arXiv subjects

Jay Strader

Publications and source records attributed to Jay Strader.

At least 19 recordsLinked to original sources

arXiv2026

A new likely pulsar binary in 47~Tucanae from continuum searches

We present evidence that the X-ray source 47~Tuc~W41, long considered to be an X-ray source powered by coronal activity, is actually a redback pulsar binary. The source continually shows $L_X = 3 \times 10^{31}$ erg s$^{-1}$ (0.5--10 keV), which is well in excess of the coronal saturation limit for active binaries in quiescence, but is consistent with the intrabinary shock observed in redback pulsars, as is its photon index of $\Gamma = 1.4\pm0.1$. In addition, using deep data from the Australia Telescope Compact Array, we show that W41 is a faint ($9.8\pm1.4 \mu$Jy at 5.5 GHz) steep spectrum ($\alpha = -1.8\pm0.4$) radio continuum source, as expected for a pulsar. Light curve modelling of Hubble Space Telescope photometry shows evidence for ellipsoidal modulation with mild irradiation of a $\sim 0.5$--$0.55 M_{\odot}$ secondary around an invisible companion, also consistent with the redback interpretation. The precise position of W41, along with its well-measured 10.4-hr orbital period, should enable it to be matched to a newly-discovered radio pulsar in future data. Our result shows that close pulsar binaries are still hiding, misclassified among active binaries, even in well-studied clusters like 47 Tuc.

astro-ph.HE↗

arXiv2026

First Results from the LSST Shadow Survey: The Restless Luminous Blue Variable AT2017des in the Virgo-Cluster Galaxy, NGC4532

The Legacy Survey of Space and Time (LSST) will start in late-summer 2026, revolutionizing transient astronomy. Here, we present the Dark Energy Camera (DECam) Shadow Survey, which is designed to maximize the science potential of LSST by shadowing LSST observations of local galaxy-cluster fields, producing a nightly cadence of these fields. The Shadow Survey will discover extremely young supernovae (SNe), SN precursors, as well as other explosive transients and exotic phenomena, helping to characterize such transients at unprecedented cadence and depth when combined with LSST. We describe our workflow, pipeline, public data releases, and candidate vetting. As an early result of Shadow, we present the fitful luminous blue variable (LBV) eruptions of AT2017des in the Virgo-Cluster galaxy NGC4532. AT2017des has short-timescale variability (of order 10 days), peaking at around $M_r=-12.5$mag, brighter than normal LBVs, and similar to the more extreme flaring of hot LBVs/SN impostors such as SN2000ch, AT2016blu, and the precursor activity of SN2009ip. Our spectral time-series reveals features typical of these hot LBVs and SN impostors/precursors. Combining our data with long-baseline photometry from additional observatories, we find that the peaks of the outbursts of AT2017des are getting brighter over time, with 2026 peak fluxes being up to 5 times greater than in 2023 and an average brightening of $\sim0.05$ mag yr$^{-1}$. The peaks of AT2017des are more luminous than those of most other LBVs, only being fainter than bright precursors such as SN2009ip, and extreme SN impostors such as AT2016blu. AT2017des may therefore be ``ramping up'' to a terminal explosion.

