[vsnet-grb-info 12191] GRB 120804A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13580
SUBJECT: GRB 120804A: Swift-XRT refined Analysis
DATE:    12/08/04 13:07:05 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

M.C. Stroh (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), C.
Pagani (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri
(INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), G. Stratta (ASDC), J.A.
Kennea (PSU) and A.Y. Lien report on behalf of the Swift-XRT team:

We have analysed 9.2 ks of XRT data for GRB 120804A (Lien  et al. GCN
Circ. 13573), from 78 s to 28.8 ks after the  BAT trigger. The data
comprise 33 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Osborne et
al. (GCN. Circ 13577).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.11 (+/-0.03).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.98 (+0.21, -0.20). The
best-fitting absorption column is  3.5 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 9.3 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 4.3 x 10^-11 (7.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.5 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 9.3 x 10^20 cm^-2
Excess significance: 5.3 sigma
Photon index:	     1.98 (+0.21, -0.20)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00529686.

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