GCN Circular 1229

GRB020127(=H1902): Localization of a Double-Peaked GRB by HETE

G. Ricker, J-L Atteia, N. Kawai, 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;

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;

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

write:

At 20:57:24.73 UTC (75444.73 s UT) on 27 January, the HETE FREGATE 
and WXM instruments detected and localized a double-peaked GRB. The 
burst, H1902, was promptly reported as a GCN Alert Notice within 97 
seconds of the detection time. [Because of the proximity of the 
nearly-full moon to the HETE optical cameras, the burst alert 
downlink contained no real time optical aspect solution, even though 
there was an accurate on-board X-ray localization. When this 
condition arises, the ground relay software computes a nominal 
localization assuming the satellite is pointed anti-sun, and 
increases the error circle diameter to a nominal 4 degrees. For this 
burst, the actual pointing direction was unusually far from nominal 
(i.e. ~8 degrees offset).]

Accurate aspect was derived for H1902 from a full data set on the 
ground. In a followup GCN Notice issued 1.76 hours after the GRB, the 
result of an initial ground analysis localization was reported with a 
90% confidence error circle radius of 12 arcmin. Further ground 
analysis of the optical aspect data has produced a significantly 
improved location which can be expressed as a circle with a 90% 
confidence radius of 8 arc minutes centered at:

RA = +08h 15m 05.7s, Dec = +36d 44' 31" (J2000)

The revised error circle reported here is displaced by 9 arc minutes 
from the  best-fit location found in the initial HETE ground analysis 
and reported in a GCN Notice (at 27 Jan 2002 22:43:00 UT).

GRB020127(=H1902) consists of two peaks separated by 5.5s, with 
durations in the FREGATE 32-400 keV band of ~2s and 0.7s, 
respectively. A total of 870 counts were detected by FREGATE in the 
first peak, and 580 counts in the second peak, respectively.  In the 
8-40 keV FREGATE band, the peak flux in 0.073s was >2 x 10-7 ergs 
cm-2 s-1(ie >7 x Crab flux). In the 2-25 keV WXM band, the 
statistical significance of the burst was 21 sigma.

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