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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 10 November

High Energy Astrophysical Phenomena

ExTraSS: a Domain Decomposed 3D NLTE Radiative Transfer spectral synthesis code for nebular phase transients

Bart F.A. van Baal and Anders Jerkstrand

In the nebular phase, supernovae are powered by radioactive decay and continuously fade, while their densities have decreased enough such that the expanding nebula becomes (largely) optically thin and the entire structure contributes to the emission. Models for the nebular phase need to take Non-Local Thermodynamic Equilibrium (NLTE) effects into account, while at the same time radiative transfer effects often cannot be ignored. To account for the asymmetric morphologies of SNe, 3D input ejecta models must be used. In this work, we present the $\texttt{ExTraSS}$ (EXplosive TRAnsient Spectral Simulator) code, which has been upgraded to be fully capable of 3D NLTE radiative transfer calculations in order to generate synthetic spectra for explosive transients in the nebular phase, with a focus on supernovae. We solve a long-standing difficulty of 3D NLTE radiative transfer – to manage generation and storage of millions of photoexcitation rates over $\gtrsim10^{5}$ of cells – by developing a new Domain Decomposition algorithm. We describe this new methodology and general code operations in detail, and analyse convergence and accuracy for $\texttt{ExTraSS}$.
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Solar and Stellar Astrophysics

MHSXtraPy – A Python code for the extrapolation of magnetohydrostatic fields on the Sun using analytical solutions

Lilli Nadol and Thomas Neukirch

We present a Python code for calculating and displaying magnetic field extrapolations from given two-dimensional boundary conditions, specifically from solar surface magnetograms. The code implements analytical magnetohydrostatic models that incorporate the transition from non-force-free to force-free magnetic fields in the solar atmosphere. It allows for different parameterisations of this transition and includes functions to compute magnetic fields, plasma pressure, and density. Fast Fourier methods ensure efficient computation, and the output includes three-dimensional visualisations of field lines and plasma structures. The implementation is optimised for accessibility and speed, making it suitable for both research and educational purposes. The only prerequisite for running the code is a Python compiler. All source code, examples, input files, solutions, and instructions are available for download from GitHub.
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Earth and Planetary Astrophysics

Using Stellar Spectral Energy Distributions to Measure Exoplanet Parameters

Sam Morrell, Tim Naylor, John Southworth et al. (+1 more)

The ability to make accurate determinations of planetary parameters is inextricably linked to measuring physical parameters of the host star, in particular the stellar radius. In this paper we fit the stellar spectral energy distributions of exoplanet hosts to measure their radii, making use of only archival photometry, the $Gaia$ parallaxes and $Gaia$ extinction maps. Using the extinction maps frees us of the degeneracy between temperature and extinction which has plagued this method in the past. The resulting radii have typical random uncertainties of about 2 per cent. We perform a quantitative study of systematic uncertainties affecting the methodology and find they are similar to, or smaller than, the random ones. We discuss how the stellar parameters can be used to derive the properties of both transiting exoplanets, and those where only a radial-velocity curve is available. We then explore in detail the improvements the method makes possible for the parameters of the PanCET sample of transiting planets. For this sample we find the best literature measurements of the planetary radii have mean uncertainties about 40 per cent larger than those presented here, with the new measurements achieving precisions of 2 per cent in radius and 10 per cent in mass. In contrast to much recent work, these transiting exoplanets parameters are derived without using theoretical models of stellar interiors, freeing them of the assumptions those models contain, and any priors for stellar age. As the data used are available for the whole sky, the method can be used for self-consistent measurements of the planetary parameters of a very large fraction of known exoplanets.
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All authors Sam Morrell, Tim Naylor, John Southworth, David K. Sing

High Energy Astrophysical Phenomena

Multi-messenger flare in the quasar PKS 0446+11

Y. Y. Kovalev, M. F. Aller, A. K. Erkenov et al. (+15 more)

The physical mechanisms driving neutrino and electromagnetic flares in blazars remain poorly understood. We investigate a prominent multi-messenger flare in the quasar PKS 1424+240 to identify the processes responsible for its high-energy emission. We analyze the IceCube-240105A high-energy neutrino event together with contemporaneous observations in the gamma-ray, X-ray, optical, and radio bands. The on- and off-flare spectral energy distributions (SEDs) are modeled within a single-zone leptohadronic framework. Multi-epoch VLBA observations from the MOJAVE program provide parsec-scale polarization data that complement the multi-wavelength light curves. No significant time delay is detected between the neutrino arrival and the flares in different energy bands. This is consistent with an extremely small jet viewing angle below 1 deg, inferred from the parsec-scale polarization structure. The flare can be reproduced by the injection of a proton population and an increase of the Doppler factor from 18 to 24. We also detect an approximately 90 deg rotation of the EVPA in the parsec-scale core during the initial phase of the flare, indicating the emergence of a shock formed by the change in the bulk plasma speed. Our comprehensive multi-messenger analysis demonstrates that the extreme beaming and sub-degree viewing angle of this distant blazar can account for the observed neutrino and electromagnetic activity. These findings strengthen the case for blazars as efficient accelerators of hadrons and as significant contributors to the observed high-energy neutrino flux.
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All authors Y. Y. Kovalev, M. F. Aller, A. K. Erkenov, J. L. Gómez, D. C. Homan, P. I. Kivokurtseva, Yu. A. Kovalev, M. L. Lister, P. V. de la Parra, A. V. Plavin, A. V. Popkov, A. B. Pushkarev, A. C. S. Readhead, E. Shablovinskaia, Yu. V. Sotnikova, O. I. Spiridonova, S. V. Troitsky, V. V. Vlasyuk

Solar and Stellar Astrophysics

The Shape of the Solar Tachocline

Sarbani Basu and Sylvain G. Korzennik

Early helioseismic results have shown that the tachocline has a prolate shape. However, the models used in those studies constrained the tachocline to be either prolate or oblate. We use helioseismic data obtained from long time series (2304 and 4608 days) to determine the shape of the solar tachocline. Like previous work, we use forward modeling methods for this work; however, we allow more flexibility for the shape of the tachocline. We find that the tachocline does indeed deviate from a simple prolate structure and bulges out at mid latitudes. The center of the tachocline lies in the radiative zone at low latitudes, in the convection zone at intermediate latitudes, and back in the radiative zone at high latitudes. The high-latitude ($ > 60^\circ$) behavior is, however, uncertain and model dependent. Models that allow more variation of the shape indicate that the tachocline at high latitudes is almost coincident with the base of the convection zone.
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Solar and Stellar Astrophysics

