GRB040912 (= H3557): A Long GRB or XRF Localized by HETE
N. Butler, 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,
Y. Nakagawa, T. Sakamoto, R. Sato, Y. Shirasaki, M. Suzuki,
T. Tamagawa, Y. Urata, T. Yamazaki, Y. Yamamoto, and A. Yoshida, on
behalf of the HETE WXM Team;
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;
C. Barraud, M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf
of the HETE FREGATE Team;
At 14:12:17 UT (13260 SOD) on 12 September 2004, the Fregate and WXM
instruments on HETE detected GRB040912 (= H3557), an unusual, long
X-ray rich GRB or XRF. The burst has been localized to a circle of
7' radius centered on
RA = 23h 56m 54s, Dec = -1d 00' 02" (J2000)
The burst duration is ~20 seconds in the 7-30 keV band, but the 2-10
keV emission extends for ~150s. Preliminary analyses of the first 40
seconds of burst data show the burst to have Epeak of 58 keV, a 2-30
keV fluence of 7e-7 erg/cms and a 30-400 keV fluence of 4e-7 erg/cm2.
While this analysis shows the burst to be an X-ray rich GRB, we
expect the ratio of 2-30/30-400 keV fluence to increase once the
analysis of the entire burst is complete, at which time H3557 may be
re-classified as an XRF.
We anticipate providing additional spectral information from this
unusual event in a subsequent GCN Circular.
This message may be cited.