[vsnet-grb-info 11650] GRB 120311A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13043
SUBJECT: GRB 120311A: Swift-XRT refined Analysis
DATE:    12/03/11 22:58:04 GMT
FROM:    Andrea Melandri at INAF-OAB  <andrea.melandri at brera.inaf.it>

A. Melandri (INAF/OAB), P. D'Avanzo (INAF/OAB) and C. B. Markwardt
(NASA/GSFC) report on behalf of the Swift-XRT team:

We have analysed 15 ks of XRT data for GRB 120311A (Markwardt  et al.
GCN Circ. 13032), from 3.2 ks to 34.5 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 13035). 

The late-time light curve (from T0+3.2 ks) can be modelled with a
single power-law decay with a decay index of alpha=1.09 (+0.13,-0.12).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.03 (+0.27, -0.25). The
best-fitting absorption column is  2.6 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 1.0 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 (6.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.6 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 1.0 x 10^21 cm^-2
Excess significance: 3.2 sigma
Photon index:	     2.03 (+0.27, -0.25)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00517469.

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