Lost Sisters Found: TESS and Gaia Reveal a Dissolving Pleiades Complex

Andrew W. Boyle, Luke G. Bouma and Andrew W. Mann

Most star clusters dissolve into the Galaxy over tens to hundreds of millions of years after they form. While recent Gaia studies have honed our view of cluster dispersal, the exact chronology of which star formation events begat which star cluster remnants remains unclear. This problem is acute after 100 Myr, when cluster remnants have spread over hundreds of parsecs and most age estimates for main sequence stars are too imprecise to link the stars to their birth events. Here we develop a Bayesian framework that combines TESS stellar rotation rates with Gaia kinematics to identify diffuse remnants of open clusters. We apply our method to the Pleiades, which previous studies have noted shows kinematic similarities to other nearby young stellar groups. We find that the Pleiades constitutes the bound core of a much larger, coeval structure that contains multiple known clusters distributed over 600 pc. We refer to this structure as the Greater Pleiades Complex. On the basis of uniform ages, coherent space velocities, detailed elemental abundances, and traceback histories, we conclude that most stars in this complex originated from the same giant molecular cloud. This work establishes a scalable approach for tracing the genealogies of nearby clusters and further cements the Pleiades as a cornerstone of stellar astrophysics. We aim to apply this methodology to other associations as part of the upcoming TESS All-Sky Rotation Survey.
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Astrophysics of Galaxies

Changing-Look Active Galactic Nuclei in SDSS-V: Host-Galaxy Properties and Black-Hole Scaling Relations

Grisha Zeltyn, Benny Trakhtenbrot, Michael Eracleous et al. (+23 more)

Changing-look active galactic nuclei (CL-AGNs) exhibit dramatic spectral variability on unexpectedly short timescales, challenging standard accretion flow models. Despite growing samples, the physical drivers of this extreme variability, and the potential link to host-galaxy properties, remain unknown. Regardless of the underlying mechanism, the transition between AGN-dominated and host-dominated spectra offers a unique opportunity to study relations between AGNs and their hosts within the same objects. We present intermediate-resolution spectroscopy of 23 CL-AGNs identified by the Sloan Digital Sky Survey V (SDSS-V), obtained with the Very Large Telescope/X-shooter and Gemini-N/GMOS. An analysis of the Mgii emission line observed in the spectra demonstrates that the majority of these sources cannot be driven by variable obscuration. Our CL-AGNs roughly follow the M_BH-sigma_* and M_BH-M_* relations of inactive galaxies, with a median black hole-to-stellar mass ratio of 0.38%. We find no evidence that the stellar population properties of our CL-AGNs, including stellar mass, age, young stellar fraction, and star-formation rate, differ from those of type 2 AGNs in SDSS. These results suggest that CL-AGNs reside in typical AGN host galaxies and that their extreme variability is likely unrelated to host-galaxy environment, supporting the idea that CL-AGNs are not a distinct population, but rather represent a phase of normal AGN activity. This result, in turn, implies that CL-AGNs can serve as useful probes of the AGN-host connection, providing access to both AGN-dominated and host-dominated spectra of the same systems.
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All authors Grisha Zeltyn, Benny Trakhtenbrot, Michael Eracleous, Scott F. Anderson, Claudio Ricci, Andrea Merloni, Jessie Runnoe, Mirko Krumpe, James Aird, Roberto J. Assef, Catarina Aydar, Franz E. Bauer, W.N. Brandt, Joel R. Brownstein, Johannes Buchner, Kaushik Chatterjee, Laura Duffy, Lorena Hernández-García, Héctor Hernández-Toledo, Anton M. Koekemoer, Sean Morrison, Castalia Alenka Negrete Peñaloza, Mara Salvato, Donald P. Schneider, Yue Shen, Marzena Śniegowska

High Energy Astrophysical Phenomena

The Type Ia Supernova 2021hem: A 2003fg-like Event in an Apparently Hostless Environment

Subhash Bose, M.D. Stritzinger, A. Malmgaard et al. (+25 more)

We report observations of Type Ia SN 2021hem, located in an apparently hostless environment. With a peak absolute B-band magnitude of -19.96 mag, and a lack of secondary maximum in near-infrared and i-band light curves make it resemble 2003fg-like events. The slowly evolving light curves, and the earliest spectrum showing CII absorption lines, further support this classification. Fireball model fit to early light curves yields a time of first light of -16.43 days relative to B-band maximum. The first detection occurs 1.51 days before the onset of the fireball-like flux rise. This early emission, and $(g - r)_0$ color, is inconsistent with circumstellar or companion interaction. Instead, shallow $^{56}$Ni mixing or an asymmetric $^{56}$Ni distribution offers a plausible explanation. SN2021hem is the fifth known 2003fg-like SN with early-time excess flux emission. The estimated mass of radioactive $^{56}$Ni in SN2021hem is $1.00\pm0.09 M_\odot$. Deep GTC imaging obtained 2.5 yr after the explosion (with $m_{lim,r}=24.4$ mag and $\mu_{lim,r} = 26.3\rm~mag~arsec^{-2}$), reveals no coincident host, thereby ruling out most faint dwarf and UDGs. Alternatively, assuming the nearest plausible AGN host galaxy, at a distance of 104 kpc, implies a hyper-velocity progenitor ejected at $\sim$2200 km/s by AGN interaction. A faint diffuse feature ~6 kpc from the SN site has also been detected in the image, with its surface brightness of a UDGs. However, it is unclear whether it is a galaxy and is associated with SN2021hem. Considering its large normalized directional light distance ($d_{DLR}\sim3-4$) from SN, and its unusual elongation, it is a candidate of low probability to be the host galaxy of SN2021hem. These results identify SN2021hem as one of the strongest candidates for a hostless SN Ia, underscoring the diversity of luminous, slowly evolving, 2003fg-like explosions.
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All authors Subhash Bose, M.D. Stritzinger, A. Malmgaard, C.J. Miller, N. Elias-Rosa, J.P.U. Fynbo, C. Ashall, C.R. Burns, J.M. DerKacy, L. Galbany, C.P. Gutiérrez, W.B. Hoogendam, E. Y. Hsiao, E.A.M. Jensen, K. Medler, Alaa Alburai, J. Anderson, E. Baron, J. Duarte, M. Gromadzki, C. Inserra, P.A. Mazzali, T.E. Müller-Bravo, P. Lundqvist, A. Reguitti, I. Salmaso, D.J. Sand, G. Valerin

