High Energy Astrophysical Phenomena
Generation of UL-Axions by a Kerr Black Hole. Part III: The fate of its Axion Wind
Guy Pelletier
In two previous articles, we have explained how super-massive Kerr Black Holes in the
nucleus of an active
galaxy or
quasar can generate a large amount of
axion particles in their magnetosphere. In that third part, we explore the possibility of observable dynamics resulting from some interaction of an
axion wind with the baryonic matter and the axionic Dark Matter in the surroundings of the closest AGNs. The
axions that we have considered are the same as those Ultra Light
Axions favored in cosmology as the main content of Dark Matter and which form Bose-Einstein Condensates, supporting a gigantic Schrödinger wave. In the paper we investigate what can be the nature of the interaction of the
axion wind with the
plasma and the hydrogen gas in the host
galaxy and its
halo. Despite the intriguing nature of a possible interaction, we show that only a kind of gravitational Tcherenkov-Vavilov effect can be efficiently operating with acoustic waves through a streaming instability. The instability is fast enough to operate efficiently in the central region of the host
galaxy up to parsec scales and makes Lyman-alpha diagnostics of the acoustic waves of hydrogen gas and
plasma possible, as well as the detection its hyperfine emission at 21 cm. However it turns out that scattering of the
axion wind is very long and thus these winds could travel over very large distances and cross other
galaxies. And then the wind travels without significant loss along its
halo and even beyond up to
quantum thermalization, which makes possible direct detection of these
axions by conversion into gamma-rays on Earth, opening a possible
axion astronomy in the local Universe. The parameters of Messier 87 indicate that it is a good candidate for developing these investigations both through the conversion of
axions into gamma-rays and Lyman alpha diagnosis in the bulge.
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Instrumentation and Methods for Astrophysics
A Missing Latent, Not a Missing Simulator: Radius-Augmented Inference for Real JWST Retrieval
Angshuman Chakravertty and P V V Raj
Amortized simulation-based inference (SBI), which is trained on radiative-transfer simulators, recovers
exoplanet atmospheres accurately on synthetic James Webb Space
Telescope (JWST) spectra but collapses when it comes to real reduced spectra. The flow posterior collapsed on real WASP-39b (importance-sampling effective sample size (ESS) = 1, best-fit ḩi}2/N = 301), and such a failure is usually blamed on missing the forward-model physics, but ruling these levers out with nested sampling first (a temperature gradient, SO2 opacity, and a high-fidelity opacity set) leaves the fit unchanged, meaning the collapse is not from the simulator misspecification but instead from a missing latent, the
planet radius. To fix this, we build MIRAGE, a radius-augmented flow-matching posterior calibrated against an independent nested-sampling reference with importance sampling and an optimal-transport map, which yields a physical and literature-consistent
retrieval of real WASP-39b (with ḩi}2/N from 301 to 0.06). This same method transfers unchanged across two instruments and three real JWST targets, including one spectrum self-reduced end-to-end from raw Mikulski Archive for Space
Telescopes(MAST) data. The lesson is cross-domain, as a latent the simulator encodes but the inference omits can masquerade as misspecification.
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High Energy Astrophysical Phenomena
Optimal Pulsar Timing Array Strategies with the Deep Synoptic Array
Tyler Cohen, Paul B. Demorest, Jeremy G. Baier et al. (+50 more)
Pulsar timing array (PTA) experiments have seen evidence for a nanohertz-frequency gravitational wave background (GWB) through coordinated
radio timing observations of millisecond
pulsars. The significance of this evidence is expected to grow and the GWB's progenitor(s) uncovered with continued observations, especially as the next generation of
radio telescopes comes online. We present a framework for simulating timing observations of a set of
pulsars with a set of
telescopes to predict the per-
pulsar optimal instrument, observing frequency, and integration time. We apply this methodology to the NANOGrav source list of 85
pulsars observed with the Green Bank
Telescope, Very Large Array, Canadian Hydrogen Intensity Mapping Experiment (CHIME), and the Deep Synoptic Array (DSA), a
radio dish array under construction in Nevada. We discuss the dominant noise contributions to the timing precision of these
pulsars and show that most are not dominated by intrinsic pulse phase jitter noise. We also determine which
pulsars should be timed with DSA and CHIME or only DSA and show that an ab initio DSA PTA is more sensitive than one which uses current instruments. Finally, we solve for the optimal integration time per
pulsar, subject to a fixed time budget, that maximizes the GWB signal-to-noise. We show that there is little benefit to optimizing over integration time for these
pulsars observed with DSA. Through Monte Carlo realizations of the PTA, we show that the GWB sensitivity improves by $\sim 5\%$ for time-optimized observations compared to the equal-time-per-source scenario with an early-science, fixed source list.
