Compton Gamma Ray Observatory Status Report #203
                        Wednesday April 9, 1997

          Questions or comments can be sent to
          Chris Shrader at the CGRO-SSC.
          Phone:  301/286-8434
          e-mail: shrader@grossc.gsfc.nasa.gov


                Guest Investigator News


The Compton Symposium is less than three weeks away! The response to the
call for papers (over 300 abstracts) and the number of registrants (over 260) has
exceeded our expectations and a memorable event is anticipated.

A reminder, the Cycle-7 NRA was issued last month, and copies are available
via the World Wide Web (http://www.hq.nasa.gov/office/oss or
http://cossc.gsfc.nasa.gov). For paper copies, contact Sandy Barnes:
barnes@grossc.gsfc.nasa.gov. Proposals are due June 12.

Following several engineering tests during March, a series of orbit-adjust 
maneuvers were successfully carried during the first week of April. As of April 
6, 1997, the 6th anniversary of its release from the Space Shuttle, the CGRO 
spacecraft is now in an orbit with mean apogee height of 517 km. An additional 
series of maneuvers during the later part of May and early June will circularize 
the orbit. The skill and dedication of the flight operations team in planning  and
executing these critical stages of the reboost operation is to be commended.  The
observatory can now be operated well into the next century without danger of
early reentry. 

Once again, a reminder - it is extremely important that we at NASA be kept
informed of any new scientific results involving CGRO. Please, if you have not
already done so add us to your preprint mailing list (be it conventional or
electronic) for any CGRO related work. Thanks in advance; CGRO Science
Support Center, Code 660.1 NASA/GSFC Geenbelt, MD 20771, atn: C. Shrader;
shrader@grossc.gsfc.nasa.gov. 
  

               Instrument Team Reports
EGRET 

EGRET concluded a extended observation of PKS 0528=134 just prior to the
orbit boost activity.  Except for possible Targets of Opportunity, the spark
chamber will remain disabled until early August.  The energy calorimeter
remains active, and the spark chamber will be automatically for bursts that
BATSE deterrmines to be within the EGRET field of view.  Several tests of the
instrument are planned during the hiatus. The EGRET team is preparing papers,
posters, and talks for the upcoming Symposium.  Software to analyze TASC
spectra as well as the primary TASC data have recently been delivered to the
GROSSC.  GI and archival data deliveries are current or ahead of schedule.


COMPTEL 

During the recent reboost maneuvers of the CGRO spacecraft, scientific
observations with COMPTEL were suspended, and the instrument placed in a
precautionary low-power state.  With the successful completion of the CGRO
orbital reboost, COMPTEL has once again resumed its normal scientific mode of
operation.

In another striking demonstration of Murphy's Law in action, the gamma-ray
burst of 5 April 1997 occurred within the field of view of COMPTEL, optimally
placed very near the instrument z-axis. Unfortunately, this GRB occurred while
COMPTEL was in its low-power state during orbital reboost, and no scientific
data could be collected for this event.

A major delivery of both low- and high-level COMPTEL data products to the
CGRO public archive at the COSSC has recently been completed. This delivery
covers the balance of Cycle 4 (VPs 422 to 429.5), as well as extensive updates to
previously delivered datasets with more recent datasets of improved quality.

Serious preparations are now underway for team-related presentations at the
upcoming 4th Compton Symposium in Williamsburg.  Among the topics to be
presented will be a review talk on the diffuse Galactic continuum emission, the
latest results on the distribution of 26Al in the Milky Way, spectral properties of
the MeV emission from the inner Galaxy, latest COMPTEL results on the Crab
and Vela pulsars, as well as a number of additional reports on individual sources.


OSSE 

OSSE operations are currently normal.  The instrument is working as designed,
with all subsystems in complete and full operation. 