Cosmology and Nongalactic Astrophysics

Null Impact of the Null Energy Condition in Current Cosmology

Robert R. Caldwell and Eric V. Linder

We clarify the role of the oft-misunderstood Null Energy Condition (NEC) in the context of the current cosmological data. In particular, the NEC implies the sum of the total energy density and pressure satisfies $\rho_{tot}+P_{tot} \ge 0$; the energy conditions do not apply separately to individual components of the cosmological fluid. Consequently, we show that under the current best-fit cosmological model no violation of the NEC takes place, past or future. Further, growth in the energy density of an individual component cannot be used to signal violation of the NEC. We illustrate these points with a worked example whereby misestimation of the matter density leads to a phase during which $\rho_{de} + P_{de} < 0$ for the effective dark energy, followed by a phantom crossing and subsequent $\rho_{de} + P_{de} > 0$. At no time is the NEC violated. We also introduce “elephant” and “chimera” classes of physics for crossing $w_{de}=-1$.
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Solar and Stellar Astrophysics

Empirical Bolometric Correction and Zero-Point Constants of Visual Magnitudes from High-Resolution Spectra

Gökhan Yücel, Selçuk Bilir, Volkan Bak{\i}ş et al. (+1 more)

A method of obtaining bolometric corrections ($BC_{\rm V}$) from observed high-resolution, high-$S/N$ spectra is described. The method is applied to spectra of 128 stars collected from the literature with well-determined effective temperatures ($T_{\rm eff}$) with $S_\lambda(V)$ transparency profiles of Bessell and Landolt. Computed $BC_{\rm V}$ are found accurate within several milimagnitudes and the effect of different $S_\lambda(V)$ is found to be no more than 0.015 mag. Measured visual to bolometric ratio ($L_{\rm V}/L$) from the sample spectra and classically determined $BC_{\rm V}$ from bolometric ($M_{\rm Bol}$) and visual ($M_{\rm V}$) absolute magnitudes helped us to determine the zero-point constant ($C_{\rm 2}$) of the $BC_{\rm V}$ scale. Determined $C_{\rm 2}$ for each star for each $S_\lambda(V)$ profile revealed $C_{\rm 2} = 2.3653\pm0.0067$ mag if $S_\lambda(V)$ profile of Bessell is used, and $C_{\rm 2} = 2.3826\pm0.0076$ mag if $S_\lambda(V)$ profile of Landolt is used. Expanding $C_{\rm Bol} = 71.197425 ...$ mag and $c_{\rm Bol} = -18.997351 ...$ mag announced by IAU2015GARB2, and using definition of $C_{\rm 2} = C_{\rm Bol}-C_{\rm V} = c_{\rm Bol}-c_{\rm V}$, where capital $C$ is for the absolute and small $c$ is for the apparent, subscripts indicating bolometric and visual, the zero-point constants: $C_{\rm V} = 68.8321\pm0.0067$ mag and $c_{\rm V} = -21.3627\pm0.0067$ mag, if $L_{\rm V}$ and are in SI units, were determined corresponding to $S_\lambda(V)$ of Bessell. The zero-point constants corresponding to $S_\lambda(V)$ of Landolt are smaller, but the difference is not more than 0.02 mag. Typical and limiting accuracies for predicting a stellar luminosity from an apparent magnitude and a distance are analyzed.
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All authors Gökhan Yücel, Selçuk Bilir, Volkan Bak{\i}ş, Zeki Eker

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

Tests of General Relativity with Einstein Telescope

Andrea Begnoni, Walter Del Pozzo, Matteo Pegorin et al. (+2 more)

Gravitational wave signals from compact binary coalescences provide powerful and reliable probes of General Relativity. To date, the LIGO-Virgo-KAGRA collaboration has provided stringent consistency tests of General Relativity predictions. In this work, we present forecasts for how accurately General Relativity can be tested using third-generation ground-based interferometers, focusing on Einstein Telescope (ET) and binary black hole mergers. Given the expected high detection rate, we use a Fisher matrix approach to simulate parameter estimation over large source catalogs, and jointly analyze events within a Bayesian hierarchical framework. We compare different ET configurations and forecast constraints on parametrized deviations of the inspiral post-Newtonian coefficients. Our results indicate that, within about four months of observations, ET could improve current LVK GWTC-3 bounds by roughly four orders of magnitude for the dipole radiation term and about two orders for higher-order coefficients. We further assess the number of detections required to confidently identify deviations from General Relativity at various post-Newtonian orders and for different detector configurations.
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All authors Andrea Begnoni, Walter Del Pozzo, Matteo Pegorin, Joachim Pomper, Angelo Ricciardone

Cosmology and Nongalactic Astrophysics

The Dark Energy Survey Supernova Program: A Reanalysis Of Cosmology Results And Evidence For Evolving Dark Energy With An Updated Type Ia Supernova Calibration

B. Popovic, P. Shah, W. D. Kenworthy et al. (+80 more)

We present improved cosmological constraints from a re-analysis of the Dark Energy Survey (DES) 5-year sample of Type Ia supernovae (DES-SN5YR). This re-analysis includes an improved photometric cross-calibration, recent white dwarf observations to cross-calibrate between DES and low redshift surveys, retraining the SALT3 light curve model and fixing a numerical approximation in the host galaxy colour law. Our fully recalibrated sample, which we call DES-Dovekie, comprises $\sim$1600 likely Type Ia SNe from DES and $\sim$200 low-redshift SNe from other surveys. With DES-Dovekie, we obtain $\Omega_{\rm m} = 0.330 \pm 0.015$ in Flat $\Lambda$CDM which changes $\Omega_{\rm m}$ by $-0.022$ compared to DES-SN5YR. Combining DES-Dovekie with CMB data from Planck, ACT and SPT and the DESI DR2 measurements in a Flat $w_0 w_a$CDM cosmology, we find $w_0 = -0.803 \pm 0.054$, $w_a = -0.72 \pm 0.21$. Our results hold a significance of $3.2\sigma$, reduced from $4.2\sigma$ for DES-SN5YR, to reject the null hypothesis that the data are compatible with the cosmological constant. This significance is equivalent to a Bayesian model preference odds of approximately 5:1 in favour of the Flat $w_0 w_a$CDM model. Using generally accepted thresholds for model preference, our updated data exhibits only a weak preference for evolving dark energy.
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All authors B. Popovic, P. Shah, W. D. Kenworthy, R. Kessler, T. M. Davis, A. Goobar, D. Scolnic, M. Vincenzi, P. Wiseman, R. Chen, E. Charleton, M. Acevedo, P. Armstrong, B.M. Boyd, D. Brout, R. Camilleri, J. Frieman, L. Galbany, M. Grayling, L. Kelsey, B. Rose, B. Sánchez, J. Lee, A. Möller, M. Smith, M. Sullivan, N. Shiamtanis, A. Alarcon, S.S. Allam, F. Andrade-Oliveira, S. Avila, D. Bacon, J. Blazek, S. Bocquet, D. Brooks, D. L. Burke, A. Carnero Rosell, J. Carretero, R. Cawthon, L. N. da Costa, M. E. da Silva Pereira, H. T. Diehl, S. Dodelson, P. Doel, S. Everett, C. Frohmaier, J. García-Bellido, D. Gruen, G. Gutierrez, K. Herner, S. R. Hinton, D. L. Hollowood, K. Honscheid, D. Huterer, D. J. James, N. Jeffrey, K. Kuehn, O. Lahav, S. Lee, C. Lidman, J. L. Marshall, J. Mena-Fernández, F. Menanteau, R. Miquel, J. Muir, J. Myles, R. L. C. Ogando, M. Paterno, A. A. Plazas Malagón, A. Porredon, J. Prat, R.C. Nichol, A. K. Romer, A. Roodman, E. Sanchez, D. Sanchez Cid, I. Sevilla-Noarbe, E. Suchyta, M. E. C. Swanson, C. To, D. L. Tucker, A. R. Walker, N. Weaverdyck

