CGRO Status Report for November 1995

[SHRADER@grossc.gsfc.nasa.gov]

 Compton Gamma Ray Observatory Status Report #187
          Thursday November 9, 1995

    Questions or comments can be sent to 
       Chris Shrader at the CGRO-SSC.
     Phone:    301/286-8434
     e-mail:   shrader@grossc.gsfc.nasa.gov
                                            

          Guest Investigator News

The revised EGRET software and data products (described in
detail below in the EGRET report) are in the process of being
installed at the GRO-SSC and will be available for public use
shortly.

During Cycle-5 there are several viewing periods for which, due
to a number of pointing constraints, there are no OSSE secondary
targets  scheduled (VP 515, 518 and 530). This means that there
were no approved Cycle-5 GI targets, nor any targets previously
observed by CGRO along the accessible region of the OSSE
scan-plane for those particular Z- and X-axis orientations. This is
not to say that there are no objects of interest there - we may just
not know about them! Maybe you have some ideas! Details on the
specific pointing constraints and how to submit a "mini-proposal"
for some target of interest will be appearing soon as on the
GRO-SSC WWW home page: URL
http://cossc.gsfc.nasa.gov/cossc/cossc.html.


                  EGRET 

EGRET operations were normal this monthly period.  Delivery of
the final phase 3 data to the GRO SSC remains on schedule, and
delivery of the phase 4 preliminary data to the GRO SSC is also
on schedule.  Interaction with guest investigators continues at a
good level.

As noted in last month's report, a very extensive review and
analysis of the whole data set has been underway to improve the
normalization values. In addition to the improvement due to the
existence of the substantial amount of data, (1) there is a change
due to small corrections to the instrument live time. (This is not a
uniform correction over the EGRET field-of-view and typically
shows a maximum deviation of ~ 15%.) and (2) there has been the
introduction of small corrections arising from excluding very short
time intervals when the instrument was in improper operational
modes.  There is also now the  introduction of energy dependent
scale factors.  (These factors are primarily important towards the
end of an EGRET spark chamber gas fill before the gas is
replaced.)  The INTMAP program, that generates the exposure
and intensity maps, is modified to use the energy dependent scale
factors. The scale factor file (scale.factor) that is accessed by the
INTMAP code currently includes the new energy dependent
factors.  The SPECTRAL program has also been updated to
incorporate energy dependent scale factors. This entire work has
now been completed for all of the publicly available data in the
GRO Science Support Center.  In addition, the normalization
factors are available for all data through vieing period 427;
normalization for subsequent viewing period will be made
available as the analyses are complete.

In a recent IAU circular, Lundgren and colleagues reported:  "An
ouburst was detected 8-22 August 1995 from the unidentified
EGRET source 2EG J0432+2910, now believed to be an AGN. 
Premlinary analysis indicates the gamma-ray flux above 100 MeV
during the flare was enhanced by a factor of 5 over the average
flux from this source in 1991-1993 observations  ----- The
combination of a gamma-ray flare, radio variability in a candidate
flat spectrum counterpart, and possible optical and X-ray
counterparts provides strong evidence that the source is in the
blazar class of radio-loud AGN."


Beginning on October 31, 1995, EGRET has been turned off to
conserve the remaining spark chamber gas while observations are
being made which are of primary interest to those using the other
instruments on GRO.  EGRET will be turned on again November
28, 1995 to observe CTA 102 and the neighboring region.


                   OSSE

OSSE operations are normal.  The instrument is working as
designed, with all subsystems in complete and full operation. The
slewing response to BATSE burst triggers has been enabled since
30 June.

Recent observations are listed in the following table.

View period         Dates               Target (owner)
    502             17-31 Oct           Geminga  (PI team)
                                        NGC 3227 (not assigned)
                                        NGC 4388 (PI team)
                                        M87      (PI team) 
                                        NGC 1068 (not assigned)
    505        31 Oct - 7 Nov           N Ecl Pole survey  (PI team) 
                                        Mrk 464 (not assigned)
    506             7-14 Nov            N Ecl Pole survey (PI team)
                                        NGC 5548  (not assigned)    
  

Data up to viewing period 336.5 have been delivered to the
Compton GRO Science Support Center archive.

The following paper has recently been accepted for publication:
"OSSE Observations of the Vela and Geminga Pulsars" by M. S.
Strickman  et al. (ApJ)


                   COMPTEL

The COMPTEL instrument is performing well and continues
routine observations.

A number of team results related to gamma-ray bursts were
presented at the recent 3rd Gamma Ray Burst Symposium
organized by the BATSE team in Huntsville.  A preprint of
COMPTEL contributions to the proceedings volume for the
conference is being prepared for distribution, and an electronic
version will also be made available on the WWW.  In further burst
news, the paper on "COMPTEL observations of the strong
gamma ray burst GRB 940217" (Winkler et al.) has just recently
appeared in A&A Vol 302, 765, 1995.  A number of gamma-ray
bursts have occurred within the field of view of COMPTEL since
the last report (GRBs 951013, 951014, 951030, 951030b,
951104, and 951107). Unfortunately, none of these was detected
at MeV energies by COMPTEL. Additional details on such
field-of-view burst events will soon be available on the
COMPTEL pages of the WWW.

A first circular has just recently been distributed on the NATO
Advanced Study Institute on "The Many Faces of Neutron Stars,"
to be held from 1-10 October 1996 in Lipari, Sicily. Further
information can be obtained via e-mail request to
NATO96@areapa.area.pa.cnr.it, or on the WWW at URL
http://www-NATO96.area.pa.cnr.it.


                    BATSE

The third Huntsville Symposium which took place October 25-27, 
was the biggest ever. Over 200 scientists gathered in Huntsville
and contributed approximately 70 oral presentations and 170
posters. The meeting was very successful with many exciting new
results, mainly based on the newly released 3B catalog.
Theoreticians are still working on the GRB origin problem.  The
meeting proceedings will be published in a two volume AIP series;
the editors will be C. Kouveliotou, M. S. Briggs and G. J.
Fishman.  The transient sources GX 339-4 and GRS 1915+105
were active over the past month. GX 339-4 is undergoing a long
low intensity outburst (more than 6 months).  It is averaging less
than 75 mCrab in the 20-100 keV band, and has been decreasing
in intensity very gradually over the past few weeks. GRS
1915+105 is bright (typically 200-300 mCrab) with daily flux
variations and no discernable trends in the light curve.

During the past 30 days (TJD 9999 - 100029) the following
pulsed sources have been detected by the BATSE pulsed source
monitor: Her X-1, Cen X-3, 4U 1626-67, OAO 1657-415, GX
1+4, GRO J2058+42, Vela X-1, and GX 301-2.

BATSE has returned to its standard trigger criteria, with triggers
based on discriminator channels 2+3 (~50-300 keV). As of
November 6 BATSE has detected  1398 gamma-ray bursts out of
a total of 3793 on-board triggers in 1658 days of operation. There
have been 766 triggers due to solar flares, 10 due to SGR events,
and 49 due to terrestrial gamma-ray flashes.

The BATSE Science Team can provide preliminary, quick-look
observations of bright sources observed by BATSE using earth 
occultation and pulse timing analysis.  This service is intended
primarily for those planning observations by  spacecraft and
balloon-borne experiments.  Requests for the service should be
made by the research team leader to the BATSE P.I., Jerry
Fishman (fishman@ssl.msfc.nasa.gov).