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All authors Tyler Cohen, Paul B. Demorest, Jeremy G. Baier, Ryan S. Lynch, Scott M. Ransom, Michael T. Lam, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Ava L. Battaglia, Paul R. Brook, Anabelle L. Brueggemann, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Timothy Dolch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Jeffrey S. Hazboun, Ross J. Jennings, Megan L. Jones, David L. Kaplan, Matthew Kerr, Duncan R. Lorimer, Jing Luo, Hugo E. Marquis, Alexander McEwen, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Cherry Ng, David J. Nice, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Paul S. Ray, Ann Schmiedekamp, Carl Schmiedekamp, Brent J. Shapiro-Albert, Ingrid H. Stairs, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Haley M. Wahl
Earth and Planetary Astrophysics
Correlations between the Carbon-to-Oxygen Ratio and the Orbital and Physical Properties of Exoplanets
Noah Ferich, Robert Royer III, Cody Shakespeare et al. (+1 more)
Studies suggest that protoplanetary disks around
stars with high carbon-to-oxygen (C/O) ratios can produce terrestrial
planets with carbon-dominated compositions instead of silicon-dominated ones. While previous work studied the
evolution of these disks and the
planets that form within them, none analyze in detail how the differences in the surface density profiles of these disks could affect the architectures and iron and siderophile contents of exoplanetary systems. Here, we present a new study that uses the N-body integrator REBOUND and data from a sequential dust condensation model to simulate the formation of
planets in systems with varying C/O ratios. We find that bulk density could be used to distinguish between silicon-rich and carbon-rich
planets, though it may not be a reliable metric on its own.
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All authors Noah Ferich, Robert Royer III, Cody Shakespeare, Jason H. Steffen
Instrumentation and Methods for Astrophysics
Near-Noiseless Single-Photon Detection in the Infrared with a Megapixel Semiconductor Array for Low-Background Astronomy
Guillaume Huber, Pavaman Bilgi, Charles-Antoine Claveau et al. (+7 more)
Sensor noise is a fundamental barrier to low-flux astronomical imaging and spectroscopy, where the ideal sensor would unambiguously distinguish individual
photon arrivals. While optical
semiconductor arrays can reach single-
photon sensitivity, comparable performance in the infrared has largely required superconducting detectors. These must be operated at temperatures near absolute zero and require substantially more power, introducing major system-level challenges. HgCdTe avalanche photodiodes offer a
semiconductor alternative by amplifying charge before readout, but dark current and tunneling effects have limited their use in the faintest regimes. Here we demonstrate single-
photon-resolving operation in a megapixel-format HgCdTe linear-mode avalanche photodiode array operated at conventional cryogenic temperature. Avalanche gain raises
photon-induced steps in non-destructive up-the-ramp data above the readout-noise floor while leaving the dark signal largely unamplified, with a false positive rate of approximately 2 false counts per thousand reads per pixel. These results establish LmAPDs as a promising route toward infrared
photon-counting focal planes for future low-background astronomical observatories.
