A bright optical transient, GOTO054206.46-670106.66, close to the LMC

ATel #17400; D. O'Neill (Birmingham), G. Ramsay, B. Godson, K. Wiersema, V. Dhillon, S. Littlefair, M. Kennedy, D. Steeghs, K. Ackley, M. J. Dyer, J. Lyman, D. K. Galloway, T. Killestein, A. Kumar, S. Belkin, O. Mogawana, M. Mlangeni, S. de Wet.
on 19 Sep 2025; 12:30 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Gavin Ramsay (gavin.ramsay@armagh.ac.uk)

Tweet

We report the discovery of a bright optical transient, GOTO054206.46-670106.66. During the routine all-sky survey of the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024), we detected a new, bright transient source in images (4x45s) taken on Sept 17 2025 16:02:59 UT and was reported to TNS as AT 2025xvc/GOTO25hfy. The source, previously uncatalogued, is detected at J2000 coordinates RA = 05:42:06.46, Dec = -67:01:06.66, with an AB magnitude in the GOTO L-band (400-700 nm; approximately g + r) of L = 12.77 +/- 0.01. The source has since continued to rise reaching L=12.32 on Sept 18 2025 16:11:00 UT. There is a very faint source in the DESI Legacy image at the transients position suggesting that it is fainter than g~20 mag in quiescence. ASAS-SN photometry (Shappee et al. 2014) reveals a non-detection down to a 5-sigma upper limit of g > 17.43 mag at Sept 15 2025 09:45:29 UT (2.3 days before the GOTO detection). It was next observed by ASAS-SN on Sept 16 2025 06:07:03 UT (1.4 days before the GOTO detection) at g=13.391 +/-0.02 mag followed by a detection in ATLAS Sept 16 08:50:17 UT at o=13.207 +/- 0.003 mag, retrieved via the forced photometry service (Smith et al 2020, Shingles et al 2021). Following the GOTO discovery, the fully robotic SAAO 1m Lesedi telescope equipped with the Mookodi low-resolution (R~350) spectrograph and imager was triggered and obtained a 600 s spectrum starting at Sept 18 2025 at 09:18:22 UT. Strong Balmer lines were detected in emission along with P Cygni profiles. Other emission lines are also detected with a full analysis being undertaken. This transient is of interest because of its rapid rise, high amplitude (>8 mag) and its on-sky location being close to the LMC. This suggests it is an outburst from accreting binary, possibly a cataclysmic variable of the nova class or a Symbiotic nova. Follow-up observations are strongly encouraged, especially spectroscopy, to follow its evolution over the 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; University of Birmingham; and the UK Science and Technology Facilities Council (STFC, grant numbers ST/T007184/1, ST/T003103/1 and ST/Z000165/1). The spectrum was obtained as part of the SAAO Lesedi Automatic Transient follow-up program.