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GCN Circular 13053

Subject
GRB 120312A: Swift-XRT refined Analysis
Date
2012-03-13T04:34:08Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows
(PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), O.M.
Littlejohns (U. Leicester) and M. Stamatikos report on behalf of the
Swift-XRT team:

We have analysed 9.9 ks of XRT data for GRB 120312A (Stamatikos  et al.
GCN Circ. 13049), from 112 s to 19.6 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. Using 2188 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 = 251.78816, +23.85817 which is equivalent to:

RA (J2000): 16h 47m 09.16s
Dec(J2000): +23d 51' 29.4"

with an uncertainty of 1.6 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.28 (+0.14, -0.13).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.54 (+0.26, -0.25). The
best-fitting absorption column is  1.4 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 4.1 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 4.9 x 10^-11 (5.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.4 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 4.1 x 10^20 cm^-2
Excess significance: 2.1 sigma
Photon index:	     1.54 (+0.26, -0.25)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00517566.

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