CGRO Biweekly Status Report

[SHRADER@grossc.gsfc.nasa.gov]

   Compton Observatory Science Report #180, Friday March 31, 1995
      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
                                                                     

                       Guest Investigator News

The proposal deadline is now only a week away!!! If you have not done
so already, please take a moment and read the short bulleted list of
changes to the NRA and proposal submission precess at the beginning
of Appendix A. The most significant things to note are that the EGRET
instrument will typically be configured in alternate gas-saving modes
for Cycle-5 and beyond -- If your using EGRET please section IV-I of
appendix G (or at least look at figure IV-3). Electronic submission
of proposal forms is now required (send a blank e-mail message to
rps@cossc.gsfc.nasa.gov for instructions - if you have questions send
us e-mail. We are additionally requiring two-sided copy and have
imposed page limits on the (optional) vitae materials appended to
proposals.

The CGRO public data archive available intermittently over the next
several days, as technical problems with our optical Juke Box
persist. Please be patient -- we realize that this is a rather
inopportune time for this to occur and we apologize for the
inconvenience.

Tom Bridgman has joined the CGRO-SSC our new OSSE Instrument
Scientist. Feel free to contact him with any OSSE related proposal
preparation or data analysis questions
(bridgman@grossc.gsfc.nasa.gov).



                         Instrument Reports

EGRET
 
The EGRET spark chamber high voltage pulsars were turned off
beginning on March 21, 1995 as planned to conserve the spark chamber
gas since the field of view was not of high priority for EGRET
observations. It will be turned on again on April 4, 1995, and normal
operations will resume at that time.


Delivery of data to the GRO SSC remains on schedule. Interaction with
guest investigators continues at a good level.


OSSE 


OSSE operations are normal. Detector motor drive #1 continues to
operate without error. The slewing response to BATSE burst triggers
is enabled. 

In viewing period 414 (21-29 Mar), the Z-axis target was LMC X-1 (PI
team) and the X-axis target was the South Galactic Pole Survey (PI
team). When both targets were occulted by the Earth, the target was
the galactic plane (PI team) near (l,b) = (280,0).

In Target of Opportunity viewing period 414.3 (29 Mar - 4 Apr), the
Z-axis target is the X-ray nova GRO J1655-40 in outburst (PI team),
and the X-axis targets are CTA 102 and QSO 2251+158 (PI team).
Spectra of the X-ray nova from the first few hours of observation
have been analyzed and give a lower limit on a thermal cutoff of ~400
keV.

Data from viewing periods 311.0, 311.3, 311.6, and 312 were delivered
to the Compton GRO Science Support Center archive these last two
weeks. The targets during these periods were the Virgo region sky
survey, PSR 1800-21, and the galactic plane near (l,b) = (343,0).


COMPTEL 

The COMPTEL instrument is performing well and continues routine
observations.
 
A cosmic gamma-ray burst was observed within the field of view of
COMPTEL on 17 March 1995.  Unfortunately, as with other recent
events, though the BATSE/BACODINE intensity threshold was exceeded
for an automated rapid-response analysis by the COMPTEL burst group,
no emission from this event was observed at MeV energies.

As elsewhere in the high-energy community, the collaboration is
extremely preoccupied at present with the preparation of proposals
(due 7 April) for CGRO Cycle 5 observations, and abstracts (due 31
March) for the upcoming Third Compton Symposium in Munich in June.
There will be a general team meeting of the COMPTEL collaboration
next week at ESA/ESTEC in The Netherlands to discuss these and other
matters.


BATSE   

The following was included in IAU Circular No. 6152:

     X-RAY NOVA 1994 IN SCORPIUS

     C. A. Wilson, B. A. Harmon, S. N. Zhang, W. S. Paciesas, and G.
     J. Fishman report for the Compton Observatory BATSE Team:  "The
     x-ray/radio transient GRO J1655-40 is undergoing a major
     outburst in hard x-rays above 20 keV.  Preliminary fluxes for
     the past several days in the band 20-100 keV are:  Mar. 17, 240
     +/- 20 mCrab; 18, 470 +/- 30; 19, 500 +/- 30; 20, 480 +/- 40;
     21, 1200 +/- 50. The source has been detectable since
     mid-February (IAUC 6147), but generally at lower intensity
     (50-300 mCrab).  The spectrum extends to at least 200 keV and is
     well fit by a power law with spectral index varying between -2.5
     and -3.1.  The spectrum tends to soften as the intensity
     increases."

The following was included in IAU Circular No. 6153:

     GX 1+4

     D. Chakrabarty, T. Koh, T. A. Prince, and B. Vaughan, California
     Institute of Technology; M. H. Finger and M. Scott, 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
     undergone another torque reversal, and resumed spinning down on
     around Mar. 2, thereby ending an extended spin-up episode that
     began on 1994 Oct. 30 (IAUC 6105).  On Mar. 17.0 UT, the
     barycentric pulse frequency was (8.21119 +/- 0.00002) x 10E-3
     sE-1, with a mean frequency derivative of (-1.25 +/- 0.04) x
     10E-12 sE-2. The phase-averaged pulsed intensity on this date
     was (9.0 +/- 0.9) x 10E-4 photon cmE-2 sE-1 keVE-1 at 30 keV,
     with a power-law photon index of 2.6 +/- 0.2 for the 20- to
     100-keV pulsed flux."


The following sources were detected by the BATSE pulsed source
monitor in the past two weeks: Her X-1, Cen X-3, 4U 1626-67, 2S
1417-624, OAO 1657-415,  GX 1+4, Vela X-1, 4U 1145-619, and GX 301-2.


As of March 28 BATSE has detected 1255 gamma-ray bursts out of a
total of 3382 on-board triggers in 1435 days of operation. There have
been 749 triggers due to solar flares with emission above 60 keV.

The BATSE team World Wide Web page is accessible to the
world at the following URL:

    
http://gammaray.msfc.nasa.gov/batse/

>From this page the reader can find a description of the instrument, a
list of sources observed by BATSE, some descriptions of results from
BATSE, some abstracts from some recent BATSE papers, PostScript files
of some BATSE preprints, and upcoming conferences related to sources
observed by BATSE, including the home page for the Third Huntsville
Gamma-Ray Burst Symposium.  We intend to make all preprints from the
group available through this page. Many pages are under development
and will be added to the home page when complete.  Suggestions for
improvement (to the author of the pages) are welcome.