GCN Circular 9031
Subject
GRB 090323: Swift-XRT refined analysis
Event
Date
2009-03-24T16:53:38Z (18 years ago)
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 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.