TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5396 SUBJECT: GRB 060804: Swift-XRT Team Refined Analysis DATE: 06/08/04 19:29:01 GMT FROM: Kim Page at U.of Leicester K.L. Page (U. Leicester) & H.Z. Ziaeepour (UCL-MSSL) report on behalf of the Swift-XRT team: We have analysed the first 6 orbits of the XRT data obtained for GRB 060804 (trigger 222546). Using these 4340 seconds of data, we find a refined position of: RA(J2000) = 07 28 49.40 Dec(J2000) = -27 12 58.7 with an uncertainty of 3.6 arcsec (90% containment). This is 0.2 arcsec from the initial XRT position stated in GCN 5394 (Ziaeepour et al.) and 53.8 arcsec from the refined BAT position in GCN 5395 (Tueller et al.) The X-ray afterglow was sufficiently faint for the XRT to collect data only in Photon Counting mode. During the first orbit, the count rate remained close to constant, at ~1.5 count s^-1. Orbits 2-6, however, show a power-law decay, with a slope alpha = 0.86 +/- 0.22. There is no evidence for spectral evolution between the first orbit (where the light-curve is flat) and the later decay, with the spectrum being well fitted with a simple power-law of Gamma = 2.24 +/- 0.22, with the Galactic absorbing column of 5.34e21 cm^-2; no excess NH is required. Between 130 and 700 seconds after the burst, the 0.3-10 keV observed (unabsorbed) flux was 6.95e-11 (1.44e-10) erg cm^-2 s^-1. If the afterglow continues to decay at the same rate, the count rate at 24 hours is predicted to be 0.012 count s^-1, corresponding to an observed (unabsorbed) flux of 6.02e-13 (1.25e-12). This circular is an official product of the Swift-XRT team.