arXiv subjects

Thomas J. Maccarone

Publications and source records attributed to Thomas J. Maccarone.

At least 19 recordsLinked to original sources

arXiv2026

COPAS: Compact Objects and the Physics of Accretion Survey I. Accreting Binaries with P < 83 Minutes

We present the first results from the Compact Objects and the Physics of Accretion Survey (COPAS), a high-cadence photometric survey focused on the detection of accreting white dwarf binaries mainly through their outbursts using TESS. From an initial sample of 2,054 cataclysmic variable (CV) candidates observed during TESS Cycle 6 and 7, we identify 11 systems with periods below 83 minutes. This includes 7 AM CVns and 4 CVs. Our Gemini spectroscopic data confirm ZTF18aaxuusk and ASASSN-21eo as AM CVns, while Gaia21akb is confirmed as a CV. We provide the first period measurements for 6 out of the 11 systems. Complementing our TESS data with ground-based observations, we measured superoutburst recurrence times of approximately one year for the AM CVn systems ASASSN-21in and ZTF18aaxuusk, and 1.8-2.0 years for the short-period CVs ASASSN-18rd and ASASSN-15ev. Using TESS, we also estimate the mass-ratio for ASASSN-19ct (q = 0.05 +/- 0.02), which is consistent with a highly evolved low-mass donor star. Though the number of ultracompact systems detected among the total sample is low (0.54%), and likely the result of observational biases and intrinsic population rareness, the reclassification of 5 systems as AM CVns highlights the importance of continuous monitoring to identify more systems through their outbursts and short periods.

astro-ph.SR↗

arXiv2026

The Lazuli Space Observatory: Architecture & Capabilities

The Lazuli Space Observatory is a 3-meter aperture astronomical facility designed for rapid-response observations and precision astrophysics across visible to near-infrared wavelengths (400-1700 nm bandpass). An off-axis, freeform telescope delivers diffraction-limited image quality (Strehl $>$0.8 at 633 nm) to three instruments across a wide, flat focal plane. The three instruments provide complementary capabilities: a Wide-field Context Camera (WCC) delivers multi-band imaging over a 35' $\times$ 12' footprint with high-cadence photometry; an Integral Field Spectrograph (IFS) provides continuous 400-1700 nm spectroscopy at R $\sim$ 100-500 for stable spectrophotometry; and an ExtraSolar Coronagraph (ESC) enables high-contrast imaging expected to reach raw contrasts of $10^{-8}$ and post-processed contrasts approaching $10^{-9}$. Operating from a 3:1 lunar-resonant orbit, Lazuli will respond to targets of opportunity in under four hours--a programmatic requirement designed to enable routine temporal responsiveness that is unprecedented for a space telescope of this size. Lazuli's technical capabilities are shaped around three broad science areas: (1) time-domain and multi-messenger astronomy, (2) stars and planets, and (3) cosmology. These capabilities enable a potent mix of science spanning gravitational wave counterpart characterization, fast-evolving transients, Type Ia supernova cosmology, high-contrast exoplanet imaging, and spectroscopy of exoplanet atmospheres. While these areas guide the observatory design, Lazuli is conceived as a general-purpose facility capable of supporting a wide range of astrophysical investigations, with open time for the global community. We describe the observatory architecture and capabilities in the preliminary design phase, with science operations anticipated following a rapid development cycle from concept to launch. [Abstract abridged]

astro-ph.IM↗

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 $Γ= 1.4\pm0.1$. In addition, using deep data from the Australia Telescope Compact Array, we show that W41 is a faint ($9.8\pm1.4 μ$Jy at 5.5 GHz) steep spectrum ($α= -1.8\pm0.4$) 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

KL Dra as a Benchmark Laboratory for Accretion-Disk Physics: Constraints from TESS and Ground-Based Surveys

