[vsnet-grb-info 11859] GRB 120422A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13249
SUBJECT: GRB 120422A: Swift-XRT refined Analysis
DATE:    12/04/22 19:23:05 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

B. Sbarufatti (INAF-OAB/PSU), G. Stratta (ASDC), P. D'Avanzo
(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 E. Troja report on behalf of the Swift-XRT team:

We have analysed 13 ks of XRT data for GRB 120422A (Troja  et al. GCN
Circ. 13243), from 101 s to 30.1 ks after the  BAT trigger. The data
comprise 307 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Beardmore et al. (GCN. Circ 13247).

The light curve can be modelled with an initial power-law decay with an
index of alpha=6.22 (+0.30, -0.28), followed by a break at T+373 s to
an alpha of 0.30 (+0.11, -0.14).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 4.5 (+0.4, -0.3). The
best-fitting absorption column is  2.5 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 3.7 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 1.9 x 10^-11 (1.7 x 10^-10) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     2.5 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 3.7 x 10^20 cm^-2
Excess significance: 8.5 sigma
Photon index:	     4.5 (+0.4, -0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00520658.

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