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IAUC 4463: 1987A; TIME ADJUSTMENT ON 1987 Dec. 31; 1986l

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                                                  Circular No. 4463
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM    Telephone 617-495-7244/7440/7444


SUPERNOVA 1987A IN THE LARGE MAGELLANIC CLOUD
     W. Sandie, G. Nakano and L. Chase, Lockheed Palo Alto Research
Laboratory; G. Fishman, C. Meegan, R. Wilson and W. Paciesas,
NASA Marshall Space Flight Center; and G. Lasche, DARPA, report:
"A balloon-borne gamma-ray spectrometer (consisting of an array
of high-purity Ge detectors, 119 cm**2, resolution 2.5 keV FWHM at
1.0 MeV, surrounded by an active NaI(Tl) collimator/Compton
suppressing anti-coincidence shield, nominally 10 cm thick) was flown
from Alice Springs, Australia, on May 29-30.  The average slant
depth of residual atmosphere in the direction of SN 1987A at float
altitude was 6.3 g cm-2 during the observation.  SN 1987A was within
the 22  FHWM field-of-view for about 3300 s during May 29.9-30.3 UT
(96 days after the observed neutrino pulse).  No excess gamma-rays
were observed at the energies of the 56Ni/56Co decay chain or from
other lines in the energy region from 0.1 to 3.0 MeV.  With 80 percent
of the data analyzed, the preliminary 3 sigma upper limit obtained
in a search for the 1238-keV line from 56Co at the instrument resolution
(about 3 keV) is 1.3 x 10**-3 photons cm-2 s-1.  The upper limit
scales as the square root of line width assumed in the search.
The corresponding limit for the 847-keV 56Co line is 1.7 x 10**-3
photons cm-2 s-1, owing to higher background at this energy.  These
data imply that there was less than 2.5 x 10**-4 solar masses of 56Co exposed
to the earth at the time of the observation.  Further analysis is
in progress using the complete data set.  Additional balloon-borne
observations are planned."
     Visual magnitudes by A. C. Beresford, Adelaide, S. Australia:
Sept. 29.47 UT, 5.2; 30.46, 5.2; Oct. 1.48, 5.3; 2.47, 5.2.


TIME ADJUSTMENT ON 1987 DECEMBER 31
     The Bureau International de l'Heure, Sevres, informs us that a
positive leap second will be introduced such that the sequence of
UTC second markers will be: 1987 Dec. 31d23h59m59s, 31d23h59m60s,
1988 Jan. 1d00h00m00s.  From 1985 July 1 to 1987 Dec. 31 the
difference UTC-TAI = -23s; beginning 1988 Jan. 1 UTC-TAI = -24s.


COMET WILSON (1986l)
     Total visual magnitude estimate by E. A. Jacobson,
Evansville, MN (0.25-m reflector): Sept. 26.45 UT, 11.4.


1987 October 3                 (4463)              Brian G. Marsden

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