astro-ph.HE↗

arXiv2026

A Long Period Stellar-Mass Black Hole Binary in $\omega$ Centauri

Modern simulations of stellar dynamics in globular clusters peg a dominant role for stellar-mass black holes, but direct evidence for black holes in clusters remains limited. We present the discovery of an astrometric stellar-mass black hole--main sequence star binary in $\omega$ Centauri, the most massive Galactic globular cluster, using Hubble Space Telescope data from the oMEGACat project and additional JWST data that span a total of 23 years. The luminous companion to the black hole is a main-sequence turnoff star, and has a period of $94^{+63}_{-42}$ years, a semi-major axis of $31^{+15}_{-12}$ AU, and an eccentricity of $e=0.72^{+0.08}_{-0.13}$. Since we observe the binary during periastron, the mass of the black hole is well-constrained even though we only observe a partial orbit: the inferred black hole mass is $4.46^{+1.22}_{-1.01}$ M$_\odot$. We call this black hole oMEGACat BH-2. This is the first astrometric discovery of a stellar-mass black hole in a globular cluster, and is the longest period black hole binary system yet discovered. The low mass of this black hole is perhaps surprising given the low metallicity of the cluster, and shows that at least some low-mass black holes form at metallicity $Z<10^{-3}$. We find that the binary is almost certainly dynamically formed and is soft, with an expected binary disruption timescale of $\sim$800 Myr. While the total number of black hole binaries in $\omega$ Centauri is uncertain, we show that existing surveys only cover a small area of parameter space, and that the presence of additional detectable black hole binaries is likely.

astro-ph.GA↗

arXiv2026

A systematic survey for hypervelocity runaways from thermonuclear supernovae

The explosion of a white dwarf (WD) in a close binary can launch a surviving runaway star at velocities of $\gtrsim 1000\, \rm km\,s^{-1}$. Such runaways provide a direct probe of thermonuclear supernovae (SNe) in double-degenerate binaries. Several candidate runaways are known, but their evolutionary states and the demographics of the broader population are uncertain. To enable robust population inference, we carry out a systematic survey for hypervelocity runaways with a simple selection function, selecting candidates based on large Gaia-inferred tangential velocities and blue colors. We classify 100% of the resulting 92 candidates using a combination of spectroscopic follow-up and archival data. The search yields ten suspected D$^6$ stars and three LP 40-365 stars. Three D$^6$ stars are new discoveries, including two hot ($T_{\rm eff} > 50,000$ K) objects and one cool ($T_{\rm eff}\approx 7,000$ K) object. We forward-model our survey under several proposed D$^6$ star evolutionary models, coupling each to a Galactic model and the survey selection function. No single model reproduces the observed diversity of D$^6$ stars, which likely reflects a range of remnant masses, ages, and heating mechanisms. Models in which runaway companions are heated by SN shocks alone are too faint and short-lived to explain most of the observed sample, while fully reheated models are too luminous and long-lived. Models with intermediate heating, as occurs in some simulations of violent mergers and partially disrupted remnants, best match the observed magnitude, distance, and kinematic-age distributions. The inferred D$^6$ star birth rate is model dependent, but the models that best match the observed population require rates of only a few percent of the Galactic SN Ia rate, perhaps implying that most SNe Ia result from WD binaries in which both components explode.

astro-ph.SR↗

arXiv2026

Search For a Counterpart to the Subsolar Mass Gravitational Wave Candidate S251112cm

The recent candidate gravitational-wave (GW) alert from a compact object merger involving at least one subsolar mass (SSM) object has prompted questions about their origins. S251112cm is reported by LIGO/Virgo with a false alarm rate of 1 per 6.2 years, nearby luminosity distance $93 \pm 27$ Mpc, and probability of containing a SSM object of 100%. Such a system, if astrophysical, likely did not involve the supersolar neutron stars or black holes invoked to explain kilonovae. One must then also invoke hitherto unobserved and speculative models to produce SSM mergers which may have electromagnetic (EM) counterparts. We introduce a framework which vets and scores candidate counterparts to SSM GW events to inform follow-up in search of any among the zoo of potential EM transients: kilonovae, kilonovae-within-supernovae, super-kilonovae, or AGN flares from binary black hole mergers. We use a suite of telescopes to perform tiling, galaxy-targeted observations, and photometric/spectroscopic follow-up of promising candidates. In near-real time, we ingest candidates reported by the community, including some of the first observations reported by the Vera C. Rubin Observatory. We vet and score a total of 456 candidates, including 67 from Rubin, but find no likely counterpart. We nonetheless highlight candidates which demonstrate the ability of our framework to distinguish between different transient types and describe strategies to maximize the chances of detecting a counterpart to the next SSM event. Our framework will be implemented in the forthcoming Multimessenger Tool for Rapid Object Vetting and Examination (TROVE).