We present the longest-term optical analysis of the AM CVn system KL Dra using $\sim11$ years of monitoring from TESS and wide-field ground-based surveys. The continuous TESS coverage allows us to characterise its frequent outbursts with unprecedented detail, providing the first comprehensive study of an AM CVn during outbursts and enabling detailed modelling of these systems. The superoutbursts in KL Dra generally include a precursor, and are followed by a series of rebrightenings after which a sequence of 3-4 large amplitude normal outbursts is observed. We fit parametric profiles to each superoutburst component (precursor, rise to plateau, plateau, decay), to rebrightenings, and to normal outbursts, which let us quantify every high state feature and investigate correlations with the system's long term supercyle evolution. Our continuous coverage reveals an average value for the supercycles, superoutbursts and normal outbursts of $60.4 \pm 0.1$ d, $5.67\pm0.03$ d and $1.17 \pm0.01$ d, respectively. The supercycle duration may be correlated with the rebrightenings duration and superoutburst amplitude, and anticorrelated with the plateau length. Within a supercycle, normal outbursts grow in amplitude and duration, and the first normal outburst is usually highly asymmetric, while subsequent normal outbursts are more symmetric. We detected superhumps in TESS superoutbursts but not in the rebrightenings or normal outbursts. We interpret the results within the disk instability model, considering additional effects, such as changes in the donor mass transfer rate.

astro-ph.SR↗

arXiv2026

BE Lyncis is not a Black Hole Binary: Lessons From Gaia and Hipparcos Astrometry

BE Lyncis (BE Lyn) is a well-studied high-amplitude $δ$ Scuti variable star (HADS). Recently, Niu et al. (2026) analyzed a 39-year baseline of times of maximum light of BE Lyn, reporting that it is the most eccentric binary known ($e \approx 0.9989$) and hosts the nearest black hole (BH) known to date. We analyze Hipparcos and Gaia astrometry of BE Lyn, predicting what the observed proper motion anomaly (PMA) over the 25 year baseline between the two missions would be were the companion really a $\gtrsim 17.5\,M_{\odot}$ BH. We find that the predicted PMA is at least an order of magnitude larger than the observed value of $\approx 1.7 \pm 0.8$ mas yr$^{-1}$, regardless of the assumed orientation of the orbit. We predict the expected Gaia DR3 RUWE for different orientations of the putative BH binary, finding that it ranges from $\approx 2.5$-$4.0$, much larger than the reported value of $1.073$. The observed value is instead consistent with a low-mass secondary or a single star. We find that BE Lyncis would have received a 7-parameter acceleration solution if it were a BH binary, in contradiction with its absence from the Gaia DR3 non-single star catalogs. Finally, we show that the reported orbit is impossible because the luminous star would overflow its Roche lobe at periastron, irrespective of inclination. We recommend caution in interpreting light-travel time effect (LTTE) models that require very high eccentricities, face-on inclinations, or large companion masses. The observed pulsation timing variations are most likely simply a result of red noise or pulsation phase evolution.

astro-ph.SR↗

arXiv2026

A study of transients from ground-based surveys reveals new ultra-compact accreting white dwarf binaries

AM CVn stars are ultra-compact semi-detached binaries consisting of a white dwarf primary and a hydrogen-depleted secondary. In this paper we present spectroscopic and photometric results of 15 transient sources pre-classified as AM CVn candidates. Our analysis confirms 9 systems of the type AM CVn, 3 hydrogen-rich cataclysmic variables (accreting white dwarfs with near-main-sequence stars for donors) and 3 systems that could be evolved cataclysmic variables. Eight of the AM CVn stars are analysed spectroscopically for the first time, which increases the number of spectroscopically confirmed AM CVns by about $10\%$. TESS data revealed the orbital period of the AM CVn star ASASSN-20pv to be $P_\mathrm{orb}=27.282\,\mathrm{min}$, which helps to constrain the possible values of its mass ratio. TESS also helped to determine the superhump periods of one AM CVn star (ASASSN-19ct, $P_\mathrm{sh}=30.94\,\mathrm{min}$) and two cataclysmic variables we classify as WZ Sge stars ($P_\mathrm{sh}=90.77\,\mathrm{min}$ for ZTF18aaaasnn and $P_\mathrm{sh}=91.6\,\mathrm{min}$ for ASASSN-15na). We identified very different abundances in the spectra of the AM CVns binaries ASASSN-15kf and ASASSN-20pv (both $P_\mathrm{orb}\sim 27.5$ min), suggesting different type of donors. Six of the studied AM CVns are X-ray sources, which helped to determine their mass accretion rates. Photometry shows that the duration of all the superoutbursts detected in the AM CVns is consistent with expectations from the disc instability model. Finally, we provide refined criteria for the identification of new systems using all-sky surveys such as LSST.

