Swift J1858.6-0814: Swift XRT and UVOT localization
ATel #12160; J. A. Kennea (PSU) and H. A. Krimm (NSF/USRA) on behalf of the Swift Team
on 3 Nov 2018; 00:39 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Transient
Swift performed a target of opportunity observation of Swift J1858.6-0814 (Krimm et al. ATEL #12151) starting on Nov 2nd at 14:30UT. A 1ks exposure in Photon Counting mode was taken. We find a previously uncatalogued point source at the following position, RA/Dec = 284.64565, -8.23789, which is equivalent to:
RA(J200) = 18h 58m 34.96s,
Dec(J2000) = -08d 14' 16.4'',
with an estimated error of 2.2 arc-seconds radius (90% confidence).
The PC mode data, corrected for pile-up, show a hard spectrum, with a photon index of 0.22 +/-0.23, with absorption consistent with the Galactic value. The PC mode light curve shows significant flaring over the short exposure, as previously reported by NICER observations (Ludlam et al., ATEL #12158).
The XRT position is consistent with stars in the UKIDSS-DR5 and Pan-STARRS PS1 catalogs. The star, designated UGPS J185834.91-081414.8 in the UKIDSS-DR5 catalog, has a J-band magnitude of 18.5.
In UVOT data, taken in three UV filters, a point source was detected at a position consistent with the XRT position, RA/Dec = 284.64549, -8.23775, equivalent to:
RA(J2000) = 18h 58m 34.9s
Dec(J2000) = -8d 14' 15.89''
This position lies 0.74 arc-seconds from the center of the XRT error region. The UVOT measured magnitudes are uvw1 = 16.87 +/- 0.20 (stat) +/- 0.03 (sys), uvm2 = 16.32 +/- 0.16 (stat) +/- 0.03 (sys), uvw2 = 17.38 +/- 0.05 (stat) +/- 0.03 (sys) in the Vega system.
The source continues to be detected in the BAT at approximately the same level reported in Krimm et al. (ATEL #12151).
