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Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 7 February

High Energy Astrophysical Phenomena

FPIC: a new Particle-In-Cell code for stationary and axisymmetric black-hole spacetimes

Claudio Meringolo and Luciano Rezzolla

In this paper we present a newly developed GRPIC code framework called FPIC, providing a detailed description of the Maxwell-equations solver, of the particle “pushers”, and of the other algorithms that are needed in this approach. We describe in detail the code, which is written in Fortran and exploits parallel architectures using MPI directives both for the fields and particles. FPIC adopts spherical Kerr-Schild coordinates, which encode the overall spherical topology of the problem while remaining regular at the event horizon. The Maxwell equations are evolved using a finite-difference time-domain solver with a leapfrog scheme, while multiple particle “pushers” are implemented for the evolution of the particles. In addition to well-known algorithms, we introduce a novel hybrid method that dynamically switches between the most appropriate scheme based on the violation of the Hamiltonian energy. We first present results for neutral particles orbiting around black holes, both in the Schwarzschild and Kerr metrics, monitoring the evolution of the Hamiltonian error across different integration schemes. We apply our hybrid approach, showing that it is capable of achieving improved energy conservation at reduced computational cost. We apply FPIC to investigate the Wald solution, first in electrovacuum and subsequently in plasma-filled configurations. In the latter case, particles with negative energy at infinity are present inside the ergosphere, indicating that the Penrose process is active. Finally, we present the split-monopole solution in a plasma-filled environment and successfully reproduce the Blandford-Znajek luminosity, finding very good agreement with analytical predictions.
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Instrumentation and Methods for Astrophysics

Sunrise III: The Wavefront Correction System

Thomas Berkefeld, Alexander Bell, Reiner Volkmer et al. (+19 more)

This paper describes the wave-front correction and image stabilisation system (CWS) developed for the Sunrise III balloon-borne telescope, and provides information about its performance as measured during the integration into the telescope and during the 2024 science flight. The fast image stabilisation is done by a correlation tracker (CT) and a fast tip-tilt mirror, low order aberrations such as defocus and coma are measured by a six-element Shack-Hartmann wavefront sensor (WFS) and corrected by an active telescope secondary mirror for automated focus and manual coma correction. The CWS is specified to deliver a stabilised image with a precision of 0.005 arcsec (rms). The autofocus adjustment is specified to maintain a focus stability of 0.01 waves in the focal plane of the CWS.
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All authors Thomas Berkefeld, Alexander Bell, Reiner Volkmer, Frank Heidecke, Tobias Preis, Thomas Sonner, Eiji Nakai, Andreas Korpi-Lagg, Achim Gandorfer, Sami K. Solanki, Jose Carlos del Toro Iniesta, Yukio Katsukawa, Pietro Bernasconi, Alex Feller, Tino L. Riethmüller, Alberto Álvarez-Herrero, Masahito Kubo, Valentín Martínez Pillet, H. N. Smitha, David Orozco Suárez, Bianca Grauf, Michael Carpenter

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

Circularly polarized gravitational waves from parity-violating scalar-tensor theory

Jia-Xi Feng, Jia-Yuan Fang and Xian Gao

We study both primordial gravitational waves (GWs) and scalar-induced gravitational waves (SIGWs) in a class of the parity-violating scalar-tensor (PVST) theory, of which the Lagrangian is the linear combination of seven ghost-free parity-violating scalar-tensor monomials dubbed the "Qi-Xiu" Lagrangians. At linear order, we obtain the quadratic action for tensor perturbations and show that parity-violating terms associated with L_1, L_2, L_5, L_6, and L_7 render the tensor propagation polarization dependent, leading to chiral primordial spectra and a nonvanishing degree of circular polarization. At second order, we derive the equation of motion for SIGWs and identify the explicit parity-violating source terms. In particular, L_3 and L_4 enter exclusively through the source term for SIGWs, allowing parity violation to arise even when the linear GWs' propagation remains effectively general-relativity-like. During the radiation-dominated era, we compute the fractional energy density of SIGWs for both monochromatic and log-normal curvature power spectra. We find that, around the peak frequency, SIGWs in PVST gravity exhibit characteristic deviations from those in general relativity, resulting in a nonzero degree of circular polarization.
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High Energy Astrophysical Phenomena

Imprints of gravitational waves from magnetar spindown in GRB X-ray afterglows

Shu-Jin Hou, Rui Xue, Fang-Kun Peng et al. (+3 more)

Given that newborn magnetars are considered potential central engines of gamma-ray bursts (GRBs), there is strong motivation to identify gravitational wave (GW) signatures within GRB samples. If the X-ray afterglow of a GRB is powered by a magnetar, and the initial spindown of the magnetar is dominated by the GW radiation induced by $r$-mode instability or magnetic-field-induced deformation, the decay of the X-ray flux would record the information of the GW radiation. We find that GRB 130603B potentially represents a rare and precious case where the spindown of the central magnetar is dominated in-turn by $r$-mode and magnetic distortion-induced GW radiation. By fitting the X-ray light curve of GRB 130603B in this model, we obtain the initial spin period of magnetar $\sim 5.3\times 10^{-4}$ s, the effective dipole magnetic field strength $\sim 5.2\times 10^{14}$ G, the ellipticity of the magnetar $\sim 1.3\times 10^{-4}$, and the amplitude of $r$-mode oscillation $\sim3.3\times 10^{-2}$. It may serve as a reliable approach for investigating neutron star physics by comparing the parameters estimated using the method presented in this manuscript with those obtained from future GW observations.
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All authors Shu-Jin Hou, Rui Xue, Fang-Kun Peng, Zhi-Gang Li, Tong Liu, Ren-Xin Xu

Astrophysics of Galaxies

Active Galactic Nuclei and STaR fOrmation in Nearby Galaxies AGNSTRONG. III. A Study on Ionized and Warm Molecular Gas Outflows of 6 Type-2 AGNs

Ruisong Xia, Chen Qin, Huynh Anh N. Le et al. (+5 more)