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arXiv2026

The Binary Populations of Stellar Streams are Set by Cluster Dynamics

We present a suite of direct N-body simulations of low mass ($<10^4~M_{\odot}$) globular cluster streams initialized with observationally-motivated binary demographics in order to understand the effect of in-cluster dynamical processing on the stream binary population. The models are initialized with a range of stellar densities and cluster orbits, and Poisson variation in the number of massive and short-lived stars. Wide binaries are disrupted on short timescales by internal tides and on long timescales by two-body encounters. Tides are most important prior to impulsive mass loss-driven cluster expansion. Close binaries ($P_{\rm orb}<10^2~\rm yr$) are most abundant at the stream center due to cluster mass segregation. The wide binary fraction and the degree of binary segregation in the resulting stream are sensitive to the initial cluster density and massive star fraction. In mock radial velocity surveys of the simulated streams, undetectable binaries have velocity amplitudes of $\sim$$0.5$-$1~\rm km~s^{-1}$, adding $\sim0.1~\rm km\ s^{-1}$ of velocity dispersion to the streams, and are dynamically depleted by $\sim10$-$60\%$ compared to the initial binary population. Custom N-body models of Milky Way streams with binaries will allow a holistic understanding of their dynamical structures in advance of upcoming multi-epoch spectroscopic surveys.

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arXiv2026

A Path to an All-Sky Survey with Roman

A deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$\sigma$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint \textit{Gaia}-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.

astro-ph.IM↗

arXiv2026

New Deep Radio Continuum Imaging Still Indicates a Large Reservoir of Undiscovered Millisecond Pulsars in Terzan 5

We present the deepest and highest-resolution radio continuum imaging of the Galactic globular cluster Terzan 5, one of the most crowded locations in the radio sky. In these new 2$-$4 GHz Karl G. Jansky Very Large Array images, we detect 38 of the 49 confirmed pulsars, including extensive multi-frequency eclipse mapping of the luminous redback Ter5A. Nonetheless, there is still a large amount of diffuse residual flux from pulsars that are fainter than our 2.5 GHz continuum detection limit of $\sim 11\,\mu$Jy. Using a range of approaches including image-based simulations, we model the fluxes of the detected pulsars together with the residual flux. We find a minimum total population of $N\sim250$ detectable pulsars in Terzan 5 and perhaps substantially more, though the luminosity function remains very uncertain. Consideration of the $\gamma$-ray properties of the cluster, though also not unambiguous to interpret, leads to consistent conclusions. These pulsar population estimates are larger than inferred from previous work and highlight Terzan 5 as a keystone target for next-generation radio facilities.

astro-ph.HE↗

arXiv2026

The fate of the failed supernova candidate M31-2014-DS1

The fate of massive stars above 20M$_{\odot}$ remains uncertain. Debate persists about whether they die as supernovae (SNe), or if they collapse directly into black holes (BHs) with little or no optical outburst -- so-called ``failed supernovae''. The source M31-2014-DS1 experienced an optical outburst in 2014 and has remained faint at visual wavelengths since then. Due to its persistent faintness, it has been proposed as a failed SN candidate. We present new observations of this candidate obtained using the James Webb Space Telescope (JWST), the Submillimeter Array (SMA), and Chandra. The JWST observations demonstrate that a luminous mid-infrared source persists at the same location a decade after the star faded at visual wavelengths. We model its current spectral energy distribution (SED) as a dust-enshrouded star. No X-ray emission is detected, disfavoring the hypothesis that the late-time luminosity is powered by accretion onto a BH. We find that the remaining source is highly obscured by an asymmetric distribution of circumstellar dust, making it difficult to quantify its physical properties using spherically symmetric radiative transfer codes. The dust geometry requires that the inferred bolometric luminosity is only a lower limit, as a significant fraction of the central source's radiation may escape without being reprocessed by dust. We discuss the implications of these findings in the context of failed SN models and consider the potential overlap with signatures expected from a stellar merger, which also seems to provide a plausible explanation of this source.

