TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5515
SUBJECT: GRB 060904A: Swift-XRT refined analysis
DATE:    06/09/04 10:50:28 GMT
FROM:    Dirk Grupe at PSU/Swift-XRT  <grupe@astro.psu.edu>

D. Grupe (PSU) reports on behalf of the Swift/XRT team



We have analyzed the first  orbit with a total observing time
of 2.06 ks of Swift XRT data of GRB 060904A (Grupe et al., GCN 5502).

The X-ray light curve displays the end of a giant flare with a
flattening of the light curve at 200s after the burst. The initial
decay slope is 3.8+/-0.2 followed by 1.3+/-0.2.

Spectral fits to the Windowed Timing mode data during the flare phase
suggest a significant absorption column density in excess of the
Galactic value (1.41e20 cm**-2). The spectrum can be fitted by a
single power law with a photon index Gamma=1.93+/-0.04 and an
absorption column density NH=1.7+/-0.1e21.

Due to the detection of GRB 060904B (Grupe et al., GCN 5505) about
about 1.5 hours after the trigger of GRB 060904A, only one orbit has
been observed on GRB 060904A and the data were only taken in Windowed
Timing mode. Therefore no photon counting  mode data exist currently
and no improved position can be given yet.



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