Active galactic nucleus (AGN)-driven gas outflows are one of the best tracers of AGN feedback in action, as these powerful outflows expel/heat or compress the surrounding interstellar medium (ISM), thus quenching or enhancing star-forming activity in their hosts. Studying the kinematics of outflows in different gas phases is crucial for comprehending how AGNs impact the ISM within their host galaxies. However, the differences in the physical natures of ionized and warm molecular gas outflows remain largely unexplored. To obtain a complete picture of AGN outflows and their feedback effects, we present a study of both ionized and warm molecular gas outflows in six type-2 AGNs ($z<0.1$) that exhibit strong ionized outflows in previous optical observations. Utilizing the Triple Spectrograph and Double Spectrograph instruments on the Palomar 200-inch Hale Telescope, we conduct spatially resolved measurements in the slit direction of strong emission lines from both ionized and warm molecular gas, such as $\rm [O\ III]$, $\rm Pa\alpha$, $\rm H_{2}$ 1-0 S(1), etc., allowing for a direct comparison of their outflow properties. One out of six AGNs shows significant ionized and warm molecular outflows in near-infrared bands, exhibiting the most powerful kinematics and highest luminosity. A positive correlation between the kinematics and AGN luminosity is shown, suggesting that more luminous AGNs, which reflect higher levels of AGN activity, tend to have a greater impact on the gases, probably driving the outflows.
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All authors Ruisong Xia, Chen Qin, Huynh Anh N. Le, Yongquan Xue, Shifu Zhu, Mengqiu Huang, Hao Liu, Xiaozhi Lin

Cosmology and Nongalactic Astrophysics

A General Formulation of the Kinematic Dipole as a Functional of Selection and Source Properties: Beyond the Ellis–Baldwin Approximation

Tsutomu T. Takeuchi

The dipole anisotropy in galaxy and QSO number counts induced by the motion of the observer (the kinematic dipole) provides an important test of cosmological isotropy and a comparison with the Cosmic Microwave Background (CMB) dipole. Traditionally, the Ellis & Baldwin expression,$\mathcal{A}=2+x(1+\alpha)$, has been widely adopted, assuming power-law number counts and a single power-law spectral energy distribution (SED). Realistic surveys, however, involve a range of non-ideal effects, including diverse SEDs, finite instrumental bandpasses, non-power-law number counts, multi-band photometry and photo-$z$ selections, and direction-dependent or stochastic detection limits. In this paper, we incorporate these effects explicitly at the theoretical level and present a unified formulation of the kinematic dipole for a general parent population and a general multi-dimensional selection function. We show that the dipole amplitude is not described by a single index, but is instead given by a functional, $\mathcal{A}[\mathcal{W},f]$, defined as the Doppler response of the selection function acting on the underlying population. We demonstrate that the classical Ellis–Baldwin result is recovered as a special limiting case of this formalism, and clarify the relation between the theoretical coefficient $\mathcal{A}$ and the dipole vector estimated from finite catalogs, separating theoretical response from statistical uncertainty. This framework provides a basis for reinterpreting reported discrepancies in kinematic dipole measurements across surveys and is directly applicable to future wide-area, multi-band observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Can Dirac neutrinos destabilize $\mathcal{Z}_2$ domain wall network?

Debasish Borah, Partha Kumar Paul and Narendra Sahu

In particle physics model building, a discrete $\mathcal{Z}_2$ symmetry is often spontaneously broken for phenomenological reasons. When this breaking occurs dynamically in the early Universe, stable domain wall networks are formed, which can eventually dominate the cosmic energy density. To avoid this problem, explicit $\mathcal{Z}_2$-breaking terms in the scalar potential are usually introduced in an ad hoc manner. In this Letter, we show that if the same $\mathcal{Z}_2$ symmetry is also responsible for generating light Dirac neutrino masses, such explicit breaking terms can instead arise radiatively from the particles involved in the Dirac mass generation. We find that the resulting bias term scales inversely with the cube of the Dirac neutrino mass, leading to a gravitational wave spectrum proportional to the sixth power of the Dirac neutrino mass. This establishes a nontrivial connection between the Dirac seesaw scale, the domain wall annihilation epoch, and the resulting stochastic gravitational wave signal. We further demonstrate that a wide range of Dirac seesaw scales can be probed by upcoming gravitational wave and cosmic microwave background experiments, while part of the parameter space simultaneously explains the observed baryon asymmetry via Dirac leptogenesis.
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Solar and Stellar Astrophysics

Emergence of a lithium dip in ~35 Myr "Snake" Open Clusters

Yun-Yi Zhang, Hai-Jun Tian, Jian-Rong Shi et al. (+2 more)

We report the discovery of a lithium dip (Li-dip) in the stellar "Snake" (age = $35 \pm 5$ Myr), challenging the classical view that Li-dips emerge only at ages $\gtrsim 150$ Myr. Using high-resolution spectra from GALAH DR4 ($R \sim 28,000$) for 211 member stars, we identify a clear depletion feature in a $T_{\mathrm{eff}}$ range of 6200–6800 K with a depth of $\Delta A(\mathrm{Li}) \approx 0.40$ dex. Our analysis reveals two key advances: the Li-dip appears $\gtrsim 100$ Myr earlier than the previous observations, and within the dip temperature range, a significant correlation is found between rotational velocity and lithium depletion. Specifically, fast rotators ($v \sin i > 25$ km s$^{-1}$) exhibit stronger lithium depletion than slow rotators ($v \sin i < 25$ km s$^{-1}$). This trend suggests that faster rotators develop stronger rotational shear at the convective-radiative boundary, which enhances turbulent mixing and accelerates lithium destruction. It is also found that the lower temperature edge of the lithium plateau can reach as low as 5500 K for the young open clusters.
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All authors Yun-Yi Zhang, Hai-Jun Tian, Jian-Rong Shi, Cheng-Cheng Xie, Xiang-Ming Yang

Astrophysics of Galaxies

Clump-Scale Dust Attenuation in Epoch of Reionization Galaxies: Spatially Resolved Properties from FirstLight Simulations

Yurina Nakazato, Kosei Matsumoto, Akio K. Inoue et al. (+3 more)