astro-ph.SR↗

arXiv2025

No evidence for accretion around the intermediate-mass black hole in Omega Centauri

For over a decade, both theoretical predictions and observational studies have suggested that $\omega$ Centauri ($\omega$ Cen), the most massive Milky Way globular cluster, might harbor an intermediate-mass black hole (IMBH). Recently, identification of fast-moving stars in the core of $\omega$ Cen provided the strongest evidence to date for the presence of such an IMBH. One of the key questions in the study of IMBHs is their accretion efficiency, which determines their radio and X-ray signatures. We investigate the accretion signature of the IMBH in $\omega$ Cen with ultra-deep radio continuum observations of the central region of the cluster. Using approximately 170 hours of Australia Telescope Compact Array observations, we achieve a root mean square noise of 1.1 $\mu$Jy at 7.25 GHz, making this the most sensitive radio image of the cluster to date. We detect no radio emission at any of the proposed centers of the cluster, imposing stringent constraints on the presence of an accreting IMBH in $\omega$ Cen. Considering the fundamental plane of black hole activity, our findings indicate that the accretion efficiency around the black hole is exceptionally low (with a conservative 3-$\sigma$ upper limit of $\epsilon \lesssim 4\times10^{-3}$).

astro-ph.HE↗

arXiv2025

Multiple outflows and delayed ejections revealed by early imaging of novae

Novae are thermonuclear eruptions on accreting white dwarfs in interacting binaries. Although most of the accreted envelope is expelled, the mechanism -- impulsive ejection, multiple outflows or prolonged winds, or a common-envelope interaction -- remains uncertain. GeV $\gamma$-ray detections from $>20$ Galactic novae establish these eruptions as nearby laboratories for shock physics and particle acceleration, underscoring the need to determine how novae eject their envelopes. Here we report on near-infrared interferometry, supported with multiwavelength observations, of two $\gamma$-ray detected novae. The images of the very fast 2021 nova V1674~Her, taken just 2--3 days after discovery, reveal the presence of two perpendicular outflows. The interaction between these outflows likely drives the observed $\gamma$-ray emission. Conversely, the images of the very slow 2021 nova V1405~Cas suggest a delay in the ejection of the bulk of the accreted envelope of more than 50 days after the start of eruption, as the nova slowly rises to visible peak and during which the envelope engulfed the system in a common envelope phase. These unprecedented images offer direct observational evidence that the mechanisms driving mass ejection from the surfaces of accreting white dwarfs are not as simple as previously thought, revealing multiple outflows and delayed ejections.

astro-ph.HE↗

arXiv2025

Optimizing Kilonova Searches: A Case Study of the Type IIb SN 2025ulz in the Localization Volume of the Low-Significance Gravitational Wave Event S250818k

Kilonovae, the ultraviolet/optical/infrared counterparts to binary neutron star mergers, are an exceptionally rare class of transients. Optical follow-up campaigns are plagued by contaminating transients, which may mimic kilonovae, but do not receive sufficient observations to measure the full photometric evolution. In this work, we present an analysis of the multi-wavelength dataset of supernova (SN) 2025ulz, a proposed kilonova candidate following the low-significance detection of gravitational waves originating from the potential binary neutron star merger S250818k. Despite an early rapid decline in brightness, our multi-wavelength observations of SN 2025ulz reveal that it is a type IIb supernova. As part of this analysis, we demonstrate the capabilities of a novel quantitative scoring algorithm to determine the likelihood that a transient candidate is a kilonova, based primarily on its 3D location and light curve evolution. We also apply our scoring algorithm to other transient candidates in the localization volume of S250818k and find that, at all times after the discovery of SN 2025ulz, there are $\geq 4$ candidates with a score comparable to SN 2025ulz, indicating that the kilonova search may have benefited from the additional follow-up of other candidates. During future kilonova searches, this type of scoring algorithm will be useful to rule out contaminating transients in real time, optimizing the use of valuable telescope resources.

