arXiv subjects

Thomas A. Prince

Publications and source records attributed to Thomas A. Prince.

At least 37 records · Page 2Linked to original sources

arXiv2022

Discovery of Two Polars from a Crossmatch of ZTF and the SRG/eFEDS X-ray Catalog

Magnetic CVs are luminous Galactic X-ray sources but have been difficult to find in purely optical surveys due to their lack of outburst behavior. The eROSITA telescope aboard the Spektr-RG (SRG) mission is conducting an all-sky X-ray survey and recently released the public eROSITA Final Equatorial Depth Survey (eFEDS) catalog. We crossmatched the eFEDS catalog with photometry from the Zwicky Transient Facility (ZTF) and discovered two new magnetic cataclysmic variables (CVs). We obtained high-cadence optical photometry and phase-resolved spectroscopy for each magnetic CV candidate and found them both to be polars. Among the newly discovered magnetic CVs is ZTFJ0850+0443, an eclipsing polar with orbital period $P_\textrm{orb} = 1.72$ hr, white dwarf mass $M_\textrm{WD} = 0.81 \pm 0.08 M_\odot$ and accretion rate $\dot{M} \sim 10^{-11} M_\odot$/yr. We suggest that ZTFJ0850+0443 is a low magnetic field strength polar, with $B_\textrm{WD} \lesssim 10$ MG. We also discovered a non-eclipsing polar, ZTFJ0926+0105, with orbital period $P_\textrm{orb} = 1.48$ hr, magnetic field strength $B_\textrm{WD} \gtrsim 26$ MG, and accretion rate $\dot{M} \sim 10^{-12} M_\odot$/yr.

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arXiv2022

A 62-minute orbital period black widow binary in a wide hierarchical triple

Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original "black widow", the 8-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20), high energy emission originating from the pulsar is irradiating and may eventually destroy a low-mass companion. These systems are not only physical laboratories that reveal the dramatic result of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars, allowing for robust tests of the neutron star equation of state. Here, we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate whose optical flux varies by a factor of more than 10. ZTF J1406+1222 pushes the boundaries of evolutionary models, falling below the 80 minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic center, making it a probe of formation channels, neutron star kick physics, and binary evolution.

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arXiv2022

Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations

There is a growing concern about an impact of low-Earth-orbit (LEO) satellite constellations on ground-based astronomical observations, in particular, on wide-field surveys in the optical and infrared. The Zwicky Transient Facility (ZTF), thanks to the large field of view of its camera, provides an ideal setup to study the effects of LEO megaconstellations - such as SpaceX's Starlink - on astronomical surveys. Here, we analyze the archival ZTF observations collected between 2019 November and 2021 September and find 5301 satellite streaks that can be attributed to Starlink satellites. We find that the number of affected images is increasing with time as SpaceX deploys more and more satellites. Twilight observations are particularly affected - a fraction of streaked images taken during twilight has increased from less than 0.5% in late 2019 to 18% in 2021 August. We estimate that once the size of the Starlink constellation reaches 10,000, essentially all ZTF images taken during twilight may be affected. However, despite the increase in satellite streaks observed during the analyzed period, the current science operations of ZTF are not yet strongly affected. We also find that redesigning Starlink satellites (by installing visors intended to block sunlight from reaching the satellite antennas to prevent reflection) reduces their brightness by a factor of 4.6 +/- 0.1 with respect to the original design in g, r, and i bands.

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arXiv2022

Discovery of a double detonation thermonuclear supernova progenitor

We present the discovery of a new double detonation progenitor system consisting of a hot subdwarf B (sdB) binary with a white dwarf companion with an P=76.34179(2) min orbital period. Spectroscopic observations are consistent with an sdB star during helium core burning residing on the extreme horizontal branch. Chimera light curves are dominated by ellipsoidal deformation of the sdB star and a weak eclipse of the companion white dwarf. Combining spectroscopic and light curve fits we find a low mass sdB star, $M_{\rm sdB}=0.383\pm0.028$ M$_\odot$ with a massive white dwarf companion, $M_{\rm WD}=0.725\pm0.026$ M$_\odot$. From the eclipses we find a blackbody temperature for the white dwarf of 26,800 K resulting in a cooling age of $\approx$25 Myrs whereas our MESA model predicts an sdB age of $\approx$170 Myrs. We conclude that the sdB formed first through stable mass transfer followed by a common envelope which led to the formation of the white dwarf companion $\approx$25 Myrs ago. Using the MESA stellar evolutionary code we find that the sdB star will start mass transfer in $\approx$6 Myrs and in $\approx$60 Myrs the white dwarf will reach a total mass of $0.92$ M$_\odot$ with a thick helium layer of $0.17$ M$_\odot$. This will lead to a detonation that will likely destroy the white dwarf in a peculiar thermonuclear supernova. PTF1 2238+7430 is only the second confirmed candidate for a double detonation thermonuclear supernova. Using both systems we estimate that at least $\approx$1% of white dwarf thermonuclear supernovae originate from sdB+WD binaries with thick helium layers, consistent with the small number of observed peculiar thermonuclear explosions.

