[vsnet-grb-info 7658] GRB 090423: Swift-XRT refined analysis

[GCN Circulars]

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  <perri at asdc.asi.it>

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.