[vsnet-grb-info 13764] GRB 130806A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15078
SUBJECT: GRB 130806A: Swift-XRT refined Analysis
DATE:    13/08/07 05:26:22 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

K.L. Page (U. Leicester) and B.P. Gompertz (U Leicester) report on
behalf of the Swift-XRT team:

We have analysed 12 ks of XRT data for GRB 130806A (Gompertz  et al.
GCN Circ. 15071),  from 77 s to 57.9 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Beardmore et al. (GCN. Circ
15072).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.57 (+0.08, -0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.6 (+0.6, -0.5). The
best-fitting absorption column is  6.8 (+4.7, -2.9) x 10^21 cm^-2,
consistent with the Galactic value of 3.9 x 10^21 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 6.1 x 10^-11 (9.0 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.8 (+4.7, -2.9) x 10^21 cm^-2
Galactic foreground: 3.9 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.6 (+0.6, -0.5)

If the light curve continues to decay with a power-law decay index of
0.57, the count rate at T+24 hours will be 2.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-13 (2.5 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/00565562.

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