[vsnet-grb-info 1745] GRB050709: Candidate X-ray Afterglow from Chandra

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3585
SUBJECT: GRB050709: Candidate X-ray Afterglow from Chandra
DATE:    05/07/13 08:36:41 GMT
FROM:    Derek Fox at CIT  <derekfox at astro.caltech.edu>

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

"We have observed the HETE localization region for GRB050709, a likely
short-hard gamma-ray burst (Butler et al., GCN 3570) with the Chandra
X-ray Observatory + ACIS, in a single 44 ksec observation beginning at
2005 July 12.2 UT (mean epoch 2.52 days after the burst).  Excluding
intervals of significant background flares, we retain 38.4 ksec good
time.  Performing a standard "wavdetect" analysis, we identify three
sources within the SXC error circle.  The fainter two of these sources
are very close to each other and are coincident with the bright radio
(NVSS/20-cm and 8.5 GHz) source identified by Cameron & Frail (GCN
3578).  The brightest source within the error circle has a total of
49.5 +/- 8.8 counts (0.3-8.0 keV) and is located at:

    RA 23:01:26.96, Dec -38:58:39.5 (J2000),

where we have made a slight (0.4") adjustment to the native astrometry
based on the optical/X-ray coincidence of three other sources in the
field, and estimate our positional uncertainty as less than 0.5".  

This position is ~1" distant from an R~20.5 mag point-like object
visible in images from the Digitized Sky Survey.  Given that our
position is marginally consistent with this object, and that we cannot
at this time demonstrate significant fading behavior, we caution
observers that the source could be revealed to be a coronally-active
star or AGN.  Nonetheless, we consider it a reasonable afterglow
candidate; in particular, the X-ray flux (~8.4E-15 erg/cm2/s, 2-10
keV) is consistent with a ~t**(-1.4) power-law decay from the
afterglow peak observed by the SXC (assuming this peak reached ~3E-10
erg/cm2/s, 2-10 keV, at 100 sec after the burst); this flux and decay
rate would also be consistent with the Swift XRT non-detection (Morgan
et al., GCN 3577).

A particularly intriguing prospect given observations of the
short-hard burst GRB050509B (Barthelmy et al., GCN 3385; Prochaska et
al., GCN 3390) is that the DSS object 1" distant from this candidate
afterglow may be the burst host galaxy."