TITLE:   GCN CIRCULAR
NUMBER:  9961
SUBJECT: GRB090926A: Swift-XRT refined analysis 
DATE:    09/09/28 21:59:52 GMT
FROM:    Loredana Vetere at PSU  <vetere@astro.psu.edu>

L. Vetere (PSU) reports on behalf of the Swift-XRT team:

We have analyzed the first 21.8 ks of Swift-XRT data of FERMI
GRB090926A (Bissaldi et al., GCN Circ. 9933). The UVOT-enhanced XRT
position for this burst was given in GCN Circ.9936 (Vetere et al.).

The data are entirely in Photon Counting (PC) mode from T+46.7 ks
to T+203 ks. The light curve shows a decaying behaviour with some
flaring activity. It is best fitted by a power-law with decay index
1.29+/-0.2. Assuming the X-ray emission from the burst continues
to decline at the present rate, the predicted count rate at T+3d
is 0.009 cts/s.

The average spectrum is best fit by an absorbed power-law model
with a photon spectral index of 2.6 (+0.3,-0.2) and an absorption
column density of 1.0 (+0.5,-0.3)e21 cm-2 in excess of the Galactic
value of 2.7e20 cm-2 (Kalberla et al. 2005). The counts-to-observed
0.3-10 keV flux conversion factor deduced from this spectrum is
3.5e-11 erg cm-2 count-1. The average observed (unabsorbed) fluxes
are 1.3 (1.9)E-12 ergs cm-2 s-1. Errors are given at the 90%
confidence level.

This circular is an official product of the Swift-XRT team.