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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 29 June

Cosmology and Nongalactic Astrophysics · Cross-listed from physics.data-an

The Squealer: Sensification of model exploration and model misfit

Andrew Gelman, Andrew H. Jaffe, Eliot Carlson et al. (+1 more)

We introduce a method for visual and auditory feedback when exploring the fit of a model to data. Starting with a best-fit curve fit to data, the user can drag the curve to a new position and the computer will emit a squeal, becoming louder and more unpleasant as the discrepancy between curve and data increases. We demonstrate with four examples: a two-parameter curve fit to golf putting data, a four-parameter curve fit to dilution assays, a fit to cosmological data sensitive to the parameters of the Big Bang model, and a nonparametric Gaussian process fit to temperature readings.
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All authors Andrew Gelman, Andrew H. Jaffe, Eliot Carlson, Philip Greengard

Solar and Stellar Astrophysics

High Resolution Spectroscopic Analysis of Chromospheric Line Evolution during an Energetic Flare on AD Leo

Younghun Oh, Seo-Won Chang, Jongchul Chae et al. (+6 more)

Active M dwarfs exhibit frequent and energetic flares that provide a unique laboratory for studying chromospheric heating processes under extreme magnetic activity. To probe the flare process of M-dwarfs, we present a high-resolution ($R\sim30{,}000$) spectroscopic case study of a superflare on AD Leo, detected on 2023 March 14 using the Bohyunsan Optical Echelle Spectrograph (BOES). Such high-energy events are rarely captured with simultaneous multi-line spectroscopy, allowing us to trace the energy partition and temporal evolution of the chromospheric lines. Based on equivalent width variations, we found that the H$\alpha$ line radiated $8.8\times10^{30}$ erg, implying a total bolometric energy ($\sim10^{33}$ erg) comparable to the largest solar flares. The Balmer series dominated the energy budget; the individual Ca II H and K lines contributed 47.5% and 26.2% of the H$\alpha$ energy, respectively, while each Ca II infrared triplet line emitted $\sim$17-19%. We confirm that the delayed peak emission, previously reported for Ca II H&K, also occurs in the Ca II triplet and Na I lines. These delays are consistent with the Neupert effect, suggesting that cumulative heating governs the gradual phase emission. While this superflare resembles solar flares in general morphology, it also displayed systematic differences in chromospheric emission. It is likely that these differences reflect the distinct atmospheric structure and quiescent chromospheric conditions of M dwarfs, rather than fundamentally different flare physics.
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All authors Younghun Oh, Seo-Won Chang, Jongchul Chae, Juhyung Kang, Soosang Kang, Kyeore Lee, Kyoung-Sun Lee, Eun-Kyung Lim, Hyun-Il Sung

High Energy Astrophysical Phenomena

Constraints on Hadronic Emission from Microquasars Detected by LHAASO

V. Vecchiotti, E. Amato, G. Giacinti et al. (+2 more)

Recently, the LHAASO collaboration reported ultra-high-energy (UHE) gamma rays from six microquasars. For five of these sources, the emission extends beyond $100$ TeV, making microquasars promising candidates for Galactic PeVatrons. We investigate whether gamma-rays around $100$ TeV originate from hadronic interactions of accelerated cosmic rays (CRs) with the ambient medium, and we estimate the contribution of these sources to the measured CR spectrum around the knee. We also place upper limits on six LHAASO microquasars with no detected UHE emission. We assume diffusion-dominated propagation of CR, with a diffusion coefficient suppressed compared to the average Galactic value near the source and equal to the Galactic value at large distances. We assume continuous injection over timescales of $t_{\rm age}=0.1-1$ Myrs. Using available measurements of the gas density, we find that hadronic interactions alone cannot fully account for the observed emission for any of the detected sources. However, in the case of GRS 1915+105 and MAXI J1820+070, the hadronic scenario may still be valid when considering acceleration efficiency higher than $10\%$. We then derive upper limits on the hadronic contribution to the observed gamma-ray flux. We estimate that the detected sources contribute at most $\sim4\%$ of the Galactic CR spectrum at $1$ PeV for an injection timescales of $0.1$ Myrs and a CR acceleration efficiency of $10 \%$. When adopting the maximum acceleration efficiency allowed by the gamma-ray observations the contribution rises to $37\%$. Longer injection timescales ($\sim 1$ Myrs) lead to contributions exceeding the observational constraints. For sources not detected at UHE, we obtained a maximum contribution of $\sim 17\%$, achieved assuming continuous injection over $1$ Myr.
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All authors V. Vecchiotti, E. Amato, G. Giacinti, G. Morlino, G. Peron

Cosmology and Nongalactic Astrophysics

Superhorizon curvature perturbations in hybrid inflation revisited

Shi Pi and Anxianyi Xiong

We revisit cosmological perturbations in multi-field inflation using the $\delta N$ formalism. By extending the analysis to directions transverse to the inflationary trajectory, we explicitly account for the geometry of the final hypersurface. Applying this framework to hybrid inflation, we identify an enhancement mechanism of the curvature perturbation driven by the growing isocurvature perturbation due to the tachyonic instability of the waterfall field. This amplification occurs during the trajectory's turn in field space, a process qualitatively distinct from the non-attractor solution in single-field inflation models such as ultra-slow-roll. The resulting power spectrum features a broad peak with a characteristic $k^3$ infrared growth and a ultraviolet spectral tilt that uniquely determines the nonlinear parameter $f_\mathrm{NL}$ of a logarithmic non-Gaussianity, all of which are primarily governed by the waterfall dynamics. We found that in hybrid inflation, the sign of $f_{\rm NL}$ is fixed by tachyonic waterfall geometry and is always positive, leading to a generic enhancement of primordial black hole formation. The enhanced curvature perturbation can simultaneously account for primordial black hole dark matter and a stochastic gravitational wave background detectable by LISA, Taiji, and TianQin.
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Instrumentation and Methods for Astrophysics

Design Method of Quasi-Lumped Element Bandpass Filters Using Superconducting Coplanar Waveguide for Millimeter-Wave Multichroic Imaging

