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All authors Lisa J. Kewley, Kathryn Grasha, Alex Garcia, Paul Torrey, Jeff Rich, Z. S. Hemler, Qian-hui Chen, Peixin Zhu, Mark Seibert, Lars Hernquist, Barry Madore
Cosmology and Nongalactic Astrophysics
Improved Constraints on Cosmic Microwave Background Circular Polarization with CLASS
Thomas Essinger-Hileman, Caleigh Ryan, Yunyang Li et al. (+25 more)
We present improved constraints on circular polarization in the
cosmic microwave background (CMB) from the Cosmology Large Angular Scale Surveyor (CLASS) experiment using data at 90, 150, and 220 GHz to complement previous results based on 40 GHz data alone. We extend constraints on circular polarization from the atmosphere to all CLASS frequencies and compare with a model of the atmospheric circular polarization spectrum. The inclusion of data at all CLASS frequencies improves upper limits on circular polarization, Stokes $V$, in the CMB by a factor of $\sim 5$ at the largest angular scales ($10 < \ell < 30$) and extends the constraints to smaller angular scales, $\ell = 700$. In combination with Planck temperature data, we provide the first limits on the temperature-circular-polarization ($TV$) power spectrum to date. Both circular polarization ($VV$) and $TV$ power spectra are consistent with zero, and CLASS places upper limits of $5.4 \times 10^{-3}$ $\mu$K$_{\text{CMB}}^2$ on $VV$ at large angular scale ($10 < \ell < 30$) and $5.8 \times 10^{-1}$ $\mu$K$_{\text{CMB}}^2$ on $TV$ at 95% confidence at $30 < \ell < 50$.
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All authors Thomas Essinger-Hileman, Caleigh Ryan, Yunyang Li, Matthew A. Petroff, John W. Appel, Charles L. Bennett, Ricardo Bustos, Carol Yan Yan Chan, David T. Chuss, Joseph Cleary, Sumit Dahal, Rahul Datta, Jullianna Denes Couto, Kevin L. Denis, Joseph R. Eimer, Joseph E. Golec, Kyle R. Helson, Jeffrey Iuliano, Tobias A. Marriage, Jeffrey J. McMahon, Ivan Padilla, Carolina Morales Perez, Karwan Rostem, Rui Shi, Deniz A. N. Valle, Duncan J. Watts, Janet L. Weiland, Edward J. Wollack
Cosmology and Nongalactic Astrophysics
A machine learning-based method for populating dark matter halos in N-body simulations with substructure
Milad Noorikuhani and Jeremy Tinker
Dark matter N-body simulations that resolve
halo substructure (subhalos) with high accuracy can be used for generating reliable catalogs of central and satellite
galaxies via
galaxy-
halo connection models. However, such simulations are computationally expensive, especially when large numbers of realizations are required for statistical analyses such as robust estimations of covariance
matrices for (statistical) cosmological quantities. In this work, we present a fast method for populating dark matter
halos in a given simulation box with subhalos extracted from a high-resolution simulation box with the same cosmology but arbitrary initial conditions. For each
halo in a given test set, the method first predicts whether it hosts at least one subhalo above a given mass threshold using a classifier built on a decision tree regressor. Then, for each predicted host, the method finds another host
halo in a given high-resolution box, using a nearest neighbor search in the space of selected
halo properties, and appropriately maps subhalos from that
halo to the test one. By applying the method to different test sets, we make predictions for abundances, distributions and three-dimensional and projected (two-dimensional) two-point correlation functions of various subhalo populations and sub-populations. In most cases, the percent errors of our predictions are well below 5%. In general, the method can be used to populate
halos in low-resolution simulation boxes with subhalos from a high-resolution simulation and also to investigate which
halo properties are (more strongly) correlated with subhalo abundance and clustering in a given dark matter simulation.
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Earth and Planetary Astrophysics
Flow dynamics of cryolava or impact melt on Titan's surface
Daniel Cordier, Bastien Bodin, Stephane Le Mouelic et al. (+1 more)
Titan, a unique body in the solar system, resembles a life-size Miller-Urey experiment where pockets of
liquid water might interact with abundant organic matter. Its young surface (less than a billion years) shows signs of material exchange with the interior, and an isotopic signature is detected in the atmosphere. Cryovolcanism and meteor impacts represent potential high energy mechanism for these exchanges. Although cryolava or impact melt properties are largely unknown, Titan's internal structure makes a significant water content in these fluids highly probable. The temperature of these fluid mixtures at the onset of the flows is above 0~$^\circ$C. The primary objective of this work is to investigate the dynamical and thermal properties of potential Titanian flows, while ensuring their spatial extents remain broadly consistent with the few available observations. We also aim to assess whether their
evolution could enable the hydrolysis of encountered organic material. On Earth, in the context of lava flow risk assessment, numerical techniques based on cellular automata have been developed for many years. This approach allows simulating the flow of Bingham fluids over distance scales of several tens of kilometers. In the context of Titan's surface, and within the explored parameter space, flows with a spatial extent of several tens of kilometers can be produced with our model. The resulting flow thickness is about a meter. The flow extent is primarily controlled by the total erupted volume and the terrain
topology. As expected, the rheology and thermo-physical properties of the erupted fluid have significant influence on the flow's extent and the cooling rate of the cryolava. We predict hydrolysis reactions between an aqueous cryolava and the organic matter likely ubiquitous on Titan's surface. Our model code is publicly available.
