[vsnet-grb-info 3392] GRB 060605: Swift-XRT Team refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5227
SUBJECT: GRB 060605: Swift-XRT Team refined analysis
DATE:    06/06/06 11:30:05 GMT
FROM:    Olivier Godet at U.of Leicester  <og19 at star.le.ac.uk>

O. Godet, K.L. Page, E. Rol, A.P. Beardmore (U. Leicester), M.J. Page
(UCL-MSSL) report on behalf of the Swift-XRT team:

We have analysed the first 5 orbits of X-ray data obtained for GRB
060605 (BAT trigger 213630).  Using 10.4 ks of Photon Counting (PC) mode
data, we find a refined position of:

RA(J2000)  =  21h 28m 37.16s
Dec(J2000) = -06d 03' 33.8"

with an uncertainty of 3.6 arcsec (90% containment). This is 0.7 and 2.7
arcsec from the on-board XRT and UVOT positions respectively and 38.8
arcsec from the on-board BAT position given in GCN 5221 by Page et al.

The source was relatively faint in the XRT. The light-curve shows the
common steep-to-flat-to-steep transition: i) for the first steep
segment, alpha_1 = 2.34 +/-0.55 followed by a break at t1 = 171 +/-26s
after the BAT trigger (T0); for the shallow decay, alpha_2 = 0.38
+0.05/-0.06 followed by another break at t2 = T0+5508 + 2029/-904s; iii)
alpha_3 = 1.23 +0.73/-0.23.

The first orbit of the WT data (from T0+99s to T0+124s) is well fitted
by a single power-law with Gamma = 1.6 +0.42/-0.39, with no strong
evidence for excess NH above the Galactic value of 5.1e20 cm^-2.  The
spectrum of the PC data from T0+126s to T0+2.4e4s is well fitted by a
single power-law with Gamma = 1.97 +/-0.06, again with no strong
evidence for excess NH above the Galactic value of 5.1e20 cm^-2. The
unabsorbed flux in the 0.3-10 keV energy band is 7.5 +0.7/-0.6 e-12 erg
cm^-2 s^-1. No significant spectral evolution is seen before and after
the second break at t2. We note that Khamitov et al. (GCN 5224) claimed
for a break in optical between T0+1 and T0+5 hours, which could be
consistent with the second break at t2 seen in the XRT light-curve. 

Assuming the decay continues to follow the temporal slope alpha_3, the
predicted count rate at T0+24 hours is 0.010 count s^-1, corresponding
to an observed (unabsorbed) flux of 4.46e-13 (5.13e-12) erg cm^-2 s^-1.

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