CGRO biWeekly Status Report

[SHRADER@GROSSC.GSFC.NASA.GOV]

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  Compton Observatory Science Report #175, Friday January 20, 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
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                     Science Support Center News

The long-awaited BATSE CD ROM is out! Numerous copies were
distributed at the Tucson AAS meeting last week. It contains the
BATSE 2B catalog, including data in FITS format, quick-look data and
a simple XMosaic driven browsing tool. Its slick! Copies are
available from the SSC.

The Cycle-5 NRA can now be browsed on our Web Home page
(http://cossc.gsfc.nasa.gov/cossc/cossc.html), downloaded (in
PostScript format) via anonymous ftp (on grossc.gsfc.nasa.gov), or
requested via snail mail from the SSC. Proposals are due April 7,
1995. 

Instructions for the (mandatory) electronic submission of all cycle-5 
proposal forms will be distributed shortly. Basically, the procedure
is as follows: 1) you fill out an ascii form which has a one-to-one
correspondence to the printed forms, OR fill a graphical form on the
Web which more or less looks like the proposal forms. 2) submit it to
an e-mail processor (or hit a key on the Webb version) which promptly
returns a LaTex form for you to print and proof read 3) fix any
mistakes and check again (repeat this step as necessary) 4) set a
"submit" flag and send again.  You now have a clean copy of your
proposal forms, tagged with the correct  proposal ID number, for
inclusion with your hard-copy submission, and we've been spared a
mountain of database entry work! Its easy!
 

                         Instrument Reports

EGRET

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

Recent papers on EGRET results include "Detection of a Gamma-Ray
Burst of Very Long Duration and Very High Energy", by Hurley et al.,
in the December 15 issue of Nature, "EGRET Detection of the Blazar
PKS 0420-014", by Radecke, et al., in the January 10 issue of the
Astrophysical Journal, and "EGRET High-Energy Gamma-Ray Pulsar
Studies, I. Young Spin-Powered Pulsars", by Thompson et al., in the
November 20 issue of the Astrophysical Journal.

At the moment, the EGRET instrument is pointed at the Large
Magellanic Cloud region.  The Large Magellanic Cloud was seen
previously, and further observations should provide details not
possible to see with just the earlier exposure. Also, it is a good
region for further AGN studies. 


OSSE

OSSE operations are normal. In particular, the motor drive for
detector #1 has functioned flawlessly since the last report.

In viewing period 409 (10-24 Jan), the Z-axis target is PKS 0506-612
(PI team), and the X-axis targets are NGC 7213 and Mrk 509 (Guest
Investigator R. Petre).

This past weekend was a busy time for slewable gamma-ray bursts. On
13 Jan (20:57 UT), BATSE sent a slew trigger at an SAA exit. This is
an error; however, it fortuitously pointed the OSSE detectors at a
burst that occurred on 14 Jan (01:00 UT), giving OSSE a spectrum for
this burst and 8 hours of searching for persistent, low-level
emission. On 15 Jan (23:40 UT), OSSE slewed to another burst and
mapped the region for 12 hours. The burst had ended before the OSSE
detectors reached the area.

Data from viewing periods 303.5 and 303.7 were delivered to the
Compton GRO Science Support Center archive this week. The targets
during these viewing periods were N Cyg 1992, NGC 5548, Cyg X-1, and
3C273.
 

COMPTEL

The COMPTEL instrument is performing well and continues routine
observations.

Three preprints describing new COMPTEL results related to AGN have
recently been distributed by the collaboration. These reports detail
"COMPTEL Observations of the Quasars 3C 273 and 3C 279" in June and
October 1991 (Williams et al.), "COMPTEL Gamma-ray Observations of
the Quasars CTA 102 and 3C 454.3" (Blom et al.), and a "New COMPTEL
Gamma-ray Source (GRO J0516-609) near PKS 0506-612/0522-611: First
Evidence for `MeV Blazars'" (Bloemen et al.). All will appear shortly
in Astronomy and Astrophysics.

Among the reports presented by team members at last week's meeting of
the AAS in Tucson was a presentation by Morris et al. describing new
evidence for Co-56 gamma-ray line emission from the type Ia supernova
SN 1991T. These new results follow from a reanalysis (with an
improved background model) of the COMPTEL data taken during two
two-week periods beginning 66 and 176 days after the supernova
explosion. A preliminary determination of the combined flux in the
two principal lines arising from Co-56 decay, at 0.85 MeV and 1.24
MeV, yields a value of (8.9+/-3.4)x10^-5 cm^-2 s^-1. Partitioning
this by the canonical production ratio the fluxes for the individual
lines are 5.3+/-2.0 (847 keV) and 3.6+/-1.4 (1238 keV). These values
are consistent with most models for type Ia supernova explosions,
given the uncertainties in the flux and the distance to the
supernova. For the Tully-Fisher distance of 13 Mpc it corresponds to
the production of 0.8-1.8 solar masses of Ni-56 by the supernova. 


BATSE

The well-known x-ray binary source LMC X-4 has been observed in the
BATSE occultation data as a relatively weak, soft source, from data
obtained since the beginning of the mission. The source is clearly
identified by its 30.5d accretion disc precession period, and its
1.4d binary orbital period. The spectrum is well-fit by a power law
with a spectral index -3.3 from 20keV to 60keV. Pulses have not yet
been detected from the source. These observations will permit studies
of the long-term behavior of this object to be made.

The following sources were detected by the BATSE pulsed source
monitor in the past two weeks: Her X-1, 4U 0115+634, Cen X-3, 4U
1626-67, 2S 1417+624, OAO 1657-415, GX 1+4, Vela X-1, and GX 301-2.
2S 1417+624 has been visible since January 4th.

As of January 18th, BATSE has detected 1211 cosmic gamma-ray bursts
out of a total of 3257 on-board triggers in 1366 days of operation.
There have been 741 triggers due to solar flares with emission above
60 keV. Since the BATSE burst trigger criteria were changed on
September 19th 1994, there have been 15 triggers due to terrestrial
gamma-ray flashes.