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The light curve of SN 1987A revisited: constraining production masses of radioactive nuclides - 2014
In this paper, We revisit the evidence for the contribution of the long-lived radioactive nuclides 44Ti, 55Fe, 56Co, 57Co, and 60Co 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 44Ti, 55Co, 56Ni, 57Ni, and 60Co, we perform a least squares fit to the constructed composite bolometric light curve. For the nickel isotopes, we obtain best fit values of M(56Ni) = (7.1 ± 0.3) × 102 M⊙ and M(57Ni) = (4.1 ± 1.8) × 10-3 M⊙. Our best fit 44Ti mass is M(44Ti) = (0.55 ± 0.17) × 10-4 M⊙. which is in disagreement with the much higher (3.1 ± 0.8) × 10-4 M⊙ recently derived from INTEGRAL observations. The half-lives of 60Co and 55Fe are quite similar, which introduces a degeneracy for the fitting algorithm. As a result, we can only give upper limits on the relevant production masses of M(55Co) < 7.2 × 10-3 M⊙ and M(60Co) < 1.7 × 10-4 M⊙. Furthermore, we find that the leptonic channels in the decay of 57Co (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 [57Ni/56Ni] = 2.5±1.1 which is still somewhat high but in agreement with gamma-ray observations and model predictions.
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