GCN Circular 12261

G. Stratta and V. D'Elia (ASDC) report on behalf of the Swift-XRT team:


We have analysed 3.8 ks of XRT data for GRB 110808A (Stratta  et al.
GCN Circ. 12256
Not found
 
 
), from 100 s to 18.0 ks after the  BAT trigger. The
data comprise 91 s in Windowed Timing (WT) mode (the first 9 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. The enhanced XRT position for this burst was given by Goad
et al. (GCN. Circ 12257).

The light curve can be modelled with an initial power-law decay with an
index of alpha=3.79 (+0.22, -0.20), followed by a break at T+459 s to
an alpha of 0.57 (+0.18, -0.23).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.07 (+0.29, -0.25). The
best-fitting absorption column is  2.9 (+1.4, -1.3) x 10^21 cm^-2, at a
redshift of 1.348 (de Ugarte Postigo et al. GCN Circ. 12258
Not found
 
 
), in
addition to the Galactic value of 1.0 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 2.2 x 10^-11 (3.5 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Galactic foreground: 1.0 x 10^20 cm^-2
Intrinsic column:    2.9 (+1.4, -1.3) x 10^21 cm^-2 at z=1.348
Photon index:	     3.07 (+0.29, -0.25)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00458918.

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