Understanding dust attenuation in galaxies at both integrated and spatially resolved scales is fundamental for accurately determining the physical properties of galaxies. Recent high-spatial-resolution observations with ALMA and JWST enable investigations of spatially resolved properties in high-redshift galaxies ($z \gtrsim 6$), but spatial variations in dust observables remain poorly constrained. We use cosmological zoom-in simulations combined with post-processing dust radiative transfer calculations for 376 clumpy galaxies at $z=6$-$9$ with stellar masses of $M_* \gtrsim 10^9 \, M_\odot$. For each system, we investigate dust attenuation and re-emission properties for three components: system-integrated, individual clumps, and diffuse regions. We find that system-integrated attenuation curves are grayer than the Calzetti curve, even when assuming MW- or SMC-type dust. Attenuation curves of individual clumps are even grayer, while diffuse regions exhibit steeper curves owing to enhanced scattering in optically thin environments. Since the effects of optical depth and dust-star geometry are intrinsically degenerate in attenuation curves, we introduce a toy model based on the IRX-$\Delta\beta$ plane, where $\Delta\beta$ denotes the difference between attenuated and intrinsic UV slopes. Applying this framework, we find that clumps have dust column densities approximately an order of magnitude higher than system-integrated values and exhibit co-spatial or dust-extended geometries. In contrast, system-integrated attenuation reflects star-extended geometries driven by contributions from optically thin diffuse regions. We apply this framework to REBELS-IFU galaxies at $z \sim 7$ and find good agreement with our simulation predictions.
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All authors Yurina Nakazato, Kosei Matsumoto, Akio K. Inoue, Daniel Ceverino, Takashi Hosokawa, Daisuke Toyouchi

Instrumentation and Methods for Astrophysics

Imagining the Alien: Human Projections and Cognitive Limitations

S. G. Djorgovski

Imagining what life on other planets, and intelligent life in particular, may be like is a long-running theme in human culture. It is a manifestation of the innate human curiosity about the Cosmos, and it has inspired numerous works of art and folklore, including whole literary and other media genres. It is a profound question, with philosophical and existential implications. There is also an obvious connection with religious beliefs, as gods and other superhuman beings were imagined in the heavens. Speculations about alien beings grew in time, and today, it is a scientific subject of astrobiology, and it is pursued through serious searches for life and intelligence in the universe. However, almost all imaginings of the alien map terrestrial life forms and human cultural, historical, and psychological phenomena to the putative aliens. This lack of individual and collective imagination may reflect our biological and cultural evolution, as our minds are formed through our experiences, perceptions of the world, and interactions with our terrestrial and human environments. As such, imagining aliens is mainly a cultural phenomenon and may reflect the intrinsic cognitive limitations of the human mind. Interestingly, we did create what is effectively an alien intelligence on this planet in the form of now rapidly evolving Artificial Intelligence (AI). As its capabilities grow, it may give us new insights into what extraterrestrial advanced intelligences may be like.
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Friday 6 February

High Energy Astrophysical Phenomena

A NICER view of the corona through time-dependent Comptonization of the quasi-periodic oscillations in nine black-hole X-ray binaries

Yuexin Zhang, Mariano Méndez, James F. Steiner et al. (+12 more)

We present a systematic study of the evolution of the corona geometry in nine black hole X-ray binaries (BHXRBs) using archival data from NICER. We identify 171 observations exhibiting quasi-periodic oscillations (QPOs) across various spectral states and model the time-averaged energy spectra of the source, as well as the energy-dependent rms and phase-lag spectra of the QPO, with the time-dependent Comptonization model vKompthdk. This allows us to simultaneously constrain the corona size and feedback fraction during outbursts. By using the power color hue diagnostics, we identify different spectral states, and observe that the QPO frequency increases from $\sim$0.1 Hz to $\sim$10 Hz in the low-hard and hard-intermediate states (LHS and HIMS), and remains approximately constant at 4–5~Hz in the soft-intermediate state (SIMS). The corona size shows significant evolution: the corona is large ($\sim10^4$–$10^5$ km) in the LHS, contracts rapidly to $\sim10^3$ km in the HIMS, and exhibits a flare-like expansion near the HIMS-to-SIMS transition. In the SIMS and high-soft state (HSS), the corona becomes compact and stable (4000–8000~km). The feedback fraction of the corona photons increases during the periods in which the corona contracts and decreases during the periods in which the corona expands, indicating a change of the disk-corona coupling. Our results are consistent with previous QPO-based studies using vKompthdk on some individual sources. This work, however, provides the first view of the coronal evolution across outbursts for a diverse BHXRB sample, offering critical insights into coronal behavior as a function of the spectral state of the source.
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All authors Yuexin Zhang, Mariano Méndez, James F. Steiner, Federico García, Candela Bellavita, Ole König, Erin Kara, Santiago Ubach Ramirez, Honghui Liu, Zuobin Zhang, Liang Zhang, Zi-Xu Yang, Kevin Alabarta, Sandeep K. Rout, Diego Altamirano

Solar and Stellar Astrophysics

A Detailed Model Atmosphere Analysis of Hot White Dwarfs in DESI DR1

Mukremin Kilic, Pierre Bergeron, Adam Moss et al. (+6 more)

We present a detailed model atmosphere analysis of hot white dwarfs in the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. Our sample includes 19,321 unique targets with $G_{\rm BP}-G_{\rm RP}\leq0$. We use the DESI spectra along with Gaia parallaxes and SDSS, Pan-STARRS, and SkyMapper photometry to perform spectroscopic and photometric fits. We find a significant discrepancy between the photometric and spectroscopic masses for DA white dwarfs (a systematic offset of 0.05-$0.06~M_\odot$), indicating problems with the broad hydrogen line profiles in DESI spectroscopy data. Our photometric fits are consistent with a peak at the canonical mass of $0.6~M_\odot$. A remarkable feature of the mass distribution is the prevalence of magnetic white dwarfs among the ultramassive DA population and that of warm DQs in the non-DA distribution. We identify 70 DQs in the DESI hot white dwarf sample, including 9 DAQs with carbon and hydrogen atmospheres. We constrain the ratio of non-DA to DA white dwarfs as a function of temperature, and discuss the implications for the spectral evolution of white dwarfs in the temperature range $10^5-10^4$ K. We also discuss unusual objects in the sample, including metal-rich white dwarfs and extremely low mass white dwarfs. This analysis provides the first look at the large sample of Gaia-selected white dwarf candidates that will be observed with multiplexed spectroscopic surveys like DESI, SDSS-V, 4MOST, and WEAVE over the next several years.
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All authors Mukremin Kilic, Pierre Bergeron, Adam Moss, Simon Blouin, Matthew J. Green, Gracyn Jewett, Manuel Barrientos, Alexander L. Albright, Warren R. Brown

