Detailed Spectroscopic Analysis of SN 1987A: The Distance to the Large Magellanic Cloud Using the Spectral-fitting Expanding Atmosphere Method

TLDR: In this article, the authors used a hydrodynamical model to model the observed spectra from day 1 to day 81 of supernova 1987A and showed that good agreement can be obtained at times up to about 60 days, if they allow for extended nickel mixing.

Abstract: Supernova 1987A remains the most well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. We model the observed spectra from Day 1 to Day 81 using a hydrodynamical model. We show that good agreement can be obtained at times up to about 60 days, if we allow for extended nickel mixing. Later than about 60 days the observed Balmer lines become stronger than our models can reproduce. We show that this is likely due to a more complicated distribution of gamma-rays than we allow for in our spherically symmetric calculations. We present synthetic light curves in UBVRIJHK and a synthetic bolometric light curve. Using this broad baseline of detailed spectroscopic models we find a distance modulus mu = 18.5 +/- 0.2 using the SEAM method of determining distances to supernovae. We find that the explosion time agrees with that of the neutrino burst and is constrained at 68 percent confidence to within +/- 0.9 days. We argue that the weak Balmer lines of our detailed model calculations casts doubt on the accuracy of the purely photometric EPM method. We also suggest that Type IIP supernovae will be most useful as distance indicators at early times due to a variety of effects.

Figures

TABLE 1 Mean Distance Moduli

Fig. 27.—Same as Fig. 25 but for the observedK light curve

Fig. 28.—Spectrum of the day 30.9 model in the IR, with the filter + atmospheric transmission for JHK. The only prominent lines are the hydrogen lines P , P , and P . Otherwise the SED is very close to a blackbody.

Fig. 10.—PHOENIX model spectrum for day 18.70, with a nickel mass fraction of 1:0 10 4 everywhere in the envelope and an increase in bolometric luminosity of 25.6% from the Blinnikov et al. (2000) original value.

Fig. 23.—Same as Fig. 19 but for the observed I light curve

Fig. 9.—PHOENIX model spectrum for day 14.52, with a nickel mass fraction of 1:0 10 4 everywhere in the envelope.