TITLE:   GCN CIRCULAR
NUMBER:  14547
SUBJECT: GRB 130502A: Swift-XRT refined Analysis
DATE:    13/05/03 20:29:32 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

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

We have analysed 2.3 ks of XRT data for GRB 130502A (Troja  et al. GCN
Circ. 14527),  from 76 s to 16.0 ks after the  BAT trigger. The data
comprise 8 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. 

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.68 (+/-0.07).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+/-0.3). The
best-fitting absorption column is  1.6 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 2.5 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 3.4 x 10^-11 (5.3 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 2.5 x 10^20 cm^-2
Excess significance: 3.2 sigma
Photon index:	     2.2 (+/-0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00554996.

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