Central Bureau for Astronomical Telegrams
IAUC 4510: 1987A
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Circular No. 4510
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
S. M. Matz, National Research Council Associate at the Naval
Research Laboratory (NRC/NRL), G. H. Share, NRL; M. D. Leising
NRC/NRL; E. L. Chupp and W. T. Vestrand, University of New Hampshire
(UNH), on behalf of their collaborators at NRL, UNH and the
Max Planck Institute (Garching), report: "We have detected gamma-ray
line emission from SN 1987A. The Gamma-Ray Spectrometer (GRS) on
NASA's Solar Maximum Mission satellite has observed a significant
net flux at about 847 keV in the background-subtracted spectra of SN
1987A in data accumulated between Aug. 1 and Oct. 31. This is the
energy of a strong gamma-ray line from the decay of 56Co. The inferred
average line flux during this period is (1.0 +/- 0.25) x 10**-3
photon cm-2 s-1 at an energy of 843 +/- 5 keV. The quoted error in
the flux includes an estimate of possible systematic effects in
determining the total photon flux; the statistical significance of
the detection is greater than 5 sigma. This feature cannot be
explained by any statistical or systematic fluctuations observed in
the seven previous years of GRS data. There is also evidence for
the presence of the 1238-keV line from 56Co decay, with an average
flux of (6 +/- 2) x 10**-4 photon cm-2 s-1. These fluxes are equivalent
to what would be observed from the decay at 55 kpc of about 2.3 x
10**-4 solar masses of exposed 56Co from Aug. 1 to Oct. 31. This is
about 1.3 percent of the total amount of 56Co thought to be present on
Aug. 1, based on the lightcurve. The observed gamma-ray line ratios
suggest that we are not observing the total mass of 56Co through a
thick envelope, but a small fraction of the total through very
little material. The first appearance of the gamma-ray lines was
roughly coincident with the first detections of x-rays by Ginga
and MIR. The line fluxes do not appear to have risen since the
initial detection. The best fit to the data indicates that the
flux is slowly declining, but the data are consistent with a wide
range of models, including a constant intensity. Based on the
best fit, we would predict that the balloon experiments launched
in recent months would have seen a flux of roughly 3 to 7 x 10**-4
photon cm-2 s-1 in the 847-keV line."
Visual magnitude estimates by A. C. Beresford, Adelaide,
South Australia: Dec. 4.47 UT, 6.1; 5.50, 6.1; 6.46, 6.1; 9.45,
6.2; 10.46, 6.2.
1987 December 11 (4510) Brian G. Marsden
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