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CGRO Biweekly Status Report

   Compton Observatory Science Report #167, Monday October 3, 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

Final preparation for the start of Cycle-4, including plans for data
distribution and implemenation GI programs are underway. If you have
an approved Cycle-4 program and have any questions about your planned
observations, data delivery, analysis software or tecnical support
please contact the appropriate CGRO-SSC Instrument Specialist or
contact the SSC directly. Cycle-4 starts tomorrow (10/04/94)!

A CD Rom containing all Gamma-Ray Burst data from the 2B catalog and
solar flare data for approximately the first 500 triggers is being
prepared by the SSC and the BATSE team. It is expected to be ready
for distribution in the December 1994 - January 1995 time frame. It
will be distrubted at future CGRO related science meetings or upon
request to the SSC.

                         Instrument Reports


EGRET Operations were normal this biweekly period. Delivery of data
to the CGRO SSC remains on schedule. Interaction with Guest
Investigators continues at a good level. 

An article setting an upper limit for the microsecond high-energy
gamma-ray bursts, predicted by Steven Hawking to be produced by the
decay of small black holes in the early universe, will appear in the
October 20, 1994 issue of the Astrophysical Journal.

Preparation has begun on the second EGRET catalog of sources; it will
include both Phase 1 and 2 data. With the addition of the Phase 2
data and an improved model of the galactic diffuse radiation, the
second catalog will show some sources with improved position
locations and revised flux estimates relative to the first catalog.
Also, the statistical significance in many cases will improve. In
order to avoid confusion between the two catalogs, a new source
naming convention is necessary. This matter has been discussed with
the Project Scientist. The second catalog will use 2EG Jhhmm(+/-)ddmm
- a form specified by the IAU.


OSSE operations are normal.

Following some small modifications to BATSE and OSSE flight software,
we re-enabled the on-board slewing response to BATSE gamma-ray burst
triggers. Bursts within 11 degrees of OSSE's scan plane will be
observed for twelve hours in a search for persistent low-level
emission. We expect of order one trigger per month.

In viewing period 339 (20 Sep - 4 Oct), the Z-axis target is PG
1416-129 (Guest Investigator R. Staubert), and the X-axis target is
MCG-5-23-16 (PI team).

Data from viewing period 226 were delivered to the Compton GRO
Science Support Center archive this week.  The targets during period
226 were the galactic plane near (l,b) = (355,0), and the Coma


The COMPTEL instrument is performing well and continues routine

The COMPTEL Burst Rapid Response Team set a new record recently in
the rapid location of a gamma-ray burst occurring within the field of
view of the telescope. Following the receipt of a BACODINE trigger
message on 21 September (=TJD 9616), the position of GRB940921 was
determined and broadcast over the network 1 hour and 25 minutes after
the event occurred (15 minutes faster than the previous best response
time). This processing time likely approaches the fastest possible
turnaround achievable with the procedures currently in place.  The
team continues to actively investigate alternative processing methods
and procedures that could lower this time further, for rapid
counterpart searches at other wavelengths.

The particulars on GRB940921 follow:

NOTICE_DATE: Fri Sep 23 22:39:25 GMT 1994
ORIG_SENDER: burst@comptel.unh.edu
BURST_DATE :  9616 TJD; 21-SEP-1994
BURST_TIME : 18493.00 SEC;  5: 8:13 UT
BURST_SCZEN:  31.3 Deg.
BURST_SCAZI:   0.7 Deg.
BURST_CLASS: Medium  (Approx  86 events)
COORD_J2000: [RAsc     Decl]   [RAsc            Decl]
============ ===============   ======================
MAXLIK_POS : [206.8d -16.8d] = [13h47m 3s -16d45m27s]
ERRBOX1_POS: [207.2d -15.7d] = [13h48m45s -15d43m 0s]
ERRBOX2_POS: [208.0d -17.4d] = [13h52m 3s -17d23m22s]
ERRBOX3_POS: [206.8d -17.9d] = [13h47m21s -17d55m 0s]
ERRBOX4_POS: [206.0d -16.2d] = [13h44m 5s -16d14m21s]
COORD_B1950: [RAsc     Decl]   [RAsc            Decl]
============ ===============   ======================
MAXLIK_POS : [206.1d -16.5d] = [13h44m27s -16d29m53s]
ERRBOX1_POS: [206.5d -15.5d] = [13h46m10s -15d27m29s]
ERRBOX2_POS: [207.4d -17.1d] = [13h49m27s -17d 7m59s]
ERRBOX3_POS: [206.2d -17.7d] = [13h44m45s -17d39m26s]
ERRBOX4_POS: [205.4d -16.0d] = [13h41m31s -15d58m41s]

