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CGRO Monthly Status Report for July 1995

    Compton Observatory Science Report #183, Tuesday, July 7 1995
      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

                       Guest Investigator News

The observatory was reoriented last week (6/30) to observe the ToO 
PKS 1622-297, a blazar QSO which was found (by EGRET) to be
exceptionally bright in high-energy gamma-rays; PIs J. Mattox (EGRET), 
W.N Johnson (OSSE). Some additional details are given in the EGRET and
OSSE instrument reports below. The ToO observations will continue
through monday 7/10.

The Cycle-5 Proposal Review process is essentially complete -
notification letters are being mailed out for any programs not
effected by the timeline. The timeline was constructed last week by
the CGRO timeline committee, and it is currently undergoing final
constraint checking by at the Goddard Flight Dynamics Facility. All
other notification letters will hopefully be mailed out next week.
Once all letters are sent, the titles and abstracts of accepted
proposals and the Cycle-5 timeline will be posted on GRONEWS and the
WWW as well. Thanks for your patience!

The CGRO Users Committee will meet at Goddard this month: July 19 and
20, 1995. Topics of discussion will include plans for the next orbit
reboost, the use of EGRET after its last gas refill, results of the
Cycle-5 proposal review and subsequent NRA releases. Guest
Investigator input, via contacting a current member of the User's
Committee, is encouraged. A listing of the committee membership and
their e-mail addresses and phone numbers is available on GRONEWS
grossc.gsfc.nasa.gov (login as GRONEWS) or on the WWW

                         Instrument Reports


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 now running ahead of
schedule. Interaction with guest investigators continues at a good

During the last month, there have been two objects which have become
very bright. Both have been reported in IAU telegrams. One is
1622-297, a radio loud, flat spectrum quasar, which had not been seen
previously. The other is GRO J1629-49, whose galactic position is
l=335.0, b=-0.4, with a 95% confidence radius in the quicklook data
of 0.7 degrees. This uncertainty will be very substantially improved
in the final analysis. Although it became one of the brighter sources
ever seen, it had not been seen before in high energy gamma rays. Its
association with a source seen at other wavelengths is not yet
certain, although there is a strong radio source listed in the
Parkes-MIT-NRAO catalog, PMNJ 1628-4936, within the present error
contour. Inquires on the former source should go to John Mattox and
on the latter to Gottfried Kanbach.

There was a summary of EGRET results presented at the Third Compton
Symposium along with several other papers. Over fifty gamma ray
emitting blazars have been seen now, and the number is still growing.
An estimate of the evolution of the gamma-ray emitting quasars has
been made by Chiang and colleagues. Common characteristics of both
blazars and pulsars are emerging. The possible detection of another
high energy gamma-ray pulsar was reported by Ramanamurthy and
coworkers at this meeting. The general EGRET summary was given by
Carl Fichtel, a pulsar summary by Pat Nolan, the galactic diffuse
summary by Stan Hunter, and the extragalactic result by Don Kniffen.

On July 10, 1995, the pointing direction changes to the Cen-A region,
which in addition to this source contains several pulsars and
previously detected high energy gamma-ray sources.


OSSE operations are normal. The slewing response to BATSE burst
triggers was enabled 30 June, following some changes to BATSE flight
software to protect against false triggers.

Recent observations are listed in the following table.

View period    Dates          Target (owner)
    422        13-20 Jun      Gal plane near (355,0)  (PI team)
                              MCG-6-30-15  (GI N. Gehrels) 
    423        20-30 Jun      Gal plane near (0,0)  (GI J. Tueller)
                              GX 304-1 (GI M. Maisack)
    423.5   30 Jun - 10 Jul   PKS 1622-297
                              Vela X-1       

Data up to viewing period 323 have been delivered to the Compton GRO
Science Support Center archive.

