Swift UV and X-ray Observation of GOTO 065054.49+593624.51

ATel #16866; Sayantan Bhattacharya (TIFR, Mumbai), Sudip Bhattacharyya (TIFR, Mumbai)
on 14 Oct 2024; 06:28 UT
Credential Certification: Sayantan Bhattacharya (sayantan34@gmail.com)

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The bright optical transient GOTO 065054.49+593624.51 was discovered by the GOTO survey on 4 October 2024 at 03:36:36 UT, with a GOTO L-band magnitude of 13.37 (ATel #16842), located at RA(J2000) = 06h 50m 54.49s, Dec(J2000) = +59°36'24.51". The transient faded by 0.26 mag in 18.5 hours (ATel #16847). Spectra from the Nordic Optical Telescope and Liverpool Telescope on Oct 8 (ATel #16858) shows a strong blue continuum with weak H\alpha and higher-order Balmer absorption lines, consistent with WZ Sge-type accreting binaries undergoing rare outbursts on a timescale of many years to decades. Following its optical discovery, the Einstein Probe (EP) detected the X-ray counterpart of GOTO 065054.49+593624.51 (ATel #16851), located 3.6" from the optical position on 2024-10-06 at 15:03:44 UTC. The unabsorbed X-ray flux was measured at 8.1(+1.9/-1.4) x 10^(-14) erg/s/cm^-2 in the 0.5-10 keV band. We report results from a Swift-ToO follow-up observation conducted on 2024-10-11 at 04:33:00 UTC, with an exposure time of 985 s. A faint X-ray source was detected at the EP coordinates, and the XRT light curve revealed a count rate of (4.1 +- 2.0) x 10^(-3) cps, corresponding to a flux of (8.9 +- 3.7)x10^(-14) ergs/cm^2/s in the 0.5-10 keV band. Due to the low count rate, a well-constrained spectral fit was not possible, so the EP spectral parameters (an absorbed power-law model with a photon index of 3.23 and a column density of 7.1 x 10^20 cm^-2) were used to estimate the flux. The Swift/UVOT image also detected a bright source at the optical location. Using the 'uvotsource' pipeline, the UVM2 magnitude was measured to be 13.97 +- 0.01 AB mag (12.28 Vega mag). This confirms the source as a slowly decaying CV, remaining in a bright state 7 days after its discovery. Continued multi-wavelength monitoring is strongly encouraged to track the evolution of this rare outburst.