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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 18 November

Cosmology and Nongalactic Astrophysics

Photon rest mass from localized fast radio bursts with improved distribution of dispersion measure from extragalactic gas

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

The assumption that photons are massless is a foundational postulate of modern physics, yet it remains subject to experimental verification. Fast radio bursts (FRBs), with their cosmological distances and precisely measured dispersion, offer an excellent laboratory for testing this hypothesis. In this work, we propose an improved distribution function for the dispersion measure arising from extragalactic gas and demonstrate that it provides an excellent fit to mock data. We then apply this distribution to constrain the photon rest mass under the $\Lambda$CDM, $w$CDM, and $w_{0}w_{a}$CDM cosmological models, the last of which is favored by recent DESI baryon acoustic oscillation observations. The corresponding 1$\sigma$ upper limits on the photon mass are found to be $4.83\times10^{-51}\,\mathrm{kg}$, $4.71\times10^{-51}\,\mathrm{kg}$, and $4.86\times10^{-51}\,\mathrm{kg}$, respectively, which are the most stringent constraints derived from FRBs to date. These results indicate that the choice of cosmological model has only a minor impact on photon-mass bounds, demonstrate that FRBs provide robust and reliable constraints, and offer strong empirical support for the massless nature of the photon.
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All authors Yuchen Zhang, Yang Liu, Hongwei Yu, Puxun Wu

High Energy Astrophysical Phenomena

The Origin of the Mg-rich Supernova Remnant J0550-6823 and the Frequency of Similar Events in the Large Magellanic Cloud

Yui Kuboike, Toshiki Sato, Hiromasa Suzuki et al. (+4 more)

Shell burning and internal mixing in massive stars play an important role in setting the initial conditions for core-collapse supernova explosions. In the late stages of stellar evolution, intense shell burning can cause distinct convective regions to merge, fundamentally restructuring the stellar interior. Although such phenomena are difficult to observe directly, the observation of “Mg-rich” supernova remnants (SNRs) has recently emerged as a potential signature of these events. In this study, we reanalyze X-ray observations of J0550–6823, a SNR in the Large Magellanic Cloud (LMC) and a new candidate Mg-rich SNR. Our spectral analysis confirms a low Ne/Mg mass ratio of $\approx$1, and its classification as Mg-rich. By comparing the observational results with pre-supernova models, we suggest that the progenitor of J0550-6823 likely had an extended convective shell that reduces the Ne/Mg ratio prior to its explosion. Furthermore, we observe that $\sim$2–3 Mg-rich SNRs exist in the LMC, suggesting that $\lesssim$10–40% of massive stars in the LMC may have had an extended convective shell, similar to what we observed in J0550-6823. This fraction would be important for understanding the final stages of the evolution of massive stars and galactic chemical evolution.
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All authors Yui Kuboike, Toshiki Sato, Hiromasa Suzuki, Kai Matsunaga, Hiroyuki Uchida, John P. Hughes, Paul P. Plucinsky

Instrumentation and Methods for Astrophysics

SPECTRUMMATE: A Low-cost Spectrometer for Small Telescopes

Hien Phan-Thanh, Nguyen Nguyen-Duc, Thuy Le-Quang et al. (+2 more)

This project presents the development and implementation of a compact spectrometer, named SPECTRUMMATE, tailored for small telescopes. Small telescopes offer several advantages: they are cost-effective, occupy less space, and are simpler to set up than larger instruments. This makes them particularly suitable for amateur astronomers and educational institutions with limited resources. Moreover, small telescopes can effectively observe bright celestial objects, enabling valuable contributions to astronomical projects. Based on the Sol'EX design, SPECTRUMMATE was constructed using optical components available at the Space and Applications Laboratory (SpaceLAB), University of Science and Technology of Hanoi, Vietnam. The instrument is designed to meet the specific needs of astronomers who require detailed analysis within the visible spectrum (SPECTRUMMATE can capture a waveband of 368 angstrom/image, spectral coverage from 4000 to 6600 angstrom, and resolving power R = 2546 at 5500 angstrom). To achieve optimal performance, the design process involved selecting and configuring optical elements, including a collimator, diffraction grating, and objective lens. Experimental setups were tested to minimize spectral dispersion while ensuring the system's compactness and ease of alignment. Spectra obtained by SPECTRUMMATE demonstrated efficient spectral calibration and the capability to capture high-resolution spectra of bright light sources, such as the Sun, making it a valuable tool for specialised spectroscopic observations. The modular design of SPECTRUMMATE also allows users to change its components easily to achieve the desired spectral range and resolution.
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All authors Hien Phan-Thanh, Nguyen Nguyen-Duc, Thuy Le-Quang, Tobias C. Hinse, Quang Nguyen-Luong

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Cosmological dynamics of interacting dark matter-dark energy in generalized Rastall gravity

Manuel Gonzalez-Espinoza, Ramón Herrera, Giovanni Otalora et al. (+2 more)

In this work, we investigate late-time interacting cosmologies within the framework of generalized Rastall gravity, where the interaction arises naturally from the non-conservation of the energy-momentum tensor. We formulate the background evolution of the dark sector as an autonomous dynamical system, defining interaction terms $Q_1=\alpha\,\dot{f}$ and $Q_2=-\dot{f}\,(1+\alpha)$, with $\alpha$ a constant parameter and $f$ a time-dependent function. Three interaction cases are studied: $f \propto \rho_m$, $f \propto \rho_{de}$, and $f \propto \rho_m + \rho_{de}$, assuming a constant dark-energy equation of state $w_{de}$. For each scenario, we derive the closed dynamical system in terms of the density parameters $(\Omega_{de}, \Omega_m)$, identify its fixed points, and analyze their stability across the parameter space. In this context, the phase-space exhibits a standard cosmological dynamics: an unstable radiation point, a transient matter saddle, and a stable late-time attractor with accelerated expansion. In addition, we utilize a joint likelihood analysis with Cosmic Chronometers, PantheonPlus, and DESI data to obtain marginalized parameter estimates at the $68\%$ and $95\%$ confidence levels, constraining the parameter space in each interaction model.
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All authors Manuel Gonzalez-Espinoza, Ramón Herrera, Giovanni Otalora, Carlos Ríos, Carlos Rodriguez-Benites

