[AAVSO-HEN] GRB 080913: Swift-XRT refined analysis

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
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TITLE:   GCN CIRCULAR
NUMBER:  8226
SUBJECT: GRB 080913: Swift-XRT refined analysis
DATE:    08/09/13 17:30:12 GMT
FROM:    Andy Beardmore at U Leicester  <apb at star.le.ac.uk>

A.P. Beardmore (U. Leicester) and P. Schady (MSSL-UCL) report on behalf
of the Swift-XRT team :

The Swift-XRT started observing the field of GRB 080913 (trigger number 
324561, Schady et al., GCN Circ. 8217) at 2008-09-13 06:48:30 UT, 94 s
after the trigger. The best XRT position is the UVOT-enhanced position
reported by Beardmore et al. (GCN Circ. 8219).

The X-ray light curve presently spans 5 orbits of photon counting mode
data from T+108 s to T+23 ks. The light curve shows a number of small
flares in the first orbit, with the largest giving a factor of ~7 
increase in count rate at T+1.8 ks, on top of a power-law decay of 
index 1.20 +0.16 -0.13.

A 2.7 ks exposure X-ray spectrum from T+108 s to T+7.6 ks can be well 
fit by an absorbed power-law with a photon index of 1.69 +0.46 -0.41 
and a column density consistent with the Galactic value of 3.2 x 10^20 cm^-2 
in the direction of the burst.  The observed  0.3-10.0 keV flux is 
(3.2 +0.9 -1.6) x 10^-12 erg cm^-2 s^-1 which corresponds to an unabsorbed 
flux of (3.7 +1.6 -1.7) x 10^-12  erg cm^-2 s^-1. The count to flux 
conversion factor is 4.6 x 10^-11 erg cm^-2 count^-1.

Providing the source continues to decay at the same rate, we predict a
count rate of 2.8 x 10^-4 count s^-1 at T+1 day.

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