[vsnet-grb-info 12064] GRB 120711B: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13453
SUBJECT: GRB 120711B: Swift-XRT refined Analysis
DATE:    12/07/12 05:58:14 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

K.L. Page (U. Leicester) and M. J. Page (UCL-MSSL) report on behalf of
the Swift-XRT team:

We have analysed 4.5 ks of XRT data for GRB 120711B (Page  et al. GCN
Circ. 13431), from 208 s to 47.2 ks after the  BAT trigger. The data
comprise 106 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. Using 551 s of PC mode data and 2 UVOT
images, we find an enhanced XRT position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
331.69137, +60.02267 which is equivalent to:

RA (J2000): 22h 06m 45.93s
Dec(J2000): +60d 01' 21.6"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.69 (+0.22, -0.17).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.8 (+0.5, -0.4). The
best-fitting absorption column is  2.4 (+0.9, -0.8) x 10^22 cm^-2, in
excess of the Galactic value of 7.2 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.5 (+0.4, -0.3) and
a best-fitting absorption column of 2.9 (+0.7, -0.6) x 10^22 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 9.9 x 10^-11 (1.7 x 10^-10) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.9 (+0.7, -0.6) x 10^22 cm^-2
Galactic foreground: 7.2 x 10^21 cm^-2
Excess significance: 5.6 sigma
Photon index:	     1.5 (+0.4, -0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00526270.

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