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CGRO biweekly Status Report - April 1, 1994

Compton Observatory Science Report #154 Friday, April 1, 1994
Chris Shrader, Compton Observatory Science Support Center

Questions or comments can be sent to the Compton SSC.
Phone: 301/286-8434
e-mail:   NSI_DECnet: GROSSC::SHRADER 
          Internet: shrader@grossc.gsfc.nasa.gov

                         Spacecraft Status

The Observatory, scientific instruments and all spacecraft
subsystems continue to performing normally. Based on the number of
packets of data delivered to instrument teams, the percentage of
full time coverage achieved with 32Kbps realtime data between March
16 and March 22 was 80%, including 17% from the GRO Remote
Terminal System (GRTS). An additional 5% coverage was achieved with
the BATSE 1Kbps data during this time. Engineering tests of the
GRTS are continuing.

                    Science Support Center News

Proposals are us! As you frantically write and we prepare for the
onslaught, please feel free to contact us with any questions
regarding the NRA, proposal submission, policy or technical issues.

There is an error with the figure V-5 of Appendix G to the NRA -
see the BATSE Instrument report for details.

Some problems have been found with the target-entry portion of the
Unix versions of the proposal form generation software. This
effects the Sun and DEC UNIX versions only but NOT THE VERSION ON
GRONEWS. For now, we recommend using the GRONEWS version or
downloading only the VMS version to use on your VAX. Unix fixes are

As noted in the last bi-weekly report, there are several items of
potential interst on GRONEWS - lists of previously awarded targets
(phase 2 & 3) and carry-over targets (phase3-->4) are available
under item 2 (it may be good to see what's been done!). 

                        Instrument Reports


OSSE operations are normal.

In viewing period 323 (22 Mar - 5 Apr), the Z-axis target is the
ADC source H1822-37.1 (Guest Investigator E. Liang), and the X-axis
targets are the blazars QSO 2251+158 and CTA 102, along with the
recent unidentified EGRET source GRO J2239+12 (Key project). The
Sun was not available for slewing on the OSSE scan plane.

We have made 700+ high time resolution gamma-ray burst time
histories from OSSE available on the Internet via Mosaic. They are
current through the end of February, 1994. The appropriate URL is:


The data are the total count rates from the four annular NaI
shields, typically sampled at 16-ms intervals and covering about 64
sec, 4 s before the burst and 60 s after. They are dumped in
response to an on-board trigger provided by BATSE, and we have
relied on the BATSE identification to eliminate the solar and
terrestrial events. Plots of the events may be browsed and the data
from individual events may be downloaded for further study. Please
note that the data are raw and in some cases contain artifacts
(especially single channel spikes) that are not associated with the
bursts. Consult the Mosaic pages for further information. Those who
would like access to the data but do not have Mosaic should contact
the OSSE team.

Data from the following viewing periods have been sent to the
Compton GRO Science Support Center archive in the last two weeks.
 period        targets
  39           GRO J0422+32, MCG+5-23-16, 3C279
  201          Her X-1, Gal plane near (l,b) = (355,0)
Delivery of the activation period and Phase 1 is now complete.
Viewing periods 201, 204, and 205 from Phase 2 have also been


EGRET operations were normal this biweekly period. The percentage
of possible data that was recorded during the period was slightly
over 80%. Interaction with guest investigators remains at a good

Now that the phase 3 deep survey is complete, together with the
basic data reduction, the scientific analyses are beginning. Some
early results should be reported at the Spring AAS meeting. Results
from the February 18, 1994 (Olympic) burst and the March 1, 1994
(Chopin [In answer to those who asked why "Chopin", it was his
birthday.]) burst will be presented at the Washington APS meeting;
those interested in bursts will want to hear this talk. Papers will
also be presented at the APS on galactic sources, the galactic
diffuse radiation, the search for microsecond bursts, and AGNs.


The COMPTEL instrument is performing well and continues routine

The anomalies reported earlier associated with the Remote Interface
Unit B (RIU-B), external to COMPTEL, which monitors the
state-of-health telemetry from the telescope, were eliminated when
the Flight Operations Team at Goddard switched the instrument to
the redundant RIU-A on March 17.

The COMPTEL operations group reports that the switch to RIU-A
occurred without problem, and the telescope continues to function
normally. The RIU problems had no effect on the quality or quantity
of flight data obtained from the instrument.

As elsewhere in the gamma-ray community, proposal-preparation
activities are reaching a peak within the collaboration, in
anticipation of the April 11 deadline for the submission of Cycle 4
GRO proposals to NASA.


