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CGRO Status Report for Jun 1996

   Compton Gamma Ray Observatory Status Report #193
                 Monday, June 10 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:

The 231 Cycle-6 proposals have now been distributed to
teams of anonymous referees. A peer-review meeting will
occur later this month, followed by a timeline development
meeting in July. Once the timeline has been developed, and
a final list of accepted proposals thus determined, budget
requests will be solicited from selected proposals
(probably during August). Cycle-6 begins on October 30,

The CGRO User's Committee is preparing for the written and
oral presentations to the NASA HQ MO&DA Senior Review. In
this review, CGRO and will be jointly evaluated and
budgeting priorities for FY 97-00 will be established. The
User's Committee will also meet during July to establish
guidelines for the Cycle-7 program. Major topics under
consideration include reinstitution and emphasis on Key
projects, revision of the proprietary data rights period
(downward from 1 year to 0-3 months) usage of the
remaining EGRET gas, and funding priorities in an era of 
shrinking budgets. Please feel free to discuss any ideas you 
may have on these issues with a User's Committee member; 
the committee members are:

khurley@sunspot.ssl.berkeley.edu   !Kevin Hurley (Chair)
cordes@astrosun.tn.cornell.edu     !Jim Cordes
josh@cfa255.harvard.edu            !Josh Grindlay
donk@pulsar.hsc.edu                !Don Kniffen
gok@mpe-garching.mpg.de            !Gottfried Kanbach
kroeger@osse.nrl.navy.mil          !Dick Kroeger
kurfess@osse.nrl.navy.mil          !Jim Kurfess
liang@spacsun.rice.edu             !Edision Liang
marscher@buast0.bu.edu             !Al Marscher
paciesas@ssl.msfc.nasa.gov         !Bill Paciesas
prince@caltech.edu,                !Tom Prince
jryan@comptel.unh.edu              !Jim Ryan
vos@mpe-garching.mpg.de            !Volker Schoenfelder
aew@ipac.caltech.e                 !Ann Wehrle
gfb@iftcr.mi.cnr.it                !Giovanni Bignami
fichtel@lheavx.gsfc.nasa.gov       !Carl Fichtel
fishman@ssl.msfc.nasa.gov          !Jerry Fishman

NASA Exofficio Members
abunner@hq.nasa.gov                !Alan Bunner
gehrels@lheavx.gsfc.nasa.gov       !Neil Gehrels
norris@grossc.gsfc.nasa.gov        !Jay Norris
shrader@grossc.gsfc.nasa.gov       !Chris Shrader 

Instrument Team Reports:


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

In case that you missed it last month, information on
EGRET is now available on the World Wide Web.  You may
access it through: 
The material includes a discussion of the EGRET
instrument and the scientific goals, the institutions
involved, a list of some major EGRET discoveries, guest
invesitgator information in relation to the GRO Science
Support Center, a list of EGRET papers in refereed
journals, and some EGRET preprints that have been accepted
by journals, but have not yet appeared in print, as well
as other material such as a picture of the instrument and
the high-energy gamma-ray all-sky map.

A paper by Reshmi Muknerjee and others on the high-energy
gamma-ray flare from PKS 0528+134 has been accepted by the
Astrophysical Journal.  Both the history of this object
and the multiwavelength coverage are described.  A
detailed relativistic SSC jet model agrees well with the
flare multiwavelength spectrum.  At the forthcoming AAS
meeting in Madison, Wisconsin, Bob Hartman and his
co-authors will be reporting on the large increase seen in
3C 279 recently and on the related multi-wavelength
coverage, as well as giving a discussion of the scientific
implications. Carl Fichtel and his  co-authors at the same
meeting will describe the BL Lac blazars that have been
seen in high-energy gamma radiation.  The report will show
a comparison of the z distribution to that of those seen
in the radio region and will describe the luminosity and
spectral shape of these objects as seen in the high-energy
gamma-ray region.  Also, Joe Esposito and colleagues will
describe his work on the high-energy gamma-ray emission
from supernovae.

Currently, the EGRET telescope is pointed at GRO J0516-609
and will move to CEN X-3 on June 11, 1996.


