CGRO Monthly Status Report for May 1995

[SHRADER@grossc.gsfc.nasa.gov]

    Compton Observatory Science Report #181, Tuesday, May 9 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

Some of you have probably noticed that this is the first CGRO status
report in a little over one month - this is because the biweekly
status report is now the monthly status report! Subsequent reports
will be issued by the 10'th of each month. Issues of sufficient
urgency may be distributed in the interims via this e-mail exploder.

A total of 229 Guest Investigator proposals were submitted for Cycle
5! This is very similar to last year (236). The over-subscription
rates for observing time on the pointed instruments range from about
3:1 to 4:1. The peer-review will be held later this month, and the
timeline committee will meet the week of June 26, 1995. We thus hope
to notify Guest Investigators of the fate of their proposals during
July. Cycle 5 observations will start on October 4, 1995.


                         Instrument Reports

EGRET

EGRET operations were normal this monthly period.  Delivery of data
to the GRO SSC remains on schedule.  Interaction with guests
investigators continues at a good level.

A paper on the evolution of blazars observed to be emitting high
energy gamma rays by J. Chiang, C. Fichtel, C. von Montigny, P.
Nolan, and  V. Petrosian has been accepted by the Astophysical
Journal. Evolution of this class of objects has been established; it
is seen to be similar to radio bright, flat spectrum AGN, although
the uncertainties are relatively large due to the small statistical
sample. The four papers on sections of the sky off the galactic plane
have now all been submitted to a journal.  The Second EGRET Catalog
received a favorable review. The suggested changes are being 
accomodated and the paper will be resubmitted shortly. We hope that
approval will come in the not too distant future. Several papers on
new results will be presented at the Third Compton Symposium in June.

Following the completion of the Mrk 421 observation on May 9, 1995,
the rest of May will be spent examining the Orion region.


OSSE 

OSSE operations are normal.  Detector motor drive #1 continues to
operate without error.  Since 10 April, the slewing response to BATSE
burst triggers  has been disabled, since the BATSE burst trigger is
set to the low energy  (25-100 keV) band.

Two gamma ray bursts occurred serendipitously within the OSSE field
of view in the last month.  Burst GRB950421 was clearly detected to
several MeV, and was in the fields of view of COMPTEL and EGRET as
well.  Burst GRB950430 we positioned to +-0.2 deg along the OSSE scan
direction.  Analysis of both bursts continues.

OSSE papers on blazars (McNaron-Brown et al., ApJL) and pulsars
(Schroeder et  al. ApJ) have recently been accepted, and preprints
are available over the WWW at URL
http://osse-www.nrl.navy.mil/gamma/osse/preprint/osselib.html.
McNaron-Brown et al. report OSSE spectra of five EGRET blazars, four
of which show clear evidence for spectral breaks between the hard
X-ray and medium  energy gamma-ray bands.  Schroeder et al. give
upper limits on low energy gamma ray emission from a large number of
radio pulsars.

Recent observations are listed in the following table.
View period    Dates          Target (owner)
    419.1 4-11 Apr  Orion (Guest Investigator H. Bloemen)
                    MCG-2-58-22 (Guest Investigator R. Petre)
    415        11-25 Apr LMC X-3 (PI team)
                    South Galactic Pole Survey (PI team)
    418        25 Apr - 9 May NGC 4151 (Guest Investigator N.
               Gehrels)
                    X Per (PI team)

Data from viewing periods 313, 314, 315, and 316 were delivered to
the Compton GRO Science Support Center archive in the last month. 
The targets during these periods were Cen A, CTA 102, the galactic
center region, PSR B1259-63, and the Virgo sky survey.


COMPTEL 

The COMPTEL instrument is performing well and continues routine
observations.

Two cosmic gamma-ray bursts were detected within the field of view of
COMPTEL on 21 and 25 April 1995.  GRB950421 was detected by BATSE,
COMPTEL, EGRET, and Ulysses; the best combined COMPTEL/IPN position
for this event is: (RA2000 = 69.35,DEC2000 = -62.22) with a 1-sigma
uncertainty of about -/+ 1.5 deg along the IPN annulus.  GRB950425
was strongly detected by COMPTEL at MeV energies (approximately 150
events); the best combined COMPTEL/IPN location is: (RA2000 = 164.86,
DEC2000 = -33.92) -/+ 1.0 deg (2-sigma) along the IPN annulus.  The
COMPTEL-determined positions for these events were distributed by the
Burst Rapid Response group to those observers who had previously
expressed interest; further information can be obtained by contacting
either Tom Harrison (tharriso@nmsu.edu), or Marc Kippen
(mkippen@comptel.unh.edu).

