CGRO Status Report for October, 1995

[SHRADER@grossc.gsfc.nasa.gov]

  Compton Observatory Science Report #186, Friday, October 6, 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

Cycle 5 is here! Observations began this week. 

Several recent updates to the CGRO Cycle-4 and -5 timelines have been
made recently, due to both the occurrence of the GRO J2058+42 target
of opportunity (see the BATSE and OSSE reports below), and due to a
computational error in the original Cycle-5 timeline generation. The
corrected versions have been distributed by electronic and normal
mail to all current Guest Investigators. 

As a consequence of Goddard's efforts to streamline its management
structure, the SSC has a new mail code: future correspondences should
to the SSC should use mail code 660.1 instead of 668.1. Otherwise,
we're all still here in the same place!


                         Instrument Reports

EGRET

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 also on schedule.
Interaction with guest investigators continues at a good level.  All
of the relevant information for phase 5 is in the computors, and we
are ready to handle the cycle 5 data . All cycle 5 guest
investigators who have expressed an interest in working with a member
of the EGRET team should have received a letter from Carl Fichtel by
now giving relevant information; if anyone has not, please contact
Carl Fichtel by e-mail. fichtel@lheavx.gsfc.nasa.gov.

Papers on high energy gamma rays from bursts will be presented at the
Huntsville Burst Meeting, along with a report on the search for
microsecond bursts predicted by the Hawking unification theory.
A very extensive improved normalization for the EGRET data that has
utilized all of the data and involved several cross-checks is nearing
completion after a long period of intense work. It will include not
only an improved normalization above 100 MeV, but normalizations for
each energy interval for each viewing period. We expect this work
including the tests and checks to be completed in six to eight weeks,
at which time it will be transferred to the Compton Gamma Ray
Observatory Science Support Center in final form for use by everyone.

Cycle 5 began on October 3 with a pointing centered on galactic
coordinates (l = 28.0, b = 3.6). As with the great majority of the
cycle 5 pointings, EGRET will be in the narrow field mode.



OSSE 

At the start of Cycle 5, after more than four years on orbit, OSSE is
working as designed, with all subsystems in complete and full
operation.

The slewing response to BATSE burst triggers has been enabled since
30 June.

Recent observations are listed in the following table.

View period    Dates          Target         (owner)
    427        22 Aug - 7 Sep MCG +8-11-11   (PI team)
                              NGC 3227       (GI R. Cameron)
    428           7-20 Sep    NGC 253        (GI D. Bhattacharya)
                              Vela region    (GI R. Diehl)
    429         20-27 Sep     AE Aqr         (GI J. Bookbinder)
                              Sco X-1        (PI team)
    429.5    27 Sep - 3 Oct   GRO J2058+42   (PI team)
                              NGC 5548       (not assigned)
    501        3-17 Oct       QSO 1741-038   (PI team)
                              3C 279         (PI team)
                              AE Aqr         (GI J. Bookbinder)

Viewing period 429.5 was a Target of Opportunity pointing designed to
help locate the X-ray pulsar GRO J2058+42 recently discovered by
BATSE. Data from the first few days were used to generate the error
box given in the IAU circular below, and the remaining days were used
for spectroscopy. OSSE clearly detects pulsations at the ~198-sec
spin period of the neutron star.  The phase-averaged spectrum above
50 keV is consistent with a 10 keV exponential cutoff.

     GRO J2058+42
         
     J. E. Grove, Naval Research Laboratory, reports on behalf of the
     Compton Gamma Ray Observatory (CGRO) OSSE team: "We have further
     constrained the position for GRO J2058+42 using the OSSE
     instrument on the CGRO. Data from a 1-dimensional scan through
     the source region were combined with the published BATSE error
     box (IAUC 6238) to yield a new 95-percent confidence region of
     size about 30' x 60', bounded by a quadrilateral with the
     following vertices (equinox 2000.0): R.A. = 21h00m.5, Decl. =
     +41o42'; 20h59m.5, +42o12'; 20h57m.5, +41o21'; 20h58m.3,
     +40o51'. Follow-up observations in other wavebands to identify
     the object are encouraged."

Data up to viewing period 332 have been delivered to the Compton GRO
Science Support Center archive.

OSSE team members have recently submitted a number of papers to be
published in the proceedings of the 1995 Compton Symposium, covering
a broad range of topics:

Galactic compact objects: (GRO J1655-40 [Kroeger et al.], Cyg X-1
[Phlips et al.], Cyg X-3 [Matz et al.], GS 1826-34 [Strickman et
al.]);  

Supernova remnants: (Cas A [The et al.], Vela SNR [Strickman et
al.]); Diffuse galactic emission (lines [Harris et al.], continuum
[Purcell et al.], positronium [Kinzer et al.], electrons in the ISM
[Skibo et al.]);  

Extragalactic objects: (blazars [McNaron-Brown et al.]); and an
overview by Kurfess. After the papers are reviewed, they will appear
with other OSSE preprints under the OSSE home page on the WWW at URL
http://osse-www.nrl.navy.mil/.