Shinsuke Uno, Kah Wuy Chin, Tai Oshima et al. (+6 more)

An on-chip band-defining filter coupled with a superconducting photon detector is a promising technology for developing multi-band imaging cameras at millimeter and submillimeter wavelengths. In this paper, we present the design of on-chip bandpass filters based on coplanar waveguide geometry, which can be easily integrated into large-format multi-band detector arrays. A lumped element filter design is suitable not only for achieving a compact footprint but also for suppressing harmonics to reduce band-to-band crosstalk in a multiplexer. However, the coplanar waveguide geometry and the photolithography process rule limit the maximum available inductance and capacitance of lumped elements, which does not sufficiently meet the requirements of filter circuits. To overcome this limitation, we have established a design method for quasi-lumped element filters, in which the maximum element size is relaxed to a quarter wavelength, exceeding the ideal lumped element size. We achieved design solutions for 150, 220, and 270 GHz 8th-order Chebyshev bandpass filters and a triplexer. We also report on the measurement results of a scaled model of the bandpass filter, demonstrating the validity of our proposed filter design.
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All authors Shinsuke Uno, Kah Wuy Chin, Tai Oshima, Satoshi Ono, Takeshi Sakai, Kazuki Watanabe, Shuhei Inoue, Tatsuya Takekoshi, Kotaro Kohno

Instrumentation and Methods for Astrophysics

Broadband anti-reflection coating for sub-terahertz optics using dielectric multilayers

Toyo Naganuma, Shinsuke Uno, Shuhei Inoue et al. (+4 more)

Sub-terahertz astronomy requires instruments capable of simultaneous observations across multiple spectral bands, motivating the development of broadband anti-reflection coatings (ARCs). We investigated low-loss dielectrics with refractive indices suitable for multilayer ARCs on polyethylene optical elements and identified candidates that partially meet the requirements. To address the remaining gaps in available refractive indices, we applied dielectric multilayer synthesis by combining newly identified thin materials with controlled bonding to realize the required effective refractive indices. As a result, the fabricated 5-layer ARC achieved reflection losses of 0.2% (average) and 3.2% (maximum) over 130-710 GHz.
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All authors Toyo Naganuma, Shinsuke Uno, Shuhei Inoue, Kazuki Watanabe, Tatsuya Takekoshi, Takeshi Sakai, Tai Oshima

Instrumentation and Methods for Astrophysics

GLTCAM: Concept of Multi-color Millimeter and Submillimeter Camera for the Greenland Telescope

Shuhei Inoue, Tatsuya Takekoshi, Shinsuke Uno et al. (+12 more)

To investigate the formation history of large-scale structure through the dynamics of galaxy clusters, we are developing a multi-color millimeter and submillimeter-wave continuum camera (GLTCAM) for deployment on the Green-land Telescope (GLT). GLTCAM will observe in six frequency bands - three in the millimeter range (150, 220, and 270 GHz) and three in the submillimeter range (350, 400, and 670 GHz). The optical design provides a compact configuration that fits within the GLT receiver cabin, while delivering diffraction-limited performance over an $18'$ field of view with minimal telecentricity error and distortion. A key advantage of this design is its uniform illumination footprint at the cold stop, which helps minimize thermal loading on both the detectors and the cryogenic stages. The focal plane module comprises a quasi-optical bandpass filter, a conical horn array coupled with planar ortho mode transducers (OMTs), and a superconducting multi-color microwave kinetic inductance detector (MKID) array. Current development efforts are focused on the three-color millimeter-wave module. The detector array employs a single-layer coplanar waveguide (CPW) architecture, which simplifies fabrication and enables scalability to large-format arrays. GLTCAM aims for the early realization of next-generation wide-field, multi-color observations as a pathfinder for future large submillimeter telescopes.
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All authors Shuhei Inoue, Tatsuya Takekoshi, Shinsuke Uno, Kazuki Watanabe, Taiki Sato, Toshihiro Tsuzuki, Satoru Mima, Tohru Taino, Kazuyuki Fujita, Shunichi Nakatsubo, Yuki Kimura, Chiko Otani, Ryohei Kawabe, Kotaro Kohno, Tai Oshima

Cosmology and Nongalactic Astrophysics

Estimating Cosmological Parameters from Localized Fast Radio Bursts: A Method for Removing Milky Way Dispersion-Measure Contributions

Yuchen Zhang, Yang Liu, Hongwei Yu et al. (+1 more)

Fast radio bursts (FRBs) are emerging as powerful probes for cosmology. However, cosmological inference based on FRB dispersion measures (DMs) is limited by uncertainties in the Milky Way contribution, including those from the Galactic interstellar medium and the Galactic halo. In this Letter, we propose a method that eliminates the Milky Way contribution by using DM differences between localized FRBs within the same sky region. The method removes the need to adopt a specific Galactic electron-density model or a prior assumption for the Galactic halo DM. We validate the reliability of the method using mock FRB samples and show that it successfully recovers the fiducial cosmological parameter. Applying the method to current localized FRB data, we obtain a constraint on $\Gamma \equiv \Omega_b H_0 f_{\rm d}$ that differs from that inferred using the conventional treatment of the Milky Way contribution. This difference highlights the importance of Milky Way DM systematics in FRB cosmology and demonstrates the potential of differential DM methods for future large samples of localized FRBs.
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All authors Yuchen Zhang, Yang Liu, Hongwei Yu, Puxun Wu

Cosmology and Nongalactic Astrophysics

Modeling survey-window and integral-constraint effects on PNG in the galaxy power spectrum with light-cone mocks

Shintaro Nakano, Masahiro Takada, Toshiki Kurita et al. (+1 more)

