[vsnet-grb-info 1730] GRB050709: A Possible Short-Hard GRB Localized by HETE

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3570
SUBJECT: GRB050709: A Possible Short-Hard GRB Localized by HETE
DATE:    05/07/11 05:06:43 GMT
FROM:    Carlo Graziani at U.Chicago  <carlo at oddjob.uchicago.edu>

N. Butler, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,
on behalf of the HETE Science Team;
 
M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,
Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,
and A. Yoshida, on behalf of the HETE WXM Team;
 
G. Crew, J. Doty, G. Prigozhin, R. Vanderspek, J. Villasenor,
J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda,
and G. Pizzichini, on behalf of the HETE Operations and HETE
Optical-SXC Teams;
 
M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;
 
report:

The HETE FREGATE, WXM, and SXC instruments detected GRB 050709 at 22:36:37
UT (81396.7 SOD) on 9 July 2005.  This was a single hard pulse 100ms long,
followed about 30s later by a soft, faint, approximately 150s long pulse
from the same location.  The later pulse was only detected by WXM and SXC,
since the spectrum of its emission was confined to below 10 keV.

The WXM obtained a localization in flight.  However, the spacecraft
attitude-control system had experienced an upset approximately 19 minutes
earlier, so HETE was drifting at the time of the trigger, and real-time
aspect information was not available.  Consequently, the location was not
distributed in real time.

Ground analysis of the data from the optical cameras has provided reliable
aspect despite the issues associated with the high spacecraft drift rate. 
A GCN Notice was sent out at 22:00:29 UT on 10 July 2005, upon the
resolution of spacecraft aspect issues.  The 90% confidence region of the
WXM location may be expressed as a circle centered at

  R.A. = +23h 01m 44s ; Dec. = -38d 59' 52" (J2000)

with a radius of 14.5'.

Ground analysis of the SXC data yields a refined location with a 90%
confidence region that may be expressed as a circle centered at

  R.A. = +23h 01m 30s ; Dec. = -38d 58' 33" (J2000)

with a radius of 1.34'.

A preliminary spectral analysis based on a fit of a cutoff power-law model
to  the initial spike indicates that Epk ~ 90 keV.  The 30-400 keV fluence
is 1.0E-06 erg cm^-2, while the  2-30 keV fluence is 4.0E-07 keV.  The
enormously softer character of the tail emission suggests that it may be
possible to interpret it as the onset of the afterglow of this burst.  If
this interpretation is correct, then GRB050709 is a localized short hard
burst.

A light curve, skymap, and spectral information for GRB 050709 are
provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB050709/