[AAVSO-HEN] GRB 081211: 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:  8657
SUBJECT: GRB 081211: Swift XRT refined analysis
DATE:    08/12/11 22:08:03 GMT
FROM:    Rhaana Starling at U of Leicester  <rlcs1 at star.le.ac.uk>

R.L.C. Starling (U. Leicester) and H.A. Krimm (CRESST/GSFC/USRA) report on 
behalf of the Swift XRT team:

We have analysed data from the first 2 orbits of Swift XRT observations of 
GRB 081211 (trigger=337115, Krimm et al. GCN Circular 8653) from 113 s to 
24 ks after the BAT trigger, all collected in Photon Counting (PC) mode.

The enhanced Swift XRT position for this GRB is given in Beardmore et al. 
(GCN Circular 8655).

We confirm that the source is fading, however, the light curve is not well 
constrained at present. A power law fit results in a decay slope of 
alpha=0.6+/-0.1, but we note that flaring may be present from 350-1000 s.

The time-averaged spectrum can be fit with an absorbed power law with 
photon index Gamma=2.4+/-0.3. There is significant absorption above the 
Galactic value (nH_Gal=1.9e20 cm^-2, Kalberla et al. 2005) amounting to a 
column of nH=(1.2+/-0.6)e21 cm^-2 (at z=0). The observed (unabsorbed) 
0.3-10 keV flux is 3.1 (5.0) e-12 erg cm^-2 s^-1. The observed 
(unabsorbed) count rate to flux conversion derived from this spectrum is 1 
count s^-1 = 3.3 (5.3) e-11 erg cm^-2.
The predicted count rate at T+24h, assuming a decay of alpha=0.6, is 0.01
count s^-1.

The results of the XRT automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00337115.

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