CGRO Biweekly Status Report

[SHRADER@GROSSC.GSFC.NASA.GOV]

Compton Observatory Science Report #165, Friday, September 2, 1994
     Chris Shrader, Compton Observatory Science Support Center

        Questions or comments can be sent to the CGRO SSC.
          Phone: 301/286-8434
          e-mail:   NSI_DECnet: GROSSC::SHRADER 
          Internet: shrader@grossc.gsfc.nasa.gov
                                                                   

                         Spacecraft Status

The Observatory, scientific instruments and all spacecraft
subsystems continue to function nearly flawlessly.


                 Science Support Center Activities

Many CGRO Guest Investigators outside of the United States have
noted that they have not yet received their notification letters
for the Cycle-4 program. We apologize for this inconvenience, but
note that THE LETTERS WERE ALL BEEN MAILED THREE OR MORE WEEKS AGO
at this time. 

Members of the CGRO-SSC, in collaboration with the EGRET team
announced the serindipitous discovery of a new gamma-ray blazar
QSO; a copy of an IAU telegram is appended:

 
     GAMMA-RAY FLARE FROM DIRECTION OF NRAO 190

     T. A. McGlynn and J. R. Mattox, Compton Observatory Science
     Support Center, Goddard Space Flight Center, NASA; W. T.
     Vestrand, University of New Hampshire; and the Compton
     Observatory EGRET Team (B. L. Dingus, D. L. Bertsch, J. A.
     Esposito, C. E. Fichtel, R. C. Hartman, S. D. Hunter, C. von
     Montigny, R. Mukherjee, P. Sreekumar, and D. J. Thompson,
     Goddard Space Flight Center, NASA; D. A. Kniffen,
     Hampden-Sydney College; Y. C. Lin, P. F. Michelson, and P. L.
     Nolan, Stanford University; E. Schneid, Grumman Aerospace
     Corporation; and G. Kanbach and H. A. Mayer-Hasselwander, Max-
     Planck-Institut fur Extraterrestrische Physik) communicate:
     "We report the detection of a gamma-ray source, having a
     position consistent with the quasar NRAO 190 (Pauliny-Toth et
     al. 1966, Ap.J. Supp. 13), in the energy range above 100 MeV
     during Aug. 9- 20. The maximum-likelihood position from the
     EGRET quicklook data is l = 197o.0, b = -29o.5 (R.A. =
     4h38m.7, Decl. = -0o41', equinox 2000.0), with a 95-percent
     error cone having a radius of at least 1 deg. The proposed
     identification is 1o from the gamma-ray position and is the
     only strong radio-loud active galactic nucleus within the
     95-percent confidence contour. EGRET will continue to view
     this region of the sky until Aug. 29. The identification is
     consistent with the typical EGRET detection of strong,
     flat-spectrum, optically-violently variable QSOs. The outburst
     has a flux at least four times the 95-percent upper limit of 8
     x 10E-8 count cmE-2 sE-1 (E > 100 MeV) obtained during the
     EGRET all-sky survey. We urge observations at other
     wavelengths to attempt to determine the characteristics of the
     outburst." 



                        Instrument Reports

EGRET

EGRET operations were normal this biweekly period. Delivery of data
to the  CGRO-SSC remains on schedule. Interaction with guest
investigators remains at a good level. 

A "glitch" occurred in the Vela Pulsar just before the observation
began yesterday. We are very anxious to see if there is any change
in the gamma-ray emission beyond the expected change in period. 

We are now in the process of making preparations for Cycle 4 and
should be finished shortly.

 
OSSE

We have disabled the newly implemented gamma-ray burst observing
strategy for the time being. The duration of the burst trigger
signal from BATSE to OSSE is used to encode OSSE's scan angle to
the burst; however there appears to be some occasional confusion in
either the generation or readout of this signal. The cause is under
investigation. Approximately 15 hours of data were lost on day
94/235 (1994 Aug 23) when OSSE slewed to the wrong location for two
separate triggers.

In viewing period 338.0 (29-31 Aug), the Z-axis target was the
recent X-ray nova GRO J1655-40 (PI team), and the X-axis target was
Cen A (PI team). 

In viewing period 338.5 (31 Aug - 20 Sep), the Z-axis target is the
Vela pulsar region (Guest Investigator A. Harding), and the X-axis
target is 3C273 (PI team).

Data from viewing periods 221 and 222 were delivered to the Compton
GRO Science Support Center archive this week. The targets during
period 221 the Crab pulsar, GT 0236+610, PSR 1951+32, and Cyg X-1.
The targets during period 222 were NGC 4151 and MCG+8-11-11.


COMPTEL 

The COMPTEL instrument is performing well and continues routine
observations.
 
 A first circular announcing the Third Compton Symposium, to be
held next summer (12-14 June 1995) in Munich, Germany, has recently
been distributed.  An expression of interest from potential
attendees is requested by October 31. Further information can be
obtained from the organizers via anonymous ftp to
cgro95.mpe-garching.mpg.de.
 
Interest is already running high for two other conferences being
organized in part by members of the collaboration: The Second
Waterville Valley Workshop on High-Energy Solar Phenomena (6-10
March 1995) in Waterville Valley, New Hampshire, and the 29th ESLAB
Symposium, "Towards the Source of Gamma-Ray Bursts," scheduled for
25-27 April 1995 at ESA/ESTEC in The Netherlands. Further details
can be found on the GRONEWS on-line bulletin board (or see below).
 
Ever on the forefront, the Astrophysics Division of ESA/ESTEC
announces that it has established its own home page on the World
Wide Web, which can be accessed at the following URL:
"http://astro.estec.esa.nl/".  Among other items of interest can be
found: contact information for members of the COMPTEL group within
the Space Science Department of ESA/ESTEC, an image of the latest
gamma-ray burst detected by COMPTEL, further details on the
upcoming ESLAB symposium on gamma-ray bursts, easy routings to
data-bases and  analysis tools inside and outside ESA and the
"patron saint" of (at least one member of) the Astrophysics
Division.


BATSE

BATSE continues to operate normally.

During the last week the BATSE pulsed source monitor has detected
pulsed emission from the x-ray binary pulsars Her X-1, Cen X-3, 4U
1626-67, OAO 1657-415, Vela X-1, and GX 301-2.

BATSE folded on board data is currently being collected for the
Crab Pulsar, the Vela Pulsar, and Her X-1. Single sweep data (31 ms
resolution) is also being collected for pulsar searches.

As of September 1st, BATSE has detected 1103 cosmic gamma-ray
bursts out of a total of 3043 on-board triggers in 1103 days of
operation. There have been 737 triggers due to solar flares with
emission above 60 keV.