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GCN Circular 4359

Subject
GRB051211A (=H3979): Refined Analysis
Date
2005-12-16T18:58:27Z (18 years ago)
From
Carlo Graziani at U.Chicago <carlo@oddjob.uchicago.edu>
N. Kawai, G. Ricker, J-L. Atteia, D. Lamb, 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, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;

report:

We have analyzed the full FREGATE+WXM+SXC data for HETE trigger H3979
(GRB051211A).

Further ground analysis shows that the HETE SXC location for GRB051211A
reported in GCN 4324 is reliable. The SXC detected a soft transient source
in both the its X and Y cameras about 35 s after the trigger without the
assistance of the WXM. The location of this source is:

R.A. = 06h 56m 13s ; Dec. = 32d 40' 44" (J2000),

with a 90% confidence error radius of 80".

The WXM did not detect this soft transient, but it detected hard x-ray
emission coincident with the Fregate event. From this hard emission, WXM
obtained a solid X location matching the SXC transient. There are several
possible WXM Y locations, but one of them matches the SXC transient: the
random probability of this is only a few percent. This triple coincidence
in time and position gives us high confidence that the SXC transient is
associated with the Fregate trigger.

The 30-400 keV light curve has a fast rise (<0.1 s) and a slower
decay. The burst had a T90 duration of 4.8s in the 6-40 keV band, and of
4.2s in the 30-400 keV band.

The integrated spectrum is well-fit by a cutoff power-law function.  The
best-fit parameters are:

alpha = -0.67 --- 90% confidence interval is [-0.90 -0.38]
Epeak = 137 keV  --- 90% confidence interval is [106 , 200]

The 2-30 keV fluence is 1.6e-7 erg/cm2, while the 30-400 keV fluence is
9.6e-7 erg/cm2.

This burst had a hardness ratio (100-300 keV fluence)/(25-100 keV
fluence) of 1.18.  This, along with its 4.2 s T90, places it 
between the long duration bursts and the short duration bursts
in the hardness ratio-duration diagram.  We note, however, that if
lognormal functions are used to describe the long and short burst duration
distributions, this burst appears more likely to belong to the short
class. Thus, a search for a possible associated low redshift host galaxy
would be of interest.

A light curve, hardness ratio-duration diagram, and spectral information
for this event are provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB051211/
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