CGRO BiWeekly Status Report

[SHRADER@grossc.gsfc.nasa.gov]

   Compton Observatory Science Report #179, Friday March 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
                                                                     

                       Guest Investigator News

A reminder -- the April 7 Cycle-5 deadline looms ever nearer!
Information on the submission process, including the NRA and
appendices, is available electronically on GRONEWS or on the Web at
http://cossc.gsfc.nasa.gov/cossc/cossc.html. Paper copies of the NRA
and appendices are still available from the SSC, but time is short.
Please make note of the bulleted list of changes (relative to
previous cycles) at the front of Appendix A. Instructions on how to
prepare and submit your proposal forms is available by sending a
blank e-mail message to rps@cossc.gsfc.nasa.gov.

Due to technical problems with the optical-disk jukebox which
contains the CGRO public data archive, the archive was unavailable
for a period of 3-4 days last week. The archive should now be back
online -- please make us aware of any problems you have with queries
or downloads. We apologize for any inconveniences caused.



                         Instrument Reports

EGRET

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

As reported in an IAU telegram by Ramanamurthy et al., the EGRET
instrument team has detected a sixth high-energy gamma-ray pulsar,
PSR 1951+32, pulsating in high energy gamma-rays at energies greater
than 100 MeV with the same 39.5 ms periodicity as detected at radio
wavelengths, using the data obtained during May 1991-July 1994 by
EGRET. It is  a weak source with a pulsed averaged integral flux of
pulsed gamma-rays of (1.6 +/- 0.2) x 10-7 cm-2 s-1.  There is no
evidence for an unpulsed component.  The pulsar radiation has a
photon spectral index of -(1.74 +/- 0.11).  Details of the emission
and its interpretation are in a paper submitted to the Astrophysical
Journal.

At the moment, EGRET continues to be pointed at a region in the
Galactic anticenter centered at l=192o and b=-3o.
 

OSSE 

OSSE operations are normal.  There have been no lost steps in motor
drive #1 in the last two weeks.  The slewing response to BATSE burst
triggers is disabled while BATSE's trigger threshold is low.

In viewing period 413 (7-21 Mar), the Z-axis target is PKS 0528+134
(PI team) and the X-axis targets are NGC 7172 and PKS 2155-304 (Guest
Investigator L. Bassani) and the South Galactic Pole Survey (PI
team).

Data from viewing period 310 was delivered to the Compton GRO Science
Support Center archive this week.  The targets during this period
were Geminga  and NGC 4151.

A number of OSSE preprints will be mailed in the next few days.  If
you  would like to be added to the OSSE preprint distribution list,
send email to tina@osse.nrl.navy.mil.  Preprints for 64 OSSE papers
are also available on the World Wide Web a few mouse-clicks from the
NRL Gamma and Cosmic Ray Astrophysics Branch home page at URL
http://osse-www.nrl.navy.mil/.  The preprint library contains
plaintext versions of all the abstracts as well as PostScript copies
of all the papers with embedded figures.  Selected figures are also
available in PostScript and GIF nearby.


COMPTEL 

The COMPTEL instrument is performing well and continues routine
observations.
 
A cosmic gamma-ray burst was observed within the field of view of
COMPTEL on the night of 12-13 March 1995.  Though this event exceeded
the BATSE/BACODINE intensity threshold for an automated
rapid-response analysis by the COMPTEL burst group, no emission from
this event was observed at MeV energies.

Three recent papers by the collaboration, one on "COMPTEL
Observations of the Crab during the CGRO Sky Survey" (by R. Much et
al.), another on "Gravitational Lensing Origin for a Possible
Gamma-ray Burst Repeater?" (by L. Hanlon et al.), and a third on
"COMPTEL Observations of the Strong Gamma-ray Burst GRB 940217" (by
C. Winkler et al.), all currently in press in Astronomy and
Astrophysics, are now available as postscript files via anonymous ftp
to unhgro.unh.edu ("cd" to the pub/papers directory); preprints are
also being prepared for distribution.

Finally, we remind all attendees to the upcoming 3rd Compton
Symposium, scheduled for June in Munich, that abstracts for
contributed presentations are due by March 31.