Solar and Stellar Astrophysics

Energy-Containing Electrons in Solar Flares: Improving Hard X-Ray and EUV Diagnostics

Yingjie Luo, Eduard P. Kontar and Debesh Bhattacharjee

Solar flares effectively accelerate particles to non-thermal energies. These accelerated electrons are responsible for energy transport and subsequent emissions in HXR, radio, and UV/EUV radiation. Due to the steeply decreasing electron spectrum, the electron population and consequently the overall flare energetics, are predominantly influenced by low-energy non-thermal electrons. However, deducing the electron distribution in this energy-containing range remains a significant challenge. In this study, we apply the warm-target HXR emission model with kappa-form injected electrons to two well-observed GOES M-class flares. Moreover, we utilize EUV observations to constrain the flaring plasma properties, which enables us to determine the characteristics of accelerated electrons across a range from a few keV to tens of keV. We demonstrate that the warm-target model reliably constrains the properties of flare-associated electrons, even accounting for the uncertainties that had previously been unaddressed. The application of a kappa distribution for the accelerated electrons allows for meaningful comparisons with electron distributions inferred from EUV observations, specifically for energy ranges below the detection threshold of RHESSI. Our results indicate that the accelerated electrons constitute only a small fraction of the total electron population within the flaring region. Moreover, the physical parameters, such as electron escape time and acceleration time scale, inferred from both the warm-target model and the EUV observations further support the scenario in which electrons undergo thermalization within the corona. This study highlights the effectiveness of integrating the warm-target model with EUV observations to accurately characterize energy-containing electrons and their associated acceleration and transport processes.
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Solar and Stellar Astrophysics

Large Magnetic Flux Rope Formation in an X2.1 Flare observed on September 6, 2011

Arpita Roddanavar, Satoshi Inoue, Keiji Hayashi et al. (+3 more)

Solar active region 11283 produced an X2.1 flare associated with a solar eruption on September 6, 2011. Observations revealed a preflare sigmoidal structure and a circular flare ribbon surrounding the typical two ribbon structure, along with remote brightenings located at a considerable distance from the main flare site. To interpret these observations in terms of the three dimensional (3D) coronal magnetic field dynamics, we conducted data constrained magnetohydrodynamic (MHD) simulations. Using a non linear force free field (NLFFF) as the initial condition, we reconstructed a realistic pre flare magnetic environment, capturing a sheared sigmoid above the polarity inversion line (PIL) surmounted by a fan spine structure. Our simulations revealed that reconnection between the sigmoidal field, the adjacent fan dome field lines, and the neighboring large loops facilitated the transfer of magnetic twist and led to the formation of a large magnetic flux rope (MFR). This transfer and propagation of twist are clearly visible throughout the MFR. As reconnection progresses, the entire fan spine structure expands along with the evolving MFR. A notable outcome of the simulation is that the footpoints of the newly formed MFR align closely with the observed circular flare ribbon and the remote brightening region. Our findings suggest that a large MFR formed during the X2.1 flare, providing a coherent explanation for the observed phenomena.
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All authors Arpita Roddanavar, Satoshi Inoue, Keiji Hayashi, Ju Jing, Wenda Cao, Haimin Wang

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

A non-local origin for massive gravity and late-time acceleration

Susobhan Mandal and S. Shankaranarayanan

The accelerated expansion of the universe poses a significant challenge to General Relativity. Non-local modifications to gravity have emerged as a compelling class of theories to address this dark energy puzzle. Building upon earlier proposals, we investigate a specific non-local modified gravity action incorporating terms like $R\Box^{-2}R$, $R^{\mu\nu}\Box^{-2}R_{\mu\nu}$, $R^{\mu\nu\sigma\delta}\Box^{-2}R_{\mu\nu\sigma\delta}$ and demonstrate that it provides a dynamical origin for a massive graviton by reducing to the standard and extended Fierz-Pauli action at the linearized level. A fixed-point analysis of the background cosmology reveals a stable de Sitter attractor, ensuring the model naturally drives accelerated expansion. Crucially, we investigate the cosmological perturbations and show that the theory's six propagating degrees of freedom are free from ghost instabilities. We further demonstrate that all large-scale tensor modes are dynamically stable and decay on the accelerating background. This ghost-free massive gravity extension provides distinct predictions for gravitational wave polarizations and is theoretically consistent with $\mathbf{\Lambda CDM}$ at late times, positioning it as a unique alternative to scalar-tensor models like $f(R)$ and Galileons. This robust stability at both the background and perturbative levels establishes our model as a consistent and compelling alternative to the standard $\Lambda$CDM paradigm.
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Instrumentation and Methods for Astrophysics

The CHASM-SWPC Dataset for Coronal Hole Detection & Analysis

Cutter Beck, Evan Smith, Khagendra Katuwal et al. (+2 more)

