GCN Circular 1103

GRB010928(=H1770): Localization of a Long GRB by HETE

G. Ricker, D. Lamb, and S. Woosley on behalf of the HETE Science Team;

G. Crew, R. Vanderspek, J. Doty, G. Monnelly, J. Villasenor, N. Butler,
T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G.
Prigozhin, J. Braga, R. Manchanda, and G. Pizzichini, on behalf of
the HETE Operations and HETE Optical-SXC Teams;

N. Kawai, M. Matsuoka, Y. Shirasaki, T. Tamagawa, K. Torii, T. Sakamoto,
A. Yoshida, E. Fenimore, M. Galassi, T. Tavenner, T. Donaghy, and
C. Graziani, on behalf of the HETE WXM Team;

J-L Atteia, M. Boer, J-F Olive, J-P Dezalay, and K. Hurley on behalf
of the HETE FREGATE Team;

write:

At 16:53:46.56 UTC (60826.56 s UT) on 28 September, the HETE FREGATE 
and WXM instruments detected and localized a long GRB. The burst, 
H1770, was promptly reported as a GCN Alert Notice within 13 seconds 
of the detection time. The burst is seen in the WXM X detector and is 
therefore well-localized in the X direction; the burst was apparently 
near the edge of the coded FOV of the WXM Y detector, resulting in a 
large uncertainty in the Y direction localization.

The X-detector data gives a good (+/- 6 arcmin) localization in the X 
direction and crude limits on Y, resulting in a localization that is 
a long, thin strip.

The coordinates (J2000) of two points along one side of the strip are:

R.A. = 23h29m44s.1, Dec. = 29o39'36"; R.A. = 23h27m05s.7, Dec. = 31o34'34"

The coordinates (J2000) of two points along the other side of the strip are:

R.A. = 23h30m42s.9, Dec. = 29o43'41"; R.A. = 23h28m04s.5, Dec. = 31o38'42"

The length of the strip is uncertain. Our best estimate is that it is 
less than 10 degrees in length, and is centered on  R.A. = 
23h28m55s.1, Dec. = 30o39'11".

The burst duration  was ~40 s, with two peaks separated by ~20 s. In 
the 8-85 keV band, a total of 6,330 counts were detected  during the 
burst, corresponding to a fluence of ~1 x 10-6 ergs cm-2; the peak 
flux was >7 x 10-8 ergs cm-2 s-1 (ie >2 x Crab flux). In the 32-400 
keV band, a total of 9,530 counts were detected during that interval, 
corresponding to a fluence of ~3 x 10-6 ergs cm-2; the peak flux 
was >2 x 10-7 ergs cm-2 s-1 (ie >14 x Crab flux).

Further refinement of the X localization is in progress; a further
attempt is also being made to improve the coarse Y localization.

Follow-up observations of this transient are encouraged.