J/ApJ/910/125 Follow-up photometry of ASASSN-14ko (Payne+, 2021)
ASASSN-14ko is a periodic nuclear transient in ESO 253-G003.
Payne A.V., Shappee B.J., Hinkle J.T., Vallely P.J., Kochanek C.S.,
Holoien T.W.-S., Auchettl K., Stanek K.Z., Thompson T.A., Neustadt J.M.M.,
Tucker M.A., Armstrong J.D., Brimacombe J., Cacella P., Cornect R.,
Denneau L., Fausnaugh M.M., Flewelling H., Grupe D., Heinze A.N.,
Lopez L.A., Monard B., Prieto J.L., Schneider A.C., Sheppard S.S.,
Tonry J.L., Weiland H.
<Astrophys. J., 910, 125 (2021)>
=2021ApJ...910..125P 2021ApJ...910..125P
ADC_Keywords: Galaxies, Seyfert; Photometry, ultraviolet; Photometry, UBVRI;
X-ray sources; Surveys; Active gal. nuclei
Keywords: Black hole physics ; Galaxies ; Seyfert galaxies ;
Galaxy accretion disks
Abstract:
We present the discovery that ASASSN-14ko is a periodically flaring
active galactic nucleus at the center of the galaxy ESO 253-G003. At
the time of its discovery by the All-Sky Automated Survey for
Supernovae (ASAS-SN), it was classified as a supernova close to the
nucleus. The subsequent 6yr of V- and g-band ASAS-SN observations
revealed that ASASSN-14ko has nuclear flares occurring at regular
intervals. The 17 observed outbursts show evidence of a decreasing
period over time, with a mean period of P0=114.2±0.4days and a
period derivative of dP/dt=-0.0017±0.0003. The most recent outburst
in 2020 May, which took place as predicted, exhibited spectroscopic
changes during the rise and had a UV bright, blackbody spectral energy
distribution similar to tidal disruption events (TDEs). The X-ray flux
decreased by a factor of 4 at the beginning of the outburst and then
returned to its quiescent flux after ∼8days. The Transiting Exoplanet
Survey Satellite observed an outburst during Sectors 4-6, revealing a
rise time of 5.60±0.05days in the optical and a decline that is best
fit with an exponential model. We discuss several possible scenarios
to explain ASASSN-14ko's periodic outbursts, but currently favor a
repeated partial TDE. The next outbursts should peak in the optical on
UT 2020 September 7.4±1.1 and UT 2020 December 26.5±1.4.
Description:
On 2014 November at 14.28 UT, the All-Sky Automated Survey for
SuperNovae (ASAS-SN; Shappee+ 2014, J/ApJ/788/48 ;
Kochanek+ 2017PASP..129j4502K 2017PASP..129j4502K) triggered on a nuclear transient
associated with ESO 253-G003 at V∼17.0mag and reported it as
ASASSN-14ko (Holoien+ 2014ATel.6732....1H 2014ATel.6732....1H & 2017, J/MNRAS/464/2672).
UltraViolet/Optical Telescope (UVOT) and X-Ray Telescope (XRT)
observations by the Neil Gehrels Swift Observatory were taken on UT
2014 November 16, 19, 21, 23, and 27 (PI: T. W.-S. Holoien,
ToO ID: 33529).
We again requested Swift data (ToO IDs: 13836, 13979, 14005) to
monitor ASASSN-14ko during quiescence and then during the outburst
predicted for UT 2020 May 18.5.
There are three additional observations of ESO 253-G003 in the Swift
data archive under the identification SWIFT J0525.3-600
(Obs ID: 37354, PI: C.B. Markwardt).
See Section 2.2 and 2.8.
As part of ongoing work to examine the long-term behavior of AGNs
observed by ASAS-SN, a full light curve of ESO 253-G003 was extracted
in 2020 February. The complete V- and g-band light curve 2014-2020
is shown in Figure 1.
ASAS-SN is a network of 20 robotic telescopes hosted by the Las
Cumbres Observatory Global Telescope (LCOGT) at five sites around the
globe. See Section 2.1.
The Asteroid Terrestrial-impact Last Alert System (ATLAS survey;
Tonry+ 2018PASP..130f4505T 2018PASP..130f4505T) consists of two 0.5m f/2 Wright Schmidt
telescopes on Haleakala and at the Mauna Loa Observatory. Designed
primarily for detecting hazardous asteroids, the telescopes obtain
four 30s exposures of 200-250 fields per night. ATLAS uses two
broadband filters, the "cyan" (c) filter covering 420-650nm and the
"orange" (o) filter covering 560-820nm. We performed forced photometry
on the subtracted ATLAS images of ASASSN-14ko. See Section 2.3.
ASASSN-14ko was observed by the Transiting Exoplanet Survey Satellite
(TESS) during Sectors 4-6, which occurred between 2018 October 18 and
2019 January 7. TESS observes in a single broadband filter, spanning
roughly 6000-10000Å with an effective wavelength of ∼7500Å. TESS
magnitudes are calibrated to the Vega system. See Section 2.4.