Coronal holes (CHs) are low-activity, low-density solar coronal regions with open magnetic field lines (Cranmer 2009). In the extreme ultraviolet (EUV) spectrum, CHs appear as dark patches. Using daily hand-drawn maps from the Space Weather Prediction Center (SWPC), we developed a semi-automated pipeline to digitize the SWPC maps into binary segmentation masks. The resulting masks constitute the CHASM-SWPC dataset, a high-quality dataset to train and test automated CH detection models, which is released with this paper. We developed CHASM (Coronal Hole Annotation using Semi-automatic Methods), a software tool for semi-automatic annotation that enables users to rapidly and accurately annotate SWPC maps. The CHASM tool enabled us to annotate 1,111 CH masks, comprising the CHASM-SWPC-1111 dataset. We then trained multiple CHRONNOS (Coronal Hole RecOgnition Neural Network Over multi-Spectral-data) architecture (Jarolim et al. 2021) neural networks using the CHASM-SWPC dataset and compared their performance. Training the CHRONNOS neural network on these data achieved an accuracy of 0.9805, a True Skill Statistic (TSS) of 0.6807, and an intersection-over-union (IoU) of 0.5668, which is higher than the original pretrained CHRONNOS model Jarolim et al. (2021) achieved an accuracy of 0.9708, a TSS of 0.6749, and an IoU of 0.4805, when evaluated on the CHASM-SWPC-1111 test set.
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All authors Cutter Beck, Evan Smith, Khagendra Katuwal, Rudra Kafle, Jacob Whitehill

Earth and Planetary Astrophysics

Shaping the Mantle: The Role of the Superheated Core After Giant Impacts

You Zhou

The Moon-forming giant impact significantly influenced the initial thermal state of Earth's mantle by generating a global magma ocean, marking the onset of mantle evolution. Recent Smoothed Particle Hydrodynamics (SPH) simulations indicate that such a collision would produce a superheated core, whose cooling would strongly influence subsequent mantle dynamics. Here, we present systematic SPH simulations of diverse giant-impact scenarios and show that the superheated core formed after the impact can trigger secondary mantle melting, thereby governing the final state of the magma ocean. To further quantify this effect, we employ a parameterized mantle-melting model to evaluate the influence of secondary melting on the lower mantle. Our results suggest three possible outcomes: complete mantle melting, the formation of a basal melt layer, or the initiation of an early superplume. Combined with recent two-phase magma-ocean solidification models, we infer that all three scenarios would result in basal melt layers of varying thickness, partially retaining the thermal energy of the superheated core. In the canonical Moon-forming scenario, the superheated core would rapidly transfer heat to Earth's lower mantle, causing secondary mantle melting within approximately 277–5983 years and generating either a basal melt layer or a fully molten mantle. Both outcomes would effectively erase primordial heterogeneities in the lower mantle and impose distinct pathways for its subsequent thermal evolution.
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High Energy Astrophysical Phenomena

Aspherical Remnants of Triple and Quadruple Detonations in Binary White Dwarfs

Logan J. Prust, Lars Bildsten and Samuel J. Boos

White dwarfs which explode by the double-detonation mechanism may have a binary white dwarf donor which is subsequently ignited by its collision with the ejecta. This results in the destruction of the donor via either the triple- or quadruple-detonation mechanism, adding significant mass to the resulting ejecta as well as modifying its structure and composition. We simulate the evolution of supernova remnants resulting from such detonations in a variety of binary progenitors and compare them against a double detonation with a surviving donor. Because of the time delay between the detonations of the two white dwarfs, high-velocity ejecta from the first explosion governs the first few centuries of remnant evolution, whereas at later times the dense core resulting from the donor detonation drives both the forward and reverse shocks to larger radii. The collision between the highest-velocity ejecta of the primary explosion and the donor carves a conical wake into the ejecta, which persists into the remnant phase regardless of whether or not the donor detonates. Our suite of simulated remnants are found to exhibit multiple distinguishing features of the explosion properties: a distinct X-ray morphology in the thermal emission and iron lines for triple detonations and smaller remnants with centrally-concentrated emission for double detonations. The remnants are also varied in their elemental abundances and distributions, particularly for lighter elements, but these have limited observational utility and are sensitive to the properties of the progenitor binary.
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High Energy Astrophysical Phenomena

Delayed radio emission in tidal disruption events from collisions of outflows driven by disk instabilities

Samantha C. Wu, Daichi Tsuna, Brenna Mockler et al. (+1 more)

Delayed radio emission has been associated with a growing proportion of tidal disruption events (TDEs). For many events, the radio synchrotron emission is inferred to originate from the interaction of mildly-relativistic outflows, launched with delay times of $\sim 100$–$1000$ d after the TDE optical peak. The mechanism behind these outflows remains uncertain, but may relate to instabilities or state transitions in the accretion disk formed from the TDE. We model the radio emission powered by the collision of mass outflows ("flares") from TDE accretion disks, considering scenarios in which two successive disk flares collide with each other, as well as collisions between the outflow and the circumnuclear medium (CNM). For flare masses of $\sim 0.01$-$0.1 M_{\odot}$, varied CNM densities, and different time intervals between ejected flares, we demonstrate that the shocks formed by the collisions have velocities $0.05c$-$0.3c$ at $\sim 10^{17}$ cm and power bright radio emission of $L_{\nu} \sim 10^{27}$-$10^{30}$ erg s$^{-1}$ Hz$^{-1}$, consistent with the properties inferred for observed events. We quantify how the typical peak timescale and flux varies for different properties of our models, and compare our model predictions to a selection of TDEs with delayed radio emission. Our models successfully reproduce the light curves and SEDs for several events, supporting the idea that delayed outflows from disk instabilities and state transitions can power late-time radio emission in TDEs.
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All authors Samantha C. Wu, Daichi Tsuna, Brenna Mockler, Anthony L. Piro

