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CGRO Status Report for December 1996
Compton Gamma Ray Observatory Status Report #199
Tuesday, December 10, 1996
Questions or comments can be sent to
Chris Shrader at the CGRO-SSC.
Phone: 301/286-8434
e-mail: shrader@grossc.gsfc.nasa.gov
Guest Investigator News
A draft of the Cycle-7 NRA has been sent to NASA Headquarters for
final editing and bureaucratic approval. We anticipate a February
1997 issue and a May 1997 proposal due date. Significant policy
changes for Cycle-7 include a reduction in the proprietary period
for observational data, a reduction in proposal page limits, and
changes in the grant eligibility requirements for Instrument Team
members. The total budget for Cycle-7 grants is expected to be
about 75% of the Cycle-6 total. Optimal exposure times for OSSE
targets may be longer in cycle 7 than in past cycles due to the
anticipated higher background levels with the observatory in a
500-km orbit. We anticipate allocating approximately 16-20 weeks
of EGRET observing time in narrow field-of-view mode. BATSE
"quick-look" flux reports will be made public promptly, as will
data resulting from unproposed ToOs or serindipitous discoveries.
The second announcement for the forthcoming 4th Compton Symposium
has been issued. The Symposium will be held in Williamsburg
Virginia on April 27-30, 1997. The abstract deadline is February
15, 1997. For more information refer to the URL:
http://osse-www.nrl.navy.mil/cgrosymp.htm on the World Wide Web.
Instrument Team Reports
EGRET
EGRET operations were normal this monthly period. Delivery of
the final phase 4 data to the GRO SSC was completed on schedule,
and delivery of the phase 5 preliminary data to the GRO SSC is
also on schedule. Interaction with guest investigators continues
at a good level.
The major paper on the details of the high-energy gamma-ray
Galactic diffuse radiation and its interpretation by Hunter et
al. has been accepted by the Astrophysical Journal. Preprints
will be available and distributed in the near future. A paper on
the study of the high-energy gamma-rays from the Sun has been
submitted to the Astrophysical Journal; the results suggest that
either solar particle acceleration continues for many hours, or
there is a trapping region wherein energy losses are very low.
EGRET will be reactivated on December 10, 1996 to begin a lengthy
observation of 3C 279.
Finally, here is a personal note from Carl Fichtel.
"In consideration of the position that I have reached in my
career including the fine results that have come from EGRET and
my desire to spend more time enjoying the worlds of art,
literature, gardens, and music, it seems a good time to step
forward into retirement while I can still hope for a reasonable
number of years of good health. I have been planning the
transition of my work here both on EGRET and in the Laboratory
for High Energy Astrophysics as a whole, and I believe the change
should be a smooth one. Klaus Pinkau will automatically become
the sole Princiapal Investigator of EGRET by the agreement with
NASA headquarters long ago. Dave Bertsch will be the routine NASA
contact.
"I shall certainly continue to be interested in learning of the
new scientific results of fundamental significance which are
expected to be forthcoming. I shall also enjoy continuing to see
my many friends from time to time as the opportunity arises.
"I wish you all health and happiness.
"Carl Fichtel"
COMPTEL
The COMPTEL instrument is performing well and continues routine
observations.
A systematic reprocessing and inspection of recent COMPTEL data
taken around the times of gamma-ray bursts occurring within the
field of view of the instrument has uncovered evidence for
COMPTEL detections of an additional 1-2 GRBs previously missed in
quick-look processing. A more detailed analysis of the data
associated with these events is currently in progress.
A paper on "New COMPTEL results on MeV gamma rays from the
Orion/Monoceros region" (Bloemen et al.) is currently in press in
the Astrophysical Journal (Letters).
A general team meeting of the collaboration was held at ESA/ESTEC
in The Netherlands from 19-22 November. At the upcoming 18th
Texas Symposium on Relatvistic Astrophysics later this month
there will be presentations on the latest COMPTEL results
relating to the cosmic diffuse gamma-ray background at MeV
energies (by Kappadath et al), gamma-ray bursts (Connors et al),
44Ti line-emission from the Cas A supernova remnant, and
unidentified high-latitude sources detected by COMPTEL (the last
two by Iyudin et al). And, at the 189th meeting of the AAS in
Toronto, there will be reports on gamma-ray bursts (Connors et
al.), solar studies (Rank et al, Young et al), and an all-sky
search for 2.2-MeV line emission from astrophysical sources
(McConnell et al).
OSSE
OSSE operations are currently normal. The instrument is working
as designed, with all subsystems in complete and full operation.
