33 research outputs found
Fundamental scaling relationships revealed in the optical light curves of tidal disruption events
We present fundamental scaling relationships between properties of the
optical/UV light curves of tidal disruption events (TDEs) and the mass of the
black hole that disrupted the star. We have uncovered these relations from the
late-time emission of TDEs. Using a sample of 63 optically-selected TDEs, the
latest catalog to date, we observed flattening of the early-time emission into
a near-constant late-time plateau for at least two-thirds of our sources.
Compared to other properties of the TDE lightcurves (e.g., peak luminosity or
decay rate) the plateau luminosity shows the tightest correlation with the
total mass of host galaxy (-value of , with a residual
scatter of 0.3 dex). Physically this plateau stems from the presence of an
accretion flow. We demonstrate theoretically and numerically that the amplitude
of this plateau emission is strongly correlated with black hole mass. By
simulating a large population of TDEs, we determine a plateau luminosity-black
hole mass scaling relationship well described by . The observed plateau
luminosities of TDEs and black hole masses in our large sample are in excellent
agreement with this simulation. Using the black hole mass predicted from the
observed TDE plateau luminosity, we reproduce the well-known scaling relations
between black hole mass and galaxy velocity dispersion. The large black hole
masses of 10 of the TDEs in our sample allow us to provide constraints on their
black hole spins, favouring rapidly rotating black holes. We add 49 (34) black
hole masses to the galaxy mass (velocity dispersion) scaling relationships,
updating and extending these correlations into the low black hole mass regime.Comment: 24 pages + appendices, 20 figures. Submitted to MNRAS, comments
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A systematic analysis of the X-ray emission in optically selected tidal disruption events: observational evidence for the unification of the optically and X-ray selected populations
We present a systematic analysis of the X-ray emission of a sample of 17
optically selected, X-ray-detected tidal disruption events (TDEs) discovered
between 2014 and 2021. The X-ray light curves show a diverse range of temporal
behaviors, with most sources not following the expected power-law decline. The
X-ray spectra are mostly extremely soft and consistent with thermal emission
from the inner region of an accretion disk that cools as the accretion rate
decreases. Three sources show the formation of a hard X-ray corona around 200
days after the UV/optical peak. The shape of the spectral energy distribution,
traced by the ratio () between the UV/optical and X-ray
luminosities, shows a wide range at
early-times, and converges to disk-like values at late-times. The evolution of the derived physical parameters favors a
decrease in the optical depth of a reprocessing layer instead of delayed disk
formation to explain the late-time X-ray brightening found in several sources.
We estimate the fraction of optically discovered TDEs with erg s to be at least , and find that the X-ray loudness
is independent of black hole mass. We combine our sample with those from X-ray
surveys to construct an X-ray luminosity function, best fitted by a broken
power-law with a brake at erg s. We show that there is no
dichotomy between optically and X-ray selected TDEs; instead, there is a
continuum of early time , at least as wide as , with optical/X-ray surveys selecting
preferentially, but not exclusively, from the higher/lower end of the
distribution. Our findings are consistent with an orientation-dependent and
time-evolving reprocessing layer, and support viewing-angle unification models.Comment: 38 pages, 23 figures, submitted to Ap
Integral Field Spectroscopy of 13 Tidal Disruption Event Hosts from the ZTF Survey
The host galaxies of tidal disruption events (TDEs) have been shown to
possess peculiar properties, including high central light concentrations,
unusual star-formation histories, and ``green'' colors. The ubiquity of these
large-scale galaxy characteristics among TDE host populations suggests they may
serve to boost the TDE rate in such galaxies by influencing the nuclear stellar
dynamics. We present the first population study of integral field spectroscopy
for thirteen TDE host galaxies across all spectral classes and X-ray
brightnesses with the purpose of investigating their large-scale properties. We
derive the black hole masses via stellar kinematics (i.e., the
relation) and find masses in the range , with a distribution dominated by black holes with . We find one object with ,
above the ``Hills mass'', which if the disrupted star was of solar type, allows
a lower limit of to be placed on its spin, lending further
support to the proposed connection between featureless TDEs and jetted TDEs. We
also explore the level of rotational support in the TDE hosts, quantified by
, a parameter which has been shown to correlate with stellar age
and may explain the peculiar host galaxy preferences of TDEs. We find that the
TDE hosts exhibit a broad range in following a similar
distribution as E+A galaxies, which have been shown to be overrepresented among
TDE host populations.Comment: 18 pages, 11 figures, 4 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
The first systematically identified repeating partial tidal disruption event
Tidal disruption events (TDEs) occur when a star enters the tidal radius of a
supermassive black hole (SMBH). If the star only grazes the tidal radius, a
fraction of the stellar mass will be accreted in a partial TDE (pTDE). The
remainder can continue orbiting and may re-disrupted at pericenter, causing a
repeating pTDE. pTDEs may be as or more common than full TDEs (fTDEs), yet few
are known. In this work, we present the discovery of the first repeating pTDE
from a systematically-selected sample, AT\,2020vdq. AT\,2020vdq was originally
identified as an optically- and radio-flaring TDE. Around years after its
discovery, it rebrightened dramatically and rapidly in the optical. The optical
flare was remarkably fast and luminous compared to previous TDEs. It was
accompanied by extremely broad () optical/UV spectral features and
faint X-ray emission (\,erg\,s), but no new
radio-emitting component. Based on the transient optical/UV spectral features
and the broadband light curve, we show that AT\,2020vdq is a repeating pTDE. We
then use it to constrain TDE models; in particular, we favor a star originally
in a very tight binary system that is tidally broken apart by the Hills
mechanism. We also constrain the repeating pTDE rate to be to
yr galaxy, with uncertainties dominated by the unknown
distribution of pTDE repeat timescales. In the Hills framework, this means the
binary fraction in the galactic nucleus is of the order few percent.Comment: 24 pages, 13 figures, submitted to Ap
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AGNs on the Move: A Search for Off-nuclear AGNs from Recoiling Supermassive Black Holes and Ongoing Galaxy Mergers with the Zwicky Transient Facility
A supermassive black hole (SMBH) ejected from the potential well of its host galaxy via gravitational wave recoil carries important information about the mass ratio and spin alignment of the pre-merger SMBH binary. Such a recoiling SMBH may be detectable as an active galactic nucleus (AGN) broad-line region offset by up to 10 kpc from a disturbed host galaxy. We describe a novel methodology using forward modeling with The Tractor to search for such offset AGNs in a sample of 5493 optically variable AGNs detected with the Zwicky Transient Facility (ZTF). We present the discovery of nine AGNs that may be spatially offset from their host galaxies and are candidates for recoiling SMBHs. Five of these offset AGNs exhibit double-peaked broad Balmer lines, which may have arisen from unobscured accretion disk emission, and four show radio emission indicative of a relativistic jet. The fraction of double-peaked emitters in our spatially offset AGN sample is significantly larger than the 16% double-peaked emitter fraction observed for ZTF AGNs overall. In our sample of variable AGNs we also identified 52 merging galaxies, including a new spectroscopically confirmed dual AGN. Finally, we detected the dramatic rebrightening of SDSS 1133, a previously discovered variable object and recoiling SMBH candidate, in ZTF. The flare was accompanied by the reemergence of strong P Cygni line features, indicating that SDSS 1133 may be an outbursting luminous blue variable star