Solar and Stellar Astrophysics

Variation of the sunspot area during the rising and declining phases of the solar cycle supports the toroidal flux loss due to flux emergence

Bidya Binay Karak, Soumya Mishra and Anu Sreedevi

Sunspots are obvious observable manifestations of the toroidal magnetic field generated through the dynamo in the convection zone. They appear in different sizes, having a wide distribution in their area. We analyse the sunspot group area of the past 13 cycles and the Bipolar Magnetic Region (BMR) flux for Cycles 23 and 24 to explore their area and flux distributions and connect with the theory. We find that, in general, the group area and BMR flux are statistically larger in the rising phase than in the declining phase of the solar cycle. This implies that the rising phase of the solar cycle is prone to drive more intense space weather. We further show that the mean and median of the area distribution during the rising phase are dependent on cycle strength. However, the distribution mean and median are cycle strength-independent or weakly dependent during the decline phases of the solar cycles, particularly during the last three years when the latitudinal bands of all cycles migrate towards the equator along the same trajectory. These results support the theoretical model of nonlinear flux loss due to flux emergence, which explains why solar cycles rise differently but decay similarly.
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Earth and Planetary Astrophysics

Coma Volatile Composition and Thermal Physics in Comet C/2022 E3 (ZTF) Measured Near Closest Approach to Earth with NASA-IRTF

Nathan X. Roth, Michael A. DiSanti, Boncho P. Bonev et al. (+9 more)

The 2023 perihelion passage of comet C/2022 E3 (ZTF) afforded an opportunity to measure the abundances and spatial distributions of coma volatiles in an Oort cloud comet at high spatial resolution near its close approach to Earth ($\Delta_\mathrm{min}\sim 0.28$ au on UT February 1). We conducted near-infrared spectroscopic observations of C/2022 E3 (ZTF) using iSHELL at the NASA Infrared Telescope Facility on UT 2023 February 9. Our measurements securely detected fluorescent emission from H$_2$O, CO, OCS, CH$_3$OH, CH$_4$, C$_2$H$_6$, C$_2$H$_2$, and HCN. For each instrumental setting we took exposures with the slit oriented parallel and also perpendicular to the projected Sun-comet vector, thereby enabling a test of the spatial distributions of these molecules. We report rotational temperatures, production rates, and abundance ratios (i.e., mixing ratios) for all sampled species. Our measurements found that molecular abundances in C/2022 E3 were depleted compared to their average values in Oort cloud comets with the exception of OCS, which was consistent. The H$_2$O production rate varied significantly and was likely tied to nucleus rotation effects. Measurements at the two slit orientations showed distinct column density and rotational temperature profiles for H$_2$O. Peak temperatures occurred off-nucleus and slower cooling was present in the anti-sunward hemisphere, consistent with the presence of icy grain sublimation in the coma.
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All authors Nathan X. Roth, Michael A. DiSanti, Boncho P. Bonev, Neil Dello Russo, Erika L. Gibb, Ronald J. Vervack Jr., Mohammad Saki, Adam J. McKay, Hideyo Kawakita, Stefanie N. Milam, Martin A. Cordiner, K. D. Foster

Astrophysics of Galaxies

Massive Star Population in the Sextans A Dwarf Galaxy from HST UV Photometry

Roberto Flores, Elena Fantino, Giuseppina Battaglia et al. (+1 more)

We build a catalog of massive (M>$8~$M$_\odot$) main sequence stars in the \mbox{metal-poor} ($\sim0.1~$Z$_\odot$) dwarf irregular galaxy Sextans A. HST WFC3 UV photometry in the 275 and 336 nm wideband filters is arranged in a Color-Magnitude Diagram (CMD), and overlaid on top of stellar evolutionary tracks from the MIST library. The star properties (mass, age, etc.) are computed with a Finite Element (FE) interpolation of the stellar tracks. The FE method, originally developed for solid mechanics problems, provides a general framework for interpolating fields inside domains of complex geometry. Besides the interpolated properties, the algorithm computes their gradients with respect to the photometry. These sensitivities provide a direct an efficient estimate of the associated uncertainties. Our catalog contains 655 stars, with the most massive one estimated at $58\pm11~$M$_\odot$. A comparison with a ground-based spectroscopic census of OB stars yields only 8 matches, evidencing the minimal overlap between both datasets. The mass estimates derived from the UV CMD and the spectral classification are in good agreement for the majority of O-type stars found in both datasets. Our catalog provides an extensive list of candidates for followup spectroscopic observation, which could improve our understanding of the early evolutionary stages of massive \mbox{low-metallicity} stars.
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All authors Roberto Flores, Elena Fantino, Giuseppina Battaglia, Antonio Aparicio

Astrophysics of Galaxies

The stellar velocity anisotropy of strong lensing massive elliptical galaxies and its role in the inference of the Hubble parameter $H_0$ using spatially resolved kinematics

Vishal Verma and Quinn Minor

One of the biggest challenges in cosmology, the Hubble Tension, requires independent measurements of $H_0$, and strong lensing with time-delay cosmography is a promising avenue. The inclusion of spatially resolved kinematic data helps break the mass–sheet degeneracy, a key limitation in strong lensing. Kinematics, however, suffers from its own degeneracy due to unknown stellar velocity anisotropy, which can bias galaxy mass profile inferences. We investigate the bias in $H_0$ using a sample of ten massive elliptical galaxies at $z=0.2$ from the Illustris $TNG100$ simulations. We generate mock line-of-sight velocity-dispersion maps resembling JWST NIRSpec observations and test four anisotropy models: Osipkov–Merritt (OM), Mamon–Lokas (ML), constant $\beta$, and a generalized–OM (gOM) profile, under both kinematics-only and joint kinematics plus strong lensing analyses. We find a sub-percent average bias in $H_{0}$ across ten galaxies with joint modeling for three models: $+0.2 \pm 1.6\%$ (ML), $-0.9 \pm 1.9\%$ (constant) and $-0.9 \pm 1.6\%$ (gOM), with $\sim 5\%$ scatter. Joint modeling reduces bias, improves precision, and mitigates outlier results. Overall, the gOM model best recovers galaxy parameters and delivers the most accurate $H_{0}$ relative to posterior uncertainties considering both analyses. However, the single-parameter OM model produces large systematic biases: with kinematics only data, $H_{0}$ errors can exceed $20\%$, and even with joint modeling, produces an overall bias of $+11.5 \pm 1.3\%$ (OM). The higher bias in OM is unlikely to average out across an ensemble of galaxies. Our findings highlight the impact of anisotropy assumptions on $H_{0}$ inference and, more broadly, in galaxy dynamics.
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Solar and Stellar Astrophysics

