[vsnet-grb-info 3848] GRB 061002: Swift-XRT Team Refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5681
SUBJECT: GRB 061002: Swift-XRT Team Refined Analysis
DATE:    06/10/02 08:02:37 GMT
FROM:    Kim Page at U.of Leicester  <kpa at star.le.ac.uk>

K.L. Page (U. Leicester) and J.K. Cannizzo (NASA/UMBC) report on behalf of 
the Swift-XRT team:

We have analysed the first 3 orbits of GRB 061002 data obtained by the
Swift-XRT. Using the 4.5 ks of Photon Counting data from the second and
third orbits (the first orbit of data was entirely in Windowed Timing
mode), we find a refined position of:

RA(J2000)  =  14 41 23.29
Dec(J2000) = +48 44 30.5

with an estimated uncertainty of 7.5 arcsec (90% confidence, including 
boresight uncertainties). This lies 7.8 arcsec from the initial XRT 
position given by Cannizzo et al. in GCN Circ. 5675, and 60.7 arcsec from 
the ground-calculated BAT position (GCN Circ. 5678; Hullinger et al.)

The X-ray light-curve shows a break from a steep decay slope of alpha_1 =
2.97 +/- 0.31 to alpha_2 = 1.25 +/- 0.12 at about 304 seconds after the
trigger.

The Windowed Timing spectrum can be modelled by a power-law with a column 
density in excess of the Galactic value in that direction. The fit 
parameters are: Gamma = 2.19 +0.36/-0.31 and NH_excess = (1.5 
+0.8/-0.7)e21 cm^-2 (in addition to NH_Galactic = 2.07e20 cm^-2). The mean 
observed (unabsorbed) flux over this first orbit (138-1345s after the 
burst) was found to be 1.24e-11 (1.90e-11) erg cm^-2 s^-1.

If the decay continues at a rate of alpha = 1.25, the estimated count rate
at 24 hours will be 4.1e-4 count s^-1, corresponding to an observed
(unabsorbed) flux of 1.86e-14 (2.79e-14) erg cm^-2 s^-1.

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