Central Bureau for Astronomical Telegrams
IAUC 5323: GALACTIC CENTER; 1991 OA; 1991s
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Circular No. 5323
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
GALACTIC CENTER
J. D. Kurfess and W. N. Johnson, Naval Research Laboratory; W.
R. Purcell, Northwestern University; and G. Jung, Universities Space
Research Association, on behalf of the Oriented Scintillation
Spectrometer Experiment (OSSE) team, report: "The OSSE onboard NASA's
Gamma-Ray Observatory observed the region of the Galactic Center
(GC) during the period July 12-26. These observations were performed
with the long direction of the OSSE field-of-view (3.8 x 11.4
deg FWHM) oriented parallel to the Galactic plane and centered on
the GC; observations were performed at latitudes b = -3.0, -1.5, 0,
+1.5, and +3.0 deg. Preliminary analysis of these data indicates
the presence of a 511-keV line and positronium continuum superimposed
on a power-law continuum. The line is found to have a width
consistent with the instrumental resolution. For the b = 0 deg
observations, the 511-keV flux was (2.9 +/- 0.5) x 10E-4 photons cmE-2
sE-1, with a positronium fraction of (0.9 +/- 0.2). These data are
consistent with a diffuse source origin, as reported by Share et al.
(1988, Ap.J. 326, 717). The 3-sigma upper limit to daily variations
in the 511-keV line flux during the observation interval is 3 x
10E-4 photons cmE-2 sE-1. If all of the observed annihilation
radiation is assumed to originate from the x-ray source 1E 1740.7-2942,
the corresponding 511-keV line flux would be (3.2 +/- 0.6) x 10E-4
photons cmE-2 sE-1. The 3-sigma upper limit for 511-keV line emission
from the x-ray binary GX 1+4 is 6 x 10E-4 photons cmE-2 sE-1.
Further OSSE observations of the Galactic plane and GC region are
scheduled that will allow the separation of compact sources of 511-
keV line emission from the diffuse component, as well as providing
periodic monitoring of the 511-keV line flux from the GC region. GC
observations are currently scheduled for 1991 Oct. 3-17, Nov. 14-27,
Dec. 12-1992 Jan. 10, and Feb. 20-Mar. 5."
1991 OA
Photometry by G. Veeder and E. Tedesco at the Infrared Telescope
Facility, Mauna Kea, on Aug. 13.451 UT: V = 16.7, B-V = +0.7.
PERIODIC COMET WIRTANEN (1991s)
Total visual magnitude estimate by A. Hale, Las Cruces, NM
(0.41-m reflector): Aug. 8.45 UT, 11.4.
1991 August 13 (5323) Daniel W. E. Green
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