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arXiv2021

Microlensing Events in the Galactic Plane Using the Zwicky Transient Facility

Microlensing is a powerful technique to study the Galactic population of "dark" objects such as exoplanets both bound and unbound, brown dwarfs, low-luminosity stars, old white dwarfs, neutron stars, and almost the only way to study isolated stellar-mass black holes. The majority of previous efforts to search for gravitational microlensing events have concentrated towards high-density fields such as the Galactic bulge. Microlensing events in the Galactic plane have the advantage of closer proximity and better constrained relative proper motions, leading to better constrained lens mass estimates at the expense of a lower optical depth compared to events towards the Galactic bulge. We use the Zwicky Transient Facility (ZTF) Data Release 5 (DR5) compiled from 2018--2021 to survey the Galactic plane in the region of $|b| < 20^\circ$. We find a total of 60 candidate microlensing events including three that show a strong microlensing parallax effect. The rate of events traces Galactic structure, decreasing exponentially as a function Galactic longitude with scale length $\ell_0 \sim 37^\circ$. On average, we find Einstein timescales of our microlensing events to be about three times as long ($\sim60$ days) compared to those towards the Galactic bulge ($\sim20$ days). This pilot project demonstrates that microlensing towards the Galactic plane shows strong promise for characterization of dark objects within the Galatic disk.

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arXiv2021

A Bright Fast Radio Burst from FRB 20200120E with Sub-100-Nanosecond Structure

We present the detection of a bright radio burst at radio frequencies between 2.2--2.3 GHz with the NASA Deep Space Network (DSN) 70 m dish (DSS-63) in Madrid, Spain from FRB~20200120E. This repeating fast radio burst (FRB) was recently discovered by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) instrument and reported to be associated with the M81 spiral galaxy at a distance of 3.6 Mpc. The high time resolution capabilities of the recording system used in this observation, together with the small amount of scattering and intrinsic brightness of the burst, allow us to explore the burst structure in unprecedented detail. We find that the burst has a duration of roughly 30 $μ$s and is comprised of several narrow components with typical separations of 2--3 $μ$s. The narrowest component has a width of $\lesssim$ 100 ns, which corresponds to a light travel time size as small as 30 m, the smallest associated with an FRB to date. The peak flux density of the narrowest burst component is 270 Jy. We estimate the total spectral luminosity of the narrowest component of the burst to be 4 $\times$ 10$^{\text{30}}$ erg s$^{\text{-1}}$ Hz$^{\text{-1}}$, which is a factor of $\sim$500 above the luminosities of the so-called "nanoshots" associated with giant pulses from the Crab pulsar. This spectral luminosity is also higher than that of the radio bursts detected from the Galactic magnetar SGR 1935+2154 during its outburst in April 2020, but it falls on the low-end of the currently measured luminosity distribution of extragalatic FRBs. These results provide further support for the presence of a continuum of FRB burst luminosities.

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arXiv2021

Multi-wavelength Observations of AT2019wey: a New Candidate Black Hole Low-mass X-ray Binary

AT2019wey (SRGA J043520.9+552226, SRGE J043523.3+552234) is a transient first reported by the ATLAS optical survey in 2019 December. It rose to prominence upon detection, three months later, by the Spektrum-Roentgen-Gamma (SRG) mission in its first all-sky survey. X-ray observations reported in Yao et al. suggest that AT2019wey is a Galactic low-mass X-ray binary (LMXB) with a black hole (BH) or neutron star (NS) accretor. Here we present ultraviolet, optical, near-infrared, and radio observations of this object. We show that the companion is a short-period (P < 16 hr) low-mass (< 1 Msun) star. We consider AT2019wey to be a candidate BH system since its locations on the L_radio--L_X and L_opt--L_X diagrams are closer to BH binaries than NS binaries. We demonstrate that from 2020 June to August, despite the more than 10 times brightening at radio and X-ray wavelengths, the optical luminosity of AT2019wey only increased by 1.3--1.4 times. We interpret the UV/optical emission before the brightening as thermal emission from a truncated disk in a hot accretion flow and the UV/optical emission after the brightening as reprocessing of the X-ray emission in the outer accretion disk. AT2019wey demonstrates that combining current wide-field optical surveys and SRG provides a way to discover the emerging population of short-period BH LMXB systems with faint X-ray outbursts.