astro-ph.SR↗

arXiv2026

Flip-flop states in X-ray binaries and changing-state AGN

We show that the flip-flop transitions in X-ray binaries (rapid cycling between different spectral states which are sometimes seen near the global state transition) show a series of analogies to the changing state phenomena (rapid changes in the emission line properties that seem to be driven by changes in the central engine) in active galactic nuclei (AGN). Specifically, (1) the timescales for the transitions scale approximately linearly with mass and (2) both phenomena occur at a few percent of the Eddington luminosity. Because most accretion physics is expected to be scale-free, it is likely that these represent two manifestations of the same phenomena. Demonstrating this would allow the use of a much wider range of observational techniques, on a much wider range of characteristic timescales, and provide a clearer pathway toward understanding these rapid transitions than is currently available. We discuss potential means to establish the connection more firmly, and to use the combination of the observational advantages of both classes of systems to develop a better understanding of the phenomenon.

astro-ph.HE↗

arXiv2026

4U 1556-60 as a very faint neutron star X-ray binary at 700 pc with an undetected radio jet

4U 1556-60 is a low-mass X-ray binary that was discovered more than 50 years ago as a persistent X-ray source; however, very little was known about it. Recently, Gaia obtained a parallax for the optical counterpart that places 4U 1556-60 at a distance of only about 700 pc, making it one of the closest X-ray binaries known to date. This close distance drastically alters what was previously assumed about the source. We revisit 4U 1556-60 in light of the newly determined distance of 700 pc, reinterpreting its literature and presenting new X-ray and radio observations to better understand various characteristics of the system. We conclude that a scenario in which 4U 1556-60 is a candidate ultracompact neutron star X-ray binary at a distance of ~700 pc is able to explain the observed properties of the source. It resides at a persistent X-ray luminosity of ~2x10^34 erg/s, an unusual value for a typical X-ray binary, but similar to several ultracompact systems. The ratio of the X-ray to optical luminosity is very high, also suggesting a physically small accretion disk. The radio jet is undetected with a very deep upper limit of 3x10^25 erg/s, which is about 10^3 times fainter than the expected black hole jet correlation, strongly indicating a neutron star accretor. The X-ray spectrum is dominated by a power law, and the X-ray timing properties are also consistent with observations of other very low accretion rate X-ray binaries. No spin or orbital periodicity are found in the X-ray data. Future observations, especially to determine its orbital period, will further aid in understanding 4U 1556-60.

astro-ph.HE↗

arXiv2026

A 682-second X-ray Periodicity in CH Cygni: Evidence for a Magnetic White Dwarf

Symbiotic stars are interacting binaries consisting of a red giant and typically a white dwarf, important as potential Type Ia supernova progenitors. Despite theoretical predictions that white dwarfs in symbiotic systems should often be magnetic, direct evidence has been elusive. We report the discovery of a $682.5 \pm 7$ s periodicity in the XMM-Newton X-ray light curve that we interpret as the spin period of the WD in CH Cygni. This detection provides strong evidence for a magnetic white dwarf in CH Cygni, making it only the second WD symbiotic star with confirmed X-ray pulsations after R Aquarii. Our discovery supports the magnetic propeller model previously proposed for CH Cygni's jet activity and state transitions.

astro-ph.HE↗

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 $\sim 11\,μ$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 $γ$-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↗

arXiv2025

The 2024 outburst of the neutron star LMXB EXO 0748-676: an investigation of bursts and eclipses with AstroSat

We present a detailed analysis of the Type-I (thermonuclear) X-ray bursts and eclipses observed from the neutron star low-mass X-ray binary (LMXB) EXO 0748--676 with AstroSat during the second known outburst of the source following a 16-year-long quiescence period. We detect three thermonuclear X-ray bursts, with two displaying simultaneous coverage in the soft X-rays. Simultaneous UV observations show evidence of reprocessed burst emissions in the far-ultraviolet band. The time-resolved spectral analysis reveals the photospheric radius expansion (PRE) nature for two bursts. We estimate the distance to the source to be $7.42\pm0.53$ kpc using the peak flux of PRE. Notably, one of the bursts exhibited a secondary peak, $\sim30$ s after the primary, particularly dominating in the softer X-rays, which reveals a correlation with the evolution of burst hotspot radius with no temperature dependence. The burst properties and corresponding flux values suggest that mixed H/He burning may have fueled the bursts. We also detect evidence of a soft excess during one burst, likely arising from the interaction of the burst photons with the surroundings. We uncover evidence for a hard X-ray deficit during the peak of all bursts and a hard lag of $\sim4$ s, which can be attributed to the Compton cooling of the corona by the burst photons. We also probe the temporal evolution and the energy dependence of the eclipses, which offer insights into the binary environment. Our study helps gain deeper insight into the physics of burst ignition, flame propagation, the burst-accretion interaction, and the evolution of LMXBs.

