Late Light Curves of Type Ia Supernovae

We extend earlier efforts to determine whether the late (t$\geq$60d)light-curves of type Ia SNe are better explained by the escape of positronsfrom the ejecta or by the complete deposition of positron kinetic energy in atrapping magnetic field We find that applying a filter efficiency correction,derived from measured spectra, to B, V, R, and I light-curves after day 50 canproduce a consistent bolometric light-curve. The V band is an accurateindicator of total emission in the 3500$\AA$ - 9700$\AA$ range, with a constantfraction ($\sim$25%) appearing in the V band after day 50. This suggests thatthe V band scales with the bolometric luminosity, and that the deposited energyis instantaneously recycled into optical emission during this epoch. Varyingbolometric corrections for the other bands are derived. We see significantevolution of the colors of SNe Ia between day 50 and day 170. We suggest thatthis may be due to the transition from spectra dominated by emission lines fromthe radioactive nucleus, $^{56}$Co, to those from the stable daughter nucleus,$^{56}$Fe. We show that the B, V, R, and I band light-curves of SNe Ia aftert$\geq$60d can be completely explained with energy deposition from $^{56}$Codecay photons and positrons if substantial positron escape occurs.Comment: ApJ submitte