Assessment of DKIST/VTF Capabilities for the Detection of Local Acoustic Source Wavefronts

Corinne Morrell, Mark P. Rast, Shah Mohammad Bahauddin et al. (+1 more)

Recent studies have demonstrated that temporal filtering can successfully identify local-acoustic-source wavefronts in radiative magnetohydrodynamic simulations of the solar photosphere. Extending this capability to observations promises new insight into the stochastic excitation of solar p-modes, the source depth distribution below the photosphere, and the dominant physical processes underlying acoustic wave excitation. Such measurements would also enable improved characterization of the complex wavefield in the lower chromosphere and open the possibility of ultra-local helioseismic diagnostics. In this work, we assess an observational strategy for the detection of local acoustic wavefronts on the Sun using the Visible Tunable Filter (VTF) instrument on the National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST). Because wavefront identification requires high spatial and temporal resolution and is limited by the small amplitudes of the wave perturbations, we focus on identifying specific wavelength combinations within spectral lines that maximize the sensitivity to the wave signal. Under the cadence and spectral resolution constraints of DKIST/VTF observations and for the particular simulated wavefront we examine, this approach suggests two possible strategies: fast monochromatic imaging at 6302.425 A, or ordered interleaved observations in the blue wing of either the Fe I 6302.5 A or Fe I 5250.6 A line (between 6302.419 A and 6302.465 A, or between 5250.579 A and 5250.607 A respectively).
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All authors Corinne Morrell, Mark P. Rast, Shah Mohammad Bahauddin, Ivan Milić

Instrumentation and Methods for Astrophysics

WFC3/UVIS: External CTE Monitoring 2009-2024

Benjamin Kuhn

This report examines Charge Transfer Efficiency (CTE) flux losses in the Wide Field Camera 3 UVIS detector aboard the Hubble Space Telescope. Spanning approximately 14 years of observations from October 2009 to February 2024, the study analyzes CTE flux loss trends across various total background levels and source fluxes. In addition to analyzing the present state of CTE flux losses, we provide updated coefficients for the empirical model for point source photometry corrections in both non-CTE-corrected (FLT) and CTE-corrected (FLC) data. Between 2009 and 2023, the rate of CTE flux loss for a 500-2000 e$^-$ source, farthest from the readout, in FLT data with a 1-3 e$^-$/pix background, is measured to be $\sim$0.05 $\Delta$mag/2051 pix/year. The recommended minimum total background level to mitigate CTE losses remains at 20-25 e$^-$/pix. At that level, we find that 500-2000 e$^-$ sources, farthest from the readout, in 2024 FLT data can suffer $\sim$23$\%$ flux loss/2051 pix. The FLC data provide some relief, but we measure a $\sim$12$\%$ flux loss/2051 pix in 2024. There continues to be a slight over-correction in some FLC results that contain backgrounds above 40 e$^-$/pix. In 2024, 8000-20000 e$^-$ sources farthest from the readout in a 40, 60, or 90 e$^-$/pix background are over-corrected by $\sim$1, 2, and 3$\%$, respectively.
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Instrumentation and Methods for Astrophysics

An Open-Source High-Level Graphical Signal Processing Language with Simulation and HDL Generation

Wei Liu, Jonathon Kocz and Dan Werthimer

The CASPER (Collaboration for Astronomy Signal Processing and Electronic Research) toolflow is a widely used framework for designing and implementing digital signal processing systems, particularly in the field of radio astronomy. It provides a set of tools and libraries that enable researchers to create custom hardware and software solutions for processing astronomical data. The CASPER toolflow has been instrumental in the development of Field-Programmable Gate Array (FPGA) based digital instruments for various radio telescopes, enabling for real-time data processing and analysis. However, the current frontend tool that CASPER uses for high-level FPGA design is based on Model Composer integrated into MATLAB/Simulink, which is a proprietary software. In this paper, we introduce Scilab as a new frontend tool for the CASPER toolflow. Scilab is an open-source software platform for numerical computation and data visualization, which offers a similar environment to MATLAB/Simulink for designing CASPER blocks, generating FPGA Intellectual Property (IP) cores, and simulating Digital Signal Processing (DSP) systems. We present our implementation of Scilab in the CASPER toolflow and demonstrate its capabilities by developing an FPGA based spectrometer on a RFSoC4x2, a commonly used CASPER platform well suited to radio astronomy applications. We have also developed Scilab support for other CASPER compatible platforms. Our results show that Scilab can successfully be used as an alternate frontend for CASPER-based designs.
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Solar and Stellar Astrophysics

SPHEREx as a frontier for infrared transients: Classification of new Galactic FU Ori outbursts and classical novae

Viraj Karambelkar, Kishalay De, Lynne A. Hillenbrand et al. (+3 more)

We demonstrate proof-of-concept of a new strategy for studying infrared (IR) transients enabled by the newly launched SPHEREx space mission, by leveraging its synergy with the NEOWISE space mission. With its fifteen year baseline and all-sky mid-IR coverage, NEOWISE provides an excellent avenue to discover thousands of slowly evolving infrared outbursts. With its all-sky spectro-photometric coverage and mid-IR sensitivity matching NEOWISE, SPHEREx is uniquely positioned to provide low-resolution IR spectra for the vast majority of these outbursts, several of which are too obscured for ground-based spectroscopic classification. As a demonstration of this approach, we present SPHEREx spectra for eight Galactic transients identified in NEOWISE. This sample includes two previously known FU Orionis-type (FUOr) outbursts whose SPHEREx spectra exhibit clear signatures of cool molecular absorption and three known classical novae showing strong emission lines in SPHEREx. Using these sources as templates, we identify two new FUOrs and one previously missed Galactic nova. Our results highlight the potential of SPHEREx for systematic explorations of the relatively underexplored dynamic infrared sky.
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All authors Viraj Karambelkar, Kishalay De, Lynne A. Hillenbrand, J. L. Sokoloski, Danielle Frostig, Julianne Dalcanton

