J/ApJ/883/111 UV-Opt LCs of ASASSN-19bt detected by TESS (Holoien+, 2019)
Discovery and early evolution of ASASSN-19bt, the first TDE detected by TESS.
Holoien T.W.-S., Vallely P.J., Auchettl K., Stanek K.Z., Kochanek C.S.,
French K.D., Prieto J.L., Shappee B.J., Brown J.S., Fausnaugh M.M., Dong S.,
Thompson T.A., Bose S., Neustadt J.M.M., Cacella P., Brimacombe J.,
Kendurkar M.R., Beaton R.L., Boutsia K., Chomiuk L., Connor T., Morrell N.,
Newman A.B., Rudie G.C., Shishkovksy L., Strader J.
<Astrophys. J., 883, 111 (2019)>
=2019ApJ...883..111H 2019ApJ...883..111H
ADC_Keywords: Photometry, ultraviolet; Optical
Keywords: accretion, accretion disks ; black hole physics ; galaxies: nuclei
Abstract:
We present the discovery and early evolution of ASASSN-19bt, a tidal
disruption event (TDE) discovered by the All-Sky Automated Survey for
Supernovae (ASAS-SN) at a distance of d∼115Mpc and the first TDE to be
detected by TESS. As the TDE is located in the TESS Continuous Viewing
Zone, our data set includes 30 minute cadence observations starting on
2018 July 25, and we precisely measure that the TDE begins to brighten
∼8.3 days before its discovery. Our data set also includes 18 epochs
of Swift UVOT and XRT observations, 2 epochs of XMM-Newton
observations, 13 spectroscopic observations, and ground data from the
Las Cumbres Observatory telescope network, spanning from 32 days
before peak through 37 days after peak. ASASSN-19bt thus has the most
detailed pre-peak data set for any TDE. The TESS light curve indicates
that the transient began to brighten on 2019 January 21.6 and that for
the first 15 days, its rise was consistent with a flux ∝t2
power-law model. The optical/UV emission is well fit by a blackbody
spectral energy distribution, and ASASSN-19bt exhibits an early spike
in its luminosity and temperature roughly 32 rest-frame days before
peak and spanning up to 14 days, which has not been seen in other
TDEs, possibly because UV observations were not triggered early enough
to detect it. It peaked on 2019 March 4.9 at a luminosity of
L∼1.3x1044erg/s and radiated E∼3.2x1050erg during the 41 day rise
to peak. X-ray observations after peak indicate a softening of the
hard X-ray emission prior to peak, reminiscent of the hard/soft states
in X-ray binaries.
Description:
ASAS-SN is an ongoing project designed to monitor the entire visible
sky in an unbiased way with a rapid cadence to discover bright, nearby
transients. To accomplish this, we use units hosted by the Las Cumbres
Observatory global telescope network (Brown+ 2013PASP..125.1031B 2013PASP..125.1031B) at
multiple sites around the globe, each consisting of four 14cm
telescopes on a common mount. ASAS-SN expanded in 2017 and currently
operates with five units, located in Hawaii, Texas, Chile, and South
Africa.
In order to maximize the synergy between ASAS-SN and TESS, ASAS-SN
monitors the TESS fields at an increased cadence. Located in the TESS
CVZ near the South Ecliptic Pole, ASASSN-19bt has been observed by
TESS almost constantly since science operations commenced in late
July of 2018.
ASASSN-19bt was discovered on 2019 January 29.91 at
RAJ2000=07:00:11.41,DEJ2000=-66:02:25.16 in g-band images obtained
from the ASAS-SN "Payne-Gaposchkin" unit located in Sutherland, South
Africa, and we promptly announced its discovery to the community via
the Transient Name Server, which assigned it the designation AT 2019ahk.
We triggered a spectroscopic follow-up observation with the
Low-dispersion Survey Spectrograph 3 (LDSS-3) mounted on the Magellan
Clay 6.5m telescope on 2019 January 31.20.
We were awarded 17 epochs of target-of-opportunity (TOO) observations
from the Neil Gehrels Swift Gamma-ray Burst Mission (Swift),
UltraViolet and Optical Telescope (UVOT), and X-ray Telescope (XRT).
See Section 2.4 and 2.6.1.
In addition to the ASAS-SN, Swift, and TESS observations, we also
obtained photometric observations in the BVri filters from Las Cumbres
Observatory 1m telescopes located in Cerro Tololo, Chile, Siding
Spring, Australia, and Sutherland, South Africa. See Section 2.5.
We obtained BVgri magnitudes of the host galaxy (2MASXJ07001137-6602251)
from the AAVSO Photometric All-Sky Survey Data Release 10 (APASS;
Henden et al. 2015), JHKS magnitudes from the Two Micron All-Sky
Survey (2MASS), and W1 and W2 measurements from the Wide-field
Infrared Survey Explorer (WISE) AllWISE data release. See Section 2.1.
