GCN Circular 2701

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;

report:

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.