TITLE: GCN CIRCULAR NUMBER: 9031 SUBJECT: GRB 090323: Swift-XRT refined analysis DATE: 09/03/24 16:53:38 GMT FROM: Matteo Perri at ISAC/ASDC M. Perri and G. Stratta (ASDC) report on behalf of the Swift-XRT team: We have analysed the first 6 ks of Swift-XRT data of the Fermi GRB 090323 (Ohno et al., GCN Circ. 9021). The data, starting at 2009-03-23 19:27:51 UT and ending at 2009-03-24 09:47:02 UT, is all taken in Photon Counting (PC) mode. The X-ray source reported by Kennea et al. (GCN Circ. 9024) is found to be fading and we thus confirm that it was the afterglow of GRB 090323. In the time interval T+70 ks-T+121 ks the X-ray light-curve can be modelled by a simple power law with a decay index alpha=2.1 (+0.9)(-0.7). The X-ray spectrum is well fit by an absorbed power-law model with a photon index of 2.2 (+/-0.4) and a column density consistent with the Galactic one in the direction of the source (1.7e20 cm**-2, Kalberla et al. 2005). The estimated 3-sigma (2-sigma) upper limit on the intrinsic column density at z=3.6 (Chornock et al., GCN Circ. 9028) is 5.1e22cm**-2 (2.7e22cm**-2). All the quoted errors are at the 90% confidence level. 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+48hr, which corresponds to an observed 0.3-10 keV flux of ~2e-13 erg/cm**2/s. This circular is an official product of the Swift-XRT Team.