TITLE:   GCN CIRCULAR
NUMBER:  10505
SUBJECT: GRB 100316D: Swift XRT refined analysis
DATE:    10/03/16 18:32:59 GMT
FROM:    Rhaana Starling at U of Leicester  <rlcs1@star.le.ac.uk>

R.L.C. Starling, P.A. Evans (U. Leicester) and M. Stamatikos (OSU/NASA/GSFC) 
report on behalf of the Swift-XRT team:

We have analysed the first orbit of Swift XRT data for GRB 100316D (Stamatikos 
et al. GCN Circ. 10496), comprising 593 s of exposure
from 143 s to 737 s after the BAT trigger. The data are solely in
Windowed Timing (WT) mode. The light curve over this time decays very 
slowly and can be modelled with a power-law with a decay index of
alpha=0.13+/-0.03.

A spectrum formed from these data can be fitted with an absorbed power-law with 
a photon spectral index of 1.42 (+/-0.04). The best-fitting absorption column 
is 5.9 (+/-0.3) x 10^21 cm^-2, in excess of the Galactic value of 7.0 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 6.6 x 10^-11 
(8.7 x 10^-11) erg cm^-2 count^-1.

If the decay contines with alpha=0.13, the predicted count rate at T+24h 
is 16 count s^-1 or an observed (unabsorbed) 0.3-10 keV flux of 1.1 (1.4) 
x10^-9 erg cm-2 s-1.

The results of the XRT-team automatic analysis are available at 
http://www.swift.ac.uk/xrt_products/00416135.

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