astro-ph.HE↗

arXiv2025

Catalog of outbursts of neutron star LMXBs

Many X-ray binaries are transiently accreting. Having statistics on their recurrence times is helpful to address questions related to binary evolution and populations, as well as the physics of binary systems. We compile a catalog of known outbursts of 87 transient neutron star (identified through bursts or pulsations) low-mass X-ray binaries, until mid-2025. Most outbursts are taken from the literature, but we also identify some outbursts from public X-ray monitoring lightcurves. We find 109 outbursts not previously identified in the literature; most are from the frequent transients GRS 1747-312 and the Rapid Burster MXB 1730-335, though we suspect that two outbursts from Liller 1 may be from another transient, besides the Rapid Burster. We also find new outbursts for 10 other systems, and verify substantial quiescent intervals for XMM J174457-2850.3, XMMU J174716.1-281048, and AX J1754.2-2754. Outburst detection has been relatively efficient since 1996 for outbursts above $F_X$(2-10)$=3\times10^{-10}$ ergs/s/cm$^2$. While several systems have many known outbursts, 40 of the 87 systems we track have zero or one recorded outburst between 1996 and 2023. This suggests that many faint Galactic Center X-ray binaries may be neutron star X-ray binaries, though we cannot completely rule out the proposition that most neutron star X-ray binaries undergo frequent outbursts below all-sky monitor detection limits.

astro-ph.HE↗

arXiv2025

First X-ray and radio polarimetry of the neutron star low-mass X-ray binary GX 17+2

We report the first polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) Z-source GX 17+2 using the Imaging X-ray Polarimetry Explorer (IXPE) and the Very Large Array (VLA). We find that the X-ray source was polarized at PD = 1.9 +/- 0.3 % (1-sigma errors) with a polarization angle of PA = 11 +/- 4 degree (1-sigma errors). Simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) observations show that the source was in the normal branch (NB) during our IXPE observations. The X-ray spectro-polarimetry results suggest a source geometry comprising an accretion disk component, a Comptonization component, and a reflection component. The VLA radio polarization study shows a PD = 2.2 +/- 0.2 % with a Faraday-corrected intrinsic polarization angle of 1 +/- 5 degree, which is an indication of the jet axis. Thus, we find the estimated X-ray PA from the source is consistent with the radio PA. We discuss the accretion geometry of the Z-source in light of our X-ray spectro-polarimetry and radio findings.

astro-ph.HE↗

arXiv2025

Long term variability of Cygnus X-1. IX. A spectral-timing comparison of Cygnus X-1 and MAXI J1820+070 in the hard state

Cygnus X-1 is a persistent, high-mass black hole X-ray binary (BHXRB) which in the hard state shows many similar properties to transient BHXRBs, along with intriguing differences, such as the lack of quasi-periodic oscillations. Here, we compare for the first time the detailed spectral-timing properties of Cyg X-1 with a transient BHXRB, MAXI J1820+070, combining data from XMM-Newton and NICER with contemporaneous INTEGRAL data to study the power spectra, rms spectra and time-lags over a broad 0.5 - 200 keV range. We select bright hard state MAXI J1820+070 data with similar power-spectral shapes to the Cyg X-1 data, to compare the source behaviours while accounting for the evolution of spectral-timing properties, notably the lags, through the hard state. Cyg X-1 shows no evidence for soft lags in the 1 - 10 Hz frequency range where they are clearly detected for MAXI J1820+070. Furthermore the low-frequency hard lags and rms-spectra evolve much more strongly during the hard state of Cyg X-1 than for MAXI J1820+070. We argue that these differences cannot be explained by the different black hole masses of these systems, but may be related to their different accretion rates and corresponding locations on the hardness-intensity diagram. We conjecture that there is a significant luminosity-dependence of coronal geometry in the hard state of BHXRBs, rather than an intrinsic difference between Cyg X-1 and transient BHXRBs. This possibility has also been suggested to explain a common time-lag feature that appears in the hard intermediate states of Cyg X-1 and transient BHXRBs.