The following papers by the collaboration are currently in press.
Most have recently been distributed as preprints, and are also
available as postscript documents via anonymous ftp from
unhgro.unh.edu (cd to the pub/papers directory).  "1.809 MeV
gamma-rays from the Vela region" (Diehl et al.); "PKS 0208-512
detected at MeV energies by COMPTEL: A new 'MeV-Blazar' candidate"
(Blom et al.); "The black-hole candidate GRO J0422+32: MeV emission
measured with COMPTEL" (van Dijk et al.); "COMPTEL upper limits to
MeV emission from the globular cluster 47 Tucanae" (O'Flaherty et
al.); "The All-Sky Pulsar Search at 0.75-30 MeV by Comptel"
(Carraminana et al.); "The detection of an unidentified variable
gamma-ray source by COMPTEL" (Williams et al.).  All will appear in
Astronomy and Astrophysics.

The recent ESLAB conference "Toward the Source of Gamma-Ray Bursts,"
held in Noordwijk, The Netherlands, was attended by about 150
scientists from 5 continents and 24 countries. About 120 papers were
presented in both poster and oral form.  There are still a limited
number of copies of the abstract book available; if you would like a
copy please send your name and address to:
eslab29@astro.estec.esa.nl.

Preparations for the Third Compton Symposium next month in Munich are
proceeding on schedule. A preliminary program including contributed
presentations has recently been distributed. Attendees should note
that conference registration and hotel reservations should have been
made by now to obtain the lowest rates. The latest information
regarding the Symposium can be found at the following URL on the Web:
http://cgro95.mpe-garching.mpg.de/cgro95.html.

Finally, the COMPTEL team announces that new WWW pages containing
general information on the COMPTEL instrument and the collaboration
are now available on the Web.  These main COMPTEL WWW pages are
accessible from the COSSC home page (at URL
http://cossc.gsfc.nasa.gov/cossc/cossc.html), and contain links to
the four COMPTEL home institutions at MPE, SRON-Utrecht, UNH, and
ESA/ESTEC.


BATSE   

Several BATSE team scientists presented papers at the 29th ESLAB
symposium, "Towards the Source of Gamma-Ray Bursts".  Michael Briggs
reviewed GRB burst global properties, focusing on isotropy and
inhomogeneity and their  implications. Jon Hakkila discussed limits
on burst repetition and the GRB intrinsic luminosity function.
Chryssa Kouveliotou reviewed SGR observations. Bonnard Teegarden
reviewed BATSE GRB Spectroscopy.  David Band discussed searches for
absorption lines in GRBs. Rob Preece discussed low- and high-energy
spectra of GRBs.

A letter to Nature by the BATSE Team and NRAO observers on the
x-ray/radio jet transient GRO J1655-40 appeared in the April 20th
issue  (Nature 374, p. 703-706). This paper describes the
relationships between the hard X-ray and radio observations of this
source.

The following sources have been detected by the BATSE pulsed source
monitor  since April 1st : Her X-1, Cen X-3, 4U 1626-67, 2S 1417-624,
OAO 1657-415,  GX 1+4, Vela X-1, 4U 1145-619, and GX 301-2. The
outburst of 4U1145-619 is the sixth from this source that has been
detected by BATSE.

The BATSE burst trigger energy range was set to 25-100 keV beginning
on April 12 (TJD 9819). From February 17 (TJD 9765) to April 12 BATSE
had been set to  trigger on energies > 100 keV. During that interval,
there were a total of 69 triggers, of which 36 were gamma-ray bursts,
7 were terrestrial gamma flashes, 1 was a solar flare, and 3 were
attributed to Cygnus X-1 fluctuations.

As of TJD May 5th BATSE has detected 1278 gamma-ray bursts out of a
total of 3437 on-board triggers in 1473 days of operation. There have
been 756 triggers due to solar flares with emission above 60 keV, 9
due to SGR events, and 48 due to terrestrial gamma-ray flashes.