Astrophysics of Galaxies

Finding the boundary: Using galaxy membership to inform galaxy cluster extent through machine learning

Christine Hao, Stephanie O'Neil, Mark Vogelsberger et al. (+3 more)

The spatial extent of the environment's impact on galaxies marks a transitional region between cluster and field galaxies. We present a data-driven method to identify this region in galaxy clusters with masses $M_{200\rm ,mean}>10^{13} M_{\odot}$ at $z = 0$. Using resolved galaxy samples from the largest simulation volume of IllustrisTNG (TNG300-1), we examine how galaxy properties vary as a function of distance to the closest cluster. We train neural networks to classify galaxies into cluster and field galaxies based on their intrinsic properties. Using this classifier, we present the first quantitative and probabilistic map of the transition region. It is represented as a broad and intrinsically scattered region near cluster outskirts, rather than a sharp physical boundary. This is the physical detection of a mixed population. In order to determine transition regions of different physical processes by training property-specific models, we categorise galaxy properties based on their underlying physics, i.e. gas, stellar, and dynamical. Changes to the dynamical properties dominate the innermost regions of the clusters of all masses. Stellar properties and gas properties, on the other hand, exhibit transitions at similar locations for low mass clusters, yet gas properties have transitions in the outermost regions for high mass clusters. These results have implications for cluster environmental studies in both simulations and observations, particularly in refining the definition of cluster boundaries while considering environmental preprocessing and how galaxies evolve under the effect of the cluster environment.
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All authors Christine Hao, Stephanie O'Neil, Mark Vogelsberger, Vinh Tran, Lamiya Mowla, Joshua S. Speagle

Astrophysics of Galaxies

The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot

Vasily Kokorev, John Chisholm, Rohan P. Naidu et al. (+19 more)

The detection of strong Balmer breaks and absorption features in Little Red Dots (LRDs) suggests they host AGN embedded within dense gas envelopes, potentially powered by super-Eddington accretion. We present GLIMPSE-17775, a luminous ($L_{\rm bol}\sim10^{45}$ erg s$^{-1}$) LRD at $z=3.501$ behind Abell S1063 ($\mu\sim2$), observed with deep JWST/NIRCam and a $\sim$20 hr (80 hr de-lensed) NIRSpec/G395M spectrum. The data reveal 40+ emission and absorption features, including a rich forest of low-ionization FeII lines and numerous broad hydrogen recombination transitions. We use this depth to test the dense-gas interpretation through five independent diagnostics. Nearly all permitted lines show exponential wings with consistent FWHM, the signature of Thomson scattering requiring $n_e\gtrsim10^8$ cm$^{-3}$. Adopting this width yields $M_{\rm BH}\sim10^{6.7}M_\odot$, a factor of ten lower than Gaussian fits, and $\lambda_{\rm Edd}\sim1.8$. Additional diagnostics support the same picture: a pronounced Balmer break ($f_{\nu,4050}/f_{\nu,3670}=2.0\pm0.1$), enhanced HeI $\lambda7065$ and $\lambda10830$ with P-Cygni absorption, Bowen-fluorescent OI $\lambda8446$-$\lambda11290$ emission requiring Ly$\beta$ pumping, and 16 FeII lines matching fluorescence models. These features indicate a dense ($n\sim10^8$ cm$^{-3}$), partially ionized cocoon where scattering and fluorescence dominate line formation, providing strong evidence that at least some LRDs are powered by super-Eddington black-hole growth in the early Universe.
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All authors Vasily Kokorev, John Chisholm, Rohan P. Naidu, Seiji Fujimoto, Hakim Atek, Gabriel Brammer, Steven L. Finkelstein, Hollis B. Akins, Danielle A. Berg, Lukas J. Furtak, Qinyue Fei, Tiger Yu-Yang Hsiao, Ivo Labbé, Jorryt Matthee, Julian B. Muñoz, Pascal A. Oesch, Richard Pan, Pierluigi Rinaldi, Alberto Saldana-Lopez, Daniel Schaerer, Marta Volonteri, Adi Zitrin

Cosmology and Nongalactic Astrophysics

JWST lensed quasar dark matter survey IV: Stringent warm dark matter constraints from the joint reconstruction of extended lensed arcs and quasar flux ratios

