TITLE: GCN CIRCULAR NUMBER: 9212 SUBJECT: GRB 090423: Swift-XRT refined analysis DATE: 09/04/23 20:06:55 GMT FROM: Matteo Perri at ISAC/ASDC G. Stratta and M. Perri (ASDC) report on behalf of the Swift-XRT Team: We have analysed the first 8.4 ks of Swift-XRT data obtained from GRB 090423 (trigger 350184; Krimm et al., GCN Circ. 9198), starting from T+110 s and ending at T+18 ks. The best position of the X-ray afterglow is the UVOT-enhanced XRT position given in Evans et al. (GCN Circ. 9205). The 0.3-10 keV X-ray light curve during the first Swift orbit shows a flare peaking at T+170s. Starting from the second orbit (T+3.9 ks) the curve is well described by a power-law model with index alpha=-1.3+/-0.1. The X-ray spectrum during the power-law decay is well fit by an absorbed power-law model with a photon index of 2.0+/-0.1 and a total column density of (8.7+/-2.5)e20 cm**-2. The Galactic column density in the direction of the source is 2.9e20 cm**-2 (Kalberla et al. 2005). The count-rate to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7(4.6)E-11 erg cm**-2 count**-1. Errors are given at the 1-sigma level. We note that the X-ray column density is consistent, within 3 sigma, with the Galactic value, consistent with the possibility that the burst is at high redshift, as reported by Cucchiara et al. (GCN Circ. 9209). Assuming the X-ray emission continues to decline at the same rate, we predict a 0.3-10 keV XRT count rate of 5e-3 count/s at T+24 hr, which corresponds to an observed 0.3-10 keV flux of ~2e-13 erg/cm**2/s. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00350184. This circular is an official product of the Swift-XRT team.