Monday 17 November

High Energy Astrophysical Phenomena

High-energy radiation from the pulsar Equatorial Current Sheet

Ioannis Contopoulos, Jerome Petri and Ioannis Dimitropoulos

Pulsars emit beams of radiation that reveal the extreme physics of neutron star magnetospheres. Yet, their understanding remains incomplete. Recent global Particle-in-Cell (PIC) simulations have raised several questions that led us to question their validity and their extrapolation to realistic particle Lorentz factors, electric and magnetic fields. We want to generate realistic sky maps of high-energy radiation from first principles. We propose a novel method to study the Equatorial Current Sheet (ECS) where most of the particle acceleration and the high-energy radiation is expected to originate. We first determine its shape and external magnetic field with a steady-state ideal force-free solution. Then, we consider the extra electric and magnetic field components that develop when dissipation is considered. Finally, we study the particle acceleration and radiation that is due to these extra field components for realistic field and particle parameters. We generate realistic sky maps of high-energy radiation and compare them with those obtained via PIC simulations. These sky maps may also be closely reproduced using the ECS of the split-monopole solution beyond the light cylinder. The ECS is probably stabilized by the normal magnetic field component that is due to the global magnetospheric reconnection. Our method helps us better understand the origin of the pulsed high-energy radiation in the pulsar magnetosphere.
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Earth and Planetary Astrophysics · Cross-listed from physics.hist-ph

The significance of Halley's Comet in the Bayeux Tapestry

Michael Lewis and Simon Portegies Zwart

A comet appears in the Bayeux Tapestry between the scene showing the death of the English king Edward the Confessor and the election of his successor, Harold Godwinson. The Tapestry's inscription only refers to this as a star, though we can see from its depiction, shown with a hairy tail, that it is a comet, now known to us as Halleys Comet P1/Halley. Behind the exciting story of the Bayeux Tapestry, however, goes a rich mythological world of intrigue, deceit, the succession of kings, and earlier sightings of the same comet. In historical accounts of many cultures, comets are generally considered portents of change rather than disaster. Here we consider the significance of the Tapestry's comet in the context of the so-called English succession crisis of 1066 with reference to other contemporary accounts of comets. We conclude that although the tapestry's illustration is suggestive and unmistakably Halleys Comet, it is not a priority for its creators to give a precise account of its arrival in the sky, but rather connect it, likely for political reasons, albeit retrospectively, to the sequential events of Edwards death and Harolds coronation. In that, the tapestry's anonymous artists provide a unique telling of its arrival.
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Instrumentation and Methods for Astrophysics

Ice Giants Pre-Decadal Survey Mission Study Report

M. Hofstadter, A. Simon, K. Reh et al. (+26 more)

The Ice Giants Study was commissioned by NASA to take a fresh look (as of 2017) at science priorities and concepts for missions to the Uranus and Neptune systems in preparation for the third Planetary Science Decadal Survey. This study was led by a Science Definition Team (SDT) and the Jet Propulsion Laboratory (JPL) with participation from Langley Research Center, Ames Research Center, The Aerospace Corporation, Purdue University, and the European Space Agency. The SDT was appointed by NASA and co-chaired by Mark Hofstadter (JPL) and Amy Simon (Goddard Space Flight Center). The Study Manager was Kim Reh (JPL) and the Study Lead was John Elliott (JPL). The study team assessed and prioritized science objectives taking into account advances since the last Decadal Survey, current and emerging technologies, mission implementation techniques and celestial mechanics. This study examined a wide range of mission architectures, flight elements, and instruments. Six of the prioritized concepts were studied via JPL's Team X process and resulting cost estimates were subjected to independent assessment by The Aerospace Corporation. Results presented herein show that high-value flagship-class mission concepts to either Uranus or Neptune are achievable within ground rule budgetary constraints.
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All authors M. Hofstadter, A. Simon, K. Reh, J. Elliott, S. Atreya, D. Banfield, J. Fortney, A. Hayes, M. Hedman, G. Hospodarsky, A. Masters, K. Mandt, M. Showalter, K. Soderlund, D. Turini, E. Turtle, P. Agrawal, T. Anderson, D. Atkinson, N. Arora, C. Borden, M. Brennan, J. Cutts, H. Hwang, M. Le, A. Petropoulos, S. Saikia, T. Spilker, W. Smythe

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

Infrared Quantum Electrodynamics and the Rayleigh-Jeans Physics

Jorge Gamboa and Natalia Tapia Arellano

Infrared quantum electrodynamics (IR-QED) acquires a natural geometric interpretation once soft photons are described as adiabatically transported electron-photon clouds. Within this framework, the relevant infrared structure is encoded in a functional Berry phase associated with the space of gauge connections, and the corresponding Berry corrections modify the Rayleigh-Jeans spectrum. The infrared scaling symmetry of the Rayleigh-Jeans law leads to a simple renormalization-group equation whose solution determines the frequency dependence of an effective factor $F_{\rm eff}(\omega)$ controlling the strength of the electron-photon cloud dressing. As a result, the energy density of the cosmic microwave background (CMB) receives a Berry-induced correction that scales as a power law and produces a frequency-dependent temperature excess in the radio domain. Although the exponent $\gamma$ governing this scaling behaviour is not fixed internally by the present formulation of IR-QED and must instead be determined phenomenologically, the existence and structure of the excess are genuine predictions of the theory. Remarkably, the resulting expression is extremely simple and naturally aligns with the deviations suggested by the ARCADE 2 data. Taken together, these results indicate that Berry phases in IR-QED may lead to observable consequences in the low-frequency tail of the CMB spectrum.
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Cosmology and Nongalactic Astrophysics

