GCN Circular 8811

P.A. Evans (U. Leicester)  and H. A. Krimm (CRESST/GSFC/USRA) report on behalf
of the Swift-XRT team:

We have analysed 5.5 ks of XRT data for GRB 090113 (Krimm et al. GCN Circ.
8804
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 ), beginning 93 s 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 8809).

The light curve can be modelled with a power-law decay with a decay index of
alpha=0.991 (+/-0.042).

A spectrum formed from the PC mode data can be fitted with an absorbed power-law
with a photon spectral index of 2.28 (+0.20, -0.19). The best-fitting absorption
column is 3.20 (+0.63, -0.58) x 10^21, in excess of the Galactic value of 6.7 x
10^20 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 (7.8 x
10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of 0.991, the
count rate at T+24 hours will be 0.0063 count s^-1, corresponding to an observed
(unabsorbed) 0.3-10 keV flux of 2.5 x 10^-13 (4.9 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/00339852.

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