TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  306
SUBJECT: GRB 990506: BATSE Observations
DATE:    99/05/10 18:01:10 GMT
FROM:    R. Marc Kippen at BATSE/UAH/MSFC  <marc.kippen@msfc.nasa.gov>

R. M. Kippen (University of Alabama in Huntsville) reports on behalf
of the BATSE GRB team:

GRB 990506 was detected by BATSE on 1999 May 6.474664 as trigger
number 7549.  The event was strong and consisted of a multi-peaked
temporal structure lasting >150 s, with significant spectral
evolution.  The T50 and T90 durations are 112.06 (-/+ 0.09) s and
131.33 (-/+ 0.20) s, respectively.  The burst's peak flux (50-300 keV;
integrated over 1.024 s) and fluence (>20 keV) are 18.58 (-/+ 0.13)
photons cmE-2 sE-1 and 2.23 (-/+ 0.02) x 10E-4 erg cmE-2,
respectively---ranking it in the top 2% (1%) of the BATSE burst flux
(fluence) distribution.  The average spectral hardness of the burst,
as estimated by the ratio of 100-300 keV counts to those in the 50-100
keV range, is H32 = 0.909 (-/+ 0.003), which is average among BATSE
bursts of this duration.  The BATSE burst location is consistent with
that measured by the IPN (BATSE/Ulysses/NEAR; GCN 298) and was used to
initiate an RXTE-PCA scan observation that resulted in the detection
of a fading x-ray source; probably the GRB afterglow (see GCN alert
notices).  A location sky-map and lightcurve for this event (and other
notable bursts) are available at the BATSE Rapid Burst Response
world-wide-web site:

          http://www.batse.msfc.nasa.gov/~kippen/batserbr/

-eof-

[GCN OP NOTE (10May99):  Due to a programming problem in processing this
Circular so close in time to the previous Circular, the NUMBER was erroneously
assigned to be 305, when in fact it should have been 306.  The archive copies
have been fixed.]