Astron. Astrophys. 359, 876-886 (2000)

7. Conclusions

Fitting light curves with a descriptive model has a number of advantages over template methods. It is suited to explore the variety among SN Ia and provides an independent way to look for correlations. A simple application of our fitting procedure has been presented to demonstrate the complicated nature of SN Ia emission through the occurrence of the peak luminosity in individual filters. The most obvious signatures for non-thermal emission from SNe Ia have so far been the infrared light curves (Elias et al. 1985) and the lack of emission near 1.2 µm (Spyromilio et al. 1994, Wheeler et al. 1998). It had also been demonstrated through spectral synthesis calculations (Höflich et al. 1996, Eastman 1997). Although there is a fairly large scatter of about 2 days in the relative epoch of filter maximum light a clear trend to earlier maxima in R and I is observed. In fact, the I maximum occurs clearly before the B maximum, a trend also observed in the JHK light curves (Elias et al. 1985, Meikle 2000).

Another application of the continuous approximation of the observations is the construction of bolometric light curves. Bolometric light curves form an important link between the explosion models and the radiation transport calculations for SNe Ia ejecta. We have demonstrated that the effects of missing passbands, distance modulus, reddening, light curve fitting and the integration methods are not critical to the shape. Amongst these, the uncertainties from the distance modulus towards individual supernovae dominate.

The shapes of the bolometric light curve of individual SNe Ia vary significantly. The secondary maxima observed in the R and I light curves show up with varying strength in the bolometric light curves as well. The variety of light curve shapes indicates subtle variations in the energy release of these explosions. Pinto & Eastman (2000b) try to explain these secondary maxima as due to the distribution of material in the inner core of the explosion, possibly connected to the explosion mechanism. If this is the case, then the detailed study of the bolometric light curves and their differences among individual SNe Ia might provide a direct "window" into the explosion.

With the currently best available distances we find that the peak luminosities of the SNe Ia in our sample display a rather large range. They imply a factor of more than 2.5 in the masses. SN 1991bg produced about 10 times less than the brightest object, SN 1991T. The range of nickel masses indicates significant differences in the explosions of SNe Ia. From the late-phase decline, we find that the change of the decline rate is rather uniform indicating similarity in change of the ray escape fraction for all SNe Ia independent of the amount of nickel produced in the explosion.

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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