We develop an analysis framework based on light-cone galaxy mock catalogs constructed from linear theory simulations in order to accurately model the impact of primordial non-Gaussianity (PNG) on galaxy power spectrum on large scales. These linear light-cone catalogs properly incorporate a variety of observational and cosmological effects, including the survey window function, the redshift evolution of matter and galaxy density fields, and redshift-space distortions (RSD). When estimating the multipole moments of the power spectrum from each light-cone mock, we employ the same estimator as used in actual analyses, thereby properly accounting for the effects of the discrete Fourier transform, the line-of-sight dependence of the fields, and wide-angle RSD effects. Using light-cone mock catalogs that mimic the BOSS survey, we demonstrate that long-wavelength modes comparable to or larger than the survey window scale, namely super-survey modes, have a significant impact on the integral constraint (IC) in power spectrum measurements. In particular, we show that the analytical treatment of the survey-window convolution and IC, which has been commonly used in previous studies, begins to lose accuracy on scales of $k\lesssim k_{\rm eq}$ (the matter-radiation equality scale), and becomes invalid in the presence of PNG. The method developed in this work enables unbiased searches for PNG using the galaxy power spectrum on long-wavelength scales probed by ongoing and future wide-area galaxy surveys.
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All authors Shintaro Nakano, Masahiro Takada, Toshiki Kurita, Ryo Terasawa

Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG

ScaleAware-JEPA: Latent Representation for Discovery in Multiscale Physical Fields

Guang-Xing Li

Continuous physical fields represent a large fraction of data under scientific investigation. Their multiscale structures are central to discovery, yet useful coordinates are not known in advance. Standard self-supervised methods define context and targets in fixed image coordinates, posing a predictive task misaligned with fields organized across a continuous scale hierarchy. We introduce ScaleAware-JEPA, a framework that constructs dense, label-free latent coordinates for continuous scalar fields. Constrained Diffusion Decomposition (CDD) separates each field into pixel-registered scale components and provides the scale coordinates that define the masking geometry. The resulting JEPA objective predicts hidden structure with a context footprint tied to the diffusion scale of each component rather than to an arbitrary patch size. Across MHD turbulence, interstellar molecular gas and urban nighttime-light structure, the learned geometry maps back to coherent morphology, forming dense structural atlases without labels or predefined segmentation rules. By tying latent prediction to the scale hierarchy of a field, ScaleAware-JEPA constructs latent coordinates through which complex physical patterns can be inspected before their relevant structures have been prescribed. Code is available at https://github.com/gxli/SA-JEPA.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Size Dependence of the Sommerfeld Enhancement for Puffy Dark Matter

Wu-Long Xu, Jin Min Yang and Wen-Na Yang

We examine the size effects in the Sommerfeld enhancement factor for puffy dark matter annihilation. First, we use the partial-wave method to study the case of puffy dark matter for which only a charge density distribution is given without specifying its internal structure. We find that by using two dimensionless parameters, we can provide a characterization of the resonance structure of the Sommerfeld enhancement. Using this approach, we demonstrate that the finite size of dark matter particle is another fundamental factor, in addition to low velocity, that affects the Sommerfeld enhancement. Then, as an example of puffy dark matter with nontrivial internal structures, we perform the analysis for the nugget-type dark matter, whose Sommerfeld enhancement factor is found to exhibit a resonant behavior similar to that of point-like particles.
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Astrophysics of Galaxies

Globular cluster formation with multiple stellar populations: A comprehensive overview of a star-cloud interaction scenario

Kenji Bekki and Madeleine McKenzie

We present a new scenario of globular cluster (GC) formation with multiple stellar populations (MPs) in which both the first and second populations (1P and 2P, respectively) of stars form from giant molecular clouds (GMCs) polluted by asymptotic giant branch (AGB) stars within and around the GMCs. Unlike previous GC formation scenarios with AGB stars being the primary polluters, the new scenario alleviates tensions with the mass-budget and dilution-timing problems The principal results based on idealized analytic models of the formation scenario are as follows. The observed fraction of 1P stars and the helium abundance spreads between the 1P and 2P as a function of GC masses can be well reproduced. The modelled GCs show O-Na, C-N, and Mg-Al anticorrelations and Si-Al, 25Mg-Al, 26Mg-Al correlations. The observed Mg-K anticorrelation can be reproduced, only if super AGB stars make a significant contribution to chemical enrichment within GMCs. The lack of correlations of Li abundances with [Na/Fe] and [Al/Fe] can be reproduced, only if about 20% of the polluting AGB stars produce Li-rich ejecta, which disfavours scenarios with polluters incapable of Li production. Iron-complex, Type-II GCs can be formed through merging of two GCs formed from two GMCs within a host dwarf galaxy at different epochs. The new scenario predicts young massive clusters formed in galaxy environments with surface star formation rate densities well below 1 M_sun/yr/kpc^2 are unlikely to evolve into GCs with MPs. It also predicts low 12C/13C ratios of 2P (~5), a [Na/Fe]-[F/Fe] anticorrelation, and P-rich star formation with [P/Fe]$>0.5$ and [N/Fe]>0.5. These predictions are tested against more than 30 observed properties of GCs with MPs, representing one of the most comprehensive observational benchmarks against a specific GC formation scenario to date.
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Earth and Planetary Astrophysics

Deuterated water and the formation of the satellites of Uranus

Michael E. Brown, Matthew Belyakov, Swaroop Chandra et al. (+5 more)

The satellites of Uranus orbit in a low-eccentricity, equatorial plane that is tilted by 98 degrees relative to the solar system – a geometry that mirrors Uranus's extreme axial tilt. Although a giant impact could have tipped Uranus, how the satellites came to share this orientation remains uncertain. Proposed formation pathways include primordial accretion followed by reorientation, formation from debris generated by the tilting impact, and reaccretion from a massive ring produced by the tidal disruption of passing bodies from the outer solar system. Current observations do not discriminate among these scenarios. Using the James Webb Space Telescope, we measured the deuterium-to-hydrogen (D/H) ration in the water ice of the five regular satellites of Uranus. We find an average D/H ratio of $2.1\pm 0.2 \times 10^{-4}$, nearly five times higher than that of Uranus and comparable to the values measured in comets. This enrichment is inconsistent with with any formation scenario in which substantial Uranian material was incorporated into the satellites, thereby excluding models that require significant mixing in an impact-derived vapor disk. The observed D/H ratios are instead compatible with models in which the satellites accreted from material that remained largely separate from Uranus, such as debris from a disrupted pre-existing satellite system or from a tidally captured outer solar system body. The innermost regular satellite, Miranda, exhibits a marginally elevated D/H ratio (2.8 $\sigma$ above the average of the other satellites), potentially indicating a distinct formation history or source of water and offering an important clue for distinguishing amount competing models.
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All authors Michael E. Brown, Matthew Belyakov, Swaroop Chandra, M. Ryleigh Davis, Merritt McDowell, Ashma Pandya, Kevin T. Trinh, Samantha K. Trumbo