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All authors Guillaume Huber, Pavaman Bilgi, Charles-Antoine Claveau, Shane Jacobson, Ian Baker, Daniel Owton, Vincent Isgar, Chris Maxey, Markus Loose, Michael Bottom
High Energy Astrophysical Phenomena
Early Emergence of SSS emission in RS Oph
J.-U. Ness, J.P. Osborne, M. Orio et al. (+3 more)
Early in the 2006 outburst of the recurrent nova RS Oph, Swift detected the onset of the super-soft-source (SSS) phase. An XMM-Newton observation on day 26.1 revealed an unusual soft X-ray spectrum containing transient narrow emission features that could not be identified with known transitions and are atypical of SSS spectra. We analyse a new XMM-Newton observation obtained at a comparable stage of the 2021 outburst and compare it with spectra from other epochs and with similar novae. A blackbody model reproduces the low-resolution 2006 EPIC/pn spectrum but fails to describe the simultaneous high-resolution RGS data. The 2021 spectrum closely resembles that observed in 2006 and consists of a slowly fading shock component and a highly variable soft component containing several unidentified features. While the shock emission evolves on timescales of days, the soft component varies on hourly timescales and dominates the observed variability. Its properties resemble those of the novae V1494 Aql and V1716 Sco, but not those of the persistent SSS Cal 87. No significant 35-s periodicity is detected. The results demonstrate that low-resolution observations can miss the complex line-dominated emission revealed by high-resolution spectroscopy. The rapidly variable soft component, together with radiative recombination continua, Fe X emission, and the previously detected 35-s period, suggests the presence of a hidden photoionising source. We conclude that these enigmatic spectra form an intermediate class between the SSe and SSa categories of Ness et al. (2013), together with V1494 Aql and V1716 Sco. Future modelling will be required to determine the relative importance of photoionisation, charge exchange, and other processes in shaping this class of intermediate SSS spectra.
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All authors J.-U. Ness, J.P. Osborne, M. Orio, S. Starrfield, S. Mitrani, E. Behar
Cosmology and Nongalactic Astrophysics
Emulation of the Halo Mass Function with Neural Networks
Olive Ross and Nicholas Battaglia
The abundance of
galaxy clusters as a function of mass — the
halo mass function (HMF) — depends strongly on cosmological parameters. Large-scale simulations are computationally expensive, motivating emulators that interpolate simulation outputs. We present a neural network emulator that maps cosmological and astrophysical parameters,
halo mass, and
redshift directly to a cumulative count of
halos above the input mass, avoiding the information loss inherent to binning and to the functional or PCA-based data reduction used in prior emulators. Each emulator prediction is accompanied by a self-estimated error, expressed in units of Poisson shot noise, that the network learns to predict alongside the
halo count itself — giving every output a built-in confidence metric. We validate the emulator with leave-one-out tests on three simulation suites — the N-body MassiveNus suite and the hydrodynamical CAMELS IllustrisTNG and SIMBA suites — spanning a range of box sizes,
redshifts, sub-grid physics, and softwares. Of all the held-out predictions ($1.2\times 10^6$ in total), 88% have model bias at or below shot noise and 99.9% are within $3\times$ shot noise. The only significant high-error tail is in MassiveNus, where the predicted model bias flags 76% of predictions exceeding $3\times$ shot noise; the remaining number of high error predictions is comparable to the number expected from shot noise alone. This emulator is publicly available and can be trained on other simulation suites making it a flexible HMF tool that can be used for cosmological and astrophysical inference.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Coexistence of strange quark stars and neutron stars: metastability and nucleation in proto-neutron stars
Mirco Guerrini, Giuseppe Pagliara, Luca Passarella et al. (+1 more)
If strange
quark matter (SQM) is absolutely stable, hadronic
neutron stars (NSs) and strange
quark stars (QSs) may coexist in the so-called two-families scenario. A key issue is explaining how hadronic NSs can survive as long-lived metastable objects, rather than promptly converting into stable QSs. Since all NSs are born as hot proto-
neutron stars (PNSs), a necessary condition for their existence is that the conditions for conversion, triggered by the nucleation of the first critical SQM droplet, are not reached in every PNS. We investigate the thermal nucleation of critical SQM droplets under representative PNS conditions, accounting for flavor-composition fluctuations and finite-size effects on color superconductivity by suppressing pairing in droplets smaller than the diquark coherence length. We define the nucleation conditions as the thermodynamic state at which a critical SQM droplet is expected to nucleate statistically within the characteristic dynamical timescale of the system. Under these conditions, the reduced nucleation barrier is nearly universal, with $W_*/T\simeq167$ to within a few units. Exploring the SQM parameter space, we show that requiring a canonical $1.4~\rm{M}_{\odot}$ NS to survive the PNS stage sets a lower bound on the
hadron-
quark surface tension $\sigma\gtrsim 67$ MeVfm$^{-2}$.
