TITLE:   GCN CIRCULAR
NUMBER:  9208
SUBJECT: GRB 090422: Swift-XRT refined analysis
DATE:    09/04/23 14:58:43 GMT
FROM:    Matteo Perri at ISAC/ASDC  <perri@asdc.asi.it>

M. Perri and G. Stratta (ASDC) report on behalf of the Swift-XRT Team:

We have analysed the first 31 ks of Swift-XRT data obtained from
GRB 090422 (trigger 349931; Ukwatta et al., GCN Circ. 9185), starting
from T+70 s and ending at T+70 ks.

The best position of the X-ray afterglow is the UVOT-enhanced XRT
position given in Beardmore et al. (GCN Circ. 9194).

The 0.3-10 keV X-ray light curve is well described by a double broken
power-law model with decay indices alpha1=-1.7+/-0.2, alpha2=-0.2+/-0.3,
alpha3=-1.0+/-0.1 and temporal breaks t1=421+/-92 s and t2=1.5+/-0.3 ks .

The X-ray spectrum is well fit by an absorbed power-law model with a
photon index of 2.5+/-0.2 and a column density of (2.3+/-0.7)e21 cm**-2
in excess to the Galactic one in the direction of the source
(1.7e21 cm**-2, Kalberla et al. 2005). The count-rate to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum is 3.6(8.7)E-11 erg cm**-2 count**-1.

Assuming the X-ray emission continues to decline at the same rate, we
predict a 0.3-10 keV XRT count rate of 2e-3 count/s at T+48hr, which
corresponds to an observed 0.3-10 keV flux of ~7e-14 erg/cm**2/s.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00349931.

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