Earth and Planetary Astrophysics

A New Strategy for Using Spectroscopic Phase Curves to Characterize Non-Transiting Planets

Ted M. Johnson and Avi M. Mandell

We introduce a new time-series analysis strategy for combined-light exoplanet spectroscopic phase curves called the Variable Planetary Infrared Excess (VPIE) method. VPIE can be used to extract information about the planetary flux contribution without the need for the planet to transit or the use of a stellar spectral model. VPIE utilizes a linear combination of a small set of individual spectra to produce an empirical model of the stellar contribution at each time step, thereby normalizing each spectrum and leaving only an imprint of the planet's flux in the residual data. We demonstrate the effectiveness of VPIE through simulated James Webb Space Telescope (JWST) observations of three known exoplanet orbiting late-type M stars: the warm giant TOI-519 b, the warm sub-Neptune GJ 876 d, and the temperate rocky planet Proxima Centauri b. Our results indicate that though VPIE is less sensitive to very efficient heat redistribution, it can successfully distinguish between various atmospheric circulation regimes (low, moderate, or high heat redistribution) and constrain planetary radii for non-unity day-night temperature ratios. While current performance for cooler targets may be limited by JWST spectroscopic capabilities at longer wavelengths, future VPIE improvements or new instrumentation could enable characterization of potentially habitable planets. VPIE offers a promising new framework for pulling back the veil on the population of non-transiting planets around nearby M-stars that are otherwise inaccessible to current techniques.
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Astrophysics of Galaxies

AGN versus Star-formation: A MUSE Analysis of NGC 1365

Kyla Mullaney, Kelly E. Whalen, Jenna Cann et al. (+3 more)

Active galactic nuclei (AGN) and star formation feedback may heat and remove gas from galaxies in a process that quenches ongoing star formation and shapes the evolution of galaxies. Potential impacts from these processes can be seen in the complex and interconnected signatures of AGN and star formation activity throughout a galaxy. Here, we analyze archival integral field unit (IFU) data for the nearby Seyfert galaxy, NGC 1365, as observed with the Multi Unit Spectroscopic Explorer (MUSE) instrument on the Very Large Telescope (VLT). Our analysis probes the ionization and kinematic properties of NGC 1365 at high spatial resolution over unprecedentedly large physical scales (approximately 40 kpc), allowing us to trace the effects of feedback throughout nearly an entire galaxy. We use these optical IFU data in conjunction with observations from the James Webb Space Telescope (JWST) and Chandra X-ray Observatory to analyze and compare maps of emission line flux, ionization state, star formation, and gas kinematics. In doing so, we identify a region of BPT-identified unexpectedly high ionization relative to surrounding areas in the star forming arms, and work to identify its source, finding that shock heating may play a significant role. Results from this analysis allow us to place constraints on the relative impact of AGN and star formation processes on the star forming gas in NGC 1365, as well as begin to inform our understanding on the global impacts of feedback in galaxy populations as a whole.
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All authors Kyla Mullaney, Kelly E. Whalen, Jenna Cann, Kimberly Weaver, Jeffrey McKaig, Sara Doan

Astrophysics of Galaxies

Exploring the dynamical evolution of binary stars in multiple-population globular clusters

J. Bruce, E. Vesperini, A. Askar et al. (+5 more)

The presence of multiple stellar populations in globular clusters leads to a complex dynamical environment that significantly influences the evolution of binary stars, which in turn impacts the evolution of the cluster itself. For this study, we used a series of Monte Carlo simulations run with the MOCCA code to investigate the long-term dynamical evolution of binary stars in globular clusters hosting two distinct stellar populations. We explored how global binary properties such as incidence, fraction, and spatial distribution evolve over time due to the unique dynamical environment associated with each population. Our results show how binaries in the more centrally concentrated second population (P2) experience increased rates of hardening and disruption relative to the first population (P1), leading to distinct radial profiles in binary incidence and fraction. We also demonstrate the difference in spatial mixing timescales for binaries compared to single stars, where binary stars in each population retain some memory of their initial configurations even after complete single star mixing. Additionally, we investigated the formation and evolution of mixed binaries (binaries composed of a P1 component and a P2 component), which form primarily within the core through dynamical interactions. Finally, we studied main sequence–white dwarf binaries and find that they represent a larger fraction of binaries in P1 compared to P2. The results of this paper highlight the interplay between cluster dynamics and the evolution of binary stars and how binaries can act as tracers of the cluster's initial conditions and dynamical evolution.
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All authors J. Bruce, E. Vesperini, A. Askar, E. Bortolan, M. Giersz, J. Hong, A. Hypki, A. P. Milone

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

Neutron Stars as Perfect Fluids: Extracting the Linearized Response Function

Irvin Martínez-Rodríguez

We develop an effective field theory framework for the conservative linear tidal response of a relativistic neutron star modeled as a perfect fluid with conserved particle number. Starting from the covariant fluid action in a curved background, we linearize about a static equilibrium configuration and obtain the quadratic action for fluid displacements coupled to metric perturbations. We then split the metric perturbation into induced and externally sourced parts, and integrate out the induced metric on a conservative matched domain using a symmetric Green kernel. The resulting effective fluid theory contains metric-mediated fluid interactions through a self-adjoint operator acting on the displacement, while the external perturbation acts as a tidal source. This self-adjoint structure permits a modal expansion of the pole sector: after projection onto conservative eigenmodes, the dynamics reduce to tidally driven oscillators with couplings fixed by relativistic inner products and overlap integrals. Matching these oscillator variables to the quadrupolar worldline theory gives analytic expressions for the modal dynamical tidal deformabilities in terms of mode frequencies, normalizations, and overlap integrals. We also identify a source-only non-pole sector generated by terms quadratic in the external perturbation. This sector does not affect the mode amplitudes, but its electric-quadrupolar projection can contribute to the full tidal response. This formulation clarifies which part of the relativistic tidal response is captured by explicit fluid modes and where a possible source-only non-pole contribution enters the worldline description.
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Cosmology and Nongalactic Astrophysics

