TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2538
SUBJECT: IPN triangulation of GRB040228 (H3066, H3067)
DATE:    04/03/02 01:15:17 GMT
FROM:    Kevin Hurley at UCBerkeley/SSL  <khurley@sunspot.ssl.berkeley.edu>

K. Hurley and T. Cline, on behalf of the Ulysses, HETE, Mars Odyssey,
and Konus GRB teams,

I. Mitrofanov, S. Charyshnikov, V. Grinkov, A. Kozyrev, M. Litvak, and
A. Sanin, on behalf of the HEND-Odyssey GRB team,

W. Boynton, C. Fellows, K. Harshman, C. Shinohara and R. Starr, on
behalf of the GRS-Odyssey GRB team,

E. Mazets and S. Golenetskii, on behalf of the Konus-Wind GRB team, and

G. Ricker, J-L Atteia, N. Kawai, D. Lamb, S. Woosley, J. Doty, R.
Vanderspek, J. Villasenor, G. Crew, G. Monnelly, N. Butler, J.G.
Jernigan, A. Levine, F. Martel, E. Morgan, G. Prigozhin, J. Braga, R.
Manchanda, G.  Pizzichini, Y. Shirasaki, C. Graziani, M. Matsuoka, T.
Tamagawa, K. Torii, T. Sakamoto, A. Yoshida, E. Fenimore, M. Galassi,
T. Tavenner, T.  Donaghy, M. Boer, J-F Olive, and J-P Dezalay, on
behalf of the HETE GRB team, report:

Mars Odyssey (HEND and GRS) and Konus-Wind observed H3066 (GRB040228 at
00536 s, GCN 2536).  In addition, Konus-Wind observed H3067 (GRB040228
at 00764 s) and the 50 s long X-ray pulse which followed it (GCN
2536).  Neither of these was observed by Odyssey, but this is
consistent with the lower intensity of H3067, and the spectral softness
of the X-ray pulse (the Odyssey lower energy threshold is ~100 keV).
Ulysses was off.

We have triangulated H3066 to an annulus centered at RA, Decl (J2000) =
222.855, -17.387 degrees, whose radius is 31.387 +/- 0.055 degrees (3
sigma).  The minimum distance between this annulus and the position of
the X-ray pulse determined by the HETE WXM is ~37 degrees; in addition,
this position is Mars-blocked to Odyssey.  We therefore conclude that
H3066 and the X-ray pulse are unrelated.

Using Mars-blocking, the IPN annulus, and the Konus ecliptic latitude
determination, we can restrict the arrival direction of H3066 to that
portion of the annulus which lies between RA, Dec = 246, -42 degrees,
and 253, -33 degrees.  This area was far outside the HETE WXM FOV,
further proof that H3066 and the X-ray pulse detected by the WXM are
unrelated.

However, Konus-Wind data indicate that the arrival directions of H3066,
H3067, and the X-ray pulse are all consistent with an ecliptic latitude
of -10 to -20 degrees.  Thus H3067 may be related either to H3066 or to
the X-ray pulse (but not both). It may also be an independent event.

Finally, we note that the Odyssey data display a strong, 5 s long pulse
~350 s after the signal corresponding to H3066.  We are investigating
the possible relation of this pulse to the other bursts.