The slewing response to BATSE burst triggers is currently
enabled, but it was disabled from 26 Nov to 5 Dec to protect
against slews from outbursts of the soft repeater SGR 1806-20,
which was active and on the scan plane. Bursts, flares,
transients, and SGRs through 2 Dec 1996 have been processed. In
the last month, 10 classical GRB triggers occurred, of which 3
produced significant responses in the shields. None produced a
significant response in the central detectors. The 10 solar
flares were relatively weak C and B class events with no clear
prompt signal in the OSSE shields or central detectors. The TGF
(trigger #5665) was seen in the shields. None of the 16 triggers
from the SGR produced an obvious signal in the shields or central
detectors. There was one triggered slew during this period, for
#5672, and SGR burst. While the slew put OSSE at the proper scan
angle, the burster was out of the field of view in the transscan
direction. The new bursts are available on the WWW at
http://www.astro.nwu.edu/astro/osse/bursts/newlist.html
"Time Variability Detected in the Gamma-Ray Emission of 3C 273 by
OSSE" by K. McNaron-Brown et al. has been accepted for
publication. It will appear in the 10 Jan 1997 issue of ApJ
Letters. It reports faster time variability and greater
luminosity in the OSSE band than previously observed. While no
spectral variability is detected, the spectral break occurs at
300(+-100) keV, significantly lower than the break at ~1 MeV
reported by Johnson et al. (1995) from 1991 June data.
Recent observations are listed in the following table. We are in
the middle of a long series of pointings designed to map the
annihilation radiation and hard X-ray continuum in the area
surrounding but not including the galactic center. This should
nicely complement observations made in earlier Cycles.
View period Dates Target (owner)
602 12-19 Nov GAL 353.6+10.7 (W.R.Purcell)
[no 2nd science target, engineering test]
603 19-26 Nov GAL 356.2+06.4 (W.R.Purcell)
[no 2nd science target, engineering test]
605.1 26 Nov - 3 Dec GAL 006.2-10.8 (W.R.Purcell)
Arp 220 (public)
604.1 3-10 Dec GAL 003.7-06.5 (W.R.Purcell)
Mrk 231 (public)
Arp 220 (public)
Low-level OSSE data products through viewing period 427 and
high-level data products through viewing period 220 have been
delivered to the Compton GRO Science Support Center archive. In
addition, by special request all subsequent public Cyg X-1 data
sets, both low and high level, have been delivered. Refer to the
CGRO-SSC page on the WWW (http://cossc.gsfc.nasa.gov), or contact
Tom Bridgman (bridgman@grossc.gsfc.nasa.gov) for more
information.
BATSE
The following items were reported in IAU circular 6512:
SGR 1806-20
K. Hurley, Space Sciences Laboratory, University of
California, Berkeley, on behalf of the Ulysses Gamma-Ray
Burst Team; C. Kouveliotou, Universities Space Research
Association and Marshall Space Flight Center (MSFC), NASA;
G. J. Fishman and C. A. Meegan, MSFC; and J. van Paradijs,
University of Amsterdam and University of Alabama,
Huntsville, report: "We have derived a much-refined position
for the transient soft-gamma-ray repeater reported on IAUC
6501, via triangulation between Ulysses and BATSE of two
bursts on Nov. 19. The position is an annulus whose radius
is 76o.990, whose halfwidth is 0.0092 deg (3-sigma
confidence level), centered at R.A. = 23h55m34s.9, Decl. =
-30 55'55" (equinox 2000.0). The combined triangulation
annuli and BATSE error circles give error boxes whose areas
are more than a factor of 100 smaller than the BATSE error
circles alone. They are consistent with the known position
of SGR 1806-20 (Murakami et al. 1994, Nature 368, 127), and
the two annuli midlines pass within 4" of this position. We
conclude that the source of these bursts, as well as of the
ones that have occurred since Oct. 30, is indeed SGR
1806-20. The latest short, soft event from this source was
detected with BATSE on Nov. 23, so continued monitoring at
other wavelengths is strongly encouraged."
The following was reported in IAU circular 6514:
GRO J2058+42
C. A. Wilson, NASA Marshall Space Flight Center; T.
Strohmayer, NASA Goddard Space Flight Center and
Universities Space Research Association; and D. Chakrabarty,
Massachusetts Institute of Technology, report: "The Compton
Observatory/BATSE instrument has observed a series of five
outbursts from the 195.6-s accreting x-ray pulsar GRO
J2058+42, with a bright initial outburst in Sept. 1995 (IAUC
6238) followed by four weaker (15-20-mCrab pulsed flux in
the 20-50-keV band) outbursts, all spaced by about 110 days.