AMICO galaxy clusters in KiDS-1000: Splashback radius from weak lensing and cluster-galaxy correlation function

G. F. Lesci, C. Giocoli, F. Marulli et al. (+9 more)

We present the splashback radius analysis of the Adaptive Matched Identifier of Clustered Objects (AMICO) galaxy cluster sample in the fourth data release of the Kilo Degree Survey (KiDS). The sample contains 9049 rich galaxy clusters within $z\in[0.1,0.8]$, with shear measurements available for 8730 of them. We measure and model the stacked reduced shear, $g_{\rm t}$, and the cluster-galaxy correlation function, $w_{\rm cg}$, in bins of observed intrinsic richness, $\lambda^*$, and redshift, $z$. Building on the methods employed in recent cosmological analyses, we model the average splashback radius, $r_{\rm sp}$, of the underlying dark matter halo distribution, accounting for the known systematic uncertainties affecting measurements and theoretical models. By modelling $g_{\rm t}$ and $w_{\rm cg}$ separately, in the cluster-centric radial range $R\in[0.4,5]$ $h^{-1}$Mpc, we constrain $r_{\rm sp}$, the mass accretion rate, $\Gamma$, and the relation between $\mathcal{R}_{\rm sp}\equiv r_{\rm sp}/r_{200\rm m}$ and the peak height, $\nu_{200\rm m}$, over the mass range $M_{200\rm m}\in[0.4,20]$ $10^{14}h^{-1}$M$_\odot$. The two probes provide consistent results that also agree with $\Lambda$-cold dark matter model predictions. Our $\mathcal{R}_{\rm sp}$ constraints are consistent with those from previous observations. For $g_{\rm t}$ and $w_{\rm cg}$, we achieve a precision of 14% and 10% per cluster stack, respectively. The higher precision of $w_{\rm cg}$, enabled by its combination with weak-lensing constraints on the mass-richness relation, highlights the complementarity of lensing and clustering in measuring $r_{\rm sp}$ and constraining the properties of the infalling material region.
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All authors G. F. Lesci, C. Giocoli, F. Marulli, M. Romanello, L. Moscardini, M. Sereno, M. Maturi, M. Radovich, G. Castignani, H. Hildebrandt, L. Ingoglia, E. Puddu

Astrophysics of Galaxies

Scavenger hunt: Selection of obscured active galactic nuclei combining multiband optical variability and colors

Demetra De Cicco, Stefano Cavuoti, Maurizio Paolillo et al. (+3 more)

As wide-field optical surveys such as Vera Rubin Observatory's Legacy Survey of Space and Time (LSST) begin operations, time-domain astronomy is facing a data revolution, paving the road for new, expanded variability studies. This work leverages the complementary power of optical variability and color selection to identify active galactic nuclei (AGN), focusing on optimizing the identification of obscured AGN, typically more challenging to distinguish from inactive galaxies based on optical variability alone. The analysis is designed to provide valuable insights in the context of performance preview for the LSST, albeit using a scaled-down version of the LSST dataset. We present the first combined AGN selection based on g+r+i band light curves from the VST-COSMOS survey, spanning 3.3 yr. We identify AGN candidates independently in each band using a random forest (RF) classifier trained on features mainly related to optical variability, along with six optical/infrared colors and a morphology indicator. We subsequently merge the three band-specific samples in order to enhance selection purity and reliability. We then focus on defining a subset of features that significantly improve the identification of obscured AGN. The RF classifiers yield a consistent performance across the three bands, highlighting the critical role of contamination. Using the combined three-band plus color selection we successfully recover $58^{+9}_{-8}\%$ of all AGN and $69^{+10}_{-8}\%$ of the known obscured AGN that have been independently confirmed in all three bands. When requiring confirmation in two out of the three bands, these fractions increase to $69^{+10}_{-8}\%$ and $80^{+10}_{-9}\%$, respectively. We also demonstrate that, while combining variability features with colors is crucial to improve obscured AGN selection, relying solely on color features returns a markedly higher contamination rate.
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All authors Demetra De Cicco, Stefano Cavuoti, Maurizio Paolillo, Vincenzo Petrecca, Ylenia Maruccia, Paula Sánchez-Sáez

Earth and Planetary Astrophysics · Cross-listed from physics.ao-ph

Machine Learning-Ready Data Sets for the Analysis and Nowcasting of Atmospheric Radiation at Aviation Altitudes

Viacheslav M Sadykov, Zachary M Watkins, Dustin Kempton et al. (+10 more)

Nowcasting and forecasting of the radiation environment in the Earth's lower atmosphere are critical for the safety of aircraft and spacecraft crews and passengers. Currently, this problem is addressed by employing statistical and physics-based models that take into account particle transport and precipitation. However, given the increased number of radiation measurements available to the community, it is possible to start developing data-driven approaches. We prepared Machine Learning-ready (ML-ready) datasets to nowcast the effective dose rates at aviation altitudes. The presented datasets contain 92,476 individual measurements from 589 flights obtained by the Automated Radiation Measurements for Aerospace Safety (ARMAS) experiment from 2013 to 2023. The ARMAS measurements are augmented with the properties of the Geospace environment, such as solar soft X-ray and proton fluxes, solar wind properties, secondary cosmic ray neutrons, space weather indexes, and global solar activity indicators (such as daily sunspot number). ARMAS data are separated into three partitions, ensuring that (1) the data points from a single flight remain within the same partition, and (2) each partition samples the flight locations and Geospace environment conditions equally. Several versions of the datasets allow predictions based on point-in-time measurements and use up to 24 hours of Geospace parameter history. The test of the use case demonstrates a possibility of nowcasting ARMAS measurements with accuracies slightly better than the considered physics-based models. The publicly available ML-ready datasets could serve as the first step in data preparation for ML-driven nowcasting and forecasting of the radiation environment.
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All authors Viacheslav M Sadykov, Zachary M Watkins, Dustin Kempton, William Jones, Sanjib K C, Griffin T Goodwin, Xiaochun He, W Kent Tobiska, Irina Kitiashvili, Christopher Mertens, Shubha Ranjan, D Glenn Deardorff, Ryan Spaulding