D. Gilman, A. M. Nierenberg, T. Treu et al. (+23 more)

We present a measurement of the free-streaming length of dark matter (DM) and subhalo abundance around 28 quadruple image strong lenses using observations from JWST MIRI presented in Paper III of this series. We improve on previous inferences on DM properties from lensed quasars by simultaneously reconstructing extended lensed arcs with image positions and relative magnifications (flux ratios). Our forward modeling framework generates full populations of subhalos, line-of-sight halos, and globular clusters, uses an accurate model for subhalo tidal evolution, and accounts for free-streaming effects on halo abundance and concentration. Modeling lensed arcs leads to more-precise model-predicted flux ratios, breaking covariance between subhalo abundance and the free-streaming scale parameterized by the half-mode mass $m_{\rm{hm}}$. Assuming subhalo abundance predicted by the semi-analytic model {\tt{galacticus}} ($N$-body simulations), we infer (Bayes factor of 10:1) $m_{\rm{hm}} < 10^{7.4} \mathrm{M}_{\odot}$ ($m_{\rm{hm}} < 10^{7.2} \mathrm{M}_{\odot}$), a 0.4 dex improvement relative to omitting lensed arcs. These bounds correspond to lower limits on thermal relic DM particle masses of $6.5$ and $7.4$ keV, respectively. Conversely, assuming DM is cold, we infer a projected mass in subhalos ($10^6 < m/M_{\odot}<10^{10.7}$) of $1.7_{-1.2}^{+2.6} \times 10^7 \ \mathrm{M}_{\odot} \ \rm{kpc^{-2}}$ at $95 \%$ confidence. This is consistent with {\tt{galacticus}} predictions ($0.9 \times 10^7 \mathrm{M}_{\odot} \ \rm{kpc^{-2}}$), but in mild tension with recent $N$-body simulations ($0.6 \times 10^7 \mathrm{M}_{\odot} \ \rm{kpc^{-2}}$). Our results are among the strongest bounds on WDM, and the most precise measurement of subhalo abundance around strong lenses. Further improvements will follow from the large sample of lenses to be discovered by Euclid, Rubin, and Roman.
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All authors D. Gilman, A. M. Nierenberg, T. Treu, C. Gannon, X. Du, H. Paugnat, S. Birrer, A. J. Benson, P. Mozumdar, K. C. Wong, D. Williams, R. E. Keeley, K. N. Abazajian, T. Anguita, V. N. Bennert, S. G. Djorgovski, S. H. Hoenig, A. Kusenko, M. Malkan, T. Morishita, V. Motta, L. A. Moustakas, W. Sheu, D. Sluse, D. Stern, M. Stiavelli

Earth and Planetary Astrophysics

The Inner Kernel of the Classical Kuiper Belt

Amir Siraj, Christopher F. Chyba and Scott Tremaine

The `kernel' of the classical Kuiper belt was discovered by Petit et al. (2011) as a visual overdensity of objects with low ecliptic inclinations and eccentricities at semimajor axes near 44 AU. This raises the question - are there other structures present in the classical Kuiper belt? If there are, clustering algorithms applied to orbits transformed into free elements may yield the best chance of discovery. Here, we derive barycentric free orbital elements for objects in the classical Kuiper belt, and use the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm to identify a new structure, which we dub the inner kernel, located at $a \sim 43 \mathrm{\; AU}$ just inward of the kernel ($a \sim 44 \mathrm{\; AU}$), which we also recover. It is yet unclear whether the inner kernel is an extension of the kernel or a distinct structure. Forthcoming observations, including those by the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) may provide further evidence for the existence of this structure, and perhaps resolve the question of whether there are two distinct structures.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Galactic magnetic fields seeded by ultralight dark photons

Joshua Berger, Amit Bhoonah, Joseph Bramante et al. (+3 more)

In this work, we show that ultralight dark photons, which couple to the Standard Model photon through kinetic mixing, can potentially source galactic scale magnetic fields. Although these magnetic fields would be too weak to detect at present in galaxies due to plasma screening effects, we show that dark photons can provide the seed magnetic field strength ($10^{-20}$ G) required for dynamo amplification in galaxies. Such dynamo-amplified magnetic fields are consistent with observations of $\mu$G strength galactic magnetic fields.
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All authors Joshua Berger, Amit Bhoonah, Joseph Bramante, J. Leo Kim, Ningqiang Song, Lawrence M. Widrow

Astrophysics of Galaxies

Roman Galactic Plane Survey Definition Committee Report

Roman Galactic Plane Survey Definition Committee

The Roman Galactic Plane Survey (RGPS) is a 700-hour program approved for early definition as a community-designed General Astrophysics Survey. It was selected following a proposal call for science programs that would benefit from an early community-based definition (Sanderson et al 2024). The community was invited to submit white papers and science pitches with a deadline of May 20, 2024; the Roman Galactic Plane Survey Definition Committee (RGPS-DC) first met on Sep 11, 2024. Based on the input provided, the RGPS-DC recommends a survey consisting of three elements: (1) a wide-field science element (691 sq deg, 541 hrs) covering the Galactic plane, Galactic latitude |b|<2 deg and Galactic longitude l=+50.1 deg to -79 deg (281 deg), in four filters (F129, F159, F184, and F213) with higher latitude extensions for the bulge, the Serpens South/W40 star formation region, and Carina, (2) a time-domain science element (19 sq deg , 130 hrs) of six fields, including the full Nuclear Stellar Disk (NSD) and Central Molecular Zone (CMZ), with coverage in seven filters and repeat observations in one or more filters with cadences from 11 minutes to weeks, and (3) a deep-field/spectroscopic science element (4 sq deg , 30 hrs) consisting of fifteen Roman pointings (with a wide range of extinction, diffuse emission, stellar density and population) using longer exposure times in seven filters in addition to grism and prism observations. This document summarizes the science that can be done with this survey, the process of survey definition, and details on all of the program elements.
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High Energy Astrophysical Phenomena

The position of SN 1987A

C. Tegkelidis, J. Larsson and D. Alp

The accurate positional measurement of Supernova (SN) 1987A is important for determining the kick velocity of its compact object and the velocities of the ejecta and various shock components. In this work, we perform absolute astrometry to determine the position of SN 1987A. We used multi-epoch Hubble Space Telescope imaging to model the early ejecta and the equatorial ring (ER). We combined our measurements and obtained the celestial coordinates in the International Celestial Reference System (ICRS) by registering the observations onto Gaia Data Release 3. The final average position of the different measurements is ${\alpha = 5^{\mathrm{h}}~ 35^{\rm{m}}~ 27^{\rm{s}}.9884(30)}$, ${\delta = -69^{\circ}~ 16'~ 11''.1134(136)}$ (ICRS J2016). The early ejecta position is located 14 mas south and 16 mas east of the ER center, with the offset being significant at 96% confidence. The offset may be due to instrument and/or filter-dependent systematics and registration uncertainties, though an intrinsic explosion offset relative to the ER remains possible. Image registration with proper motion corrections yields similar astrometry and a source proper motion of ${\mu_{\rm east} (\equiv \rm{PM_{\alpha }*}) = 1.60 \pm 0.15 ~\rm{mas ~ yr^{-1}}}$ and ${\mu_{\rm{north}} (\equiv \rm{PM_{\delta}}) = 0.44 \pm 0.09~\rm{mas ~ yr^{-1}}}$, in agreement with the typical local motion of the Large Magellanic Cloud. The absolute positional uncertainty of 21 mas adds a systematic uncertainty to the sky-plane kick velocity of ${123}~(t/40~\rm{yr})^{-1}~\rm{km~s}^{-1}$, where $t$ is the time since the explosion. Comparing the location of the compact source observed with JWST to our updated position implies a sky-plane kick of ${399\pm148~\mathrm{km~s^{-1}}}$ and a 3D kick of ${472\pm126~\mathrm{km~s^{-1}}}$, which is consistent with previous estimates.
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Solar and Stellar Astrophysics

