TITLE: GCN CIRCULAR NUMBER: 11319 SUBJECT: GRB 101008A: Swift/XRT Detection of an Afterglow with no UVOT Counterpart DATE: 10/10/08 18:34:31 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC W. H. Baumgartner (GSFC/UMBC), P. A. Evans (U Leicester), S. T. Holland (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL), C. Pagani (U Leicester), K. L. Page (U Leicester), and M. H. Siegel (PSU) report on the behalf of the Swift UVOT team: The XRT began observing the field of GRB 101008A (Baumgartner et al. 2010, GCNC 11318) at 17:35:56.9 UT, 3161.7 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 328.87463, 37.06580 which is equivalent to: RA(J2000) = 21h 55m 29.91s Dec(J2000) = +37d 03' 56.9" with an uncertainty of 3.9 arcseconds (radius, 90% containment). This location is 48 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.44 x 10^21 cm^-2, Kalberla et al. 2005), with an excess column of 3 (+4.38/-2.94) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the white filter starting 3167 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7' x 2.7' sub-image covers 100% of the XRT error circle. The preliminary 3-sigma upper limit in the white filter is 20.3 mag. No correction has been made for the expected Galactic extinction corresponding to a reddening of E_{B-V} = 0.19 mag. Photometry is on the UVOT photometry system of Poole et al. (2008).