The members of the COMPTEL collaboration formerly resident in Leiden
announce the following change in contact information:

As a result of an internal reorganization of SRON (the Space Research
Organization of the Netherlands), its laboratories in Groningen,
Leiden, and Utrecht have been combined into one organizational
entity, effective since March 1. The SRON laboratories in Leiden and
Utrecht are now being combined into one laboratory, SRON-Utrecht.
This move will be completed by the end of October.

    Our new address is:

    Sorbonnelaan 2
    3584 CA Utrecht
    The Netherlands
    Tel: (31) 30 535600
    Fax: (31) 30 540860
    Internet: user@sron.ruu.nl (already effective
                                in addition to our current address)

The e-mail user names are of the form <first initial>.<last name>:

    H.Aarts, H.Bloemen, H.Blom, J.denHerder, H.Deutekom, C.deVries, 
    L.Dubbeldam, W.Hermsen, F.Jansen, J.Kaastra, A.Klumper, L.Kuiper,
    E.Philippus, A.Nieuwenhuizen, B.Swanenburg, J.Talsma, R.vanderA,
    K.vanderBent, R.vanDijk.


The following was submitted for inclusion in an IAU Circular:


     B. A. Harmon, C. A. Wilson, W. S. Paciesas, S. N. Zhang and G.
     J. Fishman,  report for the BATSE/Compton Observatory Team: We
     have been observing  GROJ1655-40 (X-Ray Nova Scorpii 1994) in
     the 20-100 keV band at a level of  75 mCrab(+/- 30%) since Sept.
     17. This followed a more intense period  which began on Sept. 6
     (IAU Cir. No. 6075) and ended approximately on Sept.  16, where
     the source showed daily variations between 200 and 900 mCrab.
     The  spectrum continues to be well-represented by a power law
     between 20 and 200 keV with an index of approximately -3 in the
     Sept. 6-16 time period.

     GX 339-4

     We are currently observing a hard (low) state outburst of the
     black hole candidate GX 339-4. Between Sept. 24 and 26, its
     intensity in the 20-100 keV band gradually increased from 150 to
     200 mCrab (+/-15%). Due to the recent activity of several hard
     x-ray sources in the Scorpius-Ara sky region, it is difficult at
     this time to establish when the outburst began. Preliminary
     indications are that the source was first detectable around
     Sept. 5-10. Based on the behavior of previous outbursts, the
     measured thermal bremsstrahlung temperature of kT = 73+/-8 keV
     is consistent with the source being a few weeks to a month into
     its outburst.

There has been much of activity among the x-ray binary pulsars in the
last two weeks. The outburst from 2S 1417-624 is still continuing,
but the flux is now declining. Small outburst from A0535+262 and 4U
1145+619 were observed. Other sources detected by the BATSE pulsed
source monitor were Cen X-3, 4U 1626-67, OAO 1657-415, GX 1+4, Vela
X-1, and GX 301-2. 

On September 19, BATSE revised the burst trigger criteria. We are now
using channels 3 and 4 (> 100 keV), rather than channels 2 and 3 ( 50
- 300 keV). The main reason for the change is to try to get a better
sample of the atmospheric gamma-ray flashes, which have particularly
hard spectra. The burst data will be kept in a separate catalog, and
may provide additional insights into distributions of spectral
properties. We find that the new energy range results in
significantly more triggers on entry into the SAA. There is a
revision to the SAA boundaries currently in progress, which will
eliminate most of these false triggers. At some undetermined future
date, we will also spend some time triggering on channels 1 and 2 
(25 - 100 keV), to optimize for SGR's.


The BATSE group is planning to host the Third Huntsville Gamma-ray
Burst Workshop (to take place in Huntsville, AL) in October 1995. The
first circular for the workshop will be sent out in December or