BATSE 

The following was reported in IAUC 6150:

GRO J1849-03 

S. N. Zhang, B. A. Harmon, M. H. Finger, G. J. Fishman, W. S.
Paciesas, and C. A. Wilson, Marshall Space Flight Center, NASA; J. E.
Grindlay, D. Barret, and P. Bloser, Harvard-Smithsonian Center for
Astrophysics; and E. Ford, M. Tavani, and P. Kaaret, Columbia 
University, report: "Analysis of Compton Observatory BATSE data has
revealed a possible new x-ray binary system. We have observed six
outbursts from the source (GRO J1849-03), spaced at 241-day (+/- 1)
intervals in the period 1991 Apr.-1994 Dec. within an error  box R.A.
= 18h49m +/- 1m, Decl. = -3o22' +/- 30' (equinox 2000.0). The
epoch-folded light curve of the six periodic outbursts has a FWHM of
13 days and a maximum on 1991 June 5. All six outbursts show similar
light curves and spectral behavior. From 20 to 100 keV, the peak flux
is 75 +/- 20 mCrab, and the spectrum can be fit by a power-law with
photon index of -2.8 +/- 0.2. We cannot positively identify this
source with any of the nearby hard-x-ray sources (Parmar et al. 1993,
A.Ap. 279, 179; Koyama et al. 1990, Nature 343, 148) but await a more
precise source position that might be obtained with x-ray or possibly
optical/infrared observations from the next predicted outburst. An
outburst previously reported (IAUC 6096) from this location is
consistent with the light curves of the other five outbursts;
therefore we now believe that to be associated with this new source
rather than EXO 1846-031. We interpret the 241-day period as the
orbital period of a binary system. If the periodic outbursts
continue, the next outburst should peak on 1995 May 21. Observations
are encouraged during the next outburst, especially soft-x-ray and
optical/infrared observations for a more accurate location and
possible identification of this system." A new x-ray binary system
has been discovered in occultation data and reported in an IAU
circular by the BATSE team in collaboration with Harvard and Columbia
Univ. guest investigators. Six outbursts were detected from the
source, GRO J1849-03, spaced at 241 +/- 1 day intervals in the period
April 1991 to December 1994 within an error box R.A. = 18h49m +/- 1m
and Decl. = -3o22' +/- 30'. The epoch-folded light curve of the six
periodic outbursts has a FWHM of 13 days and a maximum on JD 2448412
(TJD 8412 or 5 June, 1991). From 20 keV to 100 keV, the peak flux is
75 +/- 20 mCrab and the spectrum can be fit by a power-law with
photon index of -2.8 +/- 0.2. 

The following has been submitted to the IAU circulars:

 X-ray Nova Scorpii 1994 (GRO J1655-40)

 B. A. Harmon, S. N. Zhang, W. S. Paciesas and G. J. Fishman, report,
for the BATSE Team: "Since the bright outburst of the x-ray transient
GRO J1655-40 (~1 Crab, 20-100 keV band) in hard x-rays in Dec 1994
(ending about 23 Dec), the source has exhibited two additional
episodes of variable high energy emission. The first began around 12
Jan 1995 (IAU Circ. 6128) and ended about 25 Jan. The second began
around 12 Feb and is still in progress. Both episodes show daily
variations from below 50 mCrab to over 300 mCrab (20-100 keV band).
As in the 1994 outbursts, the spectrum is a power-law extending to at
least 200 keV. However, the best-fit spectral indices are harder,
ranging between -2.5 and -1.9. No unusual hard x-ray activity was
observed in the BATSE large area detectors during the Mir/Kvant/TTM
measurements on 22 Feb and 24 Feb (IAU Circ. 6143 and R. Sunyaev,
private communication)."

In the last two weeks pulsed flux has been detected from the
following sources by the BATSE pulsed source monitor: Cen X-3,
4U1627-673, 2S 1417-624, OAO 1657-415, GX1+4, Vela X-1, GX 301-2.

The BATSE on-board burst trigger criteria remain set on Chan. 3+4
(>100 keV) in support of observations of upper atmospheric gamma-ray
flashes.  In about 10 days, they will revert back to Chan 1+2 (20-100
keV) for 30 to 60 days in order to better trigger on soft gamma-ray
transients.  It has been found that most classical GRB's will trigger
on either of these settings, with only slightly reduced efficiency. 


As of March 12th BATSE has detected 1241 gamma-ray bursts out of a
total of 3361 on-board triggers in 1419 days of operation.  There
have been 749 triggers due to solar flares with emission above 60
keV.