[vsnet-grb-info 6749] GRB 081008: Swift-XRT Refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8349
SUBJECT: GRB 081008: Swift-XRT Refined Analysis
DATE:    08/10/09 14:55:07 GMT
FROM:    Judith Racusin at PSU  <racusin at astro.psu.edu>

J. L. Racusin (PSU) reports on behalf of the Swift-XRT team:

We have analyzed the first 7 orbits of XRT data for GRB 081008 (Racusin et 
al., GCN 8344), including 315 s of WT data and 6.9 ks of PC data.  The 
UVOT-enhanced position was given by Evans et al. (GCN 8347).  The 
results of the automatic analysis of the XRT data are available at 
http://www.swift.ac.uk/xrt_products.

The 0.3-10.0 keV lightcurve shows three bright flares superimposed on a 
steep decay, followed by a plateau with a decay index of 0.9 +/- 0.1, 
breaking at 16 +/- 14 ks to a decay index of 2.0 {+1.8,-0.9}.

The WT spectrum, for which changes in the hardness ratio during the flares 
suggests spectral evolution, can be fit by an absorbed power-law, with 
photon index = 1.81 +/- 0.03 and NH = (6.7 +/- 0.8)e21 cm^-2 at z = 1.967 
(Cucchiara et al., GCN 8346), in addition to the Galactic value of 7.1e20 
cm^-2. The observed (unabsorbed) flux over this time (93-408 s after the 
trigger) is 3.1e-9 (3.9e-9) erg cm^-2 s^-1.

The PC spectrum can be fit by an absorbed power-law, with photon index = 
1.91 +/- 0.07 and NH = (5.9 {+15.1, -5.9})e20 cm^-2 at z = 1.967, 
consistent with the Galactic value. The observed (unabsorbed) flux over 
this time (412 s - 11.9 ks after the trigger) is 3.4e-11 (4.0e-11) erg 
cm^-2 s^-1.

Assuming the X-ray emission continues to decline at the same rate, we 
predict a 0.3-10.0 keV XRT count rate of 3.6e-3 counts/s at T+24hr, which 
corresponds to an observed (unabsorbed) flux of 1.4e-13 (1.7e-13) ergs 
cm^-2 s^-1.

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