GCN Circular 9918
E. A. Hoversten (PSU) and T. Sakamoto (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 090915 44647 s after the BAT trigger (Cummings & Markwardt, GCN Circ. 9912). A faint source is detected with 5.6-sigma confidence in the summed UVOT observations at the position RA, Dec (J2000) = 238.02016,15.48772 which is equivalent to: RA (J2000) = 15:52:04.84 Dec (J2000) = 15:29:15.8 with an estimated uncertainty of 0.8 arcsec (radius, 90% confidence). This position is 0.2 arcsec from the UVOT-enhanced XRT position (Beardmore, et al. GCN Circ. 9914) and the two positions agree within the error bars. It is unclear at this point if the source is fading, but follow-up Swift observations are being planned. The observed 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 ======================================================================= white 45492 52117 1647 22.15 +/- 0.24 (4.7 sigma) v 46338 52837 1583 21.08 +/- 0.39 (2.8 sigma) u 44647 51275 1647 21.40 +/- 0.43 (2.5 sigma) The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998).