THE LIGHT CURVE OF SN 1987A REVISITED: CONSTRAINING PRODUCTION MASSES OF RADIOACTIVE NUCLIDES

We revisit the evidence for the contribution of the long-lived radioactive nuclides Ti-44, Fe-55, Co-56, Co-57, and Co-60 to the UVOIR light curve of SN 1987A. We show that the V-band luminosity constitutes a roughly constant fraction of the bolometric luminosity between 900 and 1900 days, and we obtain an approximate bolometric light curve out to 4334 days by scaling the late time V-band data by a constant factor where no bolometric light curve data is available. Considering the five most relevant decay chains starting at Ti-44, Co-55, Ni-56, Ni-57, and Co-60, we perform a least squares fit to the constructed composite bolometric light curve. For the nickel isotopes, we obtain best fit values of M(Ni-56) = (7.1 +/- 0.3) x 10(-2) M-circle dot and M(Ni-57) = (4.1 +/- 1.8) x 10(-3) M-circle dot. Our best fit Ti-44 mass is M(Ti-44) = (0.55 +/- 0.17) x 10(-4) M-circle dot, which is disagreement with the much higher (3.1 +/- 0.8) x 10(-4) M-circle dot recently derived from INTEGRAL observations. The associated uncertainties far exceed the best fit values for Co-55 and Co-60 and, as a result, we only give upper limits on the production masses of M(Co-55) < 7.2 x 10(-3) M-circle dot and M(Co-60) < 1.7 x 10(-4) M-circle dot. Furthermore, we find that the leptonic channels in the decay of Co-57 (internal conversion and Auger electrons) are a significant contribution and constitute up to 15.5% of the total luminosity. Consideration of the kinetic energy of these electrons is essential in lowering our best fit nickel isotope production ratio to [Ni-57/Ni-56] = 2.5 +/- 1.1, which is still somewhat high but is in agreement with gamma-ray observations and model predictions.