The weak outbursts have each lasted about two weeks, with a
marginal decline in peak intensity over consecutive
outbursts. The most recent outburst peaked on 1996 Nov. 25
+/- 2 with a 20-50-keV pulsed flux of 14 +/- 1 mCrab. The
barycentric pulse frequency on Nov. 25.0 UT was 5.1125 +/-
0.0001 mHz. A target-of-opportunity scan of the
Compton/OSSE/BATSE error box (IAUC 6239) on Nov. 28 with the
Proportional Counter Array (PCA) on the Rossi X-ray Timing
Explorer (RXTE) constrained the 90-percent-confidence region
for the source position to a circle with 4' radius and
centered at R.A. = 20h59m.0, Decl. = +41d43' (equinox
2000.0). RXTE/PCA observed a peak flux of 11 +/- 1 mCrab
(2-30 keV) and a pulse frequency consistent with the BATSE
measurement. Optical observations of the new error circle
are strongly encouraged in order to identify the optical
companion, most likely a Be star."
The following report has been submitted for inclusion in an IAU
Circular:
GAMMA-RAY BURSTS
C. Meegan, V. Connaughton, G. Fishman (NASA/MSFC), R. M.
Kippen (UAH), C. Kouveliotou (USRA), K. Hurley (UC
Berkeley), T. Cline, D. Palmer, S. Barthelmy, P.
Butterworth, B. Teegarden, H. Seifert, J. in 't Zand
(NASA/GSFC), E. Mazets, S. Golenetskii (IOFFE) report:
Several spacecraft have detected a sequence of gamma-ray
bursts over a two day period whose locations are consistent
with a single source. The following table gives the times of
the events, the BATSE determined location with its
statistical uncertainty, an approximate duration, and the
spacecraft that detected the event.
Date Time BATSE ULYSSES WIND
UT sec) RA DEC ERR DIST DUR TGRS KONUS
(degrees) (sigma) (sec)
961027 42247 67.4 -42.4 5.6 1.4 100 no no no
961027 43322 68.7 -54.3 5.8 3.0 0.9 no no yes
961029 23677 59.4 -52.6 4.6 1.0 30 no no yes
961029 24350 59.8 -48.9 0.3 750 yes yes yes
The DIST column shows the proximity (where sigma is the
quadrature sum of the statistical errors and does not
include BATSE's ~1.6 deg systematic error) of the first
three BATSE event locations to the fourth which has the best
determined position, including Interplanetary (IPN)
locations using BATSE, Ulysses and Konus. The Ulysses-BATSE
IPN annulus is described by a center at RA=356.657 and
DEC=-31.408 (J2000) with a radius of 49.883 deg, full width
0.078 deg. The much wider Ulysses-Konus annulus defines the
end-points of the Ulysses-BATSE annular segment at
RA=59.73, DEC=-47.07 and RA=60.32, DEC=-52.58 with a 99.7%
confidence level. A soft gamma repeater (SGR) can be
excluded as a common source by the durations of the events,
as well as by their spectra, which are consistent with
classical gamma-ray bursts. The temporal structures of the
events are quite different, apparently ruling out a
gravitational lens interpretation. The third and fourth
events are very probably separate triggers from a single
burst, making the combined event the longest burst (1420
sec) ever seen in this energy range. Although a posteriori
calculations are problematic, the probability of such a
temporal and spatial coincidence of four unrelated events is
low.
On November 28, 1996, a single event upset occurred in the BATSE
flight software memory. This event occurred when GRO was in the
central part of the SAA. This altered an instruction that was
part of the code for outputting burst data. When the next burst
trigger occurred, on November 29, this instruction was executed,
causing the program to hang. As designed, a watchdog timeout
occurred, reloading and starting the default version (Rev. 0) of
the flight software from ROM. The reload caused a spurious burst
trigger. The default software was not executing a valid output
schedule, so pulsar data were lost over the next 2 days before
getting back to a normal configuration (Rev. 7). However,
continuous data, discriminator data, and burst data were useable,
though not optimum, during this period.
On November 30, two attempts were made to send commands to return
BATSE to the desired configuration. Both times, when Rev. 2 was
loaded, there was a watchdog timeout and a reset to Rev 0. It
was determined that the original crash could have corrupted the
output schedule that Rev. 2 uses. On Dec. 1, this output schedule
was reloaded, and Rev. 2 was reloaded without incident. The later
revisions were then loaded, and BATSE returned to nominal
operations.
The loss of data is estimated as approximately 25% over a period
of 3 days. The BATSE team is grateful for the excellent
cooperation of the FOT in resolving this problem.
During the last month the following pulsed sources have been
detected by the BATSE pulsed source monitor: Her X-1, Cen X-3, 4U
1626-67, OAO 1657-415, Vela X-1,and GX 301-2.
The burst trigger continues to use rates from channels 1+2 (20 -
100 keV), with thresholds of 5.5 sigma for 64ms and 256ms
timescales and 7.0 sigma for the 1.024s timescale. As of December
4 BATSE has detected 1699 gamma-ray bursts out of a total of 5601
on-board triggers in 2052 days of operation. There have been 778
triggers due to solar flares, 31 due to SGR events, 64 due to
terrestrial gamma-ray flashes, and 1477 due to the bursting
pulsar GRO J1744-28.