ar X iv : a st ro - p h / 04 02 47 3 v 1 1 9 Fe b 20 04 The Nature of SN 1961 V

The nature of SN1961V has been uncertain. Its peculiar optical light curve and slow expansion velocity are similar to those of super-outbursts 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 SN1961V, and find Object 7 identified by Filippenko et al. to be the closest to the optical and radio positions of SN1961V. 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 Car, the blue color (similar to an A2 Ib supergiant) and lack of appreciable variability are unlike known post-outburst LBVs. We have also obtained Very Long Baseline Array (VLBA) observations of SN1961V at 18 cm. The non-detection of SN1961V 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 4,400 km s, much higher than the optical expansion velocity measured in 1961. We conclude the following: (1) A SN occurred in the vicinity of SN1961V a few decades ago. (2) If the SN1961V 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 Astronomy Department, University of Illinois, 1002 W. Green Street, Urbana, IL 61801; [email protected], [email protected] Department of Physics, Marquette University, PO Box 1881, Milwaukee, WI 53201-1881; [email protected] National Radio Astronomical Observatories, PO Box 0, 1003 Lopezville Road, Socorro, NM 87801-0387; [email protected] Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks, Room 131, Norman, OK 73019; [email protected] Department of Electrical Engineering, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801; [email protected]