  On September 21 at 18950.56 SOD (05:15:50.56) UT the FREGATE gamma-ray
instrument on the High Energy Transient Explorer (HETE) detected a bright
gamma-ray burst (GRB). The burst was also seen by the X-detector on the WXM
X-ray instrument and was therefore well-localized in the X direction; however,
the burst was outside the fully-coded field-of-view of the WXM Y-detector, and
therefore information on the Y direction of the burst was limited.
Cross-correlation of the HETE and Ulysses time histories yielded an
Interplanetary Network (IPN) annulus that crosses the HETE error strip at a ~45
degree angle. The intersection of the HETE error strip and the IPN annulus
produces a diamond-shaped error region for the location of the burst having an
area of 310 square arcminutes. Based on the FREGATE and WXM light curves, the
duration of the burst is characterized by a t90 = 18.4 s in the WXM 4 - 25 keV
energy range, and 23.8 s and 21.8 s in the FREGATE 6 - 40 and 32 - 400 keV
energy ranges, respectively. The fluence of the burst in these same energy
ranges is 4.8 10^{-6}, 5.5 10^{-6}, and 11.4 10^{-6} erg cm^{-2}, respectively.
Subsequent optical and radio observations by ground-based observers have
identified the afterglow of GRB010921 and determined an apparent redshift of z
= 0.450.