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arXiv2021

A highly magnetised and rapidly rotating white dwarf as small as the Moon

White dwarfs represent the last stage of evolution of stars with mass less than about eight times that of the Sun and, like other stars, are often found in binaries. If the orbital period of the binary is short enough, energy losses from gravitational-wave radiation can shrink the orbit until the two white dwarfs come into contact and merge. Depending on the component masses, the merger can lead to a supernova of type Ia or result in a massive white dwarf. In the latter case, the white dwarf remnant is expected to be highly magnetised because of the strong magnetic dynamo that should arise during the merger, and be rapidly spinning from the conservation of the orbital angular momentum. Here we report observations of a white dwarf, ZTF J190132.9+145808.7, that exhibits these properties, but to an extreme: a rotation period of 6.94 minutes, a magnetic field ranging between 600 megagauss and 900 megagauss over its surface, and a stellar radius of about 2,100 km, slightly larger than the radius of the Moon. Such a small radius implies that the star's mass is close to the maximum white-dwarf mass, or Chandrasekhar mass. ZTF J190132.9+145808.7 is likely to be cooling through the Urca processes (neutrino emission from electron capture on sodium) because of the high densities reached in its core.

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arXiv2021

ZTFJ0038+2030: a long period eclipsing white dwarf and a substellar companion

In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with a dark, substellar companion. The lack of an infrared excess and an orbital period of 10 hours made this a potential exoplanet candidate. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of $0.50\pm0.02\,\mathrm{M_{\odot}}$ and a temperature of $10900\pm200\,$K. The companion has a mass of $0.059\pm0.004\,\mathrm{M_{\odot}}$ and a small radius of $0.0783\pm0.0013\,\mathrm{R_{\odot}}$. It is one of the smallest transiting brown dwarfs known and likely old, $\gtrsim 8\,$Gyr. The ZTF discovery efficiency of substellar objects transiting white dwarfs is limited by the number of epochs and as ZTF continues to collect data we expect to find more of these systems. This will allow us to measure period and mass distributions and allows us to understand the formation channels of white dwarfs with substellar companions.

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arXiv2021

A systematic search for outbursting AM CVn systems with the Zwicky Transient Facility

AM CVn systems are a rare type of accreting binary that consists of a white dwarf and a helium-rich, degenerate donor star. Using the Zwicky Transient Facility (ZTF), we searched for new AM CVn systems by focusing on blue, outbursting stars. We first selected outbursting stars using the ZTF alerts. We cross-matched the candidates with $Gaia$ and Pan-STARRS catalogs. The initial selection of candidates based on the $Gaia$ $BP$-$RP$ contains 1751 unknown objects. We used the Pan-STARRS $g$-$r$ and $r$-$i$ color in combination with the $Gaia$ color to identify 59 high-priority candidates. We obtained identification spectra of 35 sources, of which 18 are high priority candidates, and discovered 9 new AM CVn systems and one magnetic CV which shows only He-II lines. Using the outburst recurrence time, we estimate the orbital periods which are in the range of 29 to 50 minutes. We conclude that targeted followup of blue, outbursting sources is an efficient method to find new AM CVn systems, and we plan to followup all candidates we identified to systematically study the population of outbursting AM CVn systems.

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arXiv2021

Year 1 of the ZTF high-cadence Galactic Plane Survey: Strategy, goals, and early results on new single-mode hot subdwarf B-star pulsators

