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GCN Circular 13563

Subject
GRB 120802A: Swift-XRT refined Analysis
Date
2012-08-02T20:14:04Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), J.P. Osborne
(U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), V.
Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU) and S.T. Holland report on behalf of the Swift-XRT team:

We have analysed 7.0 ks of XRT data for GRB 120802A (Holland  et al.
GCN Circ. 13555), from 88 s to 17.6 ks after the  BAT trigger. The data
comprise 22 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Evans et al. (GCN. Circ 13558).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.7 (+/-0.4), followed by a break at T+270 s to an alpha
of 0.35 (+/-0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.10 (+0.21, -0.20). The
best-fitting absorption column is  1.5 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 9.6 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 3.6 x 10^-11 (5.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.5 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 9.6 x 10^20 cm^-2
Excess significance: 1.8 sigma
Photon index:	     2.10 (+0.21, -0.20)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00529486.

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