50 research outputs found
Zwicky Transient Facility and Globular Clusters: the gr-Band Period-Luminosity Relations for Mira Variables at Maximum Light and Their Applications to Local Galaxies
Based on 14 Miras located in 7 globular clusters, we derived the first
gr-band period-luminosity (PL) at maximum light for the large-amplitude Mira
variables using the multi-year light-curve data collected from the Zwicky
Transient Facility (ZTF). Since Miras are red variables, we applied a
color-term correction to subsets of ZTF light curves, and found that such
corrections do not have a large impact on period determinations. We applied our
derived PL relations to the known extragalactic Miras in five local galaxies
(Sextans, Leo I, Leo II, NGC6822 and IC1613), and determined their Mira-based
distances. We demonstrated that our PL relations can be applied to short-period
(<300 days) Miras, including those in the two most distant galaxies (NGC6822
and IC1613) in our sample even when only a portion of the light-curves around
maximum light have detections. We have also shown that the long-period
extragalactic Miras do not follow the PL relations extrapolated to longer
periods. Hence, our derived PL relations are only applicable to the
short-period Miras, which will be discovered in abundance in local galaxies
within the era of Vera C. Rubin Observatory's Legacy Survey of Space and Time.Comment: 12 pages, 2 Tables and 10 Figures, AJ accepte
Zwicky Transient Facility and Globular Clusters: Calibration of the gr-Band Absolute Magnitudes for the Yellow Post-Asymptotic-Giant-Branch Stars
We present the first absolute calibration for the yellow
post-asymptotic-giant-branch (PAGB) stars in the g- and r-band based on
time-series observations from the Zwicky Transient Facility. These absolute
magnitudes were calibrated using four yellow PAGB stars (one non-varying star
and three Type II Cepheids) located in the globular clusters. We provide two
calibrations of the gr-band absolute magnitudes for the yellow PAGB stars, by
using an arithmetic mean and a linear regression. We demonstrate that the
linear regression provides a better fit to the g-band absolute magnitudes for
the yellow PAGB stars. These calibrated gr-band absolute magnitudes have a
potential to be used as population II distance indicators in the era of
time-domain synoptic sky surveys.Comment: 6 pages, 3 Figures and 1 Table; AJ accepte
Microlensing Events in Five Years of Photometry from the Zwicky Transient Facility
Microlensing has a unique advantage for detecting dark objects in the Milky
Way, such as free floating planets, neutron stars, and stellar-mass black
holes. Most microlensing surveys focus towards the Galactic bulge, where higher
stellar density leads to a higher event rate. However, microlensing events in
the Galactic plane are closer, and take place over longer timescales. This
enables a better measurement of the microlensing parallax, which serves as an
independent constraint on the mass of the dark lens. In this work, we
systematically searched for microlensing events in Zwicky Transient Facility
(ZTF) Data Release 17 from 2018--2023 in the Galactic plane region . We find 124 high-confidence microlensing events and 54 possible
events. In the event selection, we use the efficient \texttt{EventFinder}
algorithm to detect microlensing signals, which could be used for large
datasets such as future ZTF data releases or data from the Rubin Observatory
Legacy Survey of Space and Time (LSST). With detection efficiencies of ZTF
fields from catalog-level simulations, we calculate the mean Einstein timescale
to be days, smaller than previous
results of the Galactic plane to within 1.5-. We calculate optical
depths and event rates, which we interpret with caution due to the use of
visual inspection in creating our final sample. With two years of additional
ZTF data in DR17, we have more than doubled the amount of microlensing events
(60) found in the three-year DR5 search and found events with longer Einstein
timescales than before.Comment: 9 figures, 3 tables. Submitted to Ap
VLASS tidal disruption events with optical flares I: the sample and a comparison to optically-selected TDEs
In this work, we use the Jansky VLA Sky Survey (VLASS) to compile the first
sample of six radio-selected tidal disruption events (TDEs) with transient
optical counterparts. While we still lack the statistics to do detailed
population studies of radio-selected TDEs, we use these events to suggest
trends in host galaxy and optical light curve properties that may correlate
with the presence of radio emission, and hence can inform optically-selected
TDE radio follow-up campaigns. We find that radio-selected TDEs tend to have
faint and cool optical flares, as well as host galaxies with low SMBH masses.