astro-ph.HE↗

arXiv2025

Hubble Space Telescope Imaging of Three Isolated Faint Dwarf Galaxies Beyond the Local Group: Pavo, Corvus A, and Kamino

We present new Hubble Space Telescope (HST) imaging of three recently discovered star-forming dwarf galaxies beyond the Local Group: Pavo, Corvus A, and Kamino. The discovery of Kamino is reported here for the first time. They rank among the most isolated faint dwarf galaxies known, hence they provide unique opportunities to study galaxy evolution at the smallest scales, free from environmental effects of more massive galaxies. Our HST data reach $\sim$2-4 magnitudes below the tip of the red giant branch for each dwarf, allowing us to measure their distances, structural properties, and recent star formation histories (SFHs). All three galaxies contain a complex stellar population of young and old stars, and are typical of field galaxies in this mass regime ($M_V=-10.62\pm0.08$ and $D=2.16^{+0.08}_{-0.07}$ Mpc for Pavo, $M_V=-10.91\pm0.10$ and $D=3.34\pm0.11$ Mpc for Corvus A, and $M_V=-12.02\pm0.12$ and $D=6.50^{+0.15}_{-0.11}$ Mpc for Kamino). Our HST-derived SFHs reveal differences among the three dwarfs: Pavo and Kamino show relatively steady, continuous star formation, while Corvus A formed $\sim$$60$% of its stellar mass by 10 Gyr ago. These results align with theoretical predictions of diverse evolutionary pathways for isolated low-mass galaxies.

astro-ph.GA↗

arXiv2025

Near-Discovery SOAR Photometry of the Third Interstellar Object: 3I/ATLAS

3I/ATLAS was discovered on UT 2025 July 1 and joins a limited but growing population of detected $\sim10^2-10^3$ m scale interstellar objects. In this paper we report photometric observations of 3I/ATLAS from the nights of UT 2025 July 3, UT 2025 July 9, and UT 2025 July 10 obtained with the Southern Astrophysical Research Telescope (SOAR). The photometric observations are taken with the Goodman High Throughput Spectrograph (HTS) in the $r'$-band. These data provide 28 photometric data points to the rapidly growing composite light curve of 3I/ATLAS. They reveal that the object did not exhibit obvious long-term variability in its brightness when these observations were taken. These observations appear to have captured two moderate and independent brightening events on UT 2025 July 9, and UT 2025 July 10. However, we perform a series of stellar contamination, stacking, and aperture experiments that demonstrate that the increases in brightness by $\sim0.8$ magnitudes appear to be a result of poor seeing and stellar contamination by close-proximity field stars. We report the mean brightnesses of 3I/ATLAS on each night of magnitude 18.14, 17.55, and 17.54 for UT 2025 July 3, 9, and 10, respectively. Moreover, the presence of cometary activity in extant images obtained contemporaneously with these data precludes them from revealing insights into the rotation of the nucleus. We conclude that the activity of 3I/ATLAS on UT 2025 July 9 and UT July 10 was consistent with the near-discovery activity levels, with no obvious outburst activity.

astro-ph.EP↗

arXiv2025

What determines the $\gamma$-ray luminosities of classical novae?

Classical novae in the Milky Way have now been well-established as high-energy GeV $\gamma$-ray sources. In novae with main-sequence companions, this emission is believed to result from shocks internal to the nova ejecta, as a later fast wind collides with an earlier slow outflow. To test this model and constrain the $\gamma$-ray production mechanism, we present a systematic study of a sample of recent Galactic novae, comparing their $\gamma$-ray properties ($\gamma$-ray luminosity and duration) with their outflow velocities, peak $V$-band magnitudes, and the decline times of their optical light curves ($t_2$). We uniformly estimate distances in a luminosity-independent manner, using spectroscopic reddening estimates combined with three-dimensional Galactic dust maps. Across our sample, $\gamma$-ray luminosities ($>$100 MeV) vary by three orders of magnitude, spanning $10^{34}-10^{37}$ erg s$^{-1}$. Novae with larger velocity of the fast outflow (or larger differential between the fast and slow outflow) have larger $\gamma$-ray luminosities, but are detectable for a shorter duration. The optical and $\gamma$-ray fluxes are correlated, consistent with substantial thermal emission in the optical from shock-heated gas. Across six novae with $\gamma$-ray and infrared light curves, evidence for dust formation appears soon after the end of the detected $\gamma$-ray emission. Dusty and non-dusty novae appear to have similar $\gamma$-ray luminosities, though novae that have more material processed by the shocks may be more likely to form dust. We find that the properties of the $\gamma$-ray emission in novae depend heavily on the ejecta properties, and are consistent with expectations for internal shocks.

