TITLE: GCN CIRCULAR NUMBER: 11442 SUBJECT: GRB 101204A Swift-XRT/UVOT afterglow candidate DATE: 10/12/06 19:22:04 GMT FROM: Boris Sbarufatti at INAF-OAB/IASFPA B. Sbarufatti (INAF-OAB/IASFPA), S. Oates (MSSL) report on behalf of the Swift-XRT and Swift-UVOT teams We have analysed 4.9 ks of XRT data for GRB 101204A (Cummings et al. GCN Circ. 11440), from 126.2 ks to 134.4 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. Using 4956 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 167.53712, -20.41924 which is equivalent to: RA (J2000): 11h 10m 08.91s Dec(J2000): -20d 25' 09.2" with an uncertainty of 2.3 arcsec (radius, 90% confidence). The source is detected at a level of 2.0+/-0.2E-3 counts/s, corresponding to a 0.3-10 keV flux of 1.4E-12 erg cm-2 s-1. At this time we are not able to tell if the source is fading. The Swift/UVOT began settled observations of the field of GRB 101204A 126199 s after the BAT trigger (Cummings et al., GCN Circ. 11440). An uncatalogued source is found at the UVOT position RA(J2000)= 167.53683 deg, DEC(J2000) = -20.42014, which is: RA (J2000) = 11:10:08.84 Dec (J2000) = -20:25:12.5 with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence). This position is consistent with the XRT candidate position. At this time we are not able to tell if this source is fading. Preliminary magnitudes using the UVOT photometric system(Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag ##################################################### v 126194 127496 1281 20.28 +/- 0.24 v 131976 133278 1281 20.71 +/- 0.34 u 127505 128780 1255 19.79 +/- 0.13 u 133286 134378 1074 19.91 +/- 0.15 ##################################################### The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel et al. 1998).