Our radio-selected TDEs also tend to have more energetic, larger radio emitting
regions than radio-detected, optically-selected TDEs. We consider possible
explanations for these trends, including by invoking super-Eddington accretion
and enhanced circumnuclear media. Finally, we constrain the radio-emitting TDE
rate to be Gpc yr.Comment: 26 pages, 5 tables, 11 figures, submitted to Ap
Panic at the ISCO: the visible accretion disks powering optical variability in ZTF AGN
About 3-10% of Type I active galactic nuclei (AGN) have double-peaked broad
Balmer lines in their optical spectra originating from the motion of gas in
their accretion disk. Double-peaked profiles arise not only in AGN, but
occasionally appear during optical flares from tidal disruption events and
changing-state AGN. In this paper we identify 250 double-peaked emitters (DPEs)
amongst a parent sample of optically variable broad-line AGN in the Zwicky
Transient Facility (ZTF) survey, corresponding to a DPE fraction of 19%. We
model spectra of the broad H alpha emission line regions and provide a catalog
of the fitted accretion disk properties for the 250 DPEs. Analysis of power
spectra derived from the 5 year ZTF light curves finds that DPEs have similar
amplitudes and power law indices to other broad-line AGN, but have lower
turnover frequencies. Follow-up spectroscopy of 12 DPEs reveals that ~50%
display significant changes in the relative strengths of their red and blue
peaks over long 10-20 year timescales, indicating that broad-line profile
changes arising from spiral arm or hotspot rotation are common amongst
optically variable DPEs. Analysis of the accretion disk parameters derived from
spectroscopic modeling provides evidence that DPEs are not in a special
accretion state, but are simply normal broad-line AGN viewed under the right
conditions for the accretion disk to be easily visible. We compare the radio
variability properties of the two samples and present radio jet imaging of 3
DPEs with disks of inclination angle 14-35 degrees. We discuss some objects
with notable light curves or unusual broad line profiles which are outliers
amongst the variable DPE population. We include inspiraling SMBH binary
candidate SDSSJ1430+2303 in our analysis, and discuss how its photometric and
spectroscopic variability is consistent with the disk-emitting AGN population
in ZTF.Comment: Submitted to ApJ. 30 pages, 10 figures, 4 tables. Comments welcome
Early-time spectroscopic modelling of the transitional Type Ia Supernova 2021rhu with TARDIS
An open question in SN Ia research is where the boundary lies between
'normal' Type Ia supernovae (SNe Ia) that are used in cosmological measurements
and those that sit off the Phillips relation. We present the spectroscopic
modelling of one such '86G-like' transitional SN Ia, SN 2021rhu, that has
recently been employed as a local Hubble Constant calibrator using a tip of the
red-giant branch measurement. We detail its modelling from -12 d until maximum
brightness using the radiative-transfer spectral-synthesis code tardis. We base
our modelling on literature delayed-detonation and deflagration models of
Chandrasekhar mass white dwarfs, as well as the double-detonation models of
sub-Chandrasekhar mass white dwarfs. We present a new method for 'projecting'
abundance profiles to different density profiles for ease of computation. Due
to the small velocity extent and low outer densities of the W7 profile, we find
it inadequate to reproduce the evolution of SN 2021rhu as it fails to match the
high-velocity calcium components. The host extinction of SN 2021rhu is
uncertain but we use modelling with and without an extinction correction to set
lower and upper limits on the abundances of individual species. Comparing these
limits to literature models we conclude that the spectral evolution of SN
2021rhu is also incompatible with double-detonation scenarios, lying more in
line with those resulting from the delayed detonation mechanism (although there
are some discrepancies, in particular a larger titanium abundance in SN 2021rhu
compared to the literature). This suggests that SN 2021rhu is likely a lower
luminosity, and hence lower temperature, version of a normal SN Ia.Comment: 25 pages, 22 figures, accepted for publication in MNRA
An Optically-Discovered Outburst from XTE J1859+226
Using the Zwicky Transient Facility, in 2021 February we identified the first
known outburst of the Black Hole X-ray Transient XTE J1859+226 since its
discovery in 1999. The outburst was visible at X-ray, UV, and optical
wavelengths for less than 20 days, substantially shorter than its 320-day full
outburst in 1999, and the observed peak luminosity was two orders of magnitude
lower. Its peak bolometric luminosity was only erg s,
implying an Eddington fraction of about . The source remained
in the hard spectral state throughout the outburst. From optical spectroscopy
measurements we estimate an outer disk radius of 10 cm. The low observed
