Swift J1858.6-0814: Localization and variability of the optical counterpart

ATel #12164; G. Vasilopoulos (Yale), C. Bailyn (Yale), J. Milburn (Caltech)
on 3 Nov 2018; 05:46 UT
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Credential Certification: Georgios Vasilopoulos (georgios.vasilopoulos@yale.edu)

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Swift J1858.6-0814: Localization and variability of the optical counterpart

G. Vasilopoulos (Yale), C. Bailyn (Yale), J. Milburn (Caltech)

Following the detection of the new galactic transient source Swift J1858.6-0814 (Krimm et al. ATEL #12151) we performed photometric follow up observations of its optical counterpart using the WASP instrument on the Hale 200" Telescope at Palomar Observatory.

We analyzed a Swift/XRT ToO observation (obsid: 00010955001) to obtain a rough localization of the source (see also Kennea et al. ATEL #12160). Optical observations were performed around the X-ray position. We identified an object consistent with the X-ray position reported by Kennea et al. ATEL #12160, that has brightened at least 2.5 magnitudes above the Pan-STARRS r' image (data release 1; Chambers+ 2016). The Pan-STARRS object ID is 98112846453925483 and its reported coordinates:

RA(J2000)= 18:58:34.893
DEC(J2000)=-08:14:14.938

A series of 20 second R-band exposures over a period of 40 minutes between 58425.11-58425.14 MJD showed the object to vary within the range r'=16.9 to r'=18.4 (+/- 0.1 magnitudes). Variability of up to 1 magnitude was observed on a timescale of 2 minutes.

Conditions were non-photometric, and magnitudes were determined by differential photometry with respect to Pan-STARRS objects 98112846446163754, 98112846438888093 and 98122846447171896.