THE SUPERNOVA IMPOSTOR IMPOSTOR SN 1961V:SPITZERSHOWS THAT ZWICKY WAS RIGHT (AGAIN)

Abstract

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 L ⊙ , than the L opt ≃ 3×10 6 L ⊙ 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 L ⊙ 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 L ⊙ 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 > ∼ 80M ⊙ , star, which means either that BH formation can be accompanied by an SN or that surprisingly high mass stars can form a NS. We also report on the mid-IR properties of the two other SN in NGC 1058, SN 1969L and SN 2007gr.

Pulsational Pair-instability Supernovae

“…The mass could be several solar masses, but the maximum luminosity comes from interacting with only the innermost, slowest moving, highest density part of that shell. A similar dramatic rise from a faint initial outburst was seen in SN 1961v Kochanek et al 2011); SN 2010mc (Ofek et al 2013); the 2012 outburst of SN 2009ip (Fraser et al 2015);andSN 2015bh (Elias-Rosa et al 2016). There is also some evidences that these events came from the explosion of very massive stars ) and, at least in the case of 2009ip, that the star was a LBV.…”

“…SN 1961v Kochanek et al 2011), an enigmatic event, that may have resulted from the explosion of a low metallicity star over 80 M , showed a similar light curve morphology and peak brightness. So did the 2012 outburst of SN 2009ip (Fraser et al 2015).…”

Early-time spectra of supernovae and their precursor winds

“…2b,c). This example of pre-explosion spectrum resembles those seen in luminous blue variables (LBVs), which are a class of unstable massive stars that are found both as a transitional stage from an O-type to a WR star (Humphreys & Davidson 1994;Groh et al 2014) and as SN progenitors (Kotak & Vink 2006;Smith et al 2007Smith et al , 2011Kochanek et al 2011;Pastorello et al 2007;Trundle et al 2008;Gal-Yam & Leonard 2009;Groh & Vink 2011;Mauerhan et al 2013;Ofek et al 2013;Groh et al 2013a,b).…”

Constraints on Type IIn supernova progenitor outbursts from the Lick Observatory Supernova Search

“…Such pre-SN eruptions in the years just before the SN sug-gest that instabilities arise during the late stages of nuclear burning (Smith & Arnett 2014;Quataert & Shiode 2012) to power mass-loss episodes that might result in a detectable brightening of the progenitor system. In fact, there have already been a few direct detections of pre-SN outbursts: SN 2006jc (Ibn; Foley et al 2007;Pastorello et al 2007Smith et al 2010a;Pastorello et al 2013;Mauerhan et al 2013a), SN 2011ht (IIn-P; Fraser et al 2013a), and arguably SN 1961V (IIn; Smith et al 2011b;Kochanek et al 2011), thus strengthening the theoretical connection between LBVs and SNe IIn.…”

“…Some theoretical models for ⋆ E-mail: cgbilinsk@gmail.com † Deceased 2011 December 12 the end stages of massive-star evolution suggest that stars with ∼ 30-60 M⊙ will collapse to form a black hole without a SN explosion (Fryer 1999;Heger et al 2003, but see O'Connor & Ott 2013. The detection of what seem to be massive luminous blue variable stars (LBVs) as the progenitors of the Type IIn SNe 1961V (Smith et al 2011b;Kochanek et al 2011), 2005gl (Gal-Yam et al 2007Gal-Yam & Leonard 2009), 2009ip (Smith et al 2010aFoley et al 2011), and 2010jl (Smith et al 2011b), however, challenge this notion.…”