Surprisingly Similar: The Mass Function of Gaia Neutron Stars and First-Born Double Neutron Stars

Aryanna Schiebelbein-Zwack, L.A.C van Son, Maya Fishbach et al. (+1 more)

The mass distribution of neutron stars encodes information about their formation and binary evolution. We compare the masses of two distinct populations: I) the recently identified Gaia neutron stars in wide orbits with solar-like companions and, II) the assumed first-born recycled pulsar in Galactic double neutron star systems. Naively, one would expect their masses to differ due to both the presumed differences in their evolutionary histories, as well as astrophysical selection effects that can filter out configurations that would merge or be disrupted. Yet, we find that their mass distributions are strikingly similar. Using a two-component Gaussian model, we find that both populations exhibit a narrow component centred near $1.3 \text{ M}_\odot$, accompanied by a broader, higher-mass component that extends the distribution toward larger masses. The highest density regions of their fitted parameter posteriors coincide by over 91.6%. Statistical tests further confirm the agreement between these distributions with a Jensen-Shannon divergence $JS < 0.08$ and an earth mover's distance of $W <0.063 \text{ M}_\odot$ at 90% credibility. This finding seems to imply that both mass functions reflect the natal mass distribution of first-born neutron stars in binary systems, supporting the hypothesis that neutron stars can be born with high masses. Consequently and perhaps surprisingly, binary evolutionary processes need not impart features on the NS mass distribution.
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All authors Aryanna Schiebelbein-Zwack, L.A.C van Son, Maya Fishbach, Will M. Farr

Instrumentation and Methods for Astrophysics · Cross-listed from stat.CO

samsara: A Continuous-Time Markov Chain Monte Carlo Sampler for Trans-Dimensional Bayesian Analysis

Gabriele Astorino, Lorenzo Valbusa Dall'Armi, Riccardo Buscicchio et al. (+3 more)

Bayesian inference requires determining the posterior distribution, a task that becomes particularly challenging when the dimension of the parameter space is large and unknown. This limitation arises in many physics problems, such as Mixture Models (MM) with an unknown number of components or the inference of overlapping signals in noisy data, as in the Laser Interferometer Space Antenna (LISA) Global Fit problem. Traditional approaches, such as product-space methods or Reversible-Jump Markov Chain Monte Carlo (RJMCMC), often face efficiency and convergence limitations. This paper presents samsara, a Continuous-Time Markov Chain Monte Carlo (CTMCMC) framework that models parameter evolution through Poisson-driven birth, death, and mutation processes. samsara is designed to sample models of unknown dimensionality. By requiring detailed balance through adaptive rate definitions, CTMCMC achieves automatic acceptance of trans-dimensional moves and high sampling efficiency. The code features waiting time weighted estimators, optimized memory storage, and a modular design for easy customization. We validate samsara on three benchmark problems: an analytic trans-dimensional distribution, joint inference of sine waves and Lorentzians in time series, and a Gaussian MM with an unknown number of components. In all cases, the code shows excellent agreement with analytical and Nested Sampling results. All these features push samsara as a powerful alternative to RJMCMC for large- and variable-dimensional Bayesian inference problems.
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All authors Gabriele Astorino, Lorenzo Valbusa Dall'Armi, Riccardo Buscicchio, Joachim Pomper, Angelo Ricciardone, Walter Del Pozzo

Earth and Planetary Astrophysics

Orbital Characterization of a Newly Discovered Small Satellite Around Quaoar

Benjamin Proudfoot, Richard Nolthenius, Bryan J. Holler et al. (+5 more)

Recent observations of a stellar occultation have revealed the presence of a previously undiscovered small satellite around Quaoar. Orbiting near Quaoar's unusual ring system, this new satellite has the potential to provide significant insights into the formation and evolution of Quaoar and its ring system. In this letter, we characterize the orbit of this newly discovered satellite, finding that it is likely on a $3.6^{+0.5}_{-0.3}$-day orbit, plausibly placing it near a 5:3 mean motion resonance with Quaoar's outermost known ring. Examining the possibility of observing the newly discovered satellite with further stellar occultations, we estimate that $\sim$hundreds of observing stations are required for recovery, since phase information about its orbit was rapidly lost after the lone detection. We also attempted to recover the satellite in JWST NIRCam imaging of Quaoar, but find no convincing detection. This non-detection is limited by the accuracy of the available NIRCam PSF models, as well as the satellite's extreme faintness and close-in orbital separation. Therefore, current-generation telescopes will likely struggle to directly image this new satellite, but near-future 30-meter-class telescopes should prove capable of detecting it. Discovery of such a satellite provides evidence that the rings around Quaoar may have been part of an initially broad collisional disk that has evolved considerably since its formation. To further explore this hypothesis, we encourage follow-up observations of the rings and satellites with stellar occultations and direct imaging, as well as updated hydrodynamical, collisional, and tidal modeling of the system.
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All authors Benjamin Proudfoot, Richard Nolthenius, Bryan J. Holler, Ana Carolina de Souza-Feliciano, Flavia L. Rommel, Cameron Collyer, Will M. Grundy, Estela Fernández-Valenzuela

Earth and Planetary Astrophysics

Beyond Point Masses. V. Weywot's Non-Keplerian Orbit

Benjamin Proudfoot, Will Grundy, Darin Ragozzine et al. (+1 more)

We present a detailed dynamical analysis of the Quaoar-Weywot system based on nearly 20 years of high-precision astrometric data, including new HST observations and stellar occultations. Our study reveals that Weywot's orbit deviates significantly from a purely Keplerian model, requiring the inclusion of Quaoar's non-spherical gravitational field and center-of-body-center-of-light (COB-COL) offsets in our orbit models. We place a robust upper limit on Weywot's orbital eccentricity ($e<0.02$), substantially lower than previous estimates, which has important implications for the strength of mean motion resonances (MMRs) acting on Quaoar's ring system. Under the assumption that Quaoar's rings lie in its equatorial plane, we detect Quaoar's dynamical oblateness, $J_2$, at $\sim$2$\sigma$ confidence. The low $J_2$ value found under that assumption implies Quaoar is differentiated, with a total bulk density of $1751\pm13$ (stat.) kg m$^{-3}$. Additionally, we detect significant COB-COL offsets likely arising from latitudinal albedo variations across Quaoar's surface. These offsets are necessary to achieve a statistically robust orbit fit and highlight the importance of accounting for surface heterogeneity when modeling the orbits of dwarf planet moons. These findings improve our understanding of Quaoar's interior and surface while providing key insights into the stability and confinement mechanisms of its rings.
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All authors Benjamin Proudfoot, Will Grundy, Darin Ragozzine, Estela Fernández-Valenzuela

