GCN Circular 8970
Subject
GRB 090309: Swift-XRT refined analysis
Date
2009-03-10T15:43:56Z (15 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P. A. Evans (U Leicester) reports on behalf of the Swift-XRT team:
We have analysed 5.5 ks of XRT data for GRB 090309 (Evans et al. GCN
Circ. 8964), from 86 s to 12.4 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Goad et al. (GCN. Circ 8969).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.38 (+0.08, -0.09).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+/-0.3). The best-fitting
absorption column is 2.8 (+1.5, -1.1) x 10^21, in excess of the Galactic
value of 1.1 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to
observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from
this spectrum is 4.0 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1.
If the light curve continues to decay with a power-law decay index of
0.38, the count rate at T+24 hours will be 0.012 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.8 x
10^-13 (8.2 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00345945.
This circular is an official product of the Swift-XRT team.