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All authors Mirco Guerrini, Giuseppe Pagliara, Luca Passarella, Alessandro Drago
Cosmology and Nongalactic Astrophysics
ROBIN-PIP: Robust Bayesian Field-Level Inference with Physics-Informed Priors
Ludvig Doeser, Simon Ding, Guilhem Lavaux et al. (+1 more)
Accurately extracting information from
galaxy surveys, particularly at non-linear scales, requires increasingly complex and flexible forward models of the observed
galaxy distribution. A key component is the
galaxy bias relation, which connects the underlying matter distribution to observed
galaxies and requires more expressive representations than those currently incorporated into
Bayesian field-level inference. Certain parameterized models for this mapping can be overparameterized, with individual parameters carrying no direct physical interpretation, making them challenging to constrain. Our objective is to guide the inference of flexible model parameters towards physically plausible regions of parameter space through physics-informed priors. These priors are derived from high-fidelity simulations, thereby enabling the indirect use of simulations that cannot be integrated directly into gradient-based field-level inference. To this end, we introduce the ROBIN-PIP (RObust
Bayesian INference with Physics-Informed Priors) framework. As a proof of concept, we jointly infer the
cosmic initial conditions and the parameters of a truncated power-law
galaxy bias model for a simulated universe. We integrate ROBIN-PIP into the
Bayesian Origin Reconstruction from
Galaxies algorithm and
benchmark against inference without the simulation-based prior. With the additional prior, posterior standard deviations of the bias model parameters are reduced by up to $20\%$ and autocorrelation lengths are reduced from $730$-$870$ to $440$-$550$, increasing the effective sample sizes. We find no bias in the recovered initial conditions, demonstrating that ROBIN-PIP guides inference towards physically consistent solutions without compromising the data likelihood and highlighting its potential to incorporate overparameterized models in field-level inference.
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All authors Ludvig Doeser, Simon Ding, Guilhem Lavaux, Jens Jasche
Solar and Stellar Astrophysics
Unresolved triples in the open cluster NGC 2437 (M 46) confirmed by the KMOS VVVX-GalCen Spectroscopic Survey
D. Minniti, T. Palma, C. O. Obasi et al. (+31 more)
Recent optical and near-IR photometric databases like Gaia data release 3 (DR3) and the VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey allow the exploration of candidate unresolved multiple systems (binaries, triples, quadruples, etc.) in nearby clusters, that need spectroscopic confirmation. NGC 2437 (M 46) is a
benchmark open cluster with well determined physical parameters. Its relative proximity (D=1.6 kpc) makes this cluster an ideal laboratory to measure the fractions of unresolved multiple systems. We aim here to identify unresolved triple and higher order systems that are reliable members of the open cluster NGC 2437, and provide the spectroscopic confirmation using radial velocities. We confirm that there is a sequence of unresolved binaries in NGC 2437, and report the discovery of a sequence of unresolved triple systems in this cluster. We corroborate membership for 13 binary systems and 8 triple systems using radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. We further select
stars with colors consistent with K-dwarfs, in order to have a controlled sample, comparable to the Solar neighborhood. We also find that the fraction of unresolved triples and quadruples is higher than that of the older open cluster Trumpler 19, studied using a similar setup, suggesting that these systems merge to form blue stragglers or get dissolved with time. We report the spectroscopic confirmation of 95% of the selected VVVX targets, thereby securing the presence of a sequence of unresolved triple systems in NGC 2437, located above the sequence of equal-mass binaries. The single
stars constitute 60% of the mass of the cluster, while the rest of the mass (40%) is lodged in the unresolved multiple systems.
