* Astronomy

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SN 1961V

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RE: Supernova 1961V

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Title: Was Fritz Zwicky's "Type V" SN 1961V a Genuine Supernova?
Authors: Filippenko, Alexei V.; Barth, Aaron J.; Bower, Geoffrey C.; Ho, Luis C.; Stringfellow, Guy S.; Goodrich, Robert W.; Porter, Alain C.
Astronomical Journal v.110, p.2261

In 1989, Goodrich and collaborators suggested that SN 1961V, a very peculiar Type II (Zwicky's "Type V") supernova, was not the final explosion of a star at the end of its life, but rather the giant eruption of a massive, luminous blue variable, like n Car. To test this hypothesis, we have used the Hubble Space Telescope to obtain optical images of the site of SN 1961V. There is a cluster of faint (V ~ 24-25 mag), blue [(V-I)_0_ = -0.4-0.5 mag] stars around the general location of the supernova. We also see a very faint (V = 25.6 ±0.3 mag), much redder [(V-I)_0_ = 1.7 mag] star barely resolved from one of the blue stars. Its brightness and colors are consistent with those of a highly reddened O-type star, as predicted by Goodrich et al. Moreover, it is the star formally closest to the known radio position of SN 1961V; the coordinates are identical, to within the uncertainties. Thus, we tentatively identify this as the post eruption star of SN 1961V; it survived the giant eruption, which was not a genuine supernova, and it is now red due to a substantial envelope of dust (A_V_ ~ 4.1 mag). However, the current data do not allow us to eliminate the possibility that this star is an unrelated red supergiant or a peculiar supernova remnant. Alternatively, the blue object adjacent to it may be the actual post- eruption star of SN 1961V. If so, the envelope of dust is not as thick: A_V_ ~ 2.2-3.2 mag, but perhaps somewhat larger if the object's colors are significantly affected by a blue light echo of SN 1961V.

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Title: The Supernova Impostor Impostor SN 1961V: Spitzer Shows That Zwicky Was Right (Again)
Authors: C.S. Kochanek (1), D.M. Szczygiel (1), K.Z. Stanek (1) ((1) Department of Astronomy and the Center for Cosmology and AstroParticle Physics, The Ohio State University)

SN 1961V, one of Zwicky's defining Type V supernovae (SN), was a peculiar transient in NGC 1058 that has variously been categorized as either a true core collapse SN leaving a black hole (BH) or neutron star (NS) remnant, or an eruption of a luminous blue variable (LBV) star. The former case is suggested by its association with a decaying non-thermal radio source, while the latter is suggested by its peculiar transient light curve and its low initial expansion velocities. The crucial difference is that the star survives a transient eruption but not an SN. All stars identified as possible survivors are significantly fainter, L_opt ~ 10^5 Lsun, than the L_opt ~ 3 10^6 Lsun progenitor star at optical wavelengths. While this can be explained by dust absorption in a shell of material ejected during the transient, the survivor must then be present as a L_IR ~ 3 10^6 Lsun mid-infrared source. Using archival Spitzer observations of the region, we show that such a luminous mid-IR source is not present. The brightest source of dust emission is only L_IR ~ 10^5 Lsun and does not correspond to the previously identified candidates for the surviving star. The dust cannot be made sufficiently distant and cold to avoid detection unless the ejection energy, mass and velocity scales are those of a SN or greater. We conclude that SN 1961V was a peculiar, but real, supernova. Its peculiarities are probably due to enhanced mass loss just prior to the SN, followed by the interactions of the SN blast wave with this ejecta. This adds to the evidence that there is a population of SN progenitors that have major mass loss episodes shortly before core collapse. The progenitor is a low metallicity, ~1/3 solar, high mass, M_ZAMS > 80 Msun, star, which means either that BH formation can be accompanied by an SN or that surprisingly high mass stars can form a NS.

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