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
was enabled on day 96/135.  Since this time there have
been no  burst triggers sent from BATSE that met the OSSE
slewing criteria.

A paper detailing results of OSSE observations of the
Orion complex has been  submitted for publication in ApJ
(Murphy at al.).  Flux levels reported by  COMPTEL of
gamma-ray line emission in the 3 - 7 MeV range suggest
that if the origin of the emission were a point source at
the center of the OSSE field of  view then OSSE
observations of the region would result in significant
detections of line emission near 4.4 and 6.1 MeV.  The
lack of compelling  evidence for an OSSE detection in this
region requires that any source of this  emission must be
more extended than the distibution of the intense CO
emission  localized around Orion A and Orion B.

Recent observations are listed in the following table.

View period      Dates        Target (owner)
    519       23 Apr-7 May    Arp 220  (GI:  C. Dermer)
                              Mrk 590  (not assigned)
                              GPLANE 95  (GI:  J. Skibo)

    520         7-21 May      PKS 0528+134  (PI team)
                              M 31  (PI team) 
                              Cyg X-2  (not assigned)

    520.4      21-28 May      PKS 2155-304  (GI:  M. Urry)
                              PKS 0235+164  (PI team)

    521      28 May-11 June   PKS 0506-612  (PI team)
                              NGC 2110  (GI:  L. Bassani)

Data through viewing period 411.5 have been delivered to
the Compton GRO Science Support Center archive.  Also,
OSSE high level data products covering  viewing periods
209, 210, 331.5, 332 and 333 were delivered to the
CGRO-SSC. 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.


The COMPTEL instrument is performing well and continues
routine operations.

During May three gamma-ray bursts were observed by COMPTEL
without detection (GRBs 960518, 960528, and 960530).  The
collaboration notes (with regret) that M. Kippen, stalwart
of the COMPTEL rapid burst-response effort, has moved on
to join the BATSE team in Huntsville, to be a few minutes
closer to those burst trigger messages; the newly
designated Keeper of the Beeper for the rapid analysis of
COMPTEL bursts is A. Connors of UNH.

Recent COMPTEL results on solar flares will be presented
(by Ryan et al. and Rank et al.) at the upcoming 188th
meeting of the AAS in Madison, Wisconsin.

Lastly, the countdown has begun toward the start of the
83rd Tour de France ...


The following was reported in IAU circular 6395:

     GRO J1744-28                                          
     C. Kouveliotou, Universities Space Research
     Association (USRA); K. Deal, P. Woods, M. Briggs,
     University of Alabama in Huntsville (UAH); B. A.
     Harmon, G. J. Fishman, Marshall Space Flight Center,
     NASA; J. van Paradijs, UAH and University of
     Amsterdam; M. H. Finger, USRA; and J. Kommers and W.
     H. G. Lewin, Massachusetts Institute of Technology,
     report: "BATSE is no longer detecting bursts or
     persistent emission from the bursting pulsar GRO
     J1744-28. A total of 3080 bursts were detected from
     this source (not corrected for earth occultation or
     other deadtime effects) between its onset on 1995
     Dec. 2 until its cessation on 1996 May 3. During most
     of this 152-day interval, the burst rate was fairly
     constant at an average of about 20 bursts/day, but
     after Apr. 27 the rate declined rapidly. The last
     detected event had a fluence of 1.2 x 10E-7 erg
     cmE-2. The pulsing signal in the persistent emission
     was last detected on Apr. 26; after this date, the
     pulsed flux was below 7 x 10E-10 erg cmE-2 sE-1
     (r.m.s., between 20 and 40 keV). Between Apr. 30 and
     May 6, earth-occultation measurement yields a 3-sigma
     upper limit on the total flux above 20 keV of 2.7 x
     10E-9 erg cmE-2 sE-1, or about 150 mCrab."          
The following was reported in IAU circular 6405:           
     CYGNUS X-1                                            
     S. N. Zhang, W. S. Paciesas, B. A. Harmon, G. J.
     Fishman, and D. Crary, Marshall Space Flight Center,
     NASA, report for the  Compton Gamma Ray Observatory
     BATSE team: "Cygnus X-1 has been decreasing rapidly
     in intensity in the band 20-200 keV, as observed by
     BATSE, roughly coincident in time with the increased
     2- to 12- keV flux reported by ASM/RXTE (see IAUC
     6404). The flux changed from 1.0 +/- 0.02 Crab units
     (20-100 keV) on May 11 to 0.5 +/- 0.02 on May 19-20.
     The energy spectrum also becomes softer during this
     time (the Optically Thin Thermal Bremsstrahlung model
     temperature being from 80 to about 50 keV). The
     r.m.s. fraction (0.01-0.488 Hz) also decreased from a
     typical value of 8 +/- 0.5 to 5 +/- 0.5 percent
     during this period."                                  
The following was reported in IAU circular 6411:           
     GRS 1915+105                                          
     S. N. Zhang, C. R. Robinson, B. A. Harmon, W. S.
     Paciesas, and G. J. Fishman, Marshall Space Flight
     Center, NASA, report for the Compton Gamma Ray
     Observatory BATSE team: "A hard x-ray outburst from
     GRS 1915+105 is being detected by BATSE/CGRO. Its 20-
     to 100- keV flux has increased almost linearly from
     an upper limit of about 50 mCrab on May 15-18 to
     about 250 mCrab on May 24 and remained bright with
     significant day-to-day variations of 20-50 percent as
     of May 27. This flux level is slightly below the
     average peak flux (about 300 mCrab) of this source
     during previous outbursts." 

