[vsnet-grb-info 3703] GRB 060906: Swift/XRT Refined Analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5537
SUBJECT: GRB 060906: Swift/XRT Refined Analysis
DATE:    06/09/06 21:02:17 GMT
FROM:    Judith Racusin at PSU  <racusin at astro.psu.edu>

J. L. Racusin, D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), D. Grupe, J. A. 
Kennea (PSU) report on behalf of the Swift XRT team:

We have analysed the Swift-XRT data from the first 6 orbits of GRB 060906 
(Racusin et al., GCN Circ. 5528), with a total exposure of 12200 seconds. 
The refined XRT position is:

RA(J2000): 2h 43m 00.66s
Dec(J2000): +30d 21' 37.82"

with an uncertainty of 4 arcseconds (90% containment).  This position is 
134 arcseconds from the refined BAT position given in GCN Circ. 5534 
(Sakamoto et al.), 3.3 arcseconds from the XRT position given in GCN 5528, 
and 5.3 arcseconds from the optical counterpart reported by Cenko et al. 
(GCN 5529).

The light-curve starts 153 seconds after the BAT trigger and shows a steep 
decline with a decay index of -3.4 +/- 1.3 followed by a flattening at 
~400 seconds described by a power-law with index -0.2 +/- 0.1, and 
breaking again at ~11000 seconds to a power-law index of -1.7 +/- 0.3.

A preliminary spectral fit to the WT data gives a spectral power law 
photon index of 2.5 +/- 0.5 in the [0.3-10] keV band, with absorption 
column density consistent with the Galactic value (9.66e20 cm^-2).  The 
average (in the time range 153-776 seconds from trigger) estimated 
unabsorbed 0.3-10 keV flux was 1.37e-11 erg cm^-2 s^-1.

The XRT count rate extrapolated to T+24 hr is estimated to be about 0.002 
counts/s, corresponding to an unabsorbed 0.3-10 keV flux of about 1.72e-13 
erg cm^-2 s^-1.

This Circular is an official product of the Swift XRT Team.