TITLE:   GCN CIRCULAR
NUMBER:  11865
SUBJECT: GRB 110402A: Swift-XRT refined Analysis
DATE:    11/04/02 11:17:47 GMT
FROM:    Claudio Pagani at U of Leicester  <cp232@star.le.ac.uk>

C. Pagani (U. Leicester) and T. N. Ukwatta (MSU) report on behalf of
the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 110402A (Ukwatta  et al.
GCN Circ. 11857), from 552 s to 24.7 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Beardmore et al. (GCN. Circ
11860).

The late-time light curve (from T0+6.4 ks) can be modelled with  a
power-law decay with a decay index of alpha=1.3 (+/-0.4).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.31 (+0.25, -0.27). The
best-fitting absorption column is  10.0 (+2.9, -5.6) x 10^20 cm^-2, in
excess of the Galactic value of 1.6 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 3.3 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     10.0 (+2.9, -5.6) x 10^20 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: 2.9 sigma
Photon index:	     2.31 (+0.25, -0.27)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00450545.

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