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GCN Circular 13724

Subject
GRB 120907A: Swift-XRT refined Analysis
Date
2012-09-07T16:38:07Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
A. Maselli  (INAF-IASFPA), V. Mangano (INAF-IASFPA), A. Melandri
(INAF-OAB), 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) and J.L. Racusin report on behalf of the Swift-XRT team:

We have analysed 16 ks of XRT data for GRB 120907A (Racusin  et al. GCN
Circ. 13716), from 93 s to 46.4 ks after the  BAT trigger. The data
comprise 76 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Goad et al. (GCN. Circ 13722).

The late-time light curve (from T0+4.5 ks) can be modelled with  a
power-law decay with a decay index of alpha=1.02 (+/-0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.91 (+0.13, -0.12). The
best-fitting absorption column is  10.0 (+3.1, -2.9) x 10^20 cm^-2, in
excess of the Galactic value of 5.4 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 3.8 x 10^-11 (4.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     10.0 (+3.1, -2.9) x 10^20 cm^-2
Galactic foreground: 5.4 x 10^20 cm^-2
Excess significance: 2.7 sigma
Photon index:	     1.91 (+0.13, -0.12)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00532871.

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