J/ApJ/909/102 LRIS sp. of SDSSJ143359.16+400636.0 nucleus (Brightman+, 2021)
A luminous X-ray transient in SDSS J143359.16+400636.0: a likely tidal
disruption event.
Brightman M., Ward C., Stern D., Mooley K., De K., Gezari S., Van Velzen S.,
Andreoni I., Graham M., Masci F.J., Riddle R., Zolkower J.
<Astrophys. J., 909, 102 (2021)>
=2021ApJ...909..102B 2021ApJ...909..102B
ADC_Keywords: X-ray sources; Spectra, optical; Galaxies, spectra
Keywords: Tidal disruption ; X-ray transient sources ; Transient sources ;
X-ray sources ; Supermassive black holes
Abstract:
We present the discovery of a luminous X-ray transient, serendipitously
detected by Swift's X-ray Telescope on 2020-February-5, located in the
nucleus of the galaxy SDSSJ143359.16+400636.0 at z=0.099 (luminosity
distance DL=456Mpc). The transient was observed to reach a peak
luminosity of ∼1044erg/s in the 0.3-10keV X-ray band, which was
∼20 times more than the peak optical/UV luminosity. Optical, UV, and
X-ray light curves from the Zwicky Transient Facility and Swift show a
decline in flux from the source consistent with t-5/3, and
observations with NuSTAR and Chandra show a soft X-ray spectrum with
photon index Γ=2.9±0.1. The X-ray/UV properties are
inconsistent with well-known active galactic nucleus properties and
have more in common with known X-ray tidal disruption events (TDEs),
leading us to conclude that it was likely a TDE. The broadband
spectral energy distribution can be described well by a disk blackbody
model with an inner disk temperature of 7.3-0.8+0.3x105K, with a
large fraction (>40%) of the disk emission upscattered into the X-ray
band. An optical spectrum taken with Keck/LRIS after the X-ray
detection reveals LINER line ratios in the host galaxy, suggesting
low-level accretion onto the supermassive black hole prior to the
event, but no broad lines or other indications of a TDE were seen. The
stellar velocity dispersion implies that the mass of the supermassive
black hole powering the event is log(MBH/M☉)=7.41±0.41, and
we estimate that at peak the Eddington fraction of this event was
∼50%. This likely TDE was not identified by wide-field optical surveys
or optical spectroscopy, indicating that more events like this would
be missed without wide-field UV or X-ray surveys.
Description:
In addition to the initial detection in the first XRT observation
(ObsID 00032818012), Swift has observed and detected the transient in
X-rays 27 times, all in photon counting mode. Previous to this, Swift
observed the position of the source 17 times, 12 times in 2013 and 5
times in 2016 where the source was not detected in X-rays.
In addition to the XRT data, Swift also observed the source with its
UVOT instrument, which has six filters, UVW2 (central wavelength
λ=1928Å), UVM2 (λ=2246Å), UVW1 (λ=2600Å),
U (λ=3465Å), B (λ=4392Å), and V (λ=5468Å).
While a UVOT source was clearly seen prior to the 2020 observations,
likely emission from the host galaxy, a small increase in brightness
measured by UVOT can be seen in the 2020 observations, though it is
much weaker than seen in the X-rays. See Section 2.1.
In order to study the hard X-ray emission from the transient, we
obtained Director's Discretionary Time observation on the Nuclear
Spectroscopic Telescope Array (NuSTAR, ObsID 90601606002), which took
place on 2020 February 13, 8 days after the X-ray transient was first
detected by Swift.
On 2020 February 16 and 29, 11 and 24 days after the initial Swift
detection, respectively, SDSS J143359.16+400636.0 was also
serendipitously observed by Chandra (ObsIDs 23171 and 23172DR) for
10ks each exposure with ACIS-S at the aim point.
Khabibullin+ (2020ATel13494....1K 2020ATel13494....1K) reported via The Astronomer's
Telegram the detection by Spectrum-Roentgen-Gamma (SRG)/eROSITA of a
very bright X-ray source, SRGet J143359.25+400638.5, centered on
SDSSJ143359.16+400636.0 on 2019 December 27, 40 days prior to the
detection of the transient with Swift/XRT. See Section 2.4.
As described in Section 2.3, the candidate optical transient
ZTF19acymzwg was detected in the g, r, and i bands by ZTF on 2019
December 14, 53 days before the detection with Swift/XRT. Previous to
this date, the field was observed on 2019 October 5 and the transient
was not detected in any filter. Once we obtained the position of the
transient, we produced ZTF light curves to produce difference-imaging
photometry at the best-fit transient position across all ZTF images of
the field taken between 2018 March 21 and 2020 May 11. We found no
evidence for nuclear activity before the flare. See Section 3.
We obtained an optical spectrum of the host galaxy nucleus with
Keck/LRIS on 2020 February 18, 13 days after the initial Swift
detection. The data were acquired using a standard long-slit mode
using a 1" slit on both the red and blue sides when the seeing was
101 in i band. See Section 4.
We carried out radio observations with the Karl G. Jansky Very Large
Array (VLA) through Director's Discretionary Time (project code
VLA/20A-579, PI: Mooley) on 2020 August 2, 180 days after the
detection by Swift. Data were obtained at C band in the 3-bit mode of
the WIDAR correlator to get a contiguous frequency coverage between 4
and 8GHz. We did not detect any radio source at the location of the
transient. See Section 5.
Objects:
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RA (ICRS) DE Designation(s)
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14 33 59.17 +40 06 36.0 SDSS J143359.16+400636 = SDSS J143359.16+400636.0
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig5.dat 35 5129 Keck/LRIS spectrum of the nucleus of
SDSS J143359.16+400636.0 taken on 2020-February-18,
13d after the X-ray transient was detected by Swift
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See also:
IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
II/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
J/ApJS/132/37 : Spectroscopy of Southern warm IR galaxies (Kewley+, 2001)
J/A+A/480/611 : XMM-Newton slew survey catalogue, XMMSL1 (Saxton+, 2008)
J/MNRAS/397/1177 : Swift-XRT observations of GRBs (Evans+, 2009)
J/A+A/512/A34 : XMM-COSMOS Type 1 AGNs (Lusso+, 2010)
J/ApJ/772/26 : AGN with WISE. II. The NDWFS Bootes field (Assef+, 2013)
J/A+A/588/A103 : 2nd ROSAT all-sky survey (2RXS) source cat. (Boller+, 2016)
J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)
J/MNRAS/455/2918 : Phot. & line luminosities for ASASSN-14li (Holoien+, 2016)
J/ApJ/819/154 : SDSS-DR7 QSOs with X-ray and UV luminosities (Lusso+, 2016)
J/ApJS/233/17 : Swift/BAT AGN sp. survey. V. X-ray data (Ricci+, 2017)
J/ApJ/883/111 : UV-Opt LCs of ASASSN-19bt detected by TESS (Holoien+, 2019)
J/ApJ/872/198 : LCs of tidal disruption flare AT2018zr (van Velzen+, 2019)
J/ApJ/902/86 : Type Ic SN 2020bvc UV to NIR LCs & opt. spectra (Ho+, 2020)
Byte-by-byte Description of file: fig5.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 0.1nm lambda [3066.4/10303] Wavelength; in Angstrom units
12- 23 E12.5 cW/m2/nm Flux [-6.02e-17/1.6e-16]? Observed flux;
in erg/cm2/s/Å units
25- 35 E11.5 cW/m2/nm e_Flux [8e-19/6.5e-17] Uncertainty in Flux
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Aug-2022