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All authors D. Minniti, T. Palma, C. O. Obasi, M. Gómez, R.K. Saito, J. G. Fernández-Trincado, J. Alonso-García, E. R. Garro, J. Corral-Santana, A. Luna, P. W. Lucas, M. G. Navarro, V. D. Ivanov, Z. Guo, J. Borissova, R. Kurtev, C. Morris, V. Fermiano, J. Osses, P. Esteves, C. Cáceres, B. Dias, S. Saroon, S. Federle, M. Lad, I. Petralia, P. Rodriguez Cuevas, J. B. Pullen, D. Bhadrakumar Sindhu, L. Gramajo, L. Baravalle, D. Galdeano, M. V. Alonso, J. L. Nilo Castellon
High Energy Astrophysical Phenomena
AT2018hyz: Predictions for a Sky Projection from a Delayed Off-Axis Jet
Ranadeep Ghosh Dastidar and Paul C Duffell
Initially discovered optically, Tidal Disruption Event (TDE) AT2018hyz was first detected in
radio 972 days later. The continued monitoring of the event revealed a late-time (1370-2160 days)
radio brightening. The source for this
radio brightening has been associated with an afterglow originating from an off-axis jet or a delayed mildly relativistic outflow. In this work, we explored the conditions required for a delayed off-axis jet to explain the observed
radio brightening. We find that the combined effect of different delay times (t_delay) and observer angles (theta_obs) can produce
radio afterglow, as observed for AT2018hyz. The further off-axis from the jet core an observer is, the shorter is the delay inferred between the optical disruption and launching of the jet. This presents a degeneracy between different theta_obs and tdelay. We estimate the sky projection of the jet for these different combinations to break this degeneracy. The spread in sky images ranges from 0.6 mas for a 30 deg off-axis observer to 0.3 mas for an observer perpendicular to the jet core. Future VLBI observations should be able resolve these structures. Thus a combined observation of the light curve and sky images for AT2018hyz (and other jetted TDEs) can be used to narrow down the observer angle and any delay in launching of the underlying jet.
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High Energy Astrophysical Phenomena
The X-ray and optical emission of the intermediate polar Swift J0614.0+1709
Nikita Rawat, Domitilla De Martino, David A. H. Buckley et al. (+5 more)
We present the first detailed X-ray and optical study of the intermediate polar Swift J0614.0+1709 based on a pointed XMM-Newton observation complemented by long-term optical photometry from TESS. A strong coherent modulation at the white dwarf
spin period was detected in X-rays, with a period of $\sim$1411 s, confirming the
magnetic nature of the system. The X-ray
spin pulse exhibits a pronounced energy dependence, with the modulation amplitude decreasing towards higher energies, consistent with phase-dependent absorption in the
accretion flow. Phase-resolved spectroscopy further shows that the
spin variability is primarily driven by changes in the covering fraction of the partial-covering absorber. The broadband X-ray spectrum is well described by a partially absorbed thermal
plasma model with a temperature of $\sim$12 keV and a soft blackbody component at $\sim$63 eV. The inferred bolometric luminosity of $\sim$5$\times$10$^{34}$ erg s$^{-1}$ places the source among the more luminous intermediate polars. The TESS observations reveal substantial sector-to-sector variability in the relative strengths of the orbital and
spin modulations. While the
spin signal remains persistently dominant, the beat modulation varies significantly and disappears entirely in one Sector, suggesting temporal changes in the contribution of the reprocessing region(s). The orbital and, to a lesser extent,
spin modulation amplitudes show some tendency to be stronger during brighter optical states, suggesting that changes in the mass transfer rate may influence the optical emission and modulation amplitudes. Overall, Swift J0614.0+1709 is a comparatively X-ray luminous intermediate polar exhibiting complex optical variability characterised by changes in pulse morphology and recurrent brightening events, making it a valuable target for future simultaneous optical and X-ray studies.
