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GCN Circular 12482

Subject
GRB 111022A: Swift-XRT refined Analysis
Date
2011-10-23T14:15:22Z (12 years ago)
From
Giulia Stratta at ASDC <stratta@asdc.asi.it>
G. Stratta (ASDC), V. D'Elia (ASDC) and S. Immler (CRESST/GSFC/UMD)
report on behalf of the Swift-XRT team:

We have analysed 1.1 ks of XRT data for GRB 111022A (Immler  et al. GCN
Circ. 12471), from 775 s to 1.9 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The refined XRT position is RA,
Dec = 275.86481, -23.67325 which is equivalent to:

RA (J2000): 18 23 27.55
Dec(J2000): -23 40 23.7

with an uncertainty of 3.6 arcsec (radius, 90% confidence). The light
curve is consistent with a constant source of mean count rate 1.1e-01
ct/sec. A power-law fit gives an index of 0.2 (+0.6, -0.7).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.3 (+0.6, -0.5). The
best-fitting absorption column is  6.8 (+4.0, -2.7) x 10^21 cm^-2, in
excess of the Galactic value of 2.2 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 4.4 x 10^-11 (1.0 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.8 (+4.0, -2.7) x 10^21 cm^-2
Galactic foreground: 2.2 x 10^21 cm^-2
Excess significance: 2.8 sigma
Photon index:	     2.3 (+0.6, -0.5)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00506070.

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