High Energy Astrophysical Phenomena

Spectral Appearance of Self-gravitating Disks Powered by Stellar Objects: Universal Effective Temperature in the Optical Continuum and Application to Little Red Dots

Yi-Xian Chen, Hanpu Liu, Ruancun Li et al. (+6 more)

We revisit the spectral appearance of extended self-gravitating accretion disks surrounding compact central objects such as supermassive black holes. Using dust-poor opacities, we show that all optically thick disk solutions possess a universal outer effective temperature of $T_{\rm eff}\sim 4000-4500$K, closely resembling compact, high-redshift sources known as Little Red Dots (LRDs). Assuming the extended disk is primarily heated by stellar sources, this “disk Hayashi limit" fixes the dominant optical continuum temperature of the disk spectrum independent of accretion rate $\dot{M}$, central mass $M_\bullet$, and disk viscosity $\alpha$, and removes the parameter-tuning required in previous disk interpretations of LRDs. The formation and accretion of embedded stellar objects can both power the emission of the outer disk and hollow out the inner disk, suppressing variable UV/X-ray associated with a standard quasar. The resulting disk emission is dominated by a luminous optical continuum while a separate, non-variable UV component arises from stellar populations on the nuclear to galaxy scale. We map the optimal region of parameter space for such systems and show that LRD-like appearances naturally emerge for $\dot{M}/\alpha \gtrsim 0.1 M_\odot /{\rm yr}$, a threshold insensitive to $M_\bullet$, below which the system may transition into classical non-self-gravitating AGN disks, potentially a later evolution stage. We expect this transition to be accompanied by the enhancement of metallicity and production of dust, giving rise to far infrared emission. This picture offers a physically motivated and quantitative framework connecting LRDs with AGNs and their associated nuclear stellar population.
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All authors Yi-Xian Chen, Hanpu Liu, Ruancun Li, Bingjie Wang, Yilun Ma, Yan-Fei Jiang, Jenny E. Greene, Eliot Quataert, Jeremy Goodman

High Energy Astrophysical Phenomena

Mapping plasma properties of Cassiopeia A with XRISM/Resolve: a Bayesian analysis via UltraSPEX

Manan Agarwal, Jacco Vink, Liyi Gu et al. (+5 more)

Mapping the physical conditions of the shocked plasma of young supernova remnants (SNR) is crucial for understanding their explosion mechanisms, ejecta structure, and large-scale asymmetries. Using $>350$ ks of XRISM/Resolve high spectral resolution observations of Cassiopeia A (Cas A), the youngest known Galactic core-collapse SNR, we present the first microcalorimeter-based plasma parameter maps of any SNR. We tessellate Cas A into $1'\times1'$ regions and fit the broadband spectra as thermal emission from two pure-metal ejecta components – corresponding to intermediate-mass elements (IMEs) and iron-group elements (IGEs) – plus nonthermal synchrotron radiation. For robust inference, we introduce UltraSPEX, a Bayesian framework that couples the SPEX plasma code with the UltraNest nested-sampling algorithm, yielding full posterior distributions and exploration of parameter degeneracies. Key findings include enhanced Ar/Si and Ca/Si abundance ratios near the base of the Si-rich jets, and a high Ni/Fe mass ratio ($0.08\pm0.015$) in the base of NE jet. IGEs ejecta exhibit systematically higher Doppler velocities and broadenings than IMEs ejecta in most regions, with maximum differences of $\sim800$ km/s and $\sim1200$ km/s, respectively; Ca shows distinct (faster) kinematics from other IMEs in several SE regions. The ionization timescale and electron temperature show a robust anti-correlation, particularly for IGEs. This relation and measured parameter values could be explained by semi-analytical models with significant ejecta clumping (overdensities of $\sim10$ for IGEs and up to $\sim100$ for IMEs) and reduced historical reverse-shock velocities. Nonthermal emission accounts for a substantial fraction, with at least 47% of the 4–6 keV continuum and dominates in the western regions, where the spectrum hardens.
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All authors Manan Agarwal, Jacco Vink, Liyi Gu, Paul P. Plucinsky, Aya Bamba, Toshiki Sato, Daniele Rogantini, Yuken Ohshiro

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

Gravitational Raman Scattering: a Systematic Toolkit for Tidal Effects in General Relativity

Mikhail M. Ivanov, Yue-Zhou Li, Julio Parra-Martinez et al. (+1 more)

We present a framework for systematic computations of scattering amplitudes for gravitational Raman scattering, – the inelastic scattering of massless fields off compact relativistic objects. We focus on the small-frequency (post-Minkowskian, PM) regime relevant for the study of tidal effects, which can be mapped onto gravitational wave observables during the inspiraling phase of a merger. We demonstrate that this setup is ideal for systematic studies of tidal effects, in a way that is free from coordinate, gauge, and field redefinition ambiguities. We use a combination of worldline effective field theory, the background field method, and advanced scattering amplitude techniques to derive phase shifts for scattering of spin-$0,1,2$ fields off generic compact objects at third PM order. We demonstrate that the inclusion of the recoil of the object is crucial for consistency of this calculation. Focusing on a particular case of black holes, we extract the leading static and dynamical Love numbers of the spin-0 field and the static Love number of the spin-1 field in four dimensions by matching our EFT amplitudes and calculations in General Relativity. We show, fully on-shell, that the leading static Love numbers vanish identically, while the dynamical Love numbers are not zero and run logarithmically. The latter resolves the ambiguities of previous off-shell matching calculations. We also extend our results to seven dimensions, where spin-2 Love numbers undergo a renormalization group running at 2PM, which we compute explicitly. In addition, we extract the leading static Love numbers of spin-0 and spin-1 fields in five dimensions, which also run.
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All authors Mikhail M. Ivanov, Yue-Zhou Li, Julio Parra-Martinez, Zihan Zhou