2004AJ....127.2850C

The nature of SN 1961V has been uncertain. Its peculiar optical light curve and slow expansion velocity are similar to those of superoutbursts of luminous blue variables (LBVs), but its nonthermal radio spectral index and declining radio luminosity are consistent with decades-old supernovae (SNe). We have obtained Hubble Space Telescope STIS images and spectra of the stars in the vicinity of SN 1961V and find object 7 identified by Filippenko and coworkers to be closest to the optical and radio positions of SN 1961V. Object 7 is the only point source detected in our STIS spectra, and only its Hα emission is detected; it cannot be the SN or its remnant because of the absence of forbidden lines. While the Hα line profile of object 7 is remarkably similar to that of η Carinae, the blue color (similar to an A2 Ib supergiant) and lack of appreciable variability are unlike known postoutburst LBVs. We have also obtained Very Long Baseline Array observations of SN 1961V at 18 cm. The nondetection of SN 1961V places a lower limit on the size of the radio-emitting region, 7.6 mas or 0.34 pc, which implies an average expansion velocity in excess of 4400 km/s, much higher than the optical expansion velocity measured in 1961. We conclude the following: (1) An SN occurred in the vicinity of SN 1961V a few decades ago. (2) If the SN 1961V light maximum originates from a giant eruption of a massive star, object 7 is the most probable candidate for the survivor, but its blue color and lack of significant variability are different from a postoutburst η Car. (3) The radio SN and object 7 could be physically associated with each other through a binary system. (4) Object 7 needs to be monitored to determine its nature and relationship to SN 1961V.