Accessing the homogeneity scale with 21 cm intensity mapping surveys

Bruno B. Bizarria, Camila P. Novaes, Felipe Avila et al. (+4 more)

The homogeneity scale, $R_{\rm H}$, offers a fundamental test of the Cosmological Principle, yet it has not yet been measured with 21cm intensity mapping surveys. A key limitation for such a measurement is the telescope beam, which artificially smooths the observed signal. We quantify this effect using the two-point correlation function and the correlation dimension, $\mathcal{D}_2(r)$, to model how beam convolution suppresses intrinsic clustering. For any given redshift $z$, we identify a maximum beam width, $\sigma_{\rm max}(z)$, beyond which the homogeneity scale cannot be recovered. This limit defines an inaccessible region in the $\sigma \times z$ parameter space, where $R_{\rm H}$ is erased by beam smoothing. Applying this framework to several current and upcoming radio telescopes, we assess their ability to probe $R_{\rm H}$. Our results provide the first quantitative forecast of the instrumental requirements for measuring the cosmic homogeneity scale with 21cm IM, and establish a theoretical basis for future observational applications.
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All authors Bruno B. Bizarria, Camila P. Novaes, Felipe Avila, Rahima Mokeddem, Helissa H. da Costa, Carlos A. Wuensche, Gabriel A. S. Silva

Cosmology and Nongalactic Astrophysics

Thermodynamic Origin of the Tully-Fisher Relation in Dark Matter Dominated Galaxies: A Theoretical-Empirical Derivation

V.K. Oikonomou

In this work we introduce the concept of self-interacting dark matter with scale-dependent equation of state, in the context of which dark matter is collisional and its equation of state is radius-dependent and has the form $P(r)=K(r)\left(\frac{\rho(r)}{\rho_{\star}}\right)^{\gamma(r)}$. We confronted the effectively 2-parameter model with 174 galaxies from the SPARC data, and we found that the rotation curves of 100 galaxies can be perfectly fitted by the model. These galaxies are dark matter dominated, mostly dwarfs, low-luminosity and low-surface-brightness spiral galaxies. We demonstrate that scale-dependent self-interacting dark matter solves the cusp-core issue for dark matter dominated galaxies. More importantly, the structure of the scale-dependent SIDM model produces in a semi-theoretically and semi-empirically way the canonical Tully-Fisher and the baryonic Tully-Fisher relations when these 100 viable dwarfs, low-surface-brightness and low-luminosity galaxies are taken into account. The behavior of the entropy function $K(r)$ is assumed to be $K(r)=K_0\times\left(1+\frac{r}{r_c}\right)^{-p}$. The perfect fits of the rotation curves come for a nearly isothermal and virialized dark matter halo, which naturally predicts the correlation $K_0\sim V_{\mathrm{max}}^2$. This correlation holds true empirically as confirmed by the data and we also find empirically $L\sim K_0^2$ from the data, thus the canonical Tully-Fisher relation is reproduced semi-theoretically and semi-empirically. We perform the same task and we find theoretically, for dark matter dominated galaxies, that $K_0\sim V_{\mathrm{flat}}^2$ which is also confirmed empirically from the data, along with the correlation $K_0\sim M_b^{0.5}$, hence the baryonic Tully-Fisher law naturally emerges in a semi-theoretical and semi-empirical manner.
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High Energy Astrophysical Phenomena

Multi-layered Fast Wind observed in XMM-Newton snapshot of Seyfert 1 Markarian 877

Xin Xiang, Jon M. Miller, Ehud Behar et al. (+4 more)

Ultra Fast Outflows (UFOs) are powerful, highly ionized winds launched from the innermost regions of Active Galactic Nuclei (AGNs), reaching velocities of 0.03 – 0.3 c and playing a key role in AGN feedback. We present a photoionization analysis of an 18 ks \xmm\ snapshot of the Seyfert 1 AGN Mrk 877, revealing three distinct UFO components with line-of-sight velocities of $0.10^{+0.005}_{-0.005}~c$ , $ 0.04^{+0.005}_{-0.004}~c$ , and $0.05^{+0.005}_{-0.004}~c$. These components span a broad range of ionization parameters and column densities, producing absorption features across both soft and hard X-ray bands. Even under the most conservative assumption for the volume filling factor, the fastest component exceeds $5\%$ of the Eddington luminosity, making it capable of driving strong galaxy-scale feedback. The soft X-ray UFO component, despite its lower ionization, shares a similar velocity as a higher-ionization component, hinting at a two-phase medium likely shaped by clumpiness or interactions with ambient material. The density profile inferred from the Absorption Measurement Distributions (AMD) and the positive trend between outflow momentum rate and radiation momentum flux suggest that wind is powered by a combination of radiative and magnetic driving.
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All authors Xin Xiang, Jon M. Miller, Ehud Behar, W. N. Brandt, Luigi Gallo, Doyee Byun, Elena Gallo

Astrophysics of Galaxies

Mapping the Cosmic-Ray Ionization Rate in the Local Galaxy with H$_3^+$

Nick Indriolo, Alexei V. Ivlev, T. Pellegrin et al. (+6 more)