BATSE contribution to the GROSSC bi-weekly report:

The following was included in IAU Circular 5955:
     4U 1145-619
     R. B. Wilson, M. H. Finger, M. Stollberg, T. A. Prince, J. M.
     Grunsfeld, B. A. Harmon, and S. N. Zhang report for the
     Compton Gamma Ray Observatory BATSE team: "An outburst from an
     x-ray pulsar is currently being observed. Pulsations were
     first detected on Mar.12.5 UT. The measured barycentric pulse
     period was 293.4464 +/-0.0016 s on Mar. 19.0. The location,
     determined on Mar. 19 using  earth-occultation mapping, is
     R.A. = 11h48m.6, Decl. = -62o03' (equinox 2000.0), with an
     error radius of 0.2 deg. This location  is consistent with
     either of the transient x-ray binary systems 4U 1145-619 or 1E
     1145.1-6141. Based on previously reported periods  of 292 and
     297 s, respectively, the source is most likely 4U  1145-619.
     The period rate of change measured between Mar. 17 and 21 was
     (-2.43 +/- 0.34) x 10E-7. The pulse shape averaged over Mar.
     16-20 consists of a narrow peak with a phase width of about 
     0.35, immediately followed by a deep 'well' with a width of
     about  0.1 in phase. The total flux in the band 20-40 keV on
     Mar. 19 was 0.5 Crab. The phase-averaged pulsed flux on that
     day was 0.3  Crab (total). These flux values each have
     uncertainties of about  10 percent. The source intensity has
     remained within 10 percent of these values through Mar. 21.0."
The following was included in IAU Circular 5959:

     GRO J1008-57

     M. H. Finger, R. B. Wilson, M. Scott, M. Stollberg, and T. A.
     Prince report for the Compton Gamma Ray Observatory (CGRO)
     BATSE pulsar team: "Pulsed hard x-ray flux in the energy range
     20-100 keV is currently being detected from the source GRO
     J1008-57. This source was discovered by CGRO in an outburst in
     1993 July (IAUC 5836, 5838) and subsequently observed by ASCA
     (IAUC 5851) and ROSAT (IAUC 5877). In the current outburst,
     pulsed flux was first  detected on 1994 Mar. 23. The
     barycentric pulse period of 93.5410 +/- 0.0014 s was
     determined for Mar. 27.0. The pulse profile consists of a
     single broad peak, as was previously observed by BATSE. The
     spectrum of the phase-averaged pulsed flux on Mar. 26 is fit
     between 20 and 100 keV by an optically-thin thermal
     bremsstrahlung model of the form A/E exp(-E/kT), with a flux
     at 45 keV of (1.0 +/- 0.2) x 10E-4 photon cmE-2 sE-1, and kT =
     17.9 +/- 4.3 keV. This is about 40 mCrab (total) in the band
     20-50 keV. If the interval between this outburst and the last
     (260 days) is near the orbital period, then a time-of-arrival
     analysis of the previous outburst requires a projected
     semi-major axis of 600-800 light seconds, and a mass function
     of 3-8 solar masses, indicating a high-mass companion."     

As of March 28th, BATSE has detected 940 cosmic gamma-ray bursts
out of a total of 2789 on-board triggers in 1070 days of operation.
There have been 729 triggers due to solar flares with emission
above 60 keV.

Addendum to BATSE report:

To guest investigators who propose Earth occultation source
measurements using BATSE for Cycle 4:

It has been brought to my attention that the Appendix G for NRA
94-OSS-O2 (January, 1994) for the Compton Gamma Ray Observatory has
some confusion regarding the figures showing the sensitivity of the
Earth occultation technique as applied to the large area BATSE
detectors (LADs). In this memo, I would like to correct this
confusion for the benefit of Cycle 4 proposers. 

Figure V-4 on page G-81 is a sensitivity curve for the LADs using
the Earth occultation based on early mission measurements and has
appeared in previous Appendix G NRAs. The binning shown is for the
standard medium energy resolution (MER) data which is obtained
continuously at 2.048 sec intervals (CONT data).

Figure V-5 on page G-82, despite what is claimed in the figure
caption, is the revised sensitivity curve for Earth occultation
measurement using an improved measurement algorithm and a longer
sampling interval around occultation steps. The binning shown is
not the standard CONT channel binning usually used. The 30-50 keV,
50-100 keV, 100-230 keV and 230-600 keV bins in Figure V-5 are
normally subdivided into 2 or 3 channels. However, the sensitivity
curve is correct for the binning indicated. This figure was also
inadvertently placed over another figure of the Crab pulse profile.

If you would like to have a postscript file of the figure showing
the revised sensitivity with the standard CONT channel binning, you
may retrieve via anonymous FTP on grossc.gsfc.nasa.gov, under

Alan Harmon
Earth Occultation Team Leader, BATSE