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Contact: F.X.Timmes
my one page vitae,
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The light curve of SN 1987A revisited: constraining production masses of radioactive nuclides (2014)

In this article, we revisit the evidence for the contribution of the long-lived radioactive nuclides $^{44}$Ti, $^{55}$Fe, $^{56}$Co, $^{57}$Co, and $^{60}$Co 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 $^{44}$Ti, $^{55}$Co, $^{56}$Ni, $^{57}$Ni, and $^{60}$Co, we perform a least squares fit to the constructed composite bolometric light curve. For the nickel isotopes, we obtain best fit values of M($^{56}$Ni) = (7.1 $\pm$ 0.3) × 102 M and M($^{57}$Ni) = (4.1 $\pm$ 1.8) × 10-3 M. Our best fit $^{44}$Ti mass is M($^{44}$Ti) = (0.55 $\pm$ 0.17) × 10-4 M. which is in disagreement with the much higher (3.1 $\pm$ 0.8) × 10-4 M recently derived from INTEGRAL observations. The half-lives of $^{60}$Co and $^{55}$Fe 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($^{55}$Co) < 7.2 × 10-3 M and M($^{60}$Co) < 1.7 × 10-4 M. Furthermore, we find that the leptonic channels in the decay of $^{57}$Co (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 [$^{57}$Ni / $^{56}$Ni] = 2.5$\pm$1.1 which is still somewhat high but in agreement with gamma-ray observations and model predictions.

[57Ni / 56Ni] after freeze-out
For canonically accepted values
Including freeze-out corrections
Importance of 57Co
Best fit