Optical outburst detected from the AM CVn binary ASASSN-14mv

ATel #13980; G. Ramsay (Armagh Observatory & Planetarium), M. Green (Tel Aviv), P. Woudt (UCT), D. Steeghs (Warwick), P. Groot (Nijmegen), C. Duffy (Armagh), D. K. Galloway (Monash), V. Dhillon (Sheffield), P. O'Brien (Leicester), S. Poshyachinda (Narit), R. Kotak (Turku), L. Nuttall (Portsmouth), R. Breton (Manchester), D. Pollacco (Warwick), E. Thrane (Monash), K. Ackley (Monash), M. Dyer (Sheffield), J. Lyman (Warwick), K. Ulaczyk (Warwick), R. Fender (Oxford), E. Koerding (Nijmegen), on behalf of the GOTO and ThunderKat collaborations.
on 29 Aug 2020; 17:31 UT
Credential Certification: Gavin Ramsay (gavin.ramsay@armagh.ac.uk)

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Gaia Alerts reported an outburst (Gaia20dyy, AT2020sak) from the AM CVn binary ASASSN-14mv (V490 Gem) on 2020-08-24 19:46:33 UT at G=15.6. This appears to be its first recorded outburst since the event starting 2014-12-29 which peaked at brighter than 12 mag, returning to quiescence (18 mag) approximately 3 months later. It showed a series of re-brightnening, or echo outbursts, starting around 10 days after maximum light. We carried out observations with the Gravitational-wave Optical Transient Observer (GOTO) on La Palma in response to the alert. We made a set of 7x60 s exposures using our B-band (400-510 nm); R-band (580-690 nm) and L-band (400-700 nm) filters, starting at 2020-08-29 05:45 UT. Using the output of the GOTO photometric pipeline we find ASSASN-14mv has preliminary mean magnitudes of B=15.6; R=15.1 and L=15.5 and confirm it is in outburst. We also obtained observations of ASASSN-14mv using 58 antennas of the MeerKAT radio telescope array in South Africa at a central frequency of 1.284 GHz and with a bandwidth of 856 MHz. The observations were obtained on 2020-08-28 from 06:26-08:38 UT. No radio source was detected at the position of ASASSN-14mv with a 3 sigma upper limit of 28.5 microJy. The source is currently visible at low elevation towards morning twilight and we encourage further observations to determine if the re-brightening events are also seen in this current outburst. 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) (https://goto-observatory.org/). ThunderKAT will run for 5 years and targets X-ray binaries, Cataclysmic Variables, Supernovae and Gamma-Ray Bursts. For further information on this programme please contact Rob Fender and/or Patrick Woudt. We thank the staff at the South African Radio Astronomy Observatory (SARAO) for their rapid scheduling of these observations. The MeerKAT telescope is operated by SARAO, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.