More optical follow-up of Swift J1858.6-0814

ATel #12186; Kaustubh Rajwade (University of Manchester), Mark Kennedy (University of Manchester), Rene Breton (University of Manchester), Benjamin Stappers (University of Manchester), Siraprapa Sanpa-arsa (NARIT), Puji Irawati (NARIT), Vik Dhillon (University of Sheffield), Tom Marsh (University of Warwick)
on 7 Nov 2018; 21:57 UT
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Credential Certification: Kaustubh Rajwade (rkaustubh10@gmail.com)

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Following the X-ray and optical detection of a new transient source, Swift J1858.6-0814 (ATel# 12151, ATel#12164, ATel#12180 ), we performed optical follow-up observations of the source using the ULTRASPEC instrument mounted on the 2.4m Thai National Telescope. The observations were performed on 6th of November starting at UT11:58:20.65 in SDSS r'-band. The exposure time per frame was 7s, with a dead time of 15 ms between the frames, and a total of 70 minutes of data were obtained The target is detected in all of our frames and the position is consistent with the position previously reported in ATel#12180. The archival Pan-STARRS r'-band magnitude of the system is 19.9705. We find that the source varies between an r'-band magnitude of 18.1 and 16.3 on a timescale of a few tens of seconds. In particular, we note the detection of a very rapid flare with a total duration < 21s in which the system brightens and fades by 0.9 magnitudes. Attached figure shows our light curve, calibrated using 3 stars in the field, the Pan-STARRS stacked g' image (top left), a 70s stack of our ULTRASPEC data (top right), and the Swift XRT position (white). Further high time resolution optical and X-ray observations are highly encouraged.

Light curve for SwiftJ1858.6-0814