Cosmology and Nongalactic Astrophysics

The poltergeist mechanism - Enhancement of scalar-induced gravitational waves with early matter-dominated era -

Keisuke Inomata, Kazunori Kohri and Takahiro Terada

Gravitational waves induced by primordial density perturbations provide a powerful probe of the Universe's thermal history, which may include an early matter-dominated (eMD) era predicted by well-motivated particle-physics models. The induced GWs can be significantly enhanced when the Universe undergoes a sudden transition from an eMD era to an era with pressure, such as a radiation or kination era. This enhancement arises from the growth of density perturbations during the eMD era and their rapid oscillations during the era with pressure. This phenomenon is called the poltergeist mechanism. In this review, we explain the essence of the poltergeist mechanism and explore concrete scenarios in which such an enhancement can occur.
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High Energy Astrophysical Phenomena

Search for steady and flaring neutrino emission from cosmic sources using the complete ANTARES dataset

ANTARES Collaboration: A. Albert, S. Alves, M. André et al. (+138 more)

ANTARES, a neutrino detector located in the depths of the Mediterranean Sea, operated successfully for over 15 years before being decommissioned in 2022. The telescope offered an ideal vantage view of the Southern Sky and benefited from optimal water properties for enhanced angular resolution. This study makes use of data collected over the entire operational period of ANTARES to search for sources of high-energy cosmic neutrinos, considering both steady and flaring emission scenarios. First, a time-integrated search for high-energy neutrino clustering across the celestial sphere is conducted. The most significant accumulation is found at coordinates $(\alpha, \delta) =(200.5^\circ\, 17.7^\circ)$ with a post-trial p-value equal to 0.38. A dedicated search in the Galactic Plane is also performed for extended sources, yielding no significant excess. Additionally, a list of potential neutrino sources are investigated. The blazar MG3 J225517+2409 is identified as the most significant object, yet the excess remains compatible with background fluctuations. A mild local excess of 2.4$\sigma$ is found for the blazar TXS 0506+056. The full sky is also examined for the presence of flaring neutrino emissions. The most significant excess in this case corresponds to a $\sim$4-day flare from the direction $(\alpha, \delta) = (141.3^\circ\, 9.8^\circ)$, with a post-trial p-value of 0.30. Finally, the directions of sources highlighted in IceCube's time-dependent searches are investigated. Temporal overlaps between ANTARES and IceCube flares are identified for PKS 1502+106 and TXS 0506+056, with an estimated chance probability of about 0.02%, making this observation particularly noteworthy.
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All authors ANTARES Collaboration: A. Albert, S. Alves, M. André, M. Ardid, S. Ardid, J.J. Aubert, J. Aublin, B. Baret, S. Basa, Y. Becherini, B. Belhorma, F. Benfenati, V. Bertin, S. Biagi, J. Boumaaza, M. Bouta, M.C. Bouwhuis, H. Brânzaş, R. Bruijn, J. Brunner, J. Busto, B. Caiffi, D. Calvo, S. Campion, A. Capone, F. Carenini, J. Carr, V. Carretero, T. Cartraud, S. Celli, L. Cerisy, M. Chabab, R. Cherkaoui El Moursli, T. Chiarusi, M. Circella, J.A.B. Coelho, A. Coleiro, R. Coniglione, P. Coyle, A. Creusot, A. F. Díaz, B. De Martino, C. Distefano, I. Di Palma, C. Donzaud, D. Dornic, D. Drouhin, T. Eberl, A. Eddymaoui, T. van Eeden, D. van Eijk, S. El Hedri, N. El Khayati, A. Enzenhöfer, P. Fermani, G. Ferrara, F. Filippini, L. Fusco, S. Gagliardini, J. García, C. Gatius Oliver, P. Gay, N. Geißelbrecht, H. Glotin, R. Gozzini, R. Gracia Ruiz, K. Graf, C. Guidi, L. Haegel, S. Hallmann, H. van Haren, A.J. Heijboer, Y. Hello, L. Hennig, J.J. Hernández-Rey, J. Hößl, F. Huang, G. Illuminati, B. Jisse-Jung, M. de Jong, P. de Jong, M. Kadler, O. Kalekin, U. Katz, A. Kouchner, I. Kreykenbohm, V. Kulikovskiy, R. Lahmann, M. Lamoureux, A. Lazo, D. Lefèvre, E. Leonora, G. Levi, S. Le Stum, S. Loucatos, J. Manczak, M. Marcelin, A. Margiotta, A. Marinelli, J.A. Martínez-Mora, P. Migliozzi, A. Moussa, R. Muller, S. Navas, E. Nezri, B. Ó Fearraigh, E. Oukacha, A.M. Păun, G.E. Păvălaş, S. Peña-Martínez, M. Perrin-Terrin, P. Piattelli, C. Poirè, V. Popa, T. Pradier, N. Randazzo, D. Real, G. Riccobene, A. Romanov, A. Sánchez Losa, A. Saina, F. Salesa Greus, D. F. E. Samtleben, M. Sanguineti, P. Sapienza, F. Schüssler, J. Seneca, M. Spurio, Th. Stolarczyk, M. Taiuti, Y. Tayalati, B. Vallage, G. Vannoye, V. Van Elewyck, S. Viola, D. Vivolo, J. Wilms, S. Zavatarelli, A. Zegarelli, J.D. Zornoza, J. Zúñiga

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

Renormalization-Group Invariant Parity-Doublet Model for Nuclear and Neutron-Star Matter

Mattia Recchi, Lorenz von Smekal and Jochen Wambach

The Parity-Doublet Model (PDM) is a chirally invariant effective theory for strong-interaction matter involving nucleons and their opposite-parity partners in a parity-doubling framework. We introduce a multiplicatively renormalizable mean-field approach to include the baryonic vacuum contributions to the resulting grand-canonical potential in an explicitly renormalization-group invariant form. As an application, we evaluate the pertinent thermodynamics of two-flavor symmetric and asymmetric nuclear matter, focusing on the restoration of spontaneously broken chiral symmetry at baryon densities and temperatures relevant for the astrophysics of neutron stars. Special attention is paid to the effect of the baryonic vacuum fluctuations on the evolution of the chiral condensate with baryon density and temperature for specific choices of the chirally invariant baryon mass m0 to demonstrate the importance of consistently including these vacuum fluctuations in the PDM.
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Astrophysics of Galaxies