Chemistry in diffuse molecular clouds relies primarily on rapid ion-molecule reactions. Formation of the initial ions, H$^+$ and H$_2^+$, is dominated by cosmic-ray ionization of H and H$_2$, making the cosmic-ray ionization rate (denoted $\zeta({\rm X})$ for species X) an important parameter for chemical modeling. We have made observations targeting absorption lines of H$_3^+$, one of the most reliable tracers of $\zeta({\rm H_2})$, toward diffuse molecular cloud sight lines where the H$_2$ column density has been directly measured in the ultraviolet, detecting H$_3^+$ in 12 out of 27 sight lines. The 3D-PDR modeling method introduced by Obolentseva et al. (2024) was used to infer cosmic-ray ionization rates in the clouds along these sight lines, and our combined sample has a mean ionization rate of $5.3\times10^{-17}$ s$^{-1}$ with standard deviation $2.5\times10^{-17}$ s$^{-1}$. By associating H$_3^+$ absorption with gas density peaks derived from the differential extinction maps of Edenhofer et al. (2024) we have constructed a sparsely sampled 3D map of the cosmic-ray ionization rate in targeted regions within about 1~kpc of the Sun. Specific regions show reasonably uniform ionization rates over length scales of tens of parsecs, with the average ionization rate in each region being different. Large differences (factor of 5) in $\zeta({\rm H_2})$ are found over length scales of about 100 pc. This supports a picture where the cosmic-ray ionization rate varies smoothly over small size scales, but is not uniform everywhere in the Galactic disk, likely being controlled by proximity to particle acceleration sites.
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All authors Nick Indriolo, Alexei V. Ivlev, T. Pellegrin, M. Obolentseva, Paola Caselli, A. M. Jacob, D. A. Neufeld, Kedron Silsbee, M. G. Wolfire

High Energy Astrophysical Phenomena

Blazars as a Potential Origin of the KM3-230213A Event

The KM3NeT Collaboration

The KM3NeT collaboration has reported the detection of the highest energy neutrino event observed to date. The energy of the event is of the order of 220 PeV hinting towards a neutrino flux at the highest energies. In this article, the potential blazar origin for this event is explored. The publicly available Astro-Multimessenger Modeling software is used to model the blazar gamma-ray and neutrino fluxes. It is concluded that a population of blazars could produce the diffuse flux compatible with the observation of the ultra-high energy event detected by the KM3NeT/ARCA detector. At the same time, the gamma-ray flux produced by such a population of blazars is consistent with the diffuse gamma-ray flux measured by the Fermi Large Area Telescope.
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Cosmology and Nongalactic Astrophysics

Large Scale White Noise and Cosmology

Gabriela Barenboim, Aurora Ireland and Albert Stebbins

The generation of white noise on large scales is a generic property of the dynamics of physical systems described by local non-linear partial differential equations. Non-linearities prevent the small scale dynamics from being erased by smoothing. Unresolved small scale dynamics act as an uncorrelated (white or Poissonian) noise (seemingly stochastic but actually deterministic) contribution to large scale dynamics. This white noise exists even when the dynamics is very nearly linear. In cases where the power spectrum is sub-Poissonian on large scales, this noise will dominate on the largest scale power no matter the amplitude of the inhomogeneities. Such is the case in the standard model of cosmology, where the primordial density power spectrum is expected to have an almost Harrison-Zel'dovich, $P[k]\sim k$, spectrum on a much broader range of scales than can be observed. Even though linear gravitational evolution dominates non-linear corrections by a factor $\sim10^5$, the non-observation of white noise on the Hubble scale precludes the extrapolation of this power law below the comoving $1\,$pc scale. More generally, observation or non-observation of large scale white noise provides a powerful probe of the universe on very small scales in the early early universe. Gravitational radiation, phase transitions, vorticity, and running of the spectral index are all phenomena that can be probed with large scale white noise. Large scale white noise is a non-optional feature of all cosmological models but one which has not heretofore been appreciated.
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Solar and Stellar Astrophysics

Dual Origins of Rapid Flare Ribbon Downflows in an X9-class Solar Flare

Ryan J. French, William H. Ashfield IV, Cole A. Tamburri et al. (+4 more)

We detect rapid downflows of 150-217 km/s in IRIS Si IV 1402.77 nm measurements of an X9-class solar flare on 2024 October 3rd. The fast redshift values persist for over 15 minutes from flare onset, and can be split into two distinct stages of behavior, suggesting that multiple mechanisms are responsible for the downwards acceleration of flare ribbon plasma. The first stage of rapid downflows are synchronized with peaks in emission from the Advanced Space-based Solar Observatory Hard X-ray Imager (ASO-S/HXI) and Large Yield Radiometer (LYRA) Lyman-alpha measurements, indicative that the chromospheric downflows (with a maximum redshift of 176 km/s) result from chromospheric condensations associated with impulsive energy release in the solar flare. Later in the event, strong Si IV flare ribbon downflows persist (to a maximum value of 217 km/s), despite the magnetic flux rate falling to zero, and high-energy HXR and Lyman-alpha measurements returning to background levels. This is reflective of downflows in the flare ribbon footpoints of flare-induced coronal rain. Hard X-ray spectral analysis supports this scenario, revealing strong non-thermal emission during the initial downflow stage, falling near background levels by the second stage. Despite these distinct and contrasting stages of ribbon behavior, Si IV Doppler velocities exhibit quasi-periodic pulsations with a constant ~50 s period across the 15-minute flare evolution (independently of loop length). We deduce that these pulsations are likely caused by MHD oscillations in the magnetic arcade. Finally, we utilize machine learning K-means clustering methods to quantify line profile variations during the stages of rapid downflows.
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All authors Ryan J. French, William H. Ashfield IV, Cole A. Tamburri, Maria D. Kazachenko, Marie Dominique, Marcel Corchado Albelo, Amir Caspi

High Energy Astrophysical Phenomena

The Scoured Spike: Suppression of Indirect Dark Matter Signals by a Hidden Companion

