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CGRO Biweekly Status Report



                                                                    
Compton Observatory Science Report #166, Friday, September 16, 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

Remarkably, a large number of overseas CGRO Guest Investigators
have not yet received their Cycle-4 proposal notification letters.
We apologize for this inconvenience and note that a list of
accepted Cycle-4 programs is available on GRONEWS (telnet to
gronews.gsfc.nasa.gov and login as "gronews", or access through
Xmosaic, URL http://cossc.gsfc.nasa.gov/).

An addendum to this status report describes a forthcoming workshop
on "HIGH VELOCITY NEUTRON STARS AND GAMMA RAY BURSTS", and includes
preliminary registration information. This information, and
announcements regarding other CGRO related meetings and workshops
are posted on GRONEWS.

The first announcement of opportunity for the 1995/96 CGRO
Postdoctoral Fellowship Program has been released. Applications are
due by December 12, 1994. Additional information is available on
GRONEWS, or by sending an inquiry to grofellow@grossc.gsfc.nasa.gov.


                        Instrument Reports

EGRET

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

A major paper on active galaxies has been accepted by the
Astrophysical Journal. In it, the properties of gamma-ray emission
from active galaxies are described. The paper includes gamma-ray
spectra and time dependent gamma-ray fluxes of detected sources.
For sources where the information is available in the literature,
multifrequency spectra covering the range from radio to gamma rays
are also included. Constraints which the EGRET observations place
upon various emission models are discussed. The paper should appear
early next year.

At the present time we are continuing the observation of the Vela
Pulsar following the glitch.


OSSE

The OSSE on-board slew response to BATSE gamma-ray burst triggers
continues to be disabled.  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 still
under investigation.  

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). During intervals when both of these
targets are occulted detectors 1 and 2 stare at PSR J0437-47 (Guest
Investigator M. Bailes).

Data from viewing periods 223 and 224 were delivered to the Compton
GRO Science Support Center archive this week. The targets during
period 223 were 1E 1740-2942, CYG X-1, and GT 0236+610.  The
targets during period 224 were SMC X-1 and 3C 120.


COMPTEL 

The COMPTEL instrument is performing well and continues routine
observations.

The Universe has been fairly quiet recently in medium-energy
gamma-rays. The routine production processing of incoming flight
data is proceeding on schedule, and progress continues on a number
of scientific investigations at the various COMPTEL sites.

At least one COMPTEL Co-PI (who shall remain nameless), however,
currently in mourning due to the premature demise of the
professional baseball season, is finding it particularly hard to
concentrate of late.


BATSE

The following items were included in IAU Circular 6075:

     2S 1417-624                                                    
           
     C. A. Wilson and R. B. Wilson, Marshall Space Flight Center, 
     NASA; M. H. Finger and S. N. Zhang, University Space Research  
     Association; and D. Chakrabarty and T. A. Prince, California  
     Institute of Technology, report for the Compton Observatory
     BATSE  Team: "An outburst of the transient x-ray binary pulsar
     2S 1417-624  is currently being observed. Pulsations in the
     energy band 20-50  keV were first detected on Aug. 26 at a
     frequency consistent with  the discovery observation of this
     source (Kelley et al. 1981, Ap.J.  243, 251). On Sept. 4-5,
     the source was detected between 20 and 70  keV with a
     phase-averaged pulsed flux of 10 +/- 2 mCrab and a total  flux
     of 75 +/- 15 mCrab. The pulse phases between Aug. 26 and Sept. 
     6 are consistent with a barycentric pulse frequency of
     5.666395(5)  x 10E-2 Hz on Aug. 31.0 UT, with a frequency
     derivative of 2.936(9)  x 10E-11 Hz/s. A search of the 20- to
     50-keV BATSE data from 1991  April to date revealed no
     previous outbursts. Optical observations  of the proposed
     Be-star companion (Grindlay et al. 1984, Ap.J. 276,  621) are
     encouraged."                                                
                                                                    
     
     X-RAY NOVA IN SCORPIUS                                         
           
     W. S. Paciesas, S. N. Zhang, C. A. Wilson, and B. A. Harmon
     report for the Compton Gamma Ray Observatory BATSE team: "We
     have  detected a second outburst of this object (GRO
     J1655-40), beginning on Sept. 6. The hard x-ray (20-100 keV)
     flux from this source had  declined rapidly from about 700 to
     about 150 mCrab over a few-day  period beginning about Aug. 12
     and remained at or below that level  through Sept. 5. Our
     preliminary flux estimates for Sept. 6 and 7  are 440 +/- 50
     and 370 +/- 30 mCrab, respectively. The rapid  decline of the
     first x-ray outburst coincides well with the  calculated
     emission time of the expanding radio lobe (IAUC 6073).  The
     reflare may portend further interesting radio and/or optical
     activity." 

The flux from 2S 1417-624 continues to increase. Other x-ray
binaries being detected during the last week by the BATSE pulsed
source monitor are Cen X-3, 4U 1626-67, OAO 1657-415, GX 1+4, Vela
X-1, and GX 301-2.

As of September 14th, BATSE has detected 1116 cosmic gamma-ray
bursts out of a total of 3063 on-board triggers in 1240 days of
operation. There have been 740 triggers due to solar flares with
emission above 60 keV.


Addendum:

  *******************************************************************

                        --- First Announcement ---

                               WORKSHOP ON 
             HIGH VELOCITY NEUTRON STARS AND GAMMA RAY BURSTS

                           15 -- 17 March 1995 
                    University of California, San Diego

  This workshop will focus on the major breakthrough in our understanding 
  of some, if not all, gamma ray bursters that has resulted from two very 
  exciting recent developments -- the evidence suggesting that most neutron 
  stars are born with high velocities -- and the apparent identification of 
  the three known soft gamma ray bursters with young, (high velocity?) neutron 
  stars still associated with supernova remnants. Multiwavelength observations 
  are providing a wealth of new information about the nature of these sources, 
  which may have important implications for the origin of all gamma ray bursts.

           Invited and contributed talks will examine the following:

       HIGH VELOCITY NEUTRON STARS -- 

           Observational evidence.

           Other related properties - intense B fields? - ms periods?

           Theories of their formation - asymmetric SN?

       SOFT GAMMA RAY BURSTERS --

           General properties of bursts.

           Identification with SNRs and plerions - high velocity NS?

           Multiwavelength observations.

           Burst energetics and emission mechanisms.
 
       CLASSICAL GAMMA RAY BURSTERS --

           Burst properties and systematics.

           Temporal and spectral comparisons with soft bursters.

           High velocity neutron star models of their origin.


                     -- ORGANIZING COMMITTEE --
     R.E. Rothschild (Chrmn), A.S. Burrows, J.M. Cordes, E.E. Fenimore, 
     D.A. Frail, K. Hurley, S.R. Kulkarni, D.Q. Lamb, R.E. Lingenfelter, 
     I. Mitrofanov, T. Murakami, R. Ramaty, M. Ruderman, V.L. Trimble, 
                          and S.E. Woosley

            If you wish to attend please respond soon, because 
         the facility capacity will limit attendance to about 50.

      A modest registration fee will cover conference proceedings, &c.

  ****************************************************************************

  ****************************************************************************

                          PRELIMINARY RESPONSE

       WORKSHOP ON HIGH VELOCITY NEUTRON STARS AND GAMMA RAY BURSTS

                           15--17 March 1995

                    University of California, San Diego



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  ****************************************************************************