GCN Circular 20034
F. E. Marshall (NASA/GSFC) and A. D'Ai (INAF-IASFPA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 161010A 3.3 hours after the INTEGRAL trigger (Mereghetti et al., GCN Circ. 20021). A source consistent with the XRT position (McCauley et al., GCN Circ. 20025) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 18:20:51.27 = 275.21364 (deg.) Dec (J2000) = -28:47:06.7 = -28.78519 (deg.) with an estimated uncertainty of about 1 arc sec. (radius, 90% confidence). As shown in the table below, the source faded in the observations using the U filter, suggesting that it could be the afterglow of the GRB. However, the GRB is only 7.8 degrees from the direction of the Galactic Center, and this is a crowded field for UVOT. Consequently, the association of the source with the GRB is not certain. Preliminary magnitudes using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag u 12034 13628 1035 18.8 +/- 0.1 u 17802 19985 744 19.0 +/- 0.1 u 23563 25993 794 19.4 +/- 0.2 u 29338 30137 787 20.4 +/- 0.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.54 in the direction of the burst (Schlegel et al. 1998).