High Energy Astrophysical Phenomena

VLBI Astrometry of Magnetars

Takuya Akahori, Sujin Eie, Kei Amada et al. (+8 more)

The origin of the strongest magnetic fields in the Universe, i.e., the origin of magnetars, is a longstanding question. An enhanced dynamo effect in an irregular supernova explosion is a possible origin, which implies a stronger kick velocity and a higher proper motion of the magnetar compared to those of ordinary pulsars as well as an irregular morphology of the host supernova remnant (SNR). However, this hypothesis is not well studied yet, because there is a lack of precise measurement of the proper motion of magnetar and of identification of the host SNR. VLBI astrometry of magnetars is a unique tool to examine the hypothesis. In this chapter, we introduce the MONSTER (Monitoring Observations of the Neutron Stars That Evolve Rapidly) Project. SKA-VLBI's unprecedented sensitivity and the highest angular resolution will allow us to dramatically expand the survey volume in which we can measure the proper motion of magnetars within a radio outburst period of a few months.
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All authors Takuya Akahori, Sujin Eie, Kei Amada, Sangita Kumari, Kohei Kurahara, Hiroto Masaoka, Hao Ding, Teruaki Enoto, Shota Kisaka, Keiichi Maeda, Kotaro Niinuma

Astrophysics of Galaxies

Magnetic Reconnection in Galaxy Clusters

Takuya Akahori, Kohei Kurahara, Shin-ya Nitta et al. (+4 more)

Galaxy clusters contain an intra-cluster medium (ICM) with temperatures of tens of millions of Kelvin. Cosmological structure formation simulations show that this diffuse gas is heated not only by adiabatic gravitational compression but also by shock waves and turbulence generated during mergers of galaxy groups and clusters. These processes are expected to produce magnetic fields and cosmic rays, observed through synchrotron polarization. One structure formed during cluster evolution is the cold front, a contact discontinuity created when colder gas moves transonically through hotter gas. Using MeerKAT, GMRT, and ATCA, we recently discovered radio emission along cold fronts in two galaxy clusters, with spectra indicating re-acceleration at the discontinuity. This presents a new puzzle because the standard mechanism in galaxy clusters, Fermi acceleration, is not naturally expected there. We propose magnetic reconnection as the re-acceleration mechanism. Compression and stretching of magnetized plasma at the discontinuity can generate current sheets that trigger reconnection, as also suggested by simulations. With AA*, we will probe broadband radio spectra at high spatial resolution to constrain where re-acceleration occurs. Polarization measurements will reveal magnetic-field structures and clarify the conditions required for magnetic reconnection.
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All authors Takuya Akahori, Kohei Kurahara, Shin-ya Nitta, Haruka Sakemi, Hiroki Akamatsu, Mami Machida, Motokazu Takizawa

Earth and Planetary Astrophysics

TOI-6884b: A low-mass brown dwarf transiting a slightly evolved star

Akanksha Khandelwal, Shubhendra Nath Das, Rishikesh Sharma et al. (+42 more)

We report the discovery of a low-mass transiting brown dwarf orbiting TOI-6884 (TIC~156514476, $T_{\rm mag}=11.4$) from NASA's Transiting Exoplanet Survey Satellite (TESS) mission. The TESS light curves initially suggested an orbital period of $\sim$14.42~days; however, our high-precision ground-based radial velocity measurements and multi-epoch time-series photometry reveal this to be a harmonic alias. We determine the true orbital period to be $4.808264^{+0.000015}_{-0.000014}$~days and confirm the substellar nature of the companion. TOI-6884b has a mass of $26.32^{+0.98}_{-0.93}\,M_{\mathrm{J}}$, a radius of $0.927^{+0.51}_{-0.52}\,R_{\mathrm{J}}$, and resides on a nearly circular orbit ($e=0.067^{+0.010}_{-0.012}$). Its host star is a late F-type slightly evolved star with $M_\star = 1.410^{+0.075}_{-0.069}\,M_\odot$,\msun, $R_\star = 1.840^{+0.072}_{-0.073}\,R_\odot$, $\log{g} = 4.057^{+0.045}_{-0.039}$, $[{\rm Fe/H}] = 0.094^{+0.073}_{-0.068}$~dex, and $T_{\rm eff}=6330^{+180}_{-160}$,\mathrm{K}$. TOI-6884b is a key addition to the small population of well-characterized transiting brown dwarfs orbiting host stars that have evolved off the main sequence. The detection of such systems will contribute to our understanding of the dynamical histories and structural evolution of short-period substellar companions around evolved stars.
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All authors Akanksha Khandelwal, Shubhendra Nath Das, Rishikesh Sharma, Abhijit Chakraborty, Churchil Dwivedi, Sanjay Baliwal, Karen A.Collins, David W. Latham, Allyson Bieryla, Cristilyn N. Watkins, Felipe Murgas, Norio Narita, Enric Palle, Steve B. Howell, Mark E. Everett, Catherine A. Clark, Polina A. Budnikova, David Ciardi, Nikitha Jithendran, Akihiko Fukui, Ashirbad Nayak, Bob Massey, Boris Safonov, Florence Libotte, Francis P. Wilkin, Gregor Srdoc, Howard M. Relles, Ivan Bonilla-Mariana, Izuru Fukuda, Jason D. Eastman, Jerome de Leon, Jesus Higuera, Kapil Bharadwaj, Keith Horne, Kendra Nguyen, Kevikumar Lad, Manuel Pichardo Marcano, Micaela Magno, Neelam JSSV Prasad, Noriharu Watanabe, Richard P. Schwarz, Sam Quinn, Santiago Paez, Toshi Suganuma, Y. Gomez Maqueo Chew