Jaden Lopez and Stefano Profumo

A massive “dark companion” – such as an intermediate-mass black hole or other compact dark object – orbiting the supermassive black hole at the Galactic Center can dynamically reshape the surrounding dark-matter spike. Through gravitational heating and angular-momentum exchange, the companion excavates a “scoured” region that lowers the inner density and suppresses the expected annihilation signal. We quantify this effect by computing the suppression of the dark-matter annihilation $J$-factor induced by such a companion, combining an analytic scouring-radius model with full numerical integrations of the modified density profile. We scan the parameter space of companion mass, orbital separation, system age, and spike slope, explicitly including the interplay with the annihilation plateau. \textcolor{black}{For canonical Gondolo–Silk spikes with $\gamma_{\rm sp} \gtrsim 2$, the scouring radius grows only weakly with injected energy because the binding energy is concentrated at small radii; however, once scouring occurs, the $J$-factor suppression can be substantial, for sufficiently massive or long-lived companions. In the shallower-spike regime with $\gamma_{\rm sp} \lesssim 2$, the same companion drives $r_{\rm scour}$ to much larger multiples of $R_{\rm core}$, and even a modest ${\sim}10^{4}\,M_\odot$ companion on a $\mathcal{O}(100)\,{\rm AU}$ orbit and $\mathcal{O}({\rm Gyr})$ age can suppress the annihilation flux by one to two orders of magnitude. Whether a steep spike is significantly suppressed therefore depends on the companion's mass and lifetime, not merely on the sign of $(2-\gamma_{\rm sp})$.} The numerical results are accurately captured (typically at the $\lesssim 10\%$ level) by a simple fitting formula in terms of a dimensionless scouring parameter that measures the ratio between the scoured region and the annihilation core. [...]
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High Energy Astrophysical Phenomena

Low-energy Radio Bursts from Magnetar XTE J1810$-$197: Implications for Fast Radio Bursts

Banshi Lal, Yogesh Maan, Moaz Abdelmaguid et al. (+3 more)

Magnetars are the leading candidate sources of fast radio bursts (FRBs). However, the observational probes of the connections between magnetars and FRBs are severely limited by the paucity of detection of highly energetic radio events from magnetars – to date, only one radio burst as energetic as FRBs has been detected from a Galactic magnetar. Here, we present a detailed analysis of a large sample of low-energy bursts detected from the magnetar XTE J1810$-$197, and probe their implications for FRB emission from magnetars. We report detection of over 97000 bright radio pulses from 242 observations of the magnetar XTE J1810$-$197 over 4.5 years and two decades in frequency (300 MHz to 6.15 GHz), using the Giant Meterwave Radio Telescope and the Green Bank Telescope, after its recent outburst onset in December 2018. We present detailed analysis of the burst fluence distributions and their trends with time as well as frequency, and the waiting time distribution. We show that XTE J1810$-$197 rapidly switches between pulsar-like and giant-pulse-like emission states, and magnetars like XTE J1810$-$197 remain viable and likely emitters of FRBs, in the form of giant-pulses with energies comparable to FRBs. We also demonstrate that the lack of the detection of an underlying periodicity in the bursts from repeating FRBs might be caused by emission across a wide range of spin phases.
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All authors Banshi Lal, Yogesh Maan, Moaz Abdelmaguid, Visweshwar Ram Marthi, Joseph D. Gelfand, Samayra Straal

Cosmology and Nongalactic Astrophysics

Exploring the Model Dependence of MCMC-Based 21 cm Power Spectrum Parameter Constraints

August Berklas and Jonathan Pober

Detection and analysis of the cosmic 21 cm signal of neutral hydrogen has long been considered the most promising route towards exploration of the Epoch of Reionization (EoR). 21CMMC, a Markov Chain Monte Carlo sampler of the seminumerical simulation code 21cmFAST, has already been used in conjunction with published upper limits on the 21 cm signal from the Murchison Widefield Array, the Low Frequency Array, and the Hydrogen Epoch of Reionization Array to constrain the astrophysics of the EoR. Here, we investigate the extent to which analysis of the EoR performed using 21CMMC is dependent on the underlying seminumerical model. We used 21cmFAST to simulate two datasets of 21 cm light-cones that differ only in the algorithm used to identify ionized regions (the so-called "bubble-finding" algorithm). We then tested 21CMMC's ability to return key astrophysical parameteres when using the different bubble-finding algorithms. We find that the performance of 21CMMC depends sensitively on the agreement between the astrophysical model of our mock data and the model used for sampling. This result has important implications for the analysis of the 21 cm signal performed using 21CMMC and further motivates investigation into model-independent analysis techniques for 21 cm EoR data.
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Astrophysics of Galaxies

How accurately can obscured galaxy luminosities be measured using spectral energy distribution fitting of near- through far-infrared observations?

Duncan Farrah, Kiana Ejercito, Andreas Efstathiou et al. (+23 more)

