TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4601
SUBJECT: GRB 060124: HETE detection and spectrum of the main peak
DATE:    06/01/26 02:07:59 GMT
FROM:    Don Lamb at U.Chicago  <lamb@oddjob.uchicago.edu>

GRB 060124: HETE detection and spectrum of the main peak

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

M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
N. Ishikawa, A. Kobayashi, J. Kotoku, M. Maetou, M. Matsuoka,
Y. Nakagawa, T. Sakamoto, R. Sato, T. Shimokawabe, Y. Shirasaki,
S. Sugita, M. Suzuki, T. Tamagawa, K. Tanaka, and A. Yoshida, on behalf
of the HETE WXM Team;

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

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

report:

The main peak of GRB 060124 (SWIFT trigger 178750, Fenimore et al. 
GCN 4586) triggered the FREGATE instrument on HETE at 16:04:09.5 UTC
(57849.5 SOD) on 24 January 2006 (HETE trigger 4012).  This time is 
557.7 s after the Swift trigger time.  The burst occurred at an angle
of about 60 degrees from the HETE boresight.  The main peak is the only
peak of this long GRB that was sufficiently bright to be seen by the
FREGATE instrument despite the large angle between the direction of the
source and the HETE boresight.

The burst locations provided by the Swift BAT and XRT instruments 
(Holland et al. GCN 4570, Fenimore et al. GCN 4586) are within the 
FREGATE FOV but outside the WXM FOV.  Consequently, we have FREGATE
data, but not WXM data, for this event.

The main peak is detected in FREGATE in the 7-40, 7-80, and 30-400 keV
bands.  It is highly structured in time, exhibiting two maxima at 13s
and 23s after the HETE trigger time.

The spectrum in the 7-400 keV energy band is best fit with a power-law
times exponential spectrum.  The best-fit values and the 90% confidence 
intervals for the low-energy photon number index alpha and Epk are

alpha: 1.17 (-0.27/+0.23)
Epk:   305 (-118/+756) keV.

These parameter estimates are consistent with the KONUS results
reported by Golenetskii et al. (GCN 4599).

The extrapolated fluence in the 2-30 keV energy band is 
(1.8 ± 0.5) x 10-6 erg cm-2, the fluence in the 30-400 keV energy
band is (9.5 ± 1) x 10-6 erg cm-2, and the extrapolated fluence in the 
2-400 keV energy band is (11 ± 1) x 10-6 erg cm-2.  The ratio of the 
2-30 keV fluence and the 30-400 keV fluence is 0.19; therefore, the 
hardness of the main peak of GRB 060124 corresponds to that of a 
classical hard GRB.

The pseudo-redshift estimate for this burst is pz = 2.3 ± 1.2