The light curve of SN 1987A revisited: constraining production masses of radioactive nuclides

TL;DR

This study revisits the radioactive nuclide contributions to SN 1987A's light curve, refining mass estimates of key isotopes and highlighting the importance of leptonic decay channels in modeling supernova luminosity.

Contribution

It provides new estimates for radioactive isotope masses in SN 1987A and emphasizes the role of leptonic decay channels, contrasting previous higher 44Ti mass measurements.

Findings

Best fit 56Ni mass: (7.1 +- 0.3) x 10^{-2} Msun

44Ti mass: (0.55 +- 0.17) x 10^{-4} Msun, lower than previous estimates

Leptonic decay channels contribute up to 15.5% of luminosity

Abstract

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) x 10^{-2} Msun and M(57Ni) = (4.1 +- 1.8) x 10^{-3} Msun. Our best fit 44Ti mass is M(44Ti) = (0.55 +- 0.17) x 10^{-4} Msun, which is in disagreement with the much higher (3.1 +- 0.8) x 10^{-4} Msun recently derived from INTEGRAL observations. The associated uncertainties far exceed the best fit values for 55Co and 60Co and, as a result, we only give upper limits on the production masses of M(55Co) < 7.2 x 10^{-3} Msun and M(60Co) < 1.7 x 10^{-4} Msun. 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 is in agreement with gamma-ray observations and model predictions.