[vsnet-grb-info 3380] GRB 060604: Swift-XRT Team refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5215
SUBJECT: GRB 060604: Swift-XRT Team refined analysis
DATE:    06/06/05 07:35:45 GMT
FROM:    Kim Page at U.of Leicester  <kpa at star.le.ac.uk>

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

We have analysed the first 3 orbits of X-ray data obtained for GRB 060604
(BAT trigger 213486).  Using 5.1 ks of Photon Counting (PC) mode data, we
find a refined position of:

RA(J2000)  =  22 28 54.97
Dec(J2000) = -10 54 59.9

with an uncertainty of 3.7 arcsec (90% containment). This is 3.3 and 4.1
arcsec from the on-board XRT and UVOT positions respectively (GCN 5212;
Page et al.) and 74.6 arcsec from the ground-calculated BAT position given
in GCN 5214 by Parsons et al.

The source was at a high enough count-rate to remain in Windowed Timing
(WT) mode for the whole of the (short) first orbit (117-255 seconds after
the trigger). During this time, the light-curve shows two strong flares,
peaking at ~137 and ~172 seconds after the burst. Underlying these flares
is a steep decay of alpha_1 = 3.07 +/- 0.20. Between the end of the WT
data and the start of the second orbit of (PC) data, there is a break to
a much shallower slope of alpha_2 = 0.48 +/- 0.20.

The WT flares show clear spectral evolution. The later PC data are well
fitted by a single power-law with Gamma = 1.89 +/- 0.14, with no evidence
for excess NH above the Galactic value of 4.57e20 cm^-2. (The 90% upper
limit for any excess is 7e20 cm^-2.)

Assuming the shallow decay contines, at 24 hours the count rate is
predicted to be 0.030 count s^-1, corresponding to an observed
(unabsorbed) flux of 1.40e-12 (1.57e-12) erg cm^-2 s^-1.

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