HETE Burst H1902

Burst H1902 summary

  • Trigger time is
    • UTC=20020127_205724
    • GRB=GRB020127+75444
  • Triggering instrument was Fregate
  • Trigger timescale was 0.16 seconds
  • Trigger detected in 30-400 keV band

Evaluation

Short burst, two peaks
  Initial position is based on incorrect aspect
  Subsequent positions were based on ground analyses
  of WXM and aspect data


GCN Circular 1229

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1229
SUBJECT: GRB020127(=H1902): Localization of a Double-Peaked GRB by HETE
DATE:    02/01/28 03:53:04 GMT
FROM:    George Ricker at MIT  

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.

This message is quotable.