Optical light curve of the Type Ia supernova 1998bu in M96 and the supernova calibration of the Hubble constant

Abstract

We present the UBV (RI) light curves of the Type Ia supernova SN 1998bu, which appeared in the nearby galaxy M96 (NGC K3C368). M96 is a spiral galaxy in the Leo I group that has a Cepheid-based distance. Our photometry allows us to calculate the absolute magnitude and reddening of this supernova. These data, when combined with measurements of the four other well-observed supernovae with Cepheid-based distances, allow us to calculate the Hubble constant with respect to the Hubble Ñow deÐned by the distant Cala n/Tololo Type Ia sample. We Ðnd a Hubble constant of 63.9^2.2(internal)^3.5(external) km s~1 Mpc~1, consistent with most previous estimates based on Type Ia supernovae. We note that the two well-observed Type Ia supernovae in Fornax, if placed at the Cepheid distance to the possible Fornax spiral NGC 1365, are apparently too faint with respect to the Cala n/Tololo sample calibrated with the Ðve Type Ia supernovae with Cepheid distances to the host galaxies.