CGRO Biweekly Status Report

[SHRADER@GROSSC.GSFC.NASA.GOV]

  Compton Observatory Science Report #171, Monday November 29, 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 spacecraft and instruments continue to perform nominally.


                  Science Support Center Activities

Appendices A-E of the Cycle-5 NRA are in the final editing stages. An
early January 1995 release is planned. Cycle-5 proposals will be due
in early April, 1995.


                         Instrument Reports

EGRET

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

A paper appeared in the Astrophysical Journal on the EGRET
observations of Ophiuchus. This is the second in a series on
molecular clouds.  A paper on the gamma ray emission on the entire
galactic plane region with the final normalization and corrections
and including an interpretation of the results in terms of the theory
of the production of the radiation will be submitted for publication
shortly.  A paper also appeared in the Astrophysical Journal on EGRET
observations of young spin powered pulsars. A paper summarizing the
EGRET AGN results for phases I and II has been accepted for
publication in the Astrophysical Journal.


OSSE

OSSE operations are normal.

In viewing period 404 (15-29 Nov), the Z-axis targets are the south
galactic pole survey and NGC 7582 (PI team), and the X-axis target is
the galactic plane near (l,b) = (+10,0).

On 94/318 at 02:02:38 UT we responded to an on-board BATSE trigger by
slewing to a scan angle of -31 degrees and remained there for a 12
hour period.  The final BATSE position placed the burst at a scan
angle of -36 deg, which is within the scan range covered by the OSSE
viewing strategy for slewable bursts, although in the transverse
direction it is near the edge of OSSE's field of view. Analysis of
the data is in progress, but it is already clear that there was no
strong emission still visible when the OSSE detectors reached the
target position.

Data from viewing period 301 were delivered to the Compton GRO
Science Support Center archive this week.  The targets during this
viewing period were the Vela pulsar, QSO 1028-313, and Mrk 279.


COMPTEL 

The COMPTEL instrument is performing well and continues routine
observations.

Several papers by the collaboration have either recently appeared, or
have been accepted for publication. These include a report in
Astronomy and Astrophysics (Vol. 290, page 487, 1994) by Carraminana
et al. on "The Temporal Behaviour of the Crab Pulsar as Seen by
COMPTEL."  In addition, two papers on gamma-ray AGN are currently in
press and will also appear in A&A : one, by Lichti et al. on
"Simultaneous and Quasi-simultaneous Observations of the Continuum
Emission of the Quasar 3C 273 from Radio to Gamma-ray Energies," and
another by Bloemen et al. on a "New COMPTEL Gamma-ray Source (GRO
J0516-609) near PKS 0506-612/0522-611: First Evidence for `MeV
Blazars'."

A complete bibliography of publications to date by the COMPTEL
collaboration is currently being compiled, and will be available in
the near future on the COMPTEL page maintained by the CGRO Science
Support Center on the World Wide Web.


BATSE

The following report was included in IAU Circular 6105:   
     GX 1+4                                                                   
          D. Chakrabarty and T. A. Prince, California Institute of            
     Technology; M. H. Finger, Universities Space Research Association;       
     and R. B. Wilson, Marshall Space Flight Center, NASA, report for         
     the Compton Gamma Ray Observatory BATSE team:  "The accreting x-ray      
     pulsar GX 1+4 has resumed spinning up, reversing the steady spin-        
     down trend that had been observed since 1987.  We observed a smooth      
     decrease in the spin-down rate, from (3.8 +/- 0.1) x 10E-12 sE-2 on      
     June 20 to zero on about Oct. 30.  During the interval Nov. 8-11,        
     the spin-up rate was (2.7 +/- 0.3) x 10E-12 sE-2, with a mean            
     barycentric pulse frequency of (8.19033 +/- 0.00003) x 10E-3 sE-1.       
     The pulsed flux has increased by a factor of three since Oct. 17,        
     when the spin-down rate was (1.5 +/- 0.2) x 10E-12 sE-2.  On Nov.        
     10, the 20- to 100-keV phase-averaged pulsed flux was 95 +/- 10          
     mCrab, with a spectrum well fit by an optically-thin thermal             
     bremsstrahlung model F(E) = (A/E)exp(-E/kT), with temperature kT =       
     35 +/- 2 keV and F(50 keV) = (2.6 +/- 0.1) x 10E-4.  The pulsed          
     emission is brighter and harder than observed during a previous          
     outburst (IAUC 5859), and is continuing to increase in intensity."       
                                                                              
The following report was included in IAU Circular 6106: 
     X-RAY NOVA IN SCORPIUS                                                   
          S. N. Zhang, B. A. Harmon, W. S. Paciesas, C. A. Wilson, and        
     G. J. Fishman report for the Compton Gamma Ray Observatory BATSE         
     Team:  "The intensity of the current outburst from this object (cf.      
     IAUC 6101) has gradually increased from 710 mCrab on Nov. 7 to a         
     peak of about 830 mCrab between Nov. 10 and 11.  It has since            
     declined to 660 mCrab as of Nov. 15.  The approximate error on           
     these intensities is 5 percent.  The photon spectrum is well fit         
     with a power law of index -3.1 +/- 0.1 during this period.               
     Immediate follow-up radio observations of this source are strongly       
     encouraged, because a giant radio outburst was reported (IAUC            
     6055) during the decline of the hard x-ray flux in August (IAUC          
     6046 and 6056).  Relativistic jets were formed shortly after that        
     (IAUC 6060)."                                                            

The following sources were detected by the BATSE pulsed source monitor in the
past two weeks: Cen X-3,  4U 1626-67, 2S 1417-624, GX 1+4, Vela X-1, 
and GX 301-2. The outburst of 2S 1417-624 has now lasted 93 days. The x-ray 
binary GX 1+4 is still spinning up.

As of November 22nd, BATSE has detected 1165 cosmic gamma-ray bursts out of a
total of 3186 on-board triggers in 1309 days of operation. There have been 740
triggers due to solar flares with emission above 60 keV. Since the BATSE 
burst trigger criteria were changed on September 19th, there have been 
8 triggers due to terrestrial gamma-ray flashes.