The flaring gamma-ray blazar PKS 1622-297 is clearly detected by OSSE
in the current Target of Opportunity viewing period. We have
submitted the following for inclusion as an IAU Circular:

PKS 1622-297 

J.D. Kurfess, J. E. Grove, K. McNaron-Brown and W. N. Johnson, Naval
Research Laboratory, on behalf of the OSSE team; J. R. Mattox,
University of Maryland and Universities Space Research Association;
S. Wagner, Landessternwarte Heidelberg; J. R. Webb, Florida
International University, communicate: "Optical observations of PKS
1622-297 at Calar Alto, La Silla, and with the SARA telescope on Kitt
Peak indicate that it is now at least 17th magnitude - at least 3
magnitudes brighter its historical value. The OSSE instrument aboard
COMPTON detects this quasar from 50-200 keV at a significance of 6
sigma during the interval June 30 - July 6, with an indication that
the flux is somewhat higher on July 5-6. The EGRET instrument aboard
the COMPTON Observatory continues to detect PKS 1622-297. The high
energy gamma ray flux peaked on June 25, and has declined since then.
The COMPTON observations have been extended until July 10, and the
OSSE instrument will continue monitoring the source through July 24.
Observations at other wavelengths continue to be very important." 


The COMPTEL instrument is performing well and continues routine

The following two papers by members of the collaboration have
recently been distributed as a preprint, and will also soon be
available as postscript documents via either anonymous ftp from
unhgro.unh.edu (cd to the pub/papers directory), or via the COMPTEL
WWW pages accessible from the COSSC home page (see below): "Spectral
Characterisation of Gamma-ray Bursts with COMPTEL and BATSE" (Hanlon
et al.); "Search for a Radio Counterpart to GRB 940301 with
Westerbork" (Hanlon et al.), both from the recent ESLAB Symposium
"Toward the Source of Gamma-ray Bursts" (Astophysics and Space
Science, in press). The article by Blom et al. on "PKS 0208-512
detected at MeV energies by COMPTEL: a new `MeV-Blazar' candidate"
has just appeared in Astronomy and Astrophysics, volume 298, page

The 3rd Compton Symposium recently held in Munich was considered a
great success by all who attended. The organizers remind all
attendees that contributions to the proceedings volume are due by
September 1. Among the many results presented at the symposium by
members of the collaboration was the first report on COMPTEL
measurements relating to the extragalactic cosmic diffuse radiation
at MeV energies; the preliminary results presented by Kappadath et
al. indicate that the "MeV bump" reported by earlier experiments may
in fact be much less pronounced than previously believed.

A new version of the COMPTEL pages on the World Wide Web will soon be
available; these will be accessible via the COMPTEL home page
maintained by the COSSC (at URL
Among other
enhancements, these new pages include improved links to the various
COMPTEL sites, as well as to the personal home pages of COMPTEL team

After the excitement of the recent Compton Symposium all attention
within the team is currently focused on the 82nd Tour de France, now
underway. After some initial controversy regarding the entry of the
Telekom team from Germany, the question on everyone's lips is: Will
Miguel "The Train" Indurain of Banesto become the first to win five
consecutive Tours? As a service to the high-energy community, the
latest Tour results and updates are now accessible in near-real time
via the main COMPTEL pages on the WWW (see above).


Hard X-ray emission continues to be detectable from the sources GX
339-4 and GRS 1716-249 = GRO J1719-24 at about the 100-150 mCrab
level in the 20-100 keV band. The outburst from GX 339-4 has lasted
about two months and is less intense than previous outbursts in
1991-1994. The initial outburst of GRO J1719-24, an x-ray nova in
Ophiuchus, was in September-October of 1993.

The following sources have been detected by the BATSE pulsed source
monitor in the last month : Her X-1, Cen X-3, 4U 1626-67, 2S
1417-624, OAO 1657-415, GX 1+4, Vela X-1, and GX 301-2. 

The paper, "The nu F_nu Peak Energy Distribution of Gamma-ray Bursts
Observed by BATSE" by R.S. Mallozzi, W.S. Paciesas, G.N. Pendleton,
M.S. Briggs, R.D. Preece, C.A. Meegan, and G.J. Fishman has been
accepted for publication in the Dec 1 issue of Astrophysical Journal.

The BATSE burst trigger continues to operated on the 25-100 keV
energy range. As of July 2 BATSE has detected 1311 gamma-ray bursts
out of a total of 3556 on-board triggers in 1531 days of operation.
There have been 757 triggers due to solar flares, 9 due to SGR
events, and 48 due to terrestrial gamma-ray flashes.