Since the Swift XRT observations showed evidence of weak X-ray
emission as the source rose to peak, we requested two deep (41.4ks
each) XMM-Newton Observatory TOO observations of the source. The first
observation was taken on 2019 March 1 (ObsID: 0831791001, PI: Auchettl),
approximately 3.5 days before peak (MJDXMM1=58543.21), while the
second observation was taken on 2019 April 15 (ObsID: 0831791101,
PI: Auchettl), approximately 42 days after peak (MJDXMM2=58589).
See Section 2.6.2.
After obtaining our first classification spectrum of ASASSN-19bt, we
began a program of spectroscopic follow-up to complement our
photometric data set. Our follow-up spectra were obtained with LDSS-3
on the 6.5m Magellan Clay telescope, the Inamori-Magellan Areal Camera
and Spectrograph (IMACS) on the 6.5m Magellan-Baade telescope, the
Goodman Spectrograph on the Southern Astrophysical Research (SOAR)
4.1m telescope, and the Wide Field Reimaging CCD Camera (WFCCD)
mounted on the du Pont 100 inch telescope. These observations
(spanning 2019 Jan 31.20 to 2019 Apr 13.09) included seven spectra
obtained prior to peak light and four spectra obtained within 3 days
of peak light. See Section 2.7.
Objects:
-----------------------------------------------------------
RA (ICRS) DE Designation(s)
-----------------------------------------------------------
07 00 11.41 -66 02 25.2 ASASSN-19bt = NAME AT 2019ahk
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 47 1009 Host-subtracted photometry of ASASSN-19bt
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See also:
B/swift : Swift Master Catalog (HEASARC, 2004-)
B/xmm : XMM-Newton Obs. Log (XMM-Newton Science Operation Center, 2012)
IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)
VII/259 : 6dF galaxy survey final redshift release (Jones+, 2009)
J/ApJ/613/682 : AGN central masses & broad-line region sizes (Peterson+, 2004)
J/ApJ/793/38 : Palomar Transient Factory photometric obs. (Arcavi+, 2014)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/ApJ/809/77 : Transiting Exoplanet Survey Satellite (TESS) (Sullivan+, 2015)
J/ApJS/224/38 : SPOGS. I. SDSS Shocked POststarburst Galaxies (Alatalo+, 2016)
J/MNRAS/463/3813 : ASASSN-15oi UBVI M2W1W2 light curves (Holoien+, 2016)
J/MNRAS/455/2918 : Phot. & line luminosities for ASASSN-14li (Holoien+, 2016)
J/ApJ/844/46 : Phot. of the transient event iPTF16fnl (Blagorodnova+, 2017)
J/ApJS/233/17 : Swift/BAT AGN spectroscopic survey. V. X-ray (Ricci+, 2017)
J/ApJ/862/2 : Post-starburst galaxy ages from SDSS (French+, 2018)
J/ApJ/870/L1 : K2 obs. of type Ia supernova SN 2018oh (Dimitriadis+, 2019)
J/ApJ/880/120 : Phot. of the tidal disruption event PS18kh (Holoien+, 2019)
J/ApJ/870/13 : K2 LC alternative analysis of ASASSN-18bt (Shappee+, 2019)
J/ApJ/872/198 : LCs of tidal disruption flare AT2018zr (van Velzen+, 2019)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 F9.3 d MJD [58490.29/58584.73] Observation MJD or
start of combined range (1)
11- 19 F9.3 d MJDEnd [58492.29/58512.3]? End of combined
observation range
21- 24 A4 --- Filt Photometric filter
26- 26 A1 --- l_omag Flag for 3σ upper limit on omag
28- 32 F5.2 mag omag [14.5/20.9] Host-subtracted AB magnitude,
corrected for Galactic extinction, in Filt (2)
34- 37 F4.2 mag e_omag [0/0.4]? Uncertainty on omag
when not an upper limit
40- 47 A8 --- Tel Telescope or Observatory Used (3)
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Note (1): A range of MJDs indicates the MJD range of all observations
combined to obtain a single magnitude measurement
Note (2): TESS data has been binned in 2-hour bins, as described in
Section 2.3, with the MJD at the center of the bin given in Column 1
Note (3): The Telescope column indicates the source of the data in each
epoch as follows:
ASAS-SN = All-Sky Automated Survey for Supernovae (ASAS-SN) survey data,
TESS = Transiting Exoplanet Survey Satellite (TESS;
Ricker+ 2015JATIS...1a4003R 2015JATIS...1a4003R) data,
LCOGT_1m = data from the Las Cumbres Observatory 1-m telescopes,
Swift = Swift UVOT data.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Mar-2021