We present the goals, strategy and first results of the high-cadence Galactic plane survey using the Zwicky Transient Facility (ZTF). The goal of the survey is to unveil the Galactic population of short-period variable stars, including short period binaries and stellar pulsators with periods less than a few hours. Between June 2018 and January 2019, we observed 64 ZTF fields resulting in 2990 deg$^2$ of high stellar density in ZTF-$r$ band along the Galactic Plane. Each field was observed continuously for 1.5 to 6 hrs with a cadence of 40 sec. Most fields have between 200 and 400 observations obtained over 2-3 continuous nights. As part of this survey we extract a total of $\approx$230 million individual objects with at least 80 epochs obtained during the high-cadence Galactic Plane survey reaching an average depth of ZTF-$r$ $\approx$20.5 mag. For four selected fields with 2 million to 10 million individual objects per field we calculate different variability statistics and find that $\approx$1-2% of the objects are astrophysically variable over the observed period. We present a progress report on recent discoveries, including a new class of compact pulsators, the first members of a new class of Roche Lobe filling hot subdwarf binaries as well as new ultracompact double white dwarfs and flaring stars. Finally we present a sample of 12 new single-mode hot subdwarf B-star pulsators with pulsation amplitudes between ZTF-$r$ = 20-76 mmag and pulsation periods between $P$ = 5.8-16 min with a strong cluster of systems with periods $\approx$ 6 min. All of the data have now been released in either ZTF Data Release 3 or data release 4.

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arXiv2021

Tails: Chasing Comets with the Zwicky Transient Facility and Deep Learning

We present Tails, an open-source deep-learning framework for the identification and localization of comets in the image data of the Zwicky Transient Facility (ZTF), a robotic optical time-domain survey currently in operation at the Palomar Observatory in California, USA. Tails employs a custom EfficientDet-based architecture and is capable of finding comets in single images in near real time, rather than requiring multiple epochs as with traditional methods. The system achieves state-of-the-art performance with 99% recall, 0.01% false positive rate, and 1-2 pixel root mean square error in the predicted position. We report the initial results of the Tails efficiency evaluation in a production setting on the data of the ZTF Twilight survey, including the first AI-assisted discovery of a comet (C/2020 T2) and the recovery of a comet (P/2016 J3 = P/2021 A3).

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arXiv2021

The ZTF Source Classification Project: I. Methods and Infrastructure

The Zwicky Transient Facility (ZTF) has been observing the entire northern sky since the start of 2018 down to a magnitude of 20.5 ($5 σ$ for 30s exposure) in $g$, $r$, and $i$ filters. Over the course of two years, ZTF has obtained light curves of more than a billion sources, each with 50-1000 epochs per light curve in $g$ and $r$, and fewer in $i$. To be able to use the information contained in the light curves of variable sources for new scientific discoveries, an efficient and flexible framework is needed to classify them. In this paper, we introduce the methods and infrastructure which will be used to classify all ZTF light curves. Our approach aims to be flexible and modular and allows the use of a dynamical classification scheme and labels, continuously evolving training sets, and the use of different machine learning classifier types and architectures. With this setup, we are able to continuously update and improve the classification of ZTF light curves as new data becomes available, training samples are updated, and new classes need to be incorporated.

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arXiv2020

Multiwavelength Radio Observations of Two Repeating Fast Radio Burst Sources: FRB 121102 and FRB 180916.J0158+65

The spectra of fast radio bursts (FRBs) encode valuable information about the source's local environment, underlying emission mechanism(s), and the intervening media along the line of sight. We present results from a long-term multiwavelength radio monitoring campaign of two repeating FRB sources, FRB 121102 and FRB 180916.J0158+65, with the NASA Deep Space Network (DSN) 70-m radio telescopes (DSS-63 and DSS-14). The observations of FRB 121102 were performed simultaneously at 2.3 and 8.4 GHz, and spanned a total of 27.3 hr between 2019 September 19 and 2020 February 11. We detected 2 radio bursts in the 2.3 GHz frequency band from FRB 121102, but no evidence of radio emission was found at 8.4 GHz during any of our observations. We observed FRB 180916.J0158+65 simultaneously at 2.3 and 8.4 GHz, and also separately in the 1.5 GHz frequency band, for a total of 101.8 hr between 2019 September 19 and 2020 May 14. Our observations of FRB 180916.J0158+65 spanned multiple activity cycles during which the source was known to be active and covered a wide range of activity phases. Several of our observations occurred during times when bursts were detected from the source between 400-800 MHz with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope. However, no radio bursts were detected from FRB 180916.J0158+65 at any of the frequencies used during our observations with the DSN radio telescopes. We find that FRB 180916.J0158+65's apparent activity is strongly frequency-dependent due to the narrowband nature of its radio bursts, which have less spectral occupancy at high radio frequencies ($\gtrsim$ 2 GHz). We also find that fewer or fainter bursts are emitted from the source at high radio frequencies. We discuss the implications of these results on possible progenitor models of repeating FRBs.