During the first two delta V engineering/test burns of the CGRO OATs engines
OSSE was left in low voltage mode until the maneuvers back to the viewing
period 617.1 science targets.  Following the first full delta V burn on day 97/091
OSSE conducted shield threshold and gain tests while chopping on the Crab 
Pulsar.  Following these engineering tests OSSE began chopping on the Sun due 
to increased activity observed by GOES.  During this time the slewing response 
to BATSE burst triggers was diabled.  The return to science operations on day 
97/097 has re-enabled the slewing response to BATSE burst triggers.

Bursts, flares, and transients through April 4, 1997 have been processed.  
During this period no slews occured in response to BATSE triggers. results are
available on the burst web site (http://www.astro.nwu.edu/astro/osse/bursts/).

Recent observations are listed in the following table. 

           617.2    24 Mar   (reboost: Butterfly test) 

           617.4    26 Mar   (reboost: Engineering burn)  

           617.6     1 Apr   (reboost: Burn #1 - Crab Pulsar)
                      2-6 Apr   (Reboost: Sun)


           617.1 -  18 Mar-10 Apr  3C 120              (W.N. Johnson)
           617.3                             GRO J2157+18        (public)
           617.5                             QSO 0834-201        (public)
           617.7   
                                             

Low-level OSSE data products through viewing period 508 are awaiting delivery
to the Compton GRO Science Support Center archive.  High-level data products
through viewing period 220 have been delivered.  In addition, by special request
all subsequent public Cyg X-1 data sets, both low and high level, have been
delivered.  Refer to the CGRO-SSC page on the WWW
(http://cossc.gsfc.nasa.gov), or contact Tom Bridgman
(bridgman@grossc.gsfc.nasa.gov) for more information.


BATSE

The following appeared in IAU Circular 6585:

   GS 1843+00                                                             
        R. B. Wilson and B. A. Harmon, Marshall Space Flight Center,      
   NASA; D. M. Scott, M. H. Finger, and C. R. Robinson, Universities      
   Space Research Association; D. Chakrabarty, Massachusetts Institute    
   of Technology; and T. A. Prince, California Institute of Technology,   
   report for the Compton Observatory BATSE Team: "Pulsations from the    
   transient x-ray binary pulsar GS 1843+00 have been detected since      
   Mar. 3 in the energy range 20-50 keV.  Using observations through      
   Mar. 9, the mean barycentric pulse frequency at epoch Mar. 6.0 UT      
   was (3.382592 +/- 0.000035) x 10E-2 Hz.  The observed spinup rate      
   during this observation is (4.18 +/- 0.12) x 10E-11 Hz sE-1. The       
   mean RMS pulsed flux integrated over 20-50 keV was (3.75 +/- 0.24)     
   x 10E-10 erg cmE-2 sE-1 on Mar. 8-9.  Earth-occultation                
   measurements indicate a steady increase in total intensity from        
   early March to Mar. 8-9, with a total flux of 5.1 +/- 0.5 x 10E-9      
   erg cmE-2 sE-1, giving a pulse fraction of about 7 percent.  The       
   thermal bremsstrahlung model (without Gaunt factor) yields a           
   temperature of 23 keV.  Pulsed and steady emission are also            
   observed on Mar. 10.  Updates to source intensity and pulse            
   frequency are posted twice-weekly for this and all other bright        
   sources detected by BATSE at the web site                              
   http://www.batse.msfc.nasa.gov.  Observations are encouraged at all    
   wavelengths, as no optical counterpart is currently known for this     
   source."                                                               

During the last month the following pulsed sources have been detected by the
BATSE pulsed source monitor: Her X-1, Cen X-3, 4U 1626-67, GS 1843+00,
OAO 1657-415,GX 1+4, Vela X-1,and GX 301-2.

The burst trigger is currently using rates from channels 2+3 (50 - 300 keV), with
thresholds of 5.5 sigma for all timescales. As of April 6 BATSE has detected
1750 gamma-ray bursts out of a total of 6055 on-board triggers in 2175 days of
operation.  There have been 782 triggers due to solar flares, 39 due to SGR
events, 64 due to terrestrial gamma-ray flashes, and 1800 due to the bursting
pulsar GRO J1744-28.