J/ApJ/898/161 500days of ASASSN-18pg multiwavelength obs. (Holoien+, 2020)
The rise and fall of ASASSN-18pg: following a TDE from early to late times.
Holoien T.W.-S., Auchettl K., Tucker M.A., Shappee B.J., Patel S.G.,
Miller-Jones J.C.A., Mockler B., Groenewald D.N., Hinkle J.T., Brown J.S.,
Kochanek C.S., Stanek K.Z., Chen P., Dong S., Prieto J.L., Thompson T.A.,
Beaton R.L., Connor T., Cowperthwaite P.S., Dahmen L., French K.D.,
Morrell N., Buckley D.A.H., Gromadzki M., Roy R., Coulter D.A.,
Dimitriadis G., Foley R.J., Kilpatrick C.D., Piro A.L., Rojas-Bravo C.,
Siebert M.R., van Velzen S.
<Astrophys. J., 898, 161 (2020)>
=2020ApJ...898..161H 2020ApJ...898..161H
ADC_Keywords: Photometry, ultraviolet; Photometry, UBVRI; Spectra, optical
Keywords: Black holes; Accretion; Galaxy accretion disks; Black hole physics;
Supermassive black holes; Tidal disruption
Abstract:
We present nearly 500 days of observations of the tidal disruption
event (TDE) ASASSN-18pg, spanning from 54 days before peak light to
441 days after peak light. Our data set includes X-ray, UV, and
optical photometry, optical spectroscopy, radio observations, and the
first published spectropolarimetric observations of a TDE. ASASSN-18pg
was discovered on 2018 July 11 by the All-Sky Automated Survey for
Supernovae (ASAS-SN) at a distance of d=78.6Mpc; with a peak UV
magnitude of m∼14, it is both one of the nearest and brightest TDEs
discovered to-date. The photometric data allow us to track both the
rise to peak and the long-term evolution of the TDE. ASASSN-18pg
peaked at a luminosity of L∼2.4x1044erg/s, and its late-time
evolution is shallower than a flux ∝t-5/3 power-law model,
similar to what has been seen in other TDEs. ASASSN-18pg exhibited
Balmer lines and spectroscopic features consistent with Bowen
fluorescence prior to peak, which remained detectable for roughly
225days after peak. Analysis of the two-component Hα profile
indicates that, if they are the result of reprocessing of emission
from the accretion disk, the different spectroscopic lines may be
coming from regions between ∼10 and ∼60 lt-days from the black hole.
No X-ray emission is detected from the TDE, and there is no evidence
of a jet or strong outflow detected in the radio. Our
spectropolarimetric observations indicate that the projected emission
region is likely not significantly aspherical, with the projected
emission region having an axis ratio of ≳0.65.
Description:
The All-Sky Automated Survey for Supernovae (ASAS-SN;
Shappee+ 2014, J/ApJ/788/48) currently is composed of five units
hosted by the Las Cumbres Observatory global telescope network in
Hawaii, Chile, Texas, and South Africa. To construct the V-band
reference image, we used only data obtained prior to 2018 May 1, and
for the g-band reference image, we used only data obtained after 2019
April 1. See Section 2.2.
Our initial Swift follow-up campaign included 25 epochs of TOO
observations between 2018 July 18 and 2018 November 6. We obtained an
additional 28 epochs of observations between 2019 January 22 and 2019
October 29. UVOT observations were obtained in the V (5468Å),
B (4392Å), U (3465Å), UVW1 (2600Å), UVM2 (2246Å), and
UVW2 (1928Å) filters in most epochs. See Section 2.3.
We also obtained uBVgri observations from the Swope 1m telescope at
Las Campanas Observatory and BVgri observations from the Las Cumbres
Observatory 0.4 and 1m telescopes located in Cerro Tololo, Chile;
Siding Spring, Australia; and Sutherland, South Africa. See Section 2.4.
We began spectroscopic follow-up observations of ASASSN-18pg following
its classification as a possible TDE and continued to monitor it
regularly through 2019 September. Our follow-up spectra were obtained
with the Robert Stobie Spectrograph (RSS) on the 10m SALT, the Gemini
Multi-Object Spectrograph (GMOS) on the 8.4m Gemini South telescope,
the Inamori-Magellan Areal Camera and Spectrograph (IMACS) on the 6.5m
Magellan-Baade telescope, LDSS-3 on the 6.5m Magellan Clay telescope,
the Goodman Spectrograph on the Southern Astrophysical Research (SOAR)
4.1m telescope, and the Wide Field Reimaging CCD Camera (WFCCD) on the
du Pont 100 inch telescope. Our observations span from 26 days prior
to peak light through 272 days after and include several spectra taken
near or before peak light. See Section 2.5.