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arXiv2020

An 8.8 minute orbital period eclipsing detached double white dwarf binary

We report the discovery of ZTF J2243+5242, an eclipsing double white dwarf binary with an orbital period of just $8.8$ minutes, the second known eclipsing binary with an orbital period less than ten minutes. The system likely consists of two low-mass white dwarfs, and will merge in approximately 400,000 years to form either an isolated hot subdwarf or an R Coronae Borealis star. Like its $6.91\, \rm min$ counterpart, ZTF J1539+5027, ZTF J2243+5242 will be among the strongest gravitational wave sources detectable by the space-based gravitational-wave detector The Laser Space Interferometer Antenna (LISA) because its gravitational-wave frequency falls near the peak of LISA's sensitivity. Based on its estimated distance of $d=2120^{+131}_{-115}\,\rm pc$, LISA should detect the source within its first few months of operation, and should achieve a signal-to-noise ratio of $87\pm5$ after four years. We find component masses of $M_A= 0.349^{+0.093}_{-0.074}\,M_\odot$ and $M_B=0.384^{+0.114}_{-0.074}\,M_\odot$, radii of $R_A=0.0308^{+0.0026}_{-0.0025}\,R_\odot$ and $R_B = 0.0291^{+0.0032}_{-0.0024}\,R_\odot$, and effective temperatures of $T_A=22200^{+1800}_{-1600}\,\rm K$ and $T_B=16200^{+1200}_{-1000}\,\rm K$. We determined all of these properties, and the distance to this system, using only photometric measurements, demonstrating a feasible way to estimate parameters for the large population of optically faint ($r>21 \, m_{\rm AB}$) gravitational-wave sources which the Vera Rubin Observatory (VRO) and LISA should identify.

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arXiv2020

The ZTF Source Classification Project: II. Periodicity and variability processing metrics

The current generation of all-sky surveys is rapidly expanding our ability to study variable and transient sources. These surveys, with a variety of sensitivities, cadences, and fields of view, probe many ranges of timescale and magnitude. Data from the Zwicky Transient Facility (ZTF) yields an opportunity to find variables on timescales from minutes to months. In this paper, we present the codebase, ztfperiodic, and the computational metrics employed for the catalogue based on ZTF's Second Data Release. We describe the publicly available, graphical-process-unit optimized period-finding algorithms employed, and highlight the benefit of existing and future graphical-process-unit clusters. We show how generating metrics as input to catalogues of this scale is possible for future ZTF data releases. Further work will be needed for future data from the Vera C. Rubin Observatory's Legacy Survey of Space and Time.

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arXiv2020

A Dual-band Radio Observation of FRB 121102 with the Deep Space Network and the Detection of Multiple Bursts

The spectra of repeating fast radio bursts (FRBs) are complex and time-variable, sometimes peaking within the observing band and showing a fractional emission bandwidth of about 10-30%. These spectral features may provide insight into the emission mechanism of repeating fast radio bursts, or they could possibly be explained by extrinsic propagation effects in the local environment. Broadband observations can better quantify this behavior and help to distinguish between intrinsic and extrinsic effects. We present results from a simultaneous 2.25 and 8.36 GHz observation of the repeating FRB 121102 using the 70 m Deep Space Network (DSN) radio telescope, DSS-43. During the 5.7 hr continuous observing session, we detected 6 bursts from FRB 121102, which were visible in the 2.25 GHz frequency band. However, none of these bursts were detected in the 8.36 GHz band, despite the larger bandwidth and greater sensitivity in the higher-frequency band. This effect is not explainable by Galactic scintillation and, along with previous multi-band experiments, clearly demonstrates that apparent burst activity depends strongly on the radio frequency band that is being observed.

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arXiv2020

A systematic search of Zwicky Transient Facility data for ultracompact binary LISA-detectable gravitational-wave sources

Using photometry collected with the Zwicky Transient Facility (ZTF), we are conducting an ongoing survey for binary systems with short orbital periods ($P_{\rm b}<1\rm \,hr)$ with the goal of identifying new gravitational-wave sources detectable by the upcoming Laser Interferometer Space Antenna (LISA). Here, we present a sample of fifteen binary systems discovered thus far, with orbital periods ranging from $6.91\rm\,min$ to $56.35\rm\,min$. Of the fifteen systems, seven are eclipsing systems which do not show signs of significant mass transfer. Additionally, we have discovered two AM Canum Venaticorum (AM CVn) systems and six systems exhibiting primarily ellipsoidal variations in their light curves. We present follow-up spectroscopy and high-speed photometry confirming the nature of these systems, estimates of their LISA signal-to-noise ratios (SNR), and a discussion of their physical characteristics.

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