95 research outputs found
Results from the Search for Tidal Disruption Flares in the GALEX Deep Imaging Survey
A supermassive black hole in the nucleus of a galaxy will be revealed when a star passes close enough to be torn apart by tidal forces and a UV/X-ray flare is emitted by the stream of stellar debris that plunges into the black hole. We initiated a program to take advantage of the UV sensitivity, large volume, and temporal sampling of the Galaxy Evolution Explorer (GALEX) Deep Imaging Survey to search for stellar disruptions in the nuclei of galaxies over a large range of redshifts. Here we present the detection of a luminous UV flare from a quiescent galaxy with the properties of a tidal disruption event
Supermassive Black Hole Binary Candidates from the Pan-STARRS1 Medium Deep Survey
We conducted a systematic search for periodically varying quasars, which are predicted manifestations of sub-pc supermassive black hole binaries (SMBHBs), in the Pan-STARRS1 Medium Deep Survey (PS1 MDS). Since the normal variability of quasars can also mimic periodicity over a small number of cycles, we have extended the temporal baseline by monitoring the candidates with the Discovery Channel Telescope and the Las Cumbres Observatory telescopes. We have also adopted a more rigorous method to evaluate the significance of the periodic candidates, by considering in the light curves a red noise background modeled as the Damped Random Walk process. While none of the candidates can be resolved by the current pulsar timing arrays (PTAs) as individual gravitational wave sources, the Large Synoptic Survey Telescope is capable of finding more periodic candidates, some of which are likely to be detected by the PTA experiment with the Square Kilometre Array
Revealing the Nature of Extreme Coronal-line Emitter SDSS J095209.56+214313.3
Extreme coronal-line emitter (ECLE) SDSSJ095209.56+214313.3, known by its
strong, fading, high ionization lines, has been a long standing candidate for a
tidal disruption event, however a supernova origin has not yet been ruled out.
Here we add several new pieces of information to the puzzle of the nature of
the transient that powered its variable coronal lines: 1) an optical light
curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that
serendipitously catches the optical flare, and 2) late-time observations of the
host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray
telescope (XRT) and the ground-based Mercator telescope. The well-sampled,
-year long, unfiltered LINEAR light curve constrains the onset of the
flare to a precision of days and enables us to place a lower limit on
the peak optical magnitude. Difference imaging allows us to estimate the
location of the flare in proximity of the host galaxy core. Comparison of the
\textsl{GALEX} data (early 2006) with the recently acquired Swift UVOT (June
2015) and Mercator observations (April 2015) demonstrate a decrease in the UV
flux over a year period, confirming that the flare was UV-bright. The
long-lived UV-bright emission, detected 1.8 rest-frame years after the start of
the flare, strongly disfavors a SN origin. These new data allow us to conclude
that the flare was indeed powered by the tidal disruption of a star by a
supermassive black hole and that TDEs are in fact capable of powering the
enigmatic class of ECLEs.Comment: Submitted to Ap
Black hole masses of tidal disruption event host galaxies
The mass of the central black hole in a galaxy that hosted a tidal disruption
event (TDE) is an important parameter in understanding its energetics and
dynamics. We present the first homogeneously measured black hole masses of a
complete sample of 12 optically/UV selected TDE host galaxies (down to
22 mag and =0.37) in the Northern sky. The mass estimates
are based on velocity dispersion measurements, performed on late time optical
spectroscopic observations. We find black hole masses in the range
310 MM210 M.
The TDE host galaxy sample is dominated by low mass black holes (10
M), as expected from theoretical predictions. The blackbody peak
luminosity of TDEs with M10 M is consistent
with the Eddington limit of the SMBH, whereas the two TDEs with M10 M have peak luminosities below their SMBH
Eddington luminosity, in line with the theoretical expectation that the
fallback rate for M10 M is sub-Eddington. In
addition, our observations suggest that TDEs around lower mass black holes
evolve faster. These findings corroborate the standard TDE picture in 10
M black holes. Our results imply an increased tension between
observational and theoretical TDE rates. By comparing the blackbody emission
radius with theoretical predictions, we conclude that the optical/UV emission
is produced in a region consistent with the stream self-intersection radius of
shallow encounters, ruling out a compact accretion disk as the direct origin of
the blackbody radiation at peak brightness.Comment: 16 pages, 9 figures. Submitted to MNRAS; including minor revisions
suggested by the refere
Optical Discovery of Probable Stellar Tidal Disruption Flares
Using archival Sloan Digital Sky Survey (SDSS) multi-epoch imaging data (Stripe 82), we have searched for the tidal disruption of stars by supermassive black holes in non-active galaxies. Two candidate tidal disruption events (TDEs) are identified. The TDE flares have optical blackbody temperatures of 2 × 10^4 K and observed peak luminosities of M_g = –18.3 and –20.4 (νL_ν = 5 × 10^(42), 4 × 10^(43) erg s^(–1), in the rest frame); their cooling rates are very low, qualitatively consistent with expectations for tidal disruption flares. The properties of the TDE candidates are examined using (1) SDSS imaging to compare them to other flares observed in the search, (2) UV emission measured by GALEX, and (3) spectra of the hosts and of one of the flares. Our pipeline excludes optically identifiable AGN hosts, and our variability monitoring over nine years provides strong evidence that these are not flares in hidden AGNs. The spectra and color evolution of the flares are unlike any SN observed to date, their strong late-time UV emission is particularly distinctive, and they are nuclear at high resolution arguing against these being first cases of a previously unobserved class of SNe or more extreme examples of known SN types. Taken together, the observed properties are difficult to reconcile with an SN or an AGN-flare explanation, although an entirely new process specific to the inner few hundred parsecs of non-active galaxies cannot be excluded. Based on our observed rate, we infer that hundreds or thousands of TDEs will be present in current and next-generation optical synoptic surveys. Using the approach outlined here, a TDE candidate sample with O(1) purity can be selected using geometric resolution and host and flare color alone, demonstrating that a campaign to create a large sample of TDEs, with immediate and detailed multi-wavelength follow-up, is feasible. A by-product of this work is quantification of the power spectrum of extreme flares in AGNs
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