We obtained photometric observations from the LCOGT. The B-, V-, g',
r', and i'-band observations were taken using the 1m telescope at
Siding Spring Observatory in New South Wales, Australia. The LCOGT
photometric observations began on 2020 April 13 in quiescence and
continued through the midpoint of the 2020 May outburst.
See Section 2.5.
Amateur astronomers at four different observatories observed
ASASSN-14ko starting shortly after it was discovered to be
periodically flaring. Data were taken at the Moondyne Observatory,
east of Perth, Australia, using a 0.4m telescope with AOX adaptive
optics between 2020 April 28 and June 8 and on a daily cadence between
2020 May 10 and 28. BC-, V-, GS-, RS-, and IC-band images were
obtained with guided 120s exposures.
Data were also collected using a 41 cm telescope at Savannah Skies
Observatory from Queensland, Australia.
ASASSN-14ko was observed from Bronberg Observatory in South Africa
using 14- and 12-inch telescopes in the R band with 15s exposures.
Finally, ASASSN-14ko was observed from Dogsheaven Observatory in
Brazil. See Section 2.6.
We also obtained seven spectra with the LCOGT Folded Low Order
whYte-pupil Double-dispersed Spectrograph (FLOYDS) at the robotic 2m
Faulkes Telescope South located at Siding Spring Observatory. These
observations were taken on 2020 April 12, 15, 24, 25, 27, 2020 May 16,
and 2020 May 17. See Section 2.7.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
05 25 18.13 -46 00 20.3 ASASSN-14ko = ASASSN -14ko
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 47 4289 Photometry of ASASSN-14ko used in this analysis
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See also:
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/ApJS/132/37 : Spectroscopy of Southern warm IR galaxies (Kewley+, 2001)
J/ApJ/560/566 : K-band galaxy LF from 2MASS (Kochanek+, 2001)
J/ApJ/676/944 : GALEX & CFHTLS cand. tidal disruption events (Gezari+, 2008)
J/ApJ/687/1201 : SN and LGRB locations in their host galaxies (Kelly+, 2008)
J/A+A/480/611 : XMM-Newton slew survey catalogue, XMMSL1 (Saxton+, 2008)
J/ApJ/696/870 : Catalina Real-time Transient Survey (CRTS) (Drake+, 2009)
J/ApJS/207/19 : Hard X-ray survey from Swift-BAT 6yrs (Baumgartner+, 2013)
J/ApJ/793/38 : Palomar Transient Factory photometric obs. (Arcavi+, 2014)
J/ApJS/210/3 : SDSS bulge, disk & stellar mass estimates (Mendel+, 2014)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/MNRAS/453/1562 : CRTS close supermassive black hole binaries (Graham+, 2015)
J/ApJ/809/77 : Transiting Exoplanet Survey Satellite (Sullivan+, 2015)
J/ApJ/821/56 : Space telescope RM project. III. NGC5548 (Fausnaugh+, 2016)
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/MNRAS/464/2672 : ASAS-SN bright supernova catalog 2013-2014 (Holoien+, 2017)
J/ApJ/836/99 : NuSTAR serendipitous survey: 40-month cat. (Lansbury+, 2017)
J/ApJ/880/120 : Phot. of the tidal disruption event PS18kh (Holoien+, 2019)
J/ApJ/883/111 : UV-Opt LCs of ASASSN-19bt detected by TESS (Holoien+, 2019)
J/ApJ/883/94 : Optical & UV follow-up of 1ES 1927+654 (Trakhtenbrot+, 2019)
J/ApJ/898/161 : 500days of ASASSN-18pg multiwavelength obs. (Holoien+, 2020)
J/ApJ/908/51 : TESS early LCs of type Ia Supernovae (Fausnaugh+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.3 d JD [2456790.49/2459000.21] Julian Date of
observation
13- 17 A5 --- Band Band/Instrument used (1)
19- 28 E10.3 --- Flambda [-2.21e-15/3.2e-12] Flux
30- 38 E9.3 --- e_Flambda [3.14e-18/3.9e-13] Uncertainty for Flambda
40- 47 A8 --- x_Flambda Units for Flambda (2)
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Note (1): All data from different sources but from the same filter
(e.g., Swift B/V, amateur astronomer B/V, LCOGT B/V) have been
converted onto a common system, Johnson-Cousins.
Band as follows:
B = Swift+LCOGT+amateur (62 occurrences);
M2 = Swift/UVM2 (14 occurrences);
TESS = Transiting Exoplanet Survey Satellite photometry (3075 occurrences);
U = Swift/U-band (14 occurrences);
V = Swift+ASAS-SN+LCOGT+amateur Johnson Cousins filter (381 occurrences);
W1 = Swift/UVW1 (14 occurrences);
W2 = Swift/UVW2 (14 occurrences);
X-ray = Swift XRT (14 occurrences);
c = ATLAS cyan (20 occurrences);
g = ASAS-SN+LCOGT+amateur (514 occurrences);
o = ATLAS orange (114 occurrences);
r = LCOGT+amateur (33 occurrences);
i = LCOG+amateur (20 occurrences).
Note (2): The X-ray data are on a scale of erg/s/cm2;
all other data is in units of erg/s/cm2/Å.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 14-Sep-2022