COMPTEL

The COMPTEL instrument is performing well and continues routine
observations, now in CGRO Cycle 5.

Preprints are currently being prepared for distribution containing
collaboration papers presented at the recent International Cosmic Ray
Conference in Rome, and the 3rd Compton Symposium in Munich.

A delivery to the COSSC public archive of low-level and first
high-level data products for Viewing Periods 308 to 323 has just
recently been completed.  This delivery also includes an update to
several Phase 1 datasets which have undergone improved processing
since their initial delivery.

There will be a general team meeting of the collaboration next week
(Oct 10-13) at the University of New Hampshire.

Preparations are nearly complete for the official celebrations
marking the beginning of the CGRO Cycle 5 observing season AND the
arrival of TJD 10000 (and the wagers have already been placed to see
which computer programs will hang due to the extra digit in the TJD
field). Our Dutch colleagues inform us that, in honor of the new
millenium in TJD, all phone numbers in Holland will change on that
date (October 10). 


BATSE

The following notice appeared in IAU Circular 6238:

     GRO J2058+42           

     C. A. Wilson, S. N. Zhang, M. H. Finger, R. B. Wilson, and M.
     Scott, Marshall Space Flight Center, NASA; and T. Koh, D.
     Chakrabarty, B. Vaughan, and T. A. Prince, California Institute
     of Technology, report for the Compton Observatory BATSE team:
     "Pulsations from a previously-uncatalogued source in the Cygnus
     region in the energy band 20-50 keV have been detected since
     Sept. 14 and continue to be detected through Sept. 25. A
     preliminary location (95-percent confidence) is bounded by a
     quadrilateral with vertices (equinox 2000.0) at R.A. = 21h03m,
     Decl. = +40o.2; 20h56m, +44o.0; 20h53m, +43o.2; 21h01m, +39o.4.
     Positions estimated independently from the pulsed and total flux
     are consistent. An rms pulsed flux of 130 +/- 40 mCrab in the
     energy band 20-50 keV was observed on Sept. 23. Observations
     between Sept. 20 and 23 show pulsations up to at least 70 keV
     and are consistent with a barycentric pulse frequency of
     5.05618(7) x 10E-3 Hz on Sept. 22.0 UT with a frequency
     derivative of 1.70(7) x 10E-11 Hz/s. The total flux, measured by
     Earth occultation, increased from < 100 mCrab on Sept. 17 to 280
     +/- 50 mCrab on Sept. 22 in the band 20-100 keV and has remained
     approximately constant (within 15 percent) from Sept. 22 to 24.
     The energy spectrum of the total flux on Sept. 20- 24 was well
     fit by an optically-thin thermal bremsstrahlung model with kT =
     17 +/- 1 keV from 20 to 100 keV." 
  
The following notice appeared in IAU Circular 6242:

     SGR 1806-20  
     
     C. Kouveliotou, G. J. Fishman, C. A. Meegan, and K. Hagedon
     report for the Compton Observatory BATSE Team: "We have detected
     transient soft-gamma-ray emission from a region consistent with
     the direction of the 'soft gamma repeater' (SGR) 1806-20. The
     BATSE location is centered at R.A. = 272 deg, Decl. = -20 deg
     and has an error radius of about 4 deg. The outburst was
     recorded on Sept. 30.72852 UT and consists of one pulse with a
     triangular shape and 60-ms duration (40 ms FWHM). The spectrum
     of the event has an upper energy cutoff of about 100 keV,
     consistent with a typical SGR spectrum. Follow-up observations
     of the source region at other wavelengths are strongly
     encouraged. "  
  
The BATSE pulsed source monitor has detected the following sources in
the last month : Her X-1, Cen X-3, GRO J1750-27, 4U 1626-67, OAO
1657-415, GX 1+4, GRO J2058+42, Vela X-1, 4U 1145-619, and GX 301-2.
The outburst from GRO J2058+42 is still being detected.

GRS 1915+105 was in outburst (100-200 mCrab in the 20-100 keV band)
from approximately September 25 to October 4. The BATSE burst trigger
is using discriminator channels 1+2 (~20-100 keV) to enhance
sensitivity to SGR events. As of October 5 BATSE has detected 1375
gamma-ray bursts out of a total of 3745 on-board triggers in 1626
days of operation. There have been 758 triggers due to solar flares,
10 due to SGR events, and 49 due to terrestrial gamma-ray flashes.

The BATSE WWW page
(
http://gammaray.msfc.nasa.gov/batse/) now
contains the program and the abstracts for the upcoming Huntsville
Burst Workshop. Several recent papers by BATSE team members are also
available.