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We present multicolor Hubble Space Telescope(HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained ?280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HSTphotometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the ?-rays produced by the radioactive decay of 56Co diminishes roughly as the inverse of time squared. We also find that by the time of the HSTphotometry, the light curve was significantly energized by the annihilation of positrons.

The locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. As part of a program to study the environments of supernovae using Hubble Space Telescope imaging data, we have examined the environment of the Type II-L supernova SN 1979C in NGC 4321 (M100). We place rigorous constraints on the mass of the SN progenitor, based on photometry of the stellar populations in its environment. The progenitor may have had an initial mass M [?] 17-18(+-3) M[?]. Moreover, 17 years after explosion we have recovered and measured the brightness of SN 1979C in several bands, e.g., m = 23.37 in F439W [[?]B; for comparison, mB(max) = 11.6].

The locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. As part of a program to study the environments of supernovae using Hubble Space Telescopeimaging data, we have examined the environment of the Type II-L supernova SN 1979C in NGC 4321 (M100). We place rigorous constraints on the mass of the SN progenitor, based on photometry of the stellar populations in its environment. The progenitor may have had an initial mass M ? 17-18(±3) M?. Moreover, 17 years after explosion we have recovered and measured the brightness of SN 1979C in several bands, e.g., m = 23.37 in F439W [?B; for comparison,mB(max) = 11.6].