Cosmology and Nongalactic Astrophysics · Cross-listed from physics.hist-ph

What Naturalness Measures: Fine-Tuning and Informational Invariants in Cosmology and Dark Matter

Stefano Profumo

Naturalness is commonly presented as an objective constraint on physical theories: a model requiring fine-tuning is judged implausible. This presentation conflates a representation-dependent quantity with an invariant one. A fine-tuning verdict depends on the choice of fundamental parameters, the prior, and the measure convention, so it does not by itself fix a feature of the world. Here, I argue that what is objective is structural: the universality class of the map from parameters to observables, invariant under admissible changes of parametrization and measure convention, and independent of any prior over parameter space; it constitutes an informational invariant. On this account naturalness is neither an aesthetic preference nor an objective probability, but a statement about the distinguishability geometry of the representations through which physics encodes observation. I trace the certainty of naturalness verdicts to a tradition, from Ockham through Dirac and Weinberg, in which parsimony and beauty are taken as guides to truth; modern naturalness inherits that tradition's authority without its successive justifications. The argument is developed in the gravitational and cosmological sector, where naturalness reasoning is sharpest and its effective-field-theory grounding is weakest. A uniform analysis across gravitational and particle dark matter candidates shows that fine-tuning tracks the analytic structure of the abundance map, not the nature of the candidate; that the resulting classification is invariant across measure conventions while the tuning number is not; and that this decomposition instantiates informational structural realism. I situate the position against the autonomy-of-scales account, which the argument largely accepts, and against the deflationary reading, which identifies the borrowed authority but discards the structural residue.
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Sunday 28 June

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Acoustic Hawking radiation as a tunnelling effect in Michel accretion

Nisha Jangid and Arnab K. Ray

Michel accretion becomes transonic at the saddle point of a dynamical system. An Eulerian perturbation on the steady inflow produces the metric of an acoustic black hole. As a high-frequency travelling wave the perturbation does not destabilize the steady inflow. Acoustic waves propagating outwards against the fluid inflow are blocked at the sonic barrier but can tunnel through it with an exponentially decaying amplitude. The Hawking temperature and the frequency of the Hawking phonons are enhanced by the spacetime geometry.
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Instrumentation and Methods for Astrophysics

Assessing the Predictability of $\delta$ Scuti Variable Stars for Spacecraft Navigation

Ahmed Khan, Linyi Hou and Siegfried Eggl

Previous studies have shown that $\delta$ Scuti stars can be used for determining spacecraft position and time similar to X-ray pulsar navigation, but open questions remain regarding the light-curve stability, and, therefore, the navigation accuracy that can be derived from $\delta$ Scuti variable stars. Here, we develop a computational framework to identify $\delta$ Scuti variable stars with light curves that are suitable for spacecraft navigation purposes. Our approach emphasizes quantifying timing uncertainty through developing metrics and evaluating such metrics in the context of spacecraft navigation. We analyze over 110 $\delta$ Scuti variable stars from the Kepler space telescope and 10 additional stars from the K2 mission. For each star, we produce a simple model of its normalized flux as a function of time, along with several metrics used to assess its suitability for navigation. Model quality was further assessed through comparing predictions with observations from the Transiting Exoplanet Survey Satellite (TESS). Out of the 120 $\delta$ Scuti variable stars we investigated in this study, 32 stars were identified as candidates predictable enough to enable spacecraft navigation.
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High Energy Astrophysical Phenomena

Pulsed Infrared Emission from Magnetar 4U 0142+61 Detected by JWST

Jeremy Hare, George G. Pavlov, Bettina Posselt et al. (+3 more)

We report on a JWST observation of the magnetar 4U 0142+61 on 2024 August 18 with the Near-Infrared Camera (NIRCam). NIRCam observed the magnetar for 33~min in timing mode, providing a time resolution of 2.5~s. In the F410M filter (pivot wavelength 4.08 $\mu$m), we measured the flux density $f_\nu = 22.9\pm0.6$ $\mu$Jy and detected pulsations at a frequency of $115.059\pm0.035$ mHz, in agreement with the magnetar's spin period at the epoch of the JWST observation. The observed pulse profile has one peak per period (although this may be due to the poor time resolution), with a lower limit on the pulsed fraction of about 10%. We compare the IR pulse profile to the NICER and NuSTAR X-ray pulse profiles and find that the IR peak overlaps with the hard X-ray peak, suggesting a magnetospheric origin for the pulsed IR emission.
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All authors Jeremy Hare, George G. Pavlov, Bettina Posselt, George Younes, Oleg Kargaltsev, Alex van Kooten

Astrophysics of Galaxies

The Lockman-SpReSO Project: A Deep X-ray Spectral View of a FIR-selected AGN Population

Mauricio Elías-Chávez, Takamitsu Miyaji, Martín Herrera-Endoqui et al. (+21 more)