Infrared-luminous galaxies are important sites of stellar and black hole mass assembly at most redshifts. Their luminosities are often estimated by fitting spectral energy distribution (SED) models to near- to far-infrared data, but the dependence of these estimates on the data used is not well-understood. Here, using observations simulated from a well-studied local sample, we compare the effects of wavelength coverage, signal-to-noise (S/N), flux calibration, angular resolution, and redshift on the recovery of starburst, AGN, and host luminosities. We show that the most important factors are wavelength coverage that spans the peak in a SED, with dense wavelength sampling. Such observations recover starburst and AGN infrared luminosities with systematic bias below $20\%$. Starburst luminosities are best recovered with far-infrared observations while AGN luminosities are best recovered with near- and mid-infrared observations, though the recovery of both are enhanced with near/mid-infrared, and far-infrared observations, respectively. Host luminosities are best recovered with near/far-infrared observations, but are usually biased low, by $\gtrsim20\%$. The recovery of starburst and AGN luminosity is enhanced by observing at high angular resolution. Starburst-dominated systems show more biased recovery of luminosities than do AGN-dominated systems. As redshift increases, far-infrared observations become more capable, and mid-infrared observations less capable, at recovering luminosities. Our results highlight the transformative power of a far-infrared instrument with dense wavelength coverage from tens to hundreds of microns for studying infrared-luminous galaxies. We tabulate estimates of systematic bias and random error for use with JWST and other observatories.
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All authors Duncan Farrah, Kiana Ejercito, Andreas Efstathiou, David Leisawitz, Athena Engholm, Irene Shivaei, Matteo Bonato, David L. Clements, Sara Petty, Lura. K. Pitchford, Charalambia Varnava, Jose Afonso, Carlotta Gruppioni, Evanthia Hatziminaoglou, Andrew Hoffman, Mark Lacy, Brenda C. Matthews, Conor Nixon, Chris Pearson, Berke Vow Ricketti, Dimitra Rigopoulou, Loren Robinson, Locke D. Spencer, Lingyu Wang, David B. Sanders, Gerard van Belle

Earth and Planetary Astrophysics

Inferring Planet and Disk Parameters from Protoplanetary Disk Images Using a Variational Autoencoder

Sayed Shafaat Mahmud, Sayantan Auddy, Neal Turner et al. (+1 more)

Dust-continuum observations of many protoplanetary disks reveal rings and gaps that are widely interpreted as evidence of ongoing planet formation. Here we present the first framework for inferring planet and disk parameters from such images using variational autoencoder (VAE) based generative machine learning (ML). The new framework is called VADER (Variational Autoencoder for Disks with Embedded Rings). We train VADER on synthetic images of dust continuum emission, generated from FARGO3D hydrodynamic simulations post-processed with Monte Carlo radiative transfer calculations. VADER infers the masses of up to three embedded planets as well as the disk parameters viscous $\alpha$, dust-to-gas ratio, Stokes number, and flaring index. VADER returns a full posterior distribution for each of these quantities. We demonstrate that VADER reconstructs disk morphologies with high structural similarity (index $>$ 0.99), accurately recovers planet parameters with $R^2 > 0.9$ across planet masses, and reliably predicts disk parameters. Applied to ALMA dust continuum images of 23 protoplanetary disks, our model returns mass estimates for embedded planets of 0.3-2~$M_{\mathrm{Jup}}$ that agree to within $1\sigma$ of published values in most cases, and infers disk parameters consistent with current literature. Once trained, the VAE performs full posterior parameter inference in a matter of minutes, offering statistical rigor with enough computational speed for application to large-scale ALMA surveys. These results establish VAE-based models as powerful tools for inferring from disk structure the masses of embedded planets and the global disk parameters, with their associated uncertainties.
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All authors Sayed Shafaat Mahmud, Sayantan Auddy, Neal Turner, Jeffrey S. Bary

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

Characteristic Decomposition for Relativistic Numerical Simulations: II. Magnetohydrodynamics

Saul A. Teukolsky

The characteristic decomposition for GRMHD in the comoving frame of the fluid has been known for a long time. However, it has not been known in the coordinate frame of the simulation and in terms of the conserved variables evolved in typical numerical simulations. This paper applies the method of quasi-invertible transformations developed in Paper I to derive this decomposition. Among other benefits, this will allow us to use the most accurate known computational methods, such as full-wave Riemann solvers. The results turn out to be simpler than expected based on earlier attempts.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Characteristic Decomposition for Relativistic Numerical Simulations: I. Hydrodynamics

Saul A. Teukolsky

The characteristic decomposition for GRMHD is not known in a form useful for current numerical simulations. This prevents us from using the most accurate known computational methods, such as full-wave Riemann solvers. In this paper, we present a new method of finding decompositions. The method is based on transformations from the comoving frame, where the fluid flow is simplest and the decomposition has been known for a long time. The key innovation we introduce is that of quasi-invertible transformations. In this first paper, we introduce these transformations using the simpler example of relativistic hydrodynamics. We recover the known decomposition for relativistic hydrodynamics in somewhat simpler form than previously derived, and without the need for computer algebra. A new result in this paper is the characteristic decomposition when the the evolution tracks the composition of a fluid in nuclear statistical equilibrium. In Paper II of this series, we apply a quasi-invertible transformation to derive the complete characteristic decomposition for GRMHD in the conserved variables used in simulations.
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High Energy Astrophysical Phenomena

Estimation of Magnetic Fields from Synchrotron Emission: Numerical Tests

Nora B. Linzer, Lucia Armillotta, Eve C. Ostriker et al. (+1 more)

We use models of spectrally resolved cosmic ray (CR) transport in TIGRESS MHD simulations of the local ISM to produce synthetic synchrotron emission and to test, on scales from a few kpc down to ~10 pc, the traditional estimate of magnetic field strength based on the assumption of equipartition between the magnetic and total CR energy densities. Our analysis shows that the traditional equipartition estimate works well at the kpc scale of the simulation box, but breaks down at smaller scales. We find that the predicted magnetic field strength can be improved at small scales by assuming a constant CR energy density across each mock radio observation. The large-scale mean CR energy density can be estimated by assuming equipartition with the large-scale mean magnetic energy density, or as a function of additional observable quantities such as the star formation rate surface density or gas weight. In addition to estimating the magnetic field strength, we use synthetic polarized emission to create maps of the magnetic field direction. We find that the true magnetic field direction can be recovered well from the mock observations.
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All authors Nora B. Linzer, Lucia Armillotta, Eve C. Ostriker, Eliot Quataert