J/AJ/161/15 Light curve of the dwarf nova AT 2020iko (Soraisam+, 2021)
AT 2020iko: a WZ Sge-type dwarf nova candidate with an anomalous precursor
event.
Soraisam M.D., DeSantis S.R., Lee C.-H., Matheson T., Narayan G., Saha A.,
Sand D.J., Stubens C., Szkody P., Wolf N., Wyatt S.D., Hosokawa R.,
Kawai N., Murata K.L.
<Astron. J., 161, 15 (2021)>
=2021AJ....161...15S 2021AJ....161...15S
ADC_Keywords: Novae; Photometry, ugriz
Keywords: Dwarf novae ; WZ Sagittae stars ; Time domain astronomy
Abstract:
The ongoing Zwicky Transient Facility (ZTF) survey is generating a
massive alert rate from a variety of optical transients and variable
stars, which are being filtered down to subsets meeting user-specified
criteria by broker systems such as the Arizona-NOIRLab Temporal
Analysis and Response to Events System (ANTARES). In a beta
implementation of the algorithm of Soraisam et al. on ANTARES, we
flagged AT 2020iko from the ZTF real-time alert stream as an anomalous
source. This source is located close to a red extended Sloan Digital
Sky Survey source. In the first few epochs of detection, it exhibited
a V-shaped brightness profile, preceded by nondetections both in ZTF
and in the All-Sky Automated Survey for Supernovae extending to 2014.
Its full light curve shows a precursor event, followed by a main
superoutburst and at least two rebrightenings. A low-resolution
spectrum of this source points to a dwarf nova (DN) nature. Although
some of the features of AT 2020iko indicate an SU UMa-type DN, its
large amplitude, presence of rebrightenings, and inferred supercycle
period of ≳6yr are in favor of AT 2020iko being a new WZ Sge- type DN
candidate, a subset of rare DNe consisting of extreme mass-ratio
(<0.1) binaries with an orbital period around the period minimum. The
precusor event of AT 2020iko brightened by 6.5mag, while its decay
spanned 3-5mag. We speculate this superoutburst is associated with a
less expanded accretion disk than in typical superoutbursts in WZ Sge
systems, with the large depth of the precursor decay implying an
extremely small mass ratio. To the best of our knowledge, such a
precursor event has not been recorded for any DN. This result serves
to demonstrate the efficacy of our real-time anomaly search algorithm.
Description:
We performed multiwavelength follow-up observations using the Sinistro
imager on the Las Cumbrers Observatory (LCO) 1m telescope at the
McDonald Observatory on three nights; UT May 4, May 6 PI:Lee), and May
10 (PI:Narayan).
2020iko was also observed simultaneously in three passbands (gp, Rc,
and Ic) with the MITSuME 0.5m telescope at Akeno Observatory on three
nights; UT May 4, May 7, and May 8.
The aggregated light curve of 2020iko includes data from Zwicky
Transient Facility (ZTF), the Asteroid Terrestrial-impact Last Alert
System (ATLAS), as well as follow-up observations. The public ZTF
survey first detected it on 2020 April 26 UT, at g=16.74, preceded by
nondetections, latest of which was on 2020 April 23 UT.
We also requested a Swift ToO observation with the X-ray Telescope
(XRT) and the UV/Optical Telescope (UVOT), which were executed about a
week later on 2020 May 13 UT around the minimum of the decline of the
main outburst.
Objects:
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RA (2000) DE Designation(s)
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09 03 26.23 +47 31 59.14 NAME AT 2020iko = ZTF20aawbodq
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 39 301 Light curve data
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See also:
II/366 : ASAS-SN catalog of variable stars (Jayasinghe+, 2018-2020)
VII/258 : Quasars and Active Galactic Nuclei (13th Ed.) (Veron+ 2010)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
J/MNRAS/441/1186 : Cataclysmic variables from CRTS (Drake+, 2014)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/MNRAS/438/L101 : First month on SN 2013ej (Valenti+, 2014)
J/AcA/65/313 : 1000 new dwarf novae from the OGLE Survey (Mroz+, 2015)
J/A+A/631/A147 : Transient processing and analysis using AMPEL (Nordin+,2019)
J/AJ/159/198 : Cataclysmic variables in the ZTF 1st-yr (Szkody+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d MJD [58965/58997] Modified Julian Date
14- 20 A7 --- Tel Telescope used
22- 28 A7 --- Band Passband used
30- 34 F5.2 mag mag [16.01/20.46] Observed magnitude in Passband
36- 39 F4.2 mag e_mag [0.03/2.31] Uncertainty in mag
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 24-Feb-2021