We present a detailed X-ray spectral analysis of the active galactic nucleus (AGN) population in the Lockman-SpReSO project, a multiwavelength campaign of FIR sources in the Lockman Hole field. Using deep XMM-Newton observations cross-matched with FIR-selected galaxies, we characterize 94 AGNs based on their X-ray spectral properties. The sample is distributed over a large redshift range of $z = 0.07-5$, and reaches a flux limit of $5 \times 10^{-16}\, \mathrm{erg\, s^{-1}\, cm^{-2}}$ in the $0.3-10\, \mathrm{keV}$ band. We model the X-ray spectra using absorbed power-law, reflection, and soft excess components to estimate intrinsic column densities ($N_{\mathrm{H}}$), rest-frame $2-10\, \mathrm{keV}$ luminosities, and iron line equivalent widths $(EW)$. Additionally, we included an advanced model fitting for Compton-thick AGNs (CT-AGNs) using the XCLUMPY model. Our results show an increase in the fraction of obscured AGNs toward higher redshifts, including the identification of one strong and two borderline CT-AGN candidates with $N_{\mathrm{H}} \gtrsim 10^{24}\, \mathrm{cm^{-2}}$. Soft excess emission is detected in 10 AGNs, with an average blackbody temperature of $0.12 \pm 0.02\, \mathrm{keV}$. We also detect the X-ray Baldwin effect in both obscured and unobscured populations, and we found a strong correlation between the torus angular width $(\sigma_\mathrm{tor})$, dust covering factor $(f_{\mathrm{cov}})$, and X-ray luminosity, described by $f_{\mathrm{cov}} = (-0.1 \pm 0.01) \times \log(L_{2-10\, \mathrm{keV}}/(10^{44}\, \mathrm{erg\, s^{-1}})) + (0.65 \pm 0.01)$, supporting the receding torus scenario. While consistent with deep X-ray surveys, the FIR selection favours the identification of dusty star-forming host galaxies and heavily obscured AGNs.
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All authors Mauricio Elías-Chávez, Takamitsu Miyaji, Martín Herrera-Endoqui, Irene Cruz-González, Yair Krongold, Héctor Hernández-Toledo, Mirjana Povic, Bereket Assefa, Mauro González-Otero, Castalia Alenka Negrete, Miguel Cerviño, J. Antonio de Diego, Miguel Sánchez-Portal, Erika Benítez, Jordi Cepa, José Antonio Vázquez Mata, Monica I. Rodriguez, Emilio J. Alfaro, J. Jesús González, Carmen P. Padilla-Torres, J. Ignacio González-Serrano, Vladimir Ávila-Reese, Ángel Bongiovanni, A. M. Perez Garcia

High Energy Astrophysical Phenomena

General Relativistic Shock Wave Solutions with Black Hole Formation: The Singular Isothermal Sphere Case

Chien-Ting J. Chen, Michael J. Cai and Fabio Pacucci

The rapid emergence at $z\gtrsim 6$ of ubiquitous populations of supermassive black holes (SMBHs) revealed by JWST and of quasars with estimated masses $M_\bullet > 10^{10} M_\odot$ demands efficient pathways for early growth. The smooth collapse of a singular isothermal sphere (SIS) has been solved analytically in full general relativity, but the shock waves that inevitably accompany such collapse have not. Here, we derive general-relativistic self-similar shock-wave solutions for the collapse of an SIS to a black hole, extending the framework of Cai & Shu (2005) to discontinuous flows. We obtain the general relativistic jump conditions for an isothermal fluid and show that they connect interior collapse solutions to exterior envelopes that may be static, expanding, or collapsing, yielding a rich family of shocks propagating at up to $\sim$40% the speed of light; the available exterior types narrow with increasing sound speed. A coordinate-matching technique that uses the zero-velocity surface uniquely bridges the Schwarzschild and comoving self-similar descriptions, completing the characterization of the growing black hole. The central accretion rate is set by the interior collapse alone and is suppressed by a factor of $\sim$5–7 relative to the smooth expansion-wave solution, while the energy released at the shock reaches $\sim$10% of the enclosed rest mass – nearly twice the 5.7% radiative efficiency of Schwarzschild accretion. These results provide an analytical energy budget for direct-collapse black hole formation, with implications for SMBH seed assembly, the dense cocoons around nascent high-redshift black holes, the recently discovered JWST's Little Red Dots, and relativistic transients such as gamma-ray bursts.
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Solar and Stellar Astrophysics

Radio Wave Propagation as a Probe of the Solar Corona and Solar Wind

K. Sasikumar Raja, Prasad Subramanian, Susanta Kumar Bisoi et al. (+3 more)

Radio waves propagating through an inhomogeneous, turbulent medium such as the solar corona and solar wind become distorted, causing the initially plane wavefronts becomes corrugated and acquire an RMS phase deviation across the wavefront. This leads to observable effects such as angular broadening of radio sources or intensity scintillation. Such waves can be used to probe the solar wind through various techniques, including angular broadening and interplanetary scintillation observations. Such observations enable the study of several key properties, such as the phase structure function, amplitude of turbulence, density modulation index, solar wind heating rates, magnetic field topology, and dissipation scales. These phenomena provide critical insights into the physical processes governing the solar corona and solar wind and its interaction with radio waves, offering valuable constraints on both coronal and solar wind turbulence and coronal magnetic field configurations. Currently, the limited number of radio sources near the ecliptic restricts our observations. However, the SKA-Low and SKA-Mid are expected to detect a significantly larger number of radio sources, thereby providing deeper insights into the solar corona, solar wind, and heliosphere. Long-term observations will be crucial to understanding how the above-mentioned parameters vary with heliocentric distance and over the solar cycle.
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All authors K. Sasikumar Raja, Prasad Subramanian, Susanta Kumar Bisoi, Janardhan Padmanabhan, Eduard Kontar, Anshu Kumari

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Nuclear equation-of-state at high density and multi-messenger astronomy: contribution of heavy-ion collisions

A. Le Fèvre

In the past decades, heavy-ion collisions (HIC) at intermediate energies have allowed to probe the nuclear equation-of-state (EoS) of both symmetric and asymmetric nuclear matter over a broad range of densities. In particular, flow has proven to be a powerful observable. Combining the symmetry energy and the symmetric nuclear matter constraints of the EoS from HIC allowed to predict a density dependence of the pressure in a neutron star, up to about 2.5 times saturation density ($n_{sat}$), which agrees with recent astronomical measurements deduced from gravitational waves and pulsar observations. So far, the accuracy from HIC expectations is comparable to the latter up to 1.5 $n_{sat}$. In these studies, a fundamental aspect is the determination of the profile of densities that are probed by experimental observables used to constrain the EoS. In the near future, new experiments like ASY-EOS performed at higher incident energy and with better accuracy will push further the frontier of the knowledge of the symmetry energy at higher density. These efforts cannot be conclusive without a reliable uncertainty determination, which is related to the reliability of transport model dependencies. Improvements and breakthroughs in transport model simulations and nuclear theory are therefore expected in a joint effort towards HIC contributions to the field of neutron-star physics, including the contribution of strangeness and of the QCD phase transition.
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Cosmology and Nongalactic Astrophysics

