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Compton Observatory Science Report #147

Compton Observatory Science Report #147 Friday, December 22, 1993

Chris Shrader, Compton Observatory Science Support Center

Questions or comments can be sent to the Compton SSC.
Phone: 301/286-8434
   Internet:  shrader@grossc.gsfc.nasa.gov

                        Spacecraft Status

The last of the CGRO reboost burns was successfully completed
last week. CGRO is now in a near circular orbit of 452-km apogee
by 449-km perigee! 

A study is planned to determine the expected orbital lifetime and
fuel margins for future reboosts. There are now two options: one
is to let the orbit decay to 350 km again (estimated at 1997).
Another is to maintain the orbit near 450 km. From a lifetime
point of view, the maintenance option would give us better fuel
efficiency whereas the 350-km option would give us less risk. In
any case, we can all rest comfortably and look forward to a long

                   Science Support Center News

Several new analysis packages have been ported to the SSC
computer systems, and after a period of beta-testing will be
available to all Guest Investigators. These are "LIKE", which is
a maximum-likelihood point source analysis package developed by
the EGRET team, and "WingSpan", which is an interactive (IDL
Based) spectral analysis tool. Each of these packages will be
available for GI use (via remote login to the SSC) in the near
future. An additional BATSE analysis tool, "BFITS" is also
undergoing testing at the SSC. It is described in the BATSE
Instrument Report below. Details regarding these and other tools
will be posted on GRONEWS.

The Cycle-4 CRGO Nasa Research Announcement is currently ready
for production and will be released in early January. An early
April (1994) due date for proposals is planned. Optional
electronic submission of proposal forms will be supported by
software currently under development at the SSC. This mode of
submission, while optional, is encouraged for any proposers with
network access, as it ensures the accuracy of transmitted
information and greatly facilitates our database maintenance
efforts. The submission software will provide the user with 
letter-quality hard copy of each form as well.

                       Instrument Reports


OSSE operations are normal. The OSSE team is grateful to everyone
involved in the very successful and smooth-running reboost
operation. Thanks for the extra years in orbit.

In viewing period 311.0 and 311.6, the Z-axis target was the
Virgo sky survey (Key project) near galactic coordinates (l,b) =
(284,+75), and the X-axis target was the radio pulsar PSR 1800-21
(Guest Investigator: J. Cordes).

In viewing period 312, the Z-axis target is the Virgo sky survey
(Key project) near galactic coordinates (l,b) = (281,+71), and
the X-axis target is the galactic plane near 343 degrees
longitude (Key project). The Sun is not accessible along the OSSE
scan plane, and the slewing response to BATSE solar flare
triggers is disabled.

Since the last report, there have been no slews to the Sun in
response to BATSE flare triggers.

Data from viewing periods 24.5 and 30 were delivered to the
Compton GRO Science Support Center Archive last week. The targets
during vp 24.5 were the galactic plane near 5 degrees longitude,
NGC 4151, and NGC 7582. The targets during vp 30 were NGC 2992
and 3C120.


EGRET operations were normal this week. The deep survey
continued. Guest Investigator interactions continued at a healthy
level. The EGRET team wishes to express their gratitude to
everyone involved with the successful reboost operation.


The COMPTEL instrument is performing well and continues routine

 During the final series of reboost maneuvers of the GRO
spacecraft from December 15-17, COMPTEL was once again placed in
a low-power mode as a safety precaution; the instrument was
reactivated without incident on 17 December 1993. The
collaboration sends its congratulations and appreciation to the
Flight Operations and Flight Dynamics teams at Goddard for their
successful completion of the CGRO orbital reboost.

The COMPTEL collaboration extends holiday greetings and best
wishes for the New Year to all friends and colleagues. 


The following report was submitted as an IAU circular item:

     GRO J1719-24 = GRS 1716-249

     B. A. Harmon, NASA/Marshall Space Flight Center, and W. S.
     Paciesas,  University of Alabama in Huntsville, report, for
     the BATSE/Compton  Observatory Team: The hard x-ray
     transient GRO J1719-24 (=GRS 1716-249),  which had been
     decreasing in intensity at about 0.3% per day from a peak of
     1.4 Crab (20-100 keV) on September 30 (IAU Cir #5900), began
     dropping much  more rapidly since approximately December 9.
     The intensities in the 20-100  keV band for 10, 13, and 15
     December were 1.1 (+/-10%), 0.9(+/-15%), and 0.4(+/-20%)
     Crab, respectively. On December 16-18 the source dropped
     below the BATSE 3-sigma one-day detection limit of 0.1 Crab.
     Preliminary indications showed no marked change in spectral
     shape during the intensity decrease. Observations in other
     wavelength bands are strongly encouraged. 

The Program BFITS has been delivered to the GROSSC and is being
installed. BFITS is a FITS-format file generating program that
operates upon BATSE Individual Burst DataBase (IBDB) files. It
takes data stored in different formats and aligns them into a
consecutive time history of count rates and errors. BFITS also
provides the current best calculation for the energy edges of the
data bins, and includes calibration information for future
channel-to- energy conversion routines. Positional information is
stored for the source and the Earth at the time of the BATSE
trigger, so that a detector response matrix can be generated with
only a BFITS file as input. BFITS operates under the TAE menuing
system (TUTOR mode), and provides detailed help for each of its
subcommands and parameters. The BATSE team recommends that burst
investigators use BFITS rather then directly reading the IBDB's.

IBDB's for 42 solar flares and 136 gamma-ray bursts were
delivered to the science support center two weeks ago and should
soon be available.