Detection of an outburst from the CV candidate AT2019ubj using GOTO observations

ATel #16159; G. Ramsay (Armagh Observatory), K. Ackley (Warwick); M. J. Dyer (Sheffield); J. Lyman (Warwick); K. Ulaczyk (Warwick); F. Jiminez-Ibarra (Monash); A. Kumar (Warwick); D. O'Neill (Warwick); D. Steeghs (Warwick); D. K. Galloway (Monash); V. Dhillon (Sheffield); P. O'Brien (Leicester); K. Noysena (NARIT); R. Kotak (Turku); R. P. Breton (Manchester); L. K. Nuttall (Portsmouth); E. Pall'e (IAC); D. Pollacco (Warwick) on behalf of the GOTO Consortium.
on 28 Jul 2023; 16:43 UT
Credential Certification: Gavin Ramsay (gavin.ramsay@armagh.ac.uk)

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We report an outburst of a transient source GOTO224626.36+283722.68 using observations made with the Gravitational-wave Optical Transient Observer (GOTO) North telescopes (Steeghs et al. 2022). Observations were being made of the field which covered the position of GRB 230728A (Salvaggio et al. GCN 34282). A set of four consecutive 90 sec exposures were made in the GOTO L-band (400-700 nm) with the mid time being 2023-07-28 04:50:35 UT (MJD=60153.2018). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same field. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks. There is a clear transient at RA=22:46:26.4 DEC=+28:37:22.7 (J2000) with a magnitude L=17.09. The position of the transient is consistent with that of AT2019ubj (=Gaia19ewl, Hodgkin et al. 2019) which had a discovery mag of G=16.79). We also searched the ZTF transient stream using the Lasair transient broker (Smith, Williams et al. 2019), and found seven outbursts (https://lasair-ztf.lsst.ac.uk/objects/ZTF19abpnkok/) with a peak mag of g=16.5. The mean Gaia mag is G=19.89 (Gaia DR3) indicating the source has an outburst amplitude of more than 3 mag. Its location on the Gaia HRD is consistent with the transient being a Cataclysmic Variable. We encourage timely spectroscopic observations to determine the exact nature of the transient. The Gravitational-wave Optical Transient Observer (GOTO) project acknowledges the support of the Monash-Warwick Alliance; University of Warwick; Monash University; University of Sheffield; University of Leicester; Armagh Observatory & Planetarium; the National Astronomical Research Institute of Thailand (NARIT); Instituto de Astrofísica de Canarias (IAC); University of Portsmouth; University of Turku, and the UK Science and Technology Facilities Council (STFC, grant numbers ST/T007184/1, ST/T003103/1).