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All authors Daniel Cordier, Bastien Bodin, Stephane Le Mouelic, Ashley G. Davies
Astrophysics of Galaxies
When Streams Curve Away: a Test of Dark Matter from Extragalactic Stellar Stream Populations
Nathaniel Starkman, Jacob Nibauer, Sarah Pearson et al. (+2 more)
The nature of dark matter sets the shape of galactic
halos: collisionless cold dark matter (CDM) predicts triaxial
halos, while scattering in self-interacting dark matter (SIDM) rounds them toward sphericity. We show that a large catalog of projected stellar stream tracks can statistically constrain
halo shapes, and therefore the particle nature of dark matter, without detailed modeling of any individual stream or gravitational potential. We develop a new
geometric diagnostic for stellar streams: if the
curvature of any segment along a stream points away from the host
galaxy's projected center of mass, then that stream falsifies broad classes of potentials, including spherical ones. We call such a segment convex. The diagnostic needs only a projected stream track and a host-center estimate, requiring no kinematics, distances, progenitor model, or fit to individual host potentials.
Halo triaxiality sets the rate at which streams show convex segments, making this rate an observable of the
halo-shape distribution and the underlying dark-matter model. We forecast that upcoming survey-scale stream morphology catalogs can discriminate between CDM and SIDM at up to $5\sigma$.
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All authors Nathaniel Starkman, Jacob Nibauer, Sarah Pearson, Sirui Wu, Lina Necib
Solar and Stellar Astrophysics
MAGiDiff: Sampling the Photospheric Vector Field from UV/EUV Filtergrams
Ruoyu Wang and David Fouhey
Photospheric vector
magnetic fields are foundational to modeling, understanding, and forecasting solar activity. These data are usually produced by inverting and disambiguating the full Stokes vector at multiple passbands, which is demanding. Here, we investigate how well we can estimate photospheric vector magnetograms from UV/EUV filtergrams. This problem is challenging and intrinsically ambiguous without polarization information, as the mapping from UV/EUV intensity to the
magnetic field is indirect and ill-posed. We introduce MAGiDiff, a machine-learning-based method that uses denoising
diffusion models to estimate vector magnetograms from UV/EUV filtergrams. As input, MAGiDiff takes a stack of filtergrams from the Solar Dynamics Observatory (SDO) / Atmospheric Imaging Assembly (AIA); as output, it is trained to estimate the disambiguated vector magnetogram as seen by Hinode / Solar Optical
Telescope-Spectro-Polarimeter (SOT-SP). We show that MAGiDiff can accurately mimic the Hinode ground-truth. Additionally, we probe MAGiDiff's understanding of the physical structure and
magnetic connectivity. On full-disk, we show that it produces plausible structures for active regions. MAGiDiff generalizes across solar cycles despite hemispheric polarity reversal, and can be fine-tuned to other EUV instruments including STEREO/EUVI and GOES-R/SUVI. While clearly not a substitute for a dedicated instrument, MAGiDiff opens the door to new capabilities.
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Solar and Stellar Astrophysics
Tracing star formation across the Rosette nebula using deep Spitzer imaging
Daniel Capela, Aleks Scholz, Koraljka Muzic et al. (+4 more)
We present a deep large-scale infrared survey of young stellar objects in the Rosette Nebula. Our analysis is based on stacked archival Spitzer/IRAC images. The images have been treated with the software DeNeb to remove nebulous emission. Our catalogue contains ~20000 sources with photometry in all 4 IRAC bands from 3.6 to 8.0 microns, complemented with near-infrared and optical data. From this database, we identify YSOs using multi-filter colour-colour criteria. We select 1528 YSOs, from which 1303 are Class II and 225 are Class I. Using this sample, we compile a list of clusters and groups of YSOs in the Rosette region, including previously known ones, plus three newly identified groups. Using our census of YSOs, in combination with the literature, we derive the Class I ratios and disk fractions for clusters in the nebula. The main clusters in the central cavity, NGC 2244 and NGC 2237 are almost devoid of Class I sources, indicating that
star formation has ceased in this area. On the other hand, in an annulus around the centre with radii of 11-16 pc, roughly coinciding with the expanding HII front, about 30% of the YSOs are Class I, a clear sign of ongoing
star formation. Other groups further out in the cloud also exhibit a high Class I ratio. Similar patterns are seen in the disk fractions. Our results are consistent with possible triggering by the expanding HII region, combined with
star formation beyond the ionisation front.
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All authors Daniel Capela, Aleks Scholz, Koraljka Muzic, Herve Bouy, Belinda Damian, Victor Almendros-Abad, Amelia Bayo