Constraints on Dark Energy and Modified Gravity Models from Fast Radio Bursts and Late-Time Geometric Probes

Bruno W. N. Ribeiro, Lázaro L. Sales, Klécio. E. L. de Farias et al. (+3 more)

We investigate the impact of 104 localized FRBs on cosmological parameter estimation when combined with three established late-time probes: Cosmic Chronometers (CC), Type Ia Supernovae (SNe), and Baryon Acoustic Oscillations (BAO). By performing a Bayesian analysis of three dark energy models ($\Lambda$CDM, $w$CDM, and CPL) and three viable $f(R)$ gravity scenarios – the Appleby-Battye (AB), Hu-Sawicki (HS), and Starobinsky (ST) models – , we find that FRBs substantially improve the constraints on the baryon density $\Omega_{\rm b}$ by $25\%$–$43\%$, the Hubble constant $H_0$ by $12\%$–$35\%$, and the SNe absolute magnitude $M_B$ by $10\%$–$32\%$. Constraints on dark energy parameters show more modest improvements, with $w$ improving by $\sim 9\%$ in $w$CDM and $(w_0,w_a)$ improving by $\sim(8,22)\%$ in the CPL parametrization. Modified gravity parameters remain weakly constrained, with improvements of only $6\%$–$15\%$, indicating the limited sensitivity of current datasets to departures from $\Lambda$CDM. The Figure of Merit analysis shows overall improvements ranging from $\sim 48\%$ ($\Lambda$CDM) to $\sim 91\%$ (CPL), driven by enhanced precision in the $(H_0, \Omega_{\rm b})$ plane. Model comparison reveals moderate statistical preference for extensions beyond $\Lambda$CDM: AIC strongly favors $w$CDM, CPL, HS, and ST with $\Delta\mathrm{AIC} < -7$, and LRT yields $p \leq 0.004$, while BIC returns to positive evidence ($-3.2 < \Delta\mathrm{BIC} < -2.7$). These results show that FRBs may be useful as a complementary probe, particularly for constraining $\Omega_{\rm b}$ and alleviating key late-time degeneracies.
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All authors Bruno W. N. Ribeiro, Lázaro L. Sales, Klécio. E. L. de Farias, Raiff H. Santos, Rafael A. Batista, Amílcar R. Queiroz

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Quark and hybrid stars with renormalization group improvement of NNLO perturbative QCD

Loïc Fernandez, Jean-Loïc Kneur, Marcus Benghi Pinto et al. (+3 more)

Recently, the NNLO perturbative QCD pressure of cold and dense symmetric matter, with arbitrary quark masses, has been resummed within the renormalization-group-optimized perturbation theory (RGOPT) framework. By being imbued with renormalization group properties, the resulting pressure is less sensitive to renormalization scale ($\Lambda\equiv X \mu_B/3$) variations than the NNLO perturbative QCD pressure. Here, we extend this by considering $\beta$-equilibrium and charge neutrality to evaluate the corresponding equation of state (EoS). We provide a compact “pocket" fitting formula for the EoS for $N_f=2+1$ massive quarks at different renormalization scale parameter ($X$) values. We describe pure quark stars as well as hybrid stars with quark-cores. Pure quark stars compatible with astrophysical observations were obtained with $X=2.71-3.30$, whereas a larger value (3.84) is needed if the secondary component of the observation GW190814 represents a neutron star. Hybrid stars were built considering three representative hadron models based on a relativistic mean-field description, and chosen to produce soft and stiff EoSs. Stable hybrid stars with masses compatible with the massive pulsar PSR J0740+6620 were obtained considering $X$ of the order of 2 to $2.71$, the largest scale giving rise to hybrid stars with a large quark core with a radius of 2 to 8 km , and the smallest to a small quark core at the center of the star.
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All authors Loïc Fernandez, Jean-Loïc Kneur, Marcus Benghi Pinto, Constança Providência, Claudia Ratti, Tulio E. Restrepo

Earth and Planetary Astrophysics

The impact of interpolation in high-resolution spectroscopy – The overlooked role of interpolation in radial velocity extraction

A. M. Silva, D. Doshi, K. Al Moulla et al. (+11 more)

We explore the impact of spectral interpolation in radial velocity (RV) time-series extracted through template-based methods. We build synthetic datasets with Gaussian profiles to evaluate flux residuals and line asymmetry that are a result from changing the sampling location of the lines. We generate synthetic spectra as a sum of Gaussian functions whose parameters were determined through an observed spectrum. The s-BART pipeline was applied to them, allowing to evaluate any biases in RV extraction introduced by its internal assumptions in line shape. Lastly, we apply the s-BART pipeline to ESPRESSO observations of four stars: two that use high-cadence observations over a single night, and two that have observations spread over multiple nights. When extracting RVs from stellar spectra, we change the interpolation algorithm, used in the process of constructing the stellar template and, afterwards, during RV extraction, comparing them with RVs extracted with a widely-used cubic-spline interpolation. We find that synthetic datasets reveal systematic biases with the largest peak-to-peak amplitudes reaching $\sim$ 20 m/s in low SNR cases, with the amplitude decreasing as the SNR of the spectra increases. In the extreme case of noise-free data, we still recover a systematic bias, albeit at the mm/s level, significantly smaller than the RV precision of state-of-the-art instruments. With real observations we find that those from high-cadence observations with small BERV variation are impacted by the choice of the interpolation algorithm. This impact is smaller in higher-SNR cases, where the peak-to-peak amplitude reaches $\sim$ 1 m/s. In the comparatively lower-SNR case we find peak-to-peak residuals as large as $\sim$ 25 m/s . In cases where the observations are spread over a larger BERV window, we find an upper limit of 20 cm/s of RV scatter for this systematic signal.
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All authors A. M. Silva, D. Doshi, K. Al Moulla, E. A. S. Cristo, É. Artigau, P. T. P. Viana, N. C. Santos, J. H. C. Martins, C. M. J. Marques, S. G. Sousa, C. San Nicolas Martinez, T. L. Campante, A. Cabral, S. Cristiani