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All authors Nikita Rawat, Domitilla De Martino, David A. H. Buckley, Koji Mukai, Martina Veresvarska, Zackery A. Irving, Simone Scaringi, Nicola Masetti
Solar and Stellar Astrophysics
Theoretical RR Lyrae Instability Strip from MESA-RSP Pulsation models and updated BaSTI Evolutionary Tracks
M. Deka, M. Marconi, R. Molinaro et al. (+6 more)
RR Lyraes (RRLs) are important tracers of old stellar populations and crucial distance indicators. To complement large variability surveys such as Gaia and Rubin-LSST, the
topology of the RRL instability strip (IS) and their period-luminosity-
metallicity (PLZ) and period-Wesenheit-
metallicity (PWZ) relations need to be updated using state-of-the-art stellar
evolution and pulsation models. We employ the updated set of BaSTI horizontal-branch (HB) evolutionary models, with finer sampling in effective temperature and
metallicity, and compute the corresponding pulsation models using the mesa-rsp module building on the approach of Marconi et al. (2015). We compute a grid of linear non-adiabatic radial pulsation models with mesa-rsp, covering -2.2 <= [Fe/H] <= +0.06 dex. Seven convection configurations are explored including the recently empirically calibrated prescription for RRLs by Kovacs et al. (2024). Analytical IS boundaries are derived for RRab and RRc pulsators and transformed into several photometric systems (Gaia, OGLE, 2MASS, and LSST) and the Kiel diagram. The updated evolutionary models do not substantially change the pulsation predictions: RRab IS edges agree well with previous results, while the RRc red edge is slightly redder. The width of the IS decreases systematically with increasing alpha_MLT, and RRc is relatively more sensitive to the convection prescription than RRab. The PLZ and PWZ relations are also in good agreement with previous empirical and theoretical calibrations across the NIR bands; however, the convection prescription giving the closest match is wavelength dependent. The predicted IS boundaries and PLZ/PWZ relations exhibit a coupled dependence on pulsation mode,
metallicity, and convective treatment, with no single prescription performing uniformly best across all observational planes.
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All authors M. Deka, M. Marconi, R. Molinaro, A. Bhardwaj, S. Cassisi, E. Luongo, G. De Somma, I. Musella, V. Ripepi
Astrophysics of Galaxies
The Impact of Simulation Resolution on Dwarf Galaxy Stellar Stream Populations in FIRE
Yasmine J. Meziani, Nondh Panithanpaisal, Robyn E. Sanderson et al. (+4 more)
Cosmological simulations allow us to study
galaxy-progenitor stream populations, allowing comparisons with observations to constrain
galaxy formation physics. Previous work found that present-day
galaxy-progenitor streams in FIRE have larger pericenters than observed in the MW, which might indicate that they tidally disrupt at larger distances, where the Galactic tides are weaker, than in the MW. One possible explanation is that they tidally disrupt too quickly because of limited resolution. At lower resolution, low-mass dwarf
galaxies can be puffier and more susceptible to disruption. We build and compare dwarf-
galaxy stream catalogs in two FIRE-2 cosmological zoom-in simulations with identical initial conditions (m12i) but different particle mass resolution (7070 $M_\odot$ and 880 $M_\odot$). The higher-resolution run yields a larger dwarf
galaxy stream population (22 streams versus 14) using the same cutoff of 100
star particles, primarily because it resolves lower-mass streams (down to $\sim10^{5}$ $M_\odot$). Both simulations form streams at galactocentric radii < 50 kpc, but the higher-resolution Triple Latte simulation produces more streams at these small radii. We find that dwarf
galaxies in the higher-resolution simulation begin disrupting at smaller pericenters than in the lower-resolution simulation. By cross-matching stream candidates, we identify counterparts for $\sim$89$\%$ of the systems in the lower-resolution simulation. For matched systems that remain on similar orbits, the higher-resolution counterparts remain intact for longer. The orbital properties of streams in the higher-resolution simulation are broadly consistent with the MW dwarf-
galaxy stream population, in contrast to the lower-resolution simulation.
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All authors Yasmine J. Meziani, Nondh Panithanpaisal, Robyn E. Sanderson, Andrew Wetzel, Pratik J. Gandhi, Philip F. Hopkins, Adriana Dropulic
Instrumentation and Methods for Astrophysics
Measuring the linear gain performance for the OrcaQuest CMOS imaging sensor
Zain Azama, Aditya Khandelwal, Ryan Dungee et al. (+3 more)
The OrcaQuest CMOS sensor by Hamamatsu Photonics has been found to exhibit a non-linear gain curve at low exposure times. This effect is characterized through the various exposure tests and data reduction pipelines detailed in this report, and a more accurate gain characterization curve is provided. Such data can be used to provide more consistent measures of pixel gain, linearity, and high framerate images.
