[vsnet-grb-info 1848] GRB050709: Second Epoch Chandra Observation

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3688
SUBJECT: GRB050709: Second Epoch Chandra Observation
DATE:    05/07/27 05:00:15 GMT
FROM:    Patrick B. Cameron at Caltech  <pbc at astro.caltech.edu>

P. B. Cameron (Caltech), F. A. Harrison (Caltech) and D. A. Frail (NRAO)
report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration:

"We have observed the HETE localization region for GRB050709 (GCN 3570)
with the Chandra X-ray Observatory + ACIS, in a second 18.2 ksec
observation beginning at 2005 July 25.86 UT (mean epoch 16.04 days after
the burst).

In contrast to earlier reports by Antonelli et al. (GCN 3686), we find
that the X-ray source reported earlier by Fox et al. (GCN 3585) has faded.
In reanalyzing both epochs, we measure 10 +/- 3 counts (0.3 - 8.0 keV) for
the second epoch, corresponding to a count rate of 5.5 +/- 1.6 e-4 cts/s.
This compares to 1.3 +/- 0.2 e-3 cts/s measured for the first epoch,
confirming that the source has faded with a decay of t**-0.46 +/- 0.18
since the first Chandra epoch. Although this decay is shallower than
typical for an afterglow, the variability implies it is the likely
counterpart to the GRB.

We thank the staff at the Chandra X-ray Center for their execution of this
Target of Opportunity observation and rapid processing of the data."