astro-ph.HE↗

arXiv2025

X-ray and radio polarimetry of the neutron star low mass X-ray binary GX 13+1

We report the X-ray and radio polarization study of the neutron star (NS) low-mass X-ray binary (LMXB) GX 13+1 using the Imaging X-ray Polarimetry Explorer (IXPE) and Very Large Array (VLA). Simultaneous Neutron Star Interior Composition Explorer (NICER) observations show that the source was in parts of the Z state during our IXPE observations, exhibiting moderate changes in the hardness intensity diagram. The source exhibits X-ray dips in the light curve along with hints of polarization swings between the dip and non-dip states. The X-ray spectro-polarimetry results suggest a source geometry comprising an accretion disk component representing the softer disk emission, along with a blackbody representing the harder emission from the boundary layer (BL) or a spreading layer (SL). We investigate the geometry of GX 13+1 by considering our X-ray and radio polarization findings.

astro-ph.HE↗

arXiv2025

Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Resolving the Hot and Ionized Universe through the Sunyaev-Zeldovich effect

An omnipresent feature of the multi-phase ``cosmic web'' is that warm/hot (>$10^5$ K) ionized gas pervades it. This gas constitutes a relevant contribution to the overall universal matter budget across multiple scales, from the several tens of Mpc-scale IGM filaments, to the Mpc ICM, all the way down to the CGM surrounding individual galaxies from ~1 kpc up to their respective virial radii (~100 kpc). The study of the hot baryonic component of cosmic matter density represents a powerful means for constraining the intertwined evolution of galactic populations and large-scale cosmological structures, for tracing the matter assembly in the Universe and its thermal history. To this end, the SZ effect provides the ideal observational tool for measurements out to the beginnings of structure formation. The SZ effect is caused by the scattering of the photons from the cosmic microwave background off the hot electrons embedded within cosmic structures, and provides a redshift-independent perspective on the thermal and kinematic properties of the warm/hot gas. Still, current and future (sub)mm facilities have been providing only a partial view of the SZ Universe due to any combination of: limited angular resolution, spectral coverage, field of view, spatial dynamic range, sensitivity. In this paper, we motivate the development of a wide-field, broad-band, multi-chroic continuum instrument for the Atacama Large Aperture Submillimeter Telescope (AtLAST) by identifying the scientific drivers that will deepen our understanding of the complex thermal evolution of cosmic structures. On a technical side, this will necessarily require efficient multi-wavelength mapping of the SZ signal with an unprecedented spatial dynamic range (from arcsecond to tens of arcminutes) and we employ theoretical forecasts to determine the key instrumental constraints for achieving our goals. [abridged]

astro-ph.CO↗

arXiv2025

X-ray and radio polarimetry of the neutron star low-mass X-ray binary 4U 1728-34

We report the first X-ray and radio polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) atoll-source 4U 1728-34 using the Imaging X-ray Polarimetry Explorer (IXPE) and Australia Telescope Compact Array (ATCA). We discovered that the X-ray source was polarized at PD = 1.9 +/- 1.0% with a polarization angle of PA = -41 +/- 16 degree. Simultaneous Neutron Star Interior Composition Explorer (NICER) observations show that the source was in a relatively hard state, marking it as the first IXPE observation of an NS atoll source in the hard state. We do not detect any significant linear polarization (LP) in the radio band, with a 3-sigma upper limit of 2% at 5.5 GHz and 1.8% at 9 GHz. Combining the radio datasets provides the deepest upper limits on the radio polarization at < 1.5% on the linear and circular polarization (measured at 7.25 GHz). The X-ray polarimetric results suggest a source geometry with a Comptonization component possibly attributed to a boundary layer (BL) emission or BL emission reflected off the disk, consistent with the other NS atoll sources.

astro-ph.HE↗

arXiv2025

X-ray polarization study of the neutron star low-mass X-ray binary GX 349+2

We report the first X-ray polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) Z-source GX 349+2 using the Imaging X-ray Polarimetry Explorer (IXPE). We discovered that the X-ray source was polarized at PD = 1.1 +/- 0.3% (1-sigma errors) with a polarization angle of PA = 32 +/- 6 degree (1-sigma errors). Simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) observations show that the source transitioned through the normal branch (NB), flaring branch (FB), and soft apex (SA) of the Z-track during our IXPE observations. The X-ray spectro-polarimetry results suggest a source geometry comprising an accretion disk component, a blackbody representing the emission from the NS surface, and a Comptonized component. We discuss the accretion geometry of the Z source in light of the spectro-polarimetric results.

astro-ph.HE↗