CGRO Status Report for October 1996

[SHRADER@grossc.gsfc.nasa.gov]

   Compton Gamma Ray Observatory Status Report #197
                 Friday October 11, 1996

      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

NASA Headquarters released the final report from the 1996
Mission Operations and Data Analysis Senior Review. These
recommendations of Senior Review Committee will serve as a
guideline to NASA in establishing the funding levels of
each of 8 astrophysics missions over the next two fiscal
years (FY97 and 98), as well as baseline estimates for the
subsequent two fiscal years. GRO did reasonably well in
the review report, ranking in the middle of the eight
reviewed missions in terms of science per dollar.  A
mission extension through the 2000 was recommended. 
Budgets will be tight though beyond 1997 due to the small
total funding available for all extended missions.

Cycle 6 officially begins next week, on October 15 1996.
We are beginning tp process Cycle-6 grants at the CGRO-SSC. 
About 80% of the second-phase(budgetary) review process has
been completed. Affected proposers will be contacted
shortly. For the current timeline, and information on all
targeted observations and current observing programs,
refer to the CGRO-SSC pages on the World Web (see below). 


BATSE earth-occultation and pulsar data products, which
have been delivered to the CGRO-SSC by the BATSE team,
will be made available in simple (ASCII) formats via the
World Wide Web in the very near future. An interface which
allows a user to browse this data based interactively, and
select desired portions of the data is undergoing beta-testing 
at the CGRO-SSC and at MSFC - stay tuned.

CGRO-SSC pages: (http://cossc.gsfc.nasa.gov).
 

Instrument Team Reports

EGRET

EGRET operations were normal this monthly period. 
Delivery of the final phase 4 data to the CGRO SSC is on
schedule, and delivery of the phase 5 preliminary data to
the CGRO SSC is also on schedule.  Interaction with guest
investigators continues at a good level.

EGRET has now seen approximately sixty blazars, and a
general picture is becoming clear.  The ones observed
typically have high-energy gamma-ray luminosities in the
range of (10^47 to 10^49)f ergs s^-1 where f is the
beaming fraction.  If f is taken to be 10^-3, as is
currently believed to be a reasonable number, then the
energy emission would typically be 10^45 ergs s-1.  Since
a typical time for a high luminosity state for a blazar is
of the order of 10^6 s, the total energy is about 10^51
ergs.  If one considers that the size of the region is
determined by the large variations sometimes occurring in
about a day, then, considering the relativistic factor,
the volume for these particles is about 10^47 cm^3. 
Hence, the energy density is of the order of 3 x 10^3 ergs
cm-3, or the relativistic particle density is of the order
of 10^6 cm-3.  These particles must be collimated to avoid
extremely rapid loss of energy, consistent with the
current concept that they are moving outward
relativistically in the jet. Recent radio results have
shown that, for at least three blazars, a radio emitting
region seems to move out rapidly from near the core of the
jet following a high-energy gamma-ray increase.  Hence, it
appears that the relativistic particles originate at least
reasonably close to the core of the jet, consistent with
some of the current theories on the origin of these
particles and the jets themselves.  These results should
give encouragement to theorists to pursue this work more
quantitatively.

Currently the EGRET telescope is observing PSR B1055-52
and will be until October 15, 1996.



COMPTEL

The COMPTEL instrument is performing well and continues
routine operations. Members of the COMPTEL operations team
will join representatives from the other instrument,
spacecraft and ground-systems teams at a meeting of the
Operations Working Group (OWG) at the NASA/GSFC on 15
October. Reboost planning and ground-systems upgrades are
on the agenda.

The long drought of non-detections of gamma-ray bursts
occurring within the field of view of COMPTEL finally
appears to be ending with the detection of the weak burst
GRB 961001.  An initial location for this event was
distributed over the BATSE/COMPTEL/NMSU rapid-response
network within a record 8.5 minutes of burst onset.  More
detailed follow-up information can be found on the COMPTEL
gamma-ray burst page on the WWW.

A major delivery of COMPTEL Cycle 4 data products to the
COSSC public archive was recently completed.  This
included both low-level and high-level data products,
including standard-processing skymaps, for viewing periods
401 to 411.

A number of papers by COMPTEL team members and guest
investigators were presented at the 2nd INTEGRAL Workshop
in St. Malo, France. These included a review of
radioactive gamma-ray line spectroscopy (Diehl), the
latest all-sky maps at MeV energies (Strong et al), recent
results on emission from the Orion region (Bloemen et al),
pulsars (Hermsen et al), and the black-hole candidate GROJ
1655-40 (van Dijk et al). Evidence for MeV-emission that
may be associated with high-velocity clouds was presented
by Blom et al, and an update on 44Ti emission from the Cas
A SNR by Iyudin et al.  Knoedlseder and Leising reported
on indications for a local extended glow of 26Al emission,
both from COMPTEL imaging as well as from a comparison
with OSSE and SMM data.