X-ray luminosity is not sufficient to irradiate the entire disk, but we observe
a surprising exponential decline in the X-ray lightcurve. These observations
highlight the potential of optical and infrared (O/IR) synoptic surveys to
discover low-luminosity activity from X-ray transients.Comment: 12 pages, 6 figures, accepted for publication in Ap
An online framework for fitting fast transient light curves
The identification of extragalactic fast optical transients (eFOTs) as potential multimessenger sources is one of the main challenges in time-domain astronomy. However, recent developments have allowed for probes of rapidly evolving transients. With the increasing number of alert streams from optical time-domain surveys, the next paradigm is building technologies to rapidly identify the most interesting transients for follow-up. One effort to make this possible is the fitting of objects to a variety of eFOT light curve models such as kilonovae and γ -ray burst (GRB) afterglows. In this work, we describe a new framework designed to efficiently fit transients to light curve models and flag them for further follow-up. We describe the pipeline’s workflow and a handful of performance metrics, including the nominal sampling time for each model. We highlight as examples ZTF20abwysqy, the shortest long gamma-ray burst discovered to date, and ZTF21abotose, a core-collapse supernova initially identified as a potential kilonova candidate
SRGeJ045359.9+622444: A 55-min Period Eclipsing AM CVn Discovered from a Joint SRG/eROSITA + ZTF Search
AM CVn systems are ultra-compact binaries where a white dwarf accretes from a
helium-rich degenerate or semi-degenerate donor. Some AM CVn systems will be
among the loudest sources of gravitational waves for the upcoming Laser
Interferometer Space Antenna (LISA), yet the formation channel of AM CVns
remains uncertain. We report the study and characterisation of a new eclipsing
AM CVn, SRGeJ045359.9+622444 (hereafter SRGeJ0453), discovered from a joint
SRG/eROSITA and ZTF program to identify cataclysmic variables (CVs). We
obtained optical photometry to confirm the eclipse of SRGeJ0453 and determine
the orbital period to be min. We
constrain the binary parameters by modeling the high-speed photometry and
radial velocity curves and find
and . The X-ray spectrum is
approximated by a power-law model with an unusually flat photon index of
previously seen in magnetic CVs with SRG/eROSITA, but verifying
the magnetic nature of SRGeJ0453 requires further investigation. Optical
spectroscopy suggests that the donor star of SRGeJ0453 could have initially
been a He star or a He white dwarf. SRGeJ0453 is the ninth eclipsing AM CVn
system published to date, and its lack of optical outbursts have made it
elusive in previous surveys. The discovery of SRGeJ0453 using joint X-ray and
optical surveys highlights the potential for discovering similar systems in the
near future.Comment: Submitted to Ap
Searching for late-time interaction signatures in Type Ia supernovae from the Zwicky Transient Facility
The nature of the progenitor systems and explosion mechanisms that give rise
to Type Ia supernovae (SNe Ia) are still debated. The interaction signature of
circumstellar material (CSM) being swept up by expanding ejecta can constrain
the type of system from which it was ejected. Most previous studies have
focused on finding CSM ejected shortly before the SN Ia explosion still
residing close to the explosion site, resulting in short delay times until the
interaction starts. We use a sample of 3627 SNe Ia from the Zwicky Transient
Facility discovered between 2018 and 2020 and search for interaction signatures
over 100 days after peak brightness. By binning the late-time light curve data
to push the detection limit as deep as possible, we identify potential
late-time rebrightening in 3 SNe Ia (SN 2018grt, SN 2019dlf, SN 2020tfc). The
late-time detections occur between 550 and 1450 d after peak brightness, have
mean absolute -band magnitudes of -16.4 to -16.8 mag and last up to a few
hundred days, significantly brighter than the late-time CSM interaction
discovered in the prototype SN 2015cp. The late-time detections all occur
within 0.8 kpc of the host nucleus and are not easily explained by nuclear
activity, another transient at a similar sky position, or data quality issues.
This suggests environment or specific progenitor characteristics playing a role
in producing potential CSM signatures in these SNe Ia. By simulating the ZTF
survey we estimate that <0.5 per cent of normal SNe Ia display late-time strong
H -dominated CSM interaction. This is equivalent to an absolute rate of
to Gpc yr assuming a constant SN
Ia rate of Mpc yr for . Weaker
interaction signatures, more similar to the strength seen in SN 2015cp, could
be more common but are difficult to constrain with our survey depth.Comment: 24 pages, 13 figures, 6 tables, A&A accepte