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.