[vsnet-grb-info 7123] GRB081221: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8704
SUBJECT: GRB081221: Fermi GBM observation
DATE:    08/12/22 16:09:29 GMT
FROM:    Colleen A. Wilson at NASA/MSFC/NSSTC  <colleen.wilson at nasa.gov>

Colleen A. Wilson-Hodge (NASA/MSFC) reports on behalf of the Fermi GBM
Team: 

"At 16:21:12.22 UT on 21 December 2008, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 081221 (trigger 251569273 / 081221681),
which was also detected by the SWIFT-BAT and XRT (Hoversten et al. 2008,
GCN 8687).

The on-ground calculated location, using the GBM trigger data, is
RA = 17.2, DEC = -24.8 (J2000 degrees, equivalent to 01 h 09 m, -24 d 50'),
with an uncertainty of less than 1.0 degree (radius, 1-sigma containment,
statistical only; there is additionally a systematic error which is
currently estimated to be 2 to 3 degrees).
 
The angle from the Fermi LAT boresight is 78 degrees.

The GBM light curve consists of a weak initial peak and a bright second peak
with a duration (T90) of about 40 s (8-1000 keV). The time-averaged spectrum
from T0+0.003 s to T0+38.401 s is adequately fit by a Band function with
Epeak = 77 +/- 1 keV, alpha = -0.42 +/- 0.03, and beta = -2.91 +/- 0.08.
These spectral parameters are consistent with Konus-Wind observations
(Golenetskii et al. 2008, GCN 8694.)

The event fluence (8-1000 keV) in this time interval is
(3.7 +/- 0.1)E-05 erg/cm^2. The 64-msec peak photon flux measured starting
from T0+19.3923 s in the 8-1000 keV band is 33 +/- 9 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."