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All authors Zain Azama, Aditya Khandelwal, Ryan Dungee, Ting S. Li, Sarik Jeram, Shaojie Chen
Instrumentation and Methods for Astrophysics · Cross-listed from cs.DL
Best practices in software citation
Phil R. Van-Lane, Floor S. Broekgaarden, Daniel S. Katz et al. (+11 more)
Software is both a foundational tool and a primary output of modern computational research, yet citation practices for software remain inconsistent, incomplete, and rarely machine-actionable. Existing infrastructure designed for paper and data citation does not adequately serve the distinct needs of software citation, leaving a gap that impedes reproducibility, misattributes scholarly credit, and obscures the labor embedded in research pipelines. Drawing on a NASA-funded community workshop held in April 2026, we present an analysis of four interconnected themes: (I)~the cultural barriers to consistent citation practice; (II)~the need for clearer community norms and conventions; (III)~gaps in existing technical infrastructure and workflow; and (IV)~the emerging challenges posed by AI-assisted research. For each theme we identify targeted interventions and assign responsibility across stakeholder groups. We conclude that meaningful progress requires simultaneous action on technical and cultural fronts. Journal editors and publishers represent the single highest-leverage point for accelerating this change, and correct citation must become the path of least resistance within researchers' existing workflows.
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All authors Phil R. Van-Lane, Floor S. Broekgaarden, Daniel S. Katz, Bhavesh Patel, Pengyin Shan, Jonathan Starr, Samantha Teplitzky, Peter K.G. Williams, Alice Allen, Lucas M. de Sá, Andrew Fullard, Sandra Gesing, Tom Wagg, Andrea Zonca
Astrophysics of Galaxies
Star Formation Mitosis: The Effects of Particle Splitting on the Star Formation Outcome
Shivan Khullar, Michael Y. Grudić, Christopher D. Matzner et al. (+3 more)
Particle splitting can increase the dynamic range in Lagrangian astrophysical simulations by several orders of magnitude. However, such methods can introduce numerical noise that may affect the rate of convergence, particularly for collapse problems where fragmentation could be artificially suppressed or enhanced. Thus it is necessary to determine how these errors propagate to key quantities of interest, and to correct or mitigate them where possible. Using GIZMO's MFM-MHD method, we perform a set of $\approx 220$ simulations of a uniform-density turbulent gas sphere undergoing collapse, systematically varying the cloud mass and radius, feedback physics, initial resolution, the pace and cadence at which we split particles and the sink (accreting) or single-age stellar population (SSP; non-accreting) particle formation prescription. Crucially, we compare with control runs that start with uniformly-high resolution without splitting. While we find no evidence for artificial fragmentation caused by splitting particles, particle splitting runs have a smoother density field than their non-splitting counterparts. Due to this, particle splitting runs exhibit minor differences in the density and
turbulence statistics. However, they form about the same total stellar mass as the control non-splitting runs, albeit with a slightly different mass spectrum. As a result, particle splitting runs have a different evolutionary history, compared to runs without particle splitting, especially when stellar feedback is present. Despite the changes seen in runs where we split particles, the numerical solution lies within the scatter inherently present in these chaotic systems, which we model by modifying the initial turbulent velocity field. Our results here argue that particle splitting generally “works" for
star formation applications, despite some systematic differences in the specifics.
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All authors Shivan Khullar, Michael Y. Grudić, Christopher D. Matzner, Philip F. Hopkins, Norman Murray, Claude-André Faucher-Giguère
Instrumentation and Methods for Astrophysics
Prototyping the Next-Generation Spectrograph for Space Exploration: Digital Micromirror Device-based Multi-Object Spectrograph (DMD-MOS) Calibration and Performance Assessment
Jiayi Emma Xu, Sarik Jeram, Shaojie Chen et al. (+7 more)
Abandoning the traditional approaches to multi-object spectrographs, the Digital Micro-mirror Device-based Multi-Object Spectrograph (DMD-MOS) leverages a robust, elegant method for creating multi-object spectroscopy slit masks through use of a DMD, which is an array of microscopic flat mirrors where each micro-mirror can be addressed to physically flip between two discrete angles. We have designed two optical channels for DMD-MOS - one for each of these two positions: 1) an imaging channel that can be used for multi-object target selection and 2) a spectrograph channel. Using this two-channel approach, DMD-MOS can simultaneously image the
telescope field of view (FOV) with the imaging channel and actuate the specific DMD micro-mirrors to send light from chosen targets into the spectrograph channel. In this work, we present the results of our laboratory testing of DMD-MOS including spectral resolution, line spread function, wavelength coverage, and the mapping between the DMD and imaging channel planes, the latter of which enables DMD-MOS and our control software to instantaneously configure the DMD to observe chosen target(s) in the acquisition field.
