TITLE: GCN CIRCULAR NUMBER: 9840 SUBJECT: GRB 090823: Swift XRT possible detection of the X-ray afterglow DATE: 09/08/25 19:20:00 GMT FROM: Dirk Grupe at PSU/Swift-XRT D. Grupe (PSU), E. Hoversten (PSU) and Jay Cummings (NASA/GSFC) report on behalf of the Swift team: We have analysed the XRT and UVOT data of the IPN burst GRB090823 (Cummings et al. GCN Circ. 9835), beginning on 2009-08-24 at 22:17, 30 hours after the Suzaku WAM trigger. The data contain 4.7 ks in XRT photon counting mode. We clearly detect a possible X-ray afterglow within the 4' BAT error circle given by Cummings and Copete et al. (GCN circs. 9838 and 9839, respectively) at RA-2000,Dec-2000=128.67676, +60.65169 which corresponds to RA-2000 = 08h 34m 42.42s Dec-2000 = +60d 39' 06.1" with an uncertainty of 5.5" During the 4.7 ks observation on 2009-08-24 the X-ray source had a count rate of (5.7+/-1.1)e-3 counts s-1 in the XRT which converts to an observed flux in the 0.3-10 keV band of (2.9+/-0.5)e-13 ergs s-1 cm-2 assuming a typical GRB afterglow spectrum. The Swift/UVOT began settled observations of the field of GRB 090823 108380 s after the BAT trigger (Cummings, et al., GCN Circ. 9835). No optical afterglow consistent with the XRT position is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits 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 109194 115699 1464 >21.8 v 110009 116640 1680 >20.1 u 108380 114954 1597 >20.7 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998). Swift is planning to re-observe the field of GRB 090823 on 2009-08-27 for 10 ks in order to see if the X-ray source has faded. This circular is an official product of the Swift team.