[vsnet-grb-info 12375] GRB 120911A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13750
SUBJECT: GRB 120911A: Swift-XRT refined Analysis
DATE:    12/09/11 16:15:12 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

K.L. Page (U. Leicester) and J. K. Cannizzo (NASA/UMBC) report on
behalf of the Swift-XRT team:

We have analysed 7.2 ks of XRT data for GRB 120911A (Cannizzo  et al.
GCN Circ. 13744), from 3.3 ks to 17.3 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
13748).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.31 (+0.22, -0.21).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.0 (+/-0.4). The
best-fitting absorption column is  8.4 (+3.4, -1.8) x 10^21 cm^-2,
consistent with the Galactic value of 6.7 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 5.4 x 10^-11 (1.0 x
10^-10) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.4 (+3.4, -1.8) x 10^21 cm^-2
Galactic foreground: 6.7 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.0 (+/-0.4)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00533268.

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