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All authors Jiayi Emma Xu, Sarik Jeram, Shaojie Chen, Ting S. Li, Ziang Chen, Zain Azam, Adi Khandelwal, Mark Barnet, Yixuan Cheng, Suresh Sivanandam
High Energy Astrophysical Phenomena
X-ray Through Radio Observations and Modeling of the Soft X-ray Flash GRB 250419A
Genevieve Schroeder, Anna Y. Q. Ho, Gavin P. Lamb et al. (+24 more)
Soft X-ray flashes (XRFs) are predicted from a variety of hypothesized phenomena, including "dirty fireballs" (relativistic jets with significant baryon loading), and gamma-ray bursts viewed marginally off-axis. For a given burst, detailed multiwavelength observations are necessary for distinguishing between possible progenitor scenarios, but the number of XRFs with such data remains small. Here we present X-ray, optical, and
radio (mm to cm) data of GRB 250419A, an XRF (with peak energy $E_p<4\,$keV) discovered by the Space-based multi-band astronomical Variable Objects Monitor. We observe a clear achromatic break in the X-ray and optical bands, and likely two spectral components in the
radio emission. The afterglow is similar to the long-duration gamma-ray burst population, but slightly underluminous, and the optical afterglow has an unusually shallow decay phase at $\lesssim2\,$d. We find that the event is well explained by a high-Lorentz factor jet with low kinetic energy ($E\sim10^{49}$-$10^{50}\,$erg), with energy injection that could arise from radial stratification and/or the jet being viewed marginally off-axis. We conclude that at least some X-ray flashes are an extension of classical gamma-ray bursts down to lower energies.
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All authors Genevieve Schroeder, Anna Y. Q. Ho, Gavin P. Lamb, Tanmoy Laskar, Daniel A. Perley, Ore Gottlieb, Tomas Ahumada, Igor Andreoni, Aleksandra Bochenek, Michael Bremer, Michael Camilo, Jonathan Carney, S. Bradley Cenko, Alessandra Corsi, Michael W. Coughlin, James Freeburn, Erica Hammerstein, Rahul Jayaraman, Mansi M. Kasliwal, Noel Klingler, Brendan O'Connor, Cassie Sevilla, Gokul P. Srinivasaragavan, Robert Stein, Jada L. Vail, Sylvain Veilleux, Lin Yan
Instrumentation and Methods for Astrophysics
Automated multi-stressor optical fiber focal ratio degradation and throughput characterization system for future massive multiplex spectroscopic survey
Daksh Singh, Ting S. Li, Sarik Jerma et al. (+1 more)
Future spectroscopic survey facilities such as Spec-S5 and the Wide-Field Spectroscopic
Telescope (WST) will contain more than 25,000 optical fibers. Characterizing the focal ratio degradation (FRD) and throughput of these fibers is essential for spectroscopic calibration, sky subtraction, and overall instrument performance, but manual testing of such large fiber populations is prohibitively time-consuming. In this work, we present an automated multi-stressor optical fiber characterization platform capable of measuring both FRD and relative throughput while systematically varying optical and mechanical stress conditions. The system enables characterization as a function of input angle, wavelength, bend radius, twist angle, and externally applied load, while also allowing combinations of stressors to be investigated simultaneously. A custom software framework automates hardware control, data acquisition, and data analysis, enabling large characterization campaigns to be performed with minimal user intervention. Validation measurements performed on a multimode optical fiber demonstrate the ability of the platform to resolve both pronounced and subtle stress-dependent variations in FRD and relative throughput. The results show the expected dependence of FRD on input angle and bend radius, reveal comparatively weak sensitivity to externally applied compressive loading under the investigated conditions, and identify a reproducible periodic dependence on fiber twist angle. In addition, relative throughput measurements indicate that the reduction in relative throughput with increasing input angle cannot be explained solely by a simple projected-area model. The automated workflow and scalability of the system provide a versatile framework for the large-scale characterization of optical fibers required by next-generation spectroscopic survey facilities.
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All authors Daksh Singh, Ting S. Li, Sarik Jerma, Shaojie Chen