TITLE:   GCN CIRCULAR
NUMBER:  14853
SUBJECT: GRB 130610A: Swift-XRT refined Analysis
DATE:    13/06/10 15:22:03 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.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),
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz
(U. Leicester) and J.R. Cummings report on behalf of the Swift-XRT
team:

We have analysed 11 ks of XRT data for GRB 130610A (Cummings  et al.
GCN Circ. 14842),  from 139 s to 25.1 ks after the  BAT trigger. The
data comprise 116 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN. Circ 14851).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.17 (+/-0.03).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.04 (+/-0.15). The
best-fitting absorption column is  2.6 (+2.8, -2.6) x 10^21 cm^-2, at a
redshift of 2.092, in addition to the Galactic value of 1.9 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 (3.9 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.9 x 10^20 cm^-2
Intrinsic column:    2.6 (+2.8, -2.6) x 10^21 cm^-2 at z=2.092
Photon index:	     2.04 (+/-0.15)

If the light curve continues to decay with a power-law decay index of
1.17, the count rate at T+24 hours will be 3.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (1.3 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00557845.

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