Solar and Stellar Astrophysics

Semi-Empirical Pulsation Reconstruction of Delta Cephei with Photometry, Radial Velocities, and Temperature Constraints

Zuhoor Elahi and Wafa Gull

We present a semi-empirical reconstruction of the pulsation behavior of the classical Cepheid delta Cephei using observed Johnson-V photometry, HARPS-N radial velocities, and published SPIPS pulsation-model curves. A cleaned AAVSO Johnson-V data set was phase folded with P = 5.366531 d, corrected for observer zero-point offsets, clipped for residual outliers, and fitted with a three-harmonic Fourier template. The resulting empirical template has Delta V about 0.833 mag, R21 about 0.382, R31 about 0.168, and a rise fraction about 0.287. After phase and vertical alignment, the published SPIPS V-band curve reproduces the empirical Johnson-V morphology with an RMS residual about 0.023 mag. A Fourier representation of the HARPS-N radial velocities gives a peak-to-peak velocity span about 40.82 km s^-1, corresponding to a preliminary radius-displacement amplitude about 4.81 solar radii for p = 1.317. Combining this radius curve with the SPIPS Teff(phi) curve yields a hybrid luminosity curve close to the published SPIPS luminosity curve. The adopted R0 = 43.7 solar radii scale gives a mean luminosity ratio L_hybrid/L_SPIPS about 1.04, while R0 = 44.9 solar radii gives about 1.10. A direct radius-scale comparison also favors the lower adopted radius scale, with an RMS offset of 0.864 solar radii relative to the SPIPS-implied radius, compared with 2.060 solar radii for the larger-radius case. These results show that the observed visual morphology, radial displacement, and temperature-driven luminosity variation are mutually consistent when placed on a common phase convention, while the absolute radius scale remains the dominant systematic.
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Earth and Planetary Astrophysics

Improving the Precision of Line-by-Line Radial Velocities: A Data-Driven Iterative Algorithm for Spectral Line Selection

Kanishk Pandey, Eric A. Ford, Joseph M. Salzer et al. (+17 more)

Independent analysis of individual spectral lines, or line-by-line (LBL) analyses, can improve upon standard cross-correlation function (CCF) methods for measuring radial velocities (RVs) because they preserve critical information about individual line shape changes that can be caused by stellar activity. In this work, we measure LBL RVs of 3,830 spectral lines across 383 days of NEID solar observations. Our LBL approach achieves an RV RMS of $2.012~\mathrm{m\,s^{-1}}$, which is slightly lower than the $2.129~\mathrm{m\,s^{-1}}$ achieved by a CCF approach using a shared line list. Then, we describe and benchmark several methods for selecting line lists based on line properties such as depth and intrinsic RV scatter. We find that these subsets have a lower RV RMS compared to either the full line list or random subsets of equal size. Motivated by these results, we present FLARES (Filtering Lines for Accurate Radial-velocity Exoplanet Search), an iterative line-selection algorithm. FLARES selects candidate spectral lines with extreme values of multiple line metrics and properties such as depth, signal-to-noise ratio, and detector position, and preferentially rejects lines whose removal produces the largest decrease in the weighted RV scatter. FLARES achieves an RV RMS of $1.122~\mathrm{m\,s^{-1}}$ using just 24 lines and performs better than the benchmark methods. We perform Monte Carlo simulations and show FLARES is robust and reproducible. Comparisons to alternative line lists chosen to have properties similar to the best FLARES-selected lines demonstrate that FLARES is successfully identifying line properties that lead to effective line lists for future extreme-precision RV measurements.
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All authors Kanishk Pandey, Eric A. Ford, Joseph M. Salzer, Jessi Cisewski-Kehe, Lily L. Zhao, Arvind F. Gupta, Michael L. Palumbo III, Ryan C. Terrien, Evan Fitzmaurice, Brady Barth, Jason T. Wright, Cullen H. Blake, Suvrath Mahadevan, Arpita Roy, Joe P. Ninan, Gudmundur Stefansson, Paul Robertson, Christian Schwab, Daniel M. Krolikowski, Leonardo A. Paredes

Solar and Stellar Astrophysics

A Reproducible AAVSO Johnson-V Fourier Template for the Prototype Cepheid Delta Cephei

Zuhoor Elahi and Wafa Gull

We present an empirical Fourier reconstruction of the observed Johnson-V light curve of the prototype Classical Cepheid Delta Cephei. The goal is not to infer a full physical stellar model but to establish a reproducible observed-light-curve benchmark for later comparison with nonlinear pulsation, synthetic photometry, Baade-Wesselink/SPIPS, GYRE-supported, and independent hydrodynamic calculations. Using an adopted period of Pobs = 5.366531 d, 244 AAVSO Johnson-V measurements were filtered to a cleaned sample of 242 points after rejecting two extreme outliers. The cleaned data span 355.09259 d and were phase folded using an empirical bright-maximum epoch of JD = 2460851.395800. We fit a low-order Fourier model to the phased light curve and adopt a third-order template as the preferred empirical morphology representation. The adopted N = 3 fit gives A0 = 3.9031, A1 = 0.3434 mag, A2 = 0.1428 mag, and A3 = 0.0531 mag, corresponding to R21 = 0.4159 and R31 = 0.1547. The template has a full Johnson-V amplitude of Delta V = 0.8544 mag, a rise fraction of frise = 0.2885, and an asymmetry index of Aasym = 0.4230. Bootstrap uncertainties are reported in the manuscript. Fourier orders N = 4-6 reduce the RMS residual by only about 0.0012 mag relative to the N = 3 model, so the third-order representation is retained as the simplest adequate empirical template. Observer-level residual diagnostics show that the remaining scatter is not purely random. This paper provides an observational morphology target rather than a physical explanation of the pulsation.
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