TITLE: GCN CIRCULAR NUMBER: 12067 SUBJECT: Swift detection of the X-ray afterglow of GRB 110604A DATE: 11/06/10 17:07:44 GMT FROM: Boris Sbarufatti at INAF-OAB/IASFPA B. Sbarufatti (INAF-OAB/IASFPA), J. Cummings (GSFC), M. De Pasquale (MSSL) report on behalf of the Swift Team. We have analyzed 14.5 ks of Photon Counting data for GRB 110604A (Barthelmy et al., GCN 12063), observed from 138 ks to 425 ks after the Konus-Wind trigger. We find a single, fading source inside the XRT field of view. Using 2497 s of XRT Photon Counting mode data and 2 UVOT images, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 270.85885, +18.39961 which is equivalent to: RA (J2000): 18h 03m 26s.12 Dec(J2000): +18d 23' 58".6 with an uncertainty of 2.4 arcsec (radius, 90% confidence). This is 9.3 arcmin away from the initial IPN position. The source was first detected at a level of (1.2+/-0.2)E-3 counts/s (equivalent to 5.1E-13 erg cm^-2 s^-1), 138 ks after the trigger, and has faded to a level of (1.4+/-0.6)E-3 counts/s at 421 ks (equivalent to 6.0E-14 erg cm^-2 s^-1). Another Swift observation is planned for June 14, 2011 in order to confirm fading. No optical source is found within the XRT error circle. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) are: Filter T_start (s) T_end (s) Exp (s) mag white 207930 237252 1399 >22.9 v 208162 237295 516 >19.6 u 207698 240533 2864 >21.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.24 in the direction of the burst (Schlegel et al. 1998). This circular is an official product of the Swift-XRT team.