GCN Circular 2536

Y. Nakagawa, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,
on behalf of the HETE Science Team;

T. Donaghy, E. Fenimore, M. Galassi, C. Graziani, M. Matsuoka,
T. Sakamoto, R. Satoh, Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Torii,
Y. Urata, T. Yamazaki, Y. Yamamoto, and A. Yoshida, on behalf of the
HETE WXM Team;

N. Butler, G. Crew, J. Doty, A. Dullighan, G. Prigozhin, R. Vanderspek,
J. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga,
R. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and
HETE Optical-SXC Teams;

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

report:

At 00:08:55.95s UTC (535.95s UT) and 00:12:44.08s UTC (764.08s UT) on
2004 February 28, the HETE-2 FREGATE instrument detected triggers H3066
and H3067.  H3066 is a multi-peaked burst with a duration of ~40s in
the FREGATE 7-80 and 30-400 keV energy bands; no significant emission
associated with H3066 is seen in the WXM 2-25 keV energy band or in the
FREGATE 7-40 keV energy band.  H3067 consists of a single peak with a
duration of ~10 seconds in the FREGATE 30-400 keV energy band; again,
no significant emission associated with H3067 is seen in the WXM 2-25
keV energy band or in the FREGATE 7-40 keV energy band.

At ~00:13:24 UTC (~800 UT) (~40 seconds after trigger H3067), an X-ray
pulse with a duration of >50 seconds is visible in the WXM 2-15 keV
energy band.  Ground analysis of the WXM data produced a localization
that was reported in a GCN Notice at 02:22:44 UT.  The WXM localization
can be expresssed as a 90% confidence rectangle whose center is at

WXM-ground: RA = +10h 12m 12s, Dec = -07d 19' 33" (J2000),

and whose corners lie at

WXM-ground: RA =  +10h 12m 55.6s, Dec = -7d 48' 36"
            RA =  +10h 11m 29.3s, Dec = -7d 47' 46"
            RA =  +10h 11m 28.8s, Dec = -6d 50' 35"
            RA =  +10h 12m 55.4s, Dec = -6d 51' 22" (J2000).

The spectrum of the X-ray pulse is such that, had it been detected
alone, it would be classified as an XRF.  However, the temporal
coincidence with the two preceding triggers suggests that the X-ray
pulse may be associated with them, and is in fact a soft late phase of
the GRB.  Because we are unable to localize either H3066 or H3067, we
are unable to confirm this possibility at this time.  An IPN
localization of either H3066 or H3067 could help to resolve the
situation, and to determine whether H3066, H3067, and the X-ray pulse
are all part of the same burst or not.

Light curves for H3066, H3067, and the X-ray pulse, and a skymap
showing the localization of the X-ray pulse is provided at the
following URL:

http://space.mit.edu/HETE/Bursts/GRB040228.