GCN Circular 231

S. M. Matz (Northwestern University), G. H. Share, R. Murphy, and J. D.
Kurfess (Naval Research Lab) report on behalf of the OSSE team:

The OSSE instrument on board the Compton Gamma-Ray Observatory detected
strong emission from GRB 990123 in its central detectors and in its
active NaI shields. While the burst was not in the detectors' field of
view, it was still detected to >3 MeV in two 16 s intervals. The rise
and first strong peak (at about trigger+25 s) are roughly (within 1--2
s) aligned at all energies. The low-energy (<100 keV) burst emission
appears to last significantly longer than the higher energy emission.
Detailed spectral analysis is underway; preliminary analysis indicates
that the average spectrum of the main burst can be well described above
0.8 MeV by a photon power law with an index of about -3.

Time histories from the OSSE central detectors in different energy
ranges from 50 keV to >3 MeV are posted on the OSSE burst web page 
( http://www.astro.nwu.edu/astro/osse/bursts/ ) along with a preliminary
spectrum of the burst. Also available are a plot and raw data for the
high time resolution (16 ms) history of the first 60 s of the burst
from the triggered OSSE shield data (>100 keV).
 
This report may be cited.