OSSE

OSSE operations are currently normal.  The instrument is
working as designed,  with all subsystems in complete and
full operation following a temporary  failure of the drive
system on detector 1 on day 96/269.  Analysis of the 
failure indicates the detector 1 drive motor failed to
step when commanded  by the flight software to step from
the OSSE X-axis target to the Z-axis  target.  The
detector motion was disabled from 02:43:01 UT until
14:22:11 UT.   A study of possible flight software
solutions to prevent this failure from occurring is
underway.

The slewing response to BATSE burst triggers is enabled
and the solar window  was enabled on day 96/262.  This
solar window enables slewing to the position  of the Sun
if the scan angle reported on board by BATSE for a
slewable burst  trigger is within a programmable range of
scan angles from the current position of the Sun.  OSSE
slewed in response to BATSE trigger #5601 on day 96/256 
(TJD: 10338) at 13:57:27 UT and to BATSE trigger #5617 on
day 96/271  (TJD: 10353) at 03:47:18 UT and mapped each of
the areas for 3 hours.  

The configuration of the "burst-regulated spectrum
multiscale" data  has been modified as follows:  256-ms
samples in 64 channels, giving 16.384  second buffer
covering the energy range 200 keV - 8 MeV.

Recent observations are listed in the following table.

     View period     Dates        Target     (owner)
    -------------------------------------------------
    529.5  27 Aug - 6 Sep     CGRO J1655-40 (PI team)
                              NGC 2992     (public)

    530     6 Sep - 3 Oct     4U 0115+634  (PI team)
   (4 days @100% response, 22 days @50%, 1 day @100%)
                              SCAN -6.5    (public)
   (gal plane study at (l,b)=(123.7,0.0))
                              NGC 4151     (GI:Zdziarski)

Low-level OSSE data products through viewing period 423
and high-level data products through viewing period 220
have been delivered to the Compton CGRO Science Support
Center archive.  In addition, by special request all
subsequent public Cyg X-1 data sets, both low and high
level, have been delivered.  Refer to the CGRO-SSC page on
the WWW (http://cossc.gsfc.nasa.gov), or contact Tom
Bridgman (bridgman@grossc.gsfc.nasa.gov) for more
information.



BATSE


BATSE operations for September have been normal. A
gamma-ray burst on September 24 was the brightest yet
detected by BATSE. The event was featured on the World
Wide Web on October 1 as the astronomy picture of the day.
A non-technical description of the burst may be found at
http://wwwssl.msfc.nasa.gov/newhome/headlines/ast26sep96_1.htm.

The Third BATSE Gamma Ray Burst Catalog appeared in the
September issue of ApJ Supplements (Meegan et al., ApJS,
106,65). This includes all bursts detected by BATSE as of
1994 September 19, a total of 1122 events. The BATSE team
is currently working on the next catalog, which will be
treated separately because of the different trigger
criteria which have been implemented at various times in
the interim.


As of October 1 BATSE has detected 1660 gamma-ray bursts
out of a total of 5514 on-board triggers in 1988 days of
operation. There have been 768 triggers due to solar
flares, 10 due to SGR events, 63 due to terrestrial
gamma-ray flashes, and 1477 due to the bursting pulsar
CGRO J1744-28.


During the last month the following pulsed sources have
been detected by the BATSE pulsed source monitor: Her X-1,
4U 0115+634,Cen X-3, 4U 1626-67, OAO 1657-415, Vela X-1,
and GX 301-2.

The following regarding the non-detection of GX 1+4 was
reported
in IAU Circular 6478:


GX 1+4
     D. Chakrabarty, Massachusetts Institute of Technology
(MIT); M. H. Finger, Universities Space Research
Association; and T. A. Prince, California Institute of
Technology, report for the Compton Observatory BATSE team:
"The accreting x-ray pulsar GX 1+4 has been undetected by
BATSE since Aug. 18, with a 90-percent-confidence upper
limit of 15 mCrab (20-60 keV) for the pulsed intensity. 
This is the first time that GX 1+4 has remained below our
15-mCrab detection threshold for longer than a month,
since we began continuous BATSE monitoring of its pulsed
flux in 1991.  When last detected on Aug. 18.5 UT, the
phase-averaged pulsed intensity of GX 1+4 was 29 +/- 4
mCrab and the barycentric pulse frequency was (8.0381 +/-
0.0001) x 10E-3 Hz.  The pulse frequency derivative
changed from (-3.7 +/- 0.2) x 10E-12 Hz sE-1 during May
28-June 12, to (0.0 +/- 0.2) x 10E-12 Hz sE-1 during July
27-Aug. 6, suggesting that a torque reversal may have
occurred in early Aug. (cf. IAUC 6105, 6153).  The
phase-averaged pulsed intensity flared from 59 +/- 5 mCrab
on June 4.5 to a maximum of 204 +/- 5 mCrab on Aug. 5.5,
before dropping below our detection threshold."


The outburst of 4U 0115 + 634 observed by RXTE reported in
IAUC 6482 was observed by BATSE very weakly on Oct.
1-3,1996.

The outburst of 4U 1145-619 observed by RXTE reported in
IAUC 6486 was observed by BATSE starting on Oct. 1,1996,
with the outburst still in progress as of the date of this
report. The source reached a level of about 140 mCrab in
the 20-50 keV band.