Stellar Populations in Satellite Galaxies in Close Pairs

Anne E. Sansom, Ignacio Ferreras and Benjamin F. McDonald

Satellite galaxies that are near to massive primary galaxies in close pairs can have stellar population ages that are more similar to their primaries than expected. This is one way in which close pairs of galaxies show galactic conformity, which is thought to be driven by assembly bias. Such conformity is seen in ages, morphologies and star formation rates in different samples. This paper revisits a high signal-to-noise SDSS spectroscopic sample, by spectral fitting of new stellar population models, to investigate satellite galaxy properties of age, metallicity and alpha-element abundance. We find the clear signature of age conformity, as previously seen, but no clear evidence for conformity in metallicity or abundance ratios. The offsets showing age conformity are not caused by age-metallicity degeneracies. There is a suggestion in these data that lower velocity dispersion satellites have increased [alpha/Fe] compared to a control sample of passive galaxies, however this needs further observations to be verified. Our results also suggest an intriguing turnover in the age trends of the satellites at the highest velocity dispersion, perhaps reflecting the onset of environment-related processes in the most massive groups.
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Solar and Stellar Astrophysics

Rethinking mass transfer: a unified semianalytical framework for circular and eccentric binaries. II. Orbital evolution due to nonconservative mass transfer

A. Parkosidis, S. Toonen, E. Laplace et al. (+1 more)

Although mass transfer (MT) has been studied primarily in circular binaries, observations show that it also occurs in eccentric systems. We investigate orbital evolution during nonconservative MT in eccentric orbits, a process especially relevant for binaries containing compact objects (COs). We examined four angular momentum loss (AML) modes: Jeans, isotropic reemission, orbital-AML, and $L_2$ mass loss, with the last mode being the most efficient AML mode. For a fixed AML mode and accretion efficiency, orbital evolution is correlated: orbits either widen while becoming more eccentric, or shrink while circularizing. Jeans mode generally yields orbital widening and eccentricity pumping, whereas $L_2$ mass loss typically leads to orbital shrinkage and eccentricity damping. Isotropic reemission and orbital-AML show an intermediate behavior. Adopting isotropic reemission, we demonstrate that eccentric MT produces compact binaries that merge via gravitational waves (GW) within a Hubble time, whereas the same systems would instead merge during MT under traditional modeling. We further show that, in eccentric orbits, the gravitational potential at $L_2$ becomes lower than at $L_1$ across a wide range of mass ratios and eccentricities, naturally linking eccentricity to $L_2$ mass loss. Eccentric MT may therefore lead to the formation of the circumbinary disks observed around eccentric post-red-giant-branch and post-asymptotic-giant-branch systems. Since interacting binaries containing COs are frequently eccentric, $L_2$ mass loss offers a new robust pathway to orbital tightening during eccentric MT, contributing to the formation rate of GW sources. This model can treat orbital evolution due to conservative and nonconservative MT in arbitrary eccentricities, with applications ranging from MT on the main sequence to GW progenitors.
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All authors A. Parkosidis, S. Toonen, E. Laplace, F. Dosopoulou

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Identification and characterization of distorted gravitational waves by lensing using deep learning

Juno C. L. Chan, Lorena Magaña Zertuche, Jose María Ezquiaga et al. (+3 more)

Gravitational waves (GWs) can be distorted by intervening mass distributions while propagating, leading to frequency-dependent modulations that imprint a distinct signature on the observed waveforms. Bayesian inference for GW lensing with conventional sampling methods is costly, and the problem is exacerbated by the rapidly growing GW catalog. Moreover, assessing the statistical significance of lensed candidates requires thousands, if not millions, of simulations to estimate the background from noise fluctuations and waveform systematics, which is infeasible with standard samplers. We present a novel method, DINGO-lensing, for performing inference on lensed GWs, extending the neural posterior estimation framework DINGO. By comparing our results with those using conventional samplers, we show that the compute time of parameter estimation of lensed GWs can be reduced from weeks to seconds, while preserving accuracy both in the posterior distributions and the evidence ratios. We train our neural networks with LIGO detector noise at design sensitivity and a lens model that accommodates two overlapping images with a constant $\pi/2$ phase shift. We show that the lensing parameters are recovered with millisecond precision for the time delays. We also demonstrate that our network can identify signals diffracted by point masses, highlighting its flexibility for searches. By simulating thousands of lensed and nonlensed events, we determine how the detectability changes with different source properties. DINGO-lensing provides a scalable and efficient avenue for identifying and characterizing gravitationally lensed GW events in the upcoming observing runs.
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All authors Juno C. L. Chan, Lorena Magaña Zertuche, Jose María Ezquiaga, Rico K. L. Lo, Luka Vujeva, Joey Bowman

High Energy Astrophysical Phenomena

Pulse profile modelling of the accretion-powered millisecond pulsar SAX J1808.4-3658 using NICER data from its 2019 and 2022 outbursts

Bas Dorsman, Tuomo Salmi, Anna L. Watts et al. (+5 more)

Pulse profile modelling is a relativistic ray-tracing technique that has provided constraints on parameters, with a focus on mass and radius, of five rotation-powered millisecond pulsars. While the technique can also be applied to accretion-powered millisecond pulsars (AMPs), this requires accounting for the X-rays from the accretion disc and has only been applied to archival data from the Rossi X-ray Timing Explorer. Here, we apply a previously developed neutron star and accretion disc model to the NICER (Neutron star Interior Composition Explorer) data of the 2019 and 2022 outbursts of SAX J1808.4-3658. We find that a single circular hotspot model is insufficient to explain the data. Modelling with two hotspots and an accretion disc model provides better phase-residuals, but a spectral residual at around 1 keV remains. In contrast, we find a good fit with a flexible background approach, replacing the accretion disk. However, the inferred parameters are not robust due to a degeneracy in the origin of the non-pulsed radiation, which can be caused either by the background or a hotspot that is at least partially in view throughout a full rotation. This work represents an important next step in pulse profile modelling of AMPs by analysing NICER data and underlines the need for more accurate accretion disc and hotspot modelling to achieve robust parameter constraints. We expect the inclusion of higher energy and polarimetric data will provide complementary constraints on inclination, hotspot colatitude, and hotspot size, improving the accuracy of pulse profile modelling of AMPs.
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All authors Bas Dorsman, Tuomo Salmi, Anna L. Watts, Mason Ng, Anna Bobrikova, Vladislav Loktev, Juri Poutanen, Joern Wilms