THE LOW-VELOCITY, RAPIDLY FADING TYPE Ia SUPERNOVA 2002es

SN 2002es is a peculiar subluminous Type Ia supernova (SN Ia) with a\ncombination of observed characteristics never before seen in a SN Ia. At\nmaximum light, SN 2002es shares spectroscopic properties with the underluminous\nSN 1991bg subclass of SNe Ia, but with substantially lower expansion velocities\n(~6000 km/s) more typical of the SN 2002cx subclass. Photometrically, SN 2002es\ndiffers from both SN 1991bg-like and SN 2002cx-like supernovae. Although at\nmaximum light it is subluminous (M_B=-17.78 mag), SN 2002es has a relatively\nbroad light curve (Dm15(B)=1.28 +/- 0.04 mag), making it a significant outlier\nin the light-curve width vs. luminosity relationship. We estimate a 56Ni mass\nof 0.17 +/- 0.05 M_sun synthesized in the explosion, relatively low for a SN\nIa. One month after maximum light, we find an unexpected plummet in the\nbolometric luminosity. The late-time decay of the light curves is inconsistent\nwith our estimated 56Ni mass, indicating that either the light curve was not\ncompletely powered by 56Ni decay or the ejecta became optically thin to\ngamma-rays within a month after maximum light. The host galaxy is classified as\nan S0 galaxy with little to no star formation, indicating the progenitor of SN\n2002es is likely from an old stellar population. We also present a less\nextensive dataset for SN 1999bh, an object which shares similar observed\nproperties. Both objects were found as part of the Lick Observatory Supernova\nSearch, allowing us to estimate that these objects should account for ~2.5% of\nSNe Ia within a fixed volume. We find that current theoretical models are\nunable to explain the observed of characteristics of SN 2002es.\n