The following was reported in IAU circular 6413:

     EXO 2030+375                                          
     M. T. Stollberg, University of Alabama in Huntsville;
     R. B.  Wilson, Marshall Space Flight Center; M. H.
     Finger, Universities  Space Research Association; and
     T. A. Prince, California Institute of Technology,
     report for the Compton Gamma Ray Observatory BATSE
     team: "Pulsations from the Be/x-ray transient pulsar
     EXO 2030+375 have been observed during Apr. 1-7 and
     May 17-22. Outbursts began 4-5 days before the
     periastron passages predicted by the orbital  model
     of Stollberg et al. (1993, AIP Conference Proc. 308,
     255).  All prior outbursts observed by BATSE occurred
     after periastron.  The measured pulse period for the
     first outburst, after correcting for orbital motion,
     was 41.6773 +/- 0.0015 s on 1996 Apr. 2.5 UT. The rms
     pulsed flux (20-50 keV) peaked on that day at 16 +/-
     3  mCrab. The second outburst had an orbit-corrected
     pulse period of 41.67781 +/- 0.00083 s on 1996 May
     19.5. The rms pulsed flux (20- 50 keV) peaked at 15
     +/- 3 mCrab on May 21.5. Thirteen consecutive
     outbursts were observed previously by BATSE from 1992
     Feb. 8 to  1993 Aug. 28. During that time, the pulse
     period of EXO 2030+375 decreased from 41.6839 +/-
     0.0011 s on 1992 Feb. 10.5 to 41.6708  +/- 0.0015 s
     on 1993 Aug. 23.5 for a mean period rate of -8.5
     ms/yr. Over the 21 orbital periods during which the
     source was not detected, the mean period rate was
     +2.3 ms/yr. The next periastron passage is predicted
     to occur on 1996 July 7."         

During the last month the following pulsed sources have
been detected by the BATSE pulsed source monitor: Her X-1,
Cen X-3, 4U 1626-67, EX 02030+375, OAO 1657-415, GX 1+4,
GRO J2058+42, Vela X-1, and GX 301-2. 

The burst trigger is currently using count rates from
50-300 keV energy range. As of June 6 BATSE has detected
1550 gamma-ray bursts out of a total of 5382 on-board
triggers in 1871 days of operation. There have been 767
triggers due to solar flares, 10 due to SGR events, 54 due
to terrestrial gamma-ray flashes, and 1477 due to the
bursting pulsar GRO J1744-28.

A series of 20 triggers in a row has occurred that were
all gamma-ray bursts.