We observed ASASSN-18pg using the Australia Telescope Compact Array
(ATCA) in the 15mm band, using the Compact Array Broadband Backend to
provide 2x2048MHz of bandwidth, centered at 16.7 and 21.2GHz. Our
initial observation was made on 2018 July 20 (08:18-13:29 UT). We made
a second ATCA observation on 2018 August 6 (12:20-17:18 UT). We
conclude that ASASSN-18pg was not detected in the radio. We note,
however, that both of these observations were taken prior to
ASASSN-18pg reaching its peak brightness (see Section 3.1), so it is
possible that the tidal disruption event (TDE) could have exhibited
radio emission at later times that was not detectable prior to peak.
See Section 2.6.
Objects:
-----------------------------------------------------------
RA (ICRS) DE Designation(s)
-----------------------------------------------------------
16 10 58.77 -60 55 23.2 ASASSN-18pg = NAME AT 2018dyb
-----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 53 579 Host-subtracted photometry of ASASSN-18pg
fig3.dat 47 54523 Spectroscopic evolution of ASASSN-18pg spanning
from 26days prior to peak through 407days after peak
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See also:
II/226 : Stellar polarization catalogs agglomeration (Heiles, 2000)
J/ApJ/613/682 : AGN central masses (Peterson+, 2004)
J/MNRAS/383/445 : Radial velocities in Norma cluster (A3627) (Woudt+, 2008)
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/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 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/ApJ/873/92 : Opt. & UV evolution of iPTF15af (Blagorodnova+, 2019)
J/ApJ/883/111 : UV-Opt LCs of ASASSN-19bt detected by TESS (Holoien+, 2019)
J/ApJ/880/120 : Phot. of the tidal disruption event PS18kh (Holoien+, 2019)
J/ApJ/872/198 : UV-Opt LC of AT2018zr (van Velzen+, 2019)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.3 d MJD MJD or lower MJD range (1)
10 A1 --- --- [-]
11- 19 F9.3 d MJD2 ? Upper MJD range (1)
21- 22 A2 --- Filt Photometric Filter (ugri, UBVM2W1W2)
24 A1 --- l_mag The 3σ upper detection limit on mag
25- 29 F5.2 mag mag [13.8/18.4] Apparent AB magnitude in Filt (2)
33- 36 F4.2 mag e_mag [0.02/0.5]? Lower Uncertainty on the Magnitude
40- 43 F4.2 mag E_mag [0.02/0.5]? Upper Uncertainty on the Magnitude
45- 53 A9 --- Tel Telescope or Observatory used (3)
--------------------------------------------------------------------------------
Note (1): A range of MJDs indicates the MJD range of all observations combined
to obtain a single magnitude measurement.
Note (2): All magnitudes are in the AB system and have been corrected for
Galactic extinction.
Note (3): Facility as follows:
ASAS-SN = ASAS-SN survey data (48 occurrences)
Swope = the 1-m Swope telescope at Las Campanas Observatory
(128 occurrences)
LCOGT_04m = Las Cumbres Observatory 0.4-m telescope (82 occurrences)
LCOGT_1m = Las Cumbres Observatory 1-m telescope (116 occurrences)
Swift = Swift UVOT data (205 occurrences)
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Byte-by-byte Description of file: fig3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- Tel Telescope/Instrument identifier (1)
20- 29 A10 "Y/M/D" Date Observation date
31- 36 F6.1 0.1nm lambda [2958.9/9753.1] Wavelength in Angstrom units
38- 47 E10.3 cW/m2/nm Flux [-4.84e-15/1.4e-13] Flux density
in erg/s/cm2/Å units
--------------------------------------------------------------------------------
Note (1): Telescope/Instrument as follows:
duPont:WFCCD = The Wide Field Reimaging CCD Camera on the du Pont
100 inch telescope (21389 occurrences)
SOAR:Goodman_M1+M2 = The Goodman Spectrograph on the Southern Astrophysical
Research 4.1m telescope (14254 occurrences)
Baade:IMACS = The Inamori-Magellan Areal Camera and Spectrograph on
the 6.5m Magellan-Baade telescope (5102 occurrences)
SOAR:Goodman_M1 = The Goodman Spectrograph on the Southern Astrophysical
Research 4.1m telescope (3695 occurrences)
SALT:RSS = The Robert Stobie Spectrograph on the 10m SALT
(3615 occurrences)
Clay:LDSS-3 = LDSS-3 on the 6.5m Magellan Clay telescope
(3138 occurrences)
duPont:B&C = The Boller & Chivens Spectrograph on the du Pont
100 inch telescope (1829 occurrences)
GeminiS:GMOS = The Gemini Multi-Object Spectrograph on the 8.4m
Gemini South telescope (1501 occurrences)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 30-Nov-2021