astro-ph.HE↗

arXiv2025

The X-ray Source Population of the Metal-Rich Globular Cluster NGC 6528

We present the first study of the X-ray sources in one of the most metal-rich globular clusters in the Galaxy, NGC 6528. Using relatively deep (66 ksec) archival imaging from the Chandra X-ray Observatory, we identify 18 sources within the half-light radius of the cluster, all in the range $L_X \sim 10^{31}$-$10^{32}$erg s$^{-1}$ (0.5-7 keV). By combining these data with photometry from the Hubble Space Telescope and other sources, we classify the X-ray sources as a likely mix of cataclysmic variables and active binaries, though one or more of the brighter objects could be a quiescent low-mass X-ray binary. For this cluster, it appears that the X-ray binary-enhancing effects of high metallicity are outweighed by the cluster's advanced dynamical evolution, leading to a relatively modest X-ray source population.

astro-ph.HE↗

arXiv2025

The Karl G. Jansky Very Large Array Local Group L-band Survey (LGLBS)

We present the Local Group L-Band Survey (LGLBS), a Karl G. Jansky Very Large Array (VLA) survey producing the highest quality 21-cm and 1-2 GHz radio continuum images to date for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA's spectral multiplexing power, we simultaneously survey the 21-cm line at high 0.4 km/s velocity resolution, the 1-2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC6822, IC10, IC1613, and the Wolf-Lundmark-Melotte Galaxy (WLM), we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of $< 5''$ ($10{-}20$~pc) for the 21-cm line with $<10^{20}$~cm$^{-2}$ column density sensitivity, and even sharper views ($< 2''$; $5{-}10$~pc) of the continuum. Targeting these nearby galaxies ($D\lesssim1$ Mpc) reveals a sharp, resolved view of the atomic gas, including 21-cm absorption, and continuum emission from supernova remnants and HII regions. These datasets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21-cm HI data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest physical resolution 21-cm observations of any external galaxies beyond the LMC and SMC.

astro-ph.GA↗

arXiv2025

The NGC3109 Satellite System: The First Systematic Resolved Search for Dwarf Galaxies Around a SMC-mass Host

We report the results of the deepest search to date for dwarf galaxies around NGC3109, a barred spiral galaxy with a mass similar to that of the Small Magellanic Cloud (SMC), using a semi-automated search method. Using the Dark Energy Camera (DECam), we survey a region covering a projected distance of $\sim$70 kpc of NGC 3109 ($D$ = 1.3 Mpc, $R_\mathrm{vir}\sim$ 90 kpc, $M\sim10^8M_\ast$) as part of the MADCASH and DELVE-DEEP programs. Through our resolved and newly designed semi-resolved searches, we successfully recover the known satellites Antlia and Antlia B. We identified a promising candidate, which was later confirmed to be a background dwarf through deep follow-up observations. Our detection limits are well defined, with the sample $\sim 80\%$ complete down to $M_V\sim-$8.0 , and includes detections of dwarf galaxies as faint as $M_V\sim-$6.0. This is the first comprehensive study of a satellite system through resolved star around an SMC mass host. Our results show that NGC 3109 has more bright ($M_V\sim-$9.0) satellites than the mean predictions from cold dark matter (CDM) models, but well within the host-to-host scatter. A larger sample of LMC/SMC-mass hosts is needed to test whether or not the observations are consistent with current model expectations.

astro-ph.GA↗