The shape of the light curve peak of radioactive--powered core--collapse
"stripped--envelope" supernovae constrains the ejecta mass, nickel mass, and
kinetic energy by the brightness and diffusion time for a given opacity and
observed expansion velocity. Late--time light curves give constraints on the
ejecta mass and energy, given the gamma--ray opacity. Previous work has shown
that the principal light curve peaks for SN~IIb with small amounts of hydrogen
and for hydrogen/helium--deficient SN~Ib/c are often rather similar near
maximum light, suggesting similar ejecta masses and kinetic energies, but that
late--time light curves show a wide dispersion, suggesting a dispersion in
ejecta masses and kinetic energies. It was also shown that SN~IIb and SN~Ib/c
can have very similar late--time light curves, but different ejecta velocities
demanding significantly different ejecta masses and kinetic energies. We
revisit these topics by collecting and analyzing well--sampled single--band and
quasi--bolometric light curves from the literature. We find that the late--time
light curves of stripped--envelope core--collapse supernovae are heterogeneous.
We also show that the observed properties, the photospheric velocity at peak,
the rise time, and the late decay time, can be used to determine the mean
opacity appropriate to the peak. The opacity determined in this way is
considerably smaller than common estimates. We discuss how the small effective
opacity may result from recombination and asymmetries in the ejecta.Comment: Substantially changed from previously-posted version, 29 pages, 8
figures, accepted for publication in Monthly Notices of the Royal
Astronomical Societ
