LATE-TIME LIGHT CURVES OF TYPE II SUPERNOVAE: PHYSICAL PROPERTIES OF SUPERNOVAE AND THEIR ENVIRONMENT

We present BVRIJHK-band photometry of six core-collapse supernovae, SNe 1999bw, 2002hh, 2003gd, 2004et, 2005cs, and 2006bc, measured at late epochs (>2 yr) based on the Hubble Space Telescope (HST), and the Gemini North, and WIYN telescopes. We also show the JHK light curves of supernova impostor SN 2008S up to day 575 because it was serendipitously in our SN 2002hh field of view. Of our 43 HST observations in total, 36 observations are successful in detecting the light from the SNe alone and measuring magnitudes of all the targets. HST observations show a resolved scattered light echo around SN 2003gd at day 1520 and around SN 2002hh at day 1717. Our Gemini and WIYN observations detected SNe 2002hh and 2004et as well. Combining our data with previously published data, we show VRIJHK-band light curves and estimate decline magnitude rates at each band in four different phases. Our prior work on these light curves and other data indicate that dust is forming in our targets from days ∼300 to 400, supporting SN dust formation theory. In this paper we focus on other physical properties derived from late-time light curves. We estimate 56Ni masses for our targets (0.5-14 × 10–2 M☉) from the bolometric light curve of each of days ∼150-300 using SN 1987A as a standard (7.5 × 10–2 M☉). The flattening or sometimes increasing fluxes in the late-time light curves of SNe 2002hh, 2003gd, 2004et, and 2006bc indicate the presence of light echoes. We estimate the circumstellar hydrogen density of the material causing the light echo and find that SN 2002hh is surrounded by relatively dense materials (n(H) >400 cm–3) and SNe 2003gd and 2004et have densities more typical of the interstellar medium (∼1 cm–3). We analyze the sample as a whole in the context of physical properties derived in prior work. The 56Ni mass appears well correlated with progenitor mass with a slope of 0.31 × 10–2, supporting the previous work by Maeda et al., who focus on more massive Type II SNe. The dust mass does not appear to be correlated with progenitor mass.