We present new photometric and spectroscopic observations of an unusual luminous blue variable (LBV) in NGC 3432, covering three major outbursts in 2008 October, 2009 April and 2009 November. Previously, this star experienced an outburst also in 2000 (known as SN 2000ch). During outbursts the star reached an absolute magnitude between −12.1 and −12.8. Its spectrum showed H, He i and Fe ii lines with P-Cygni profiles during and soon after the eruptive phases, while only intermediate-width lines in pure emission (including He iiλ4686) were visible during quiescence. The fast-evolving light curve soon after the outbursts, the quasi-modulated light curve, the peak magnitude and the overall spectral properties are consistent with multiple episodes of variability of an extremely active LBV. However, the widths of the spectral lines indicate unusually high wind velocities (1500–2800 km s^(−1)), similar to those observed in Wolf–Rayet stars. Although modulated light curves are typical of LBVs during the S-Dor variability phase, the luminous maxima and the high frequency of outbursts are unexpected in S-Dor variables. Such extreme variability may be associated with repeated ejection episodes during a giant eruption of an LBV. Alternatively, it may be indicative of a high level of instability shortly preceding the core-collapse or due to interaction with a massive, binary companion. In this context, the variable in NGC 3432 shares some similarities with the famous stellar system HD 5980 in the Small Magellanic Cloud, which includes an erupting LBV and an early Wolf–Rayet star.

Multiple major outbursts from a restless luminous blue variable in NGC 3432

SN 1961V, one of Zwicky's defining Type V supernovae (SNe), 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 star. The former case is suggested by its possible 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{sub opt} {approx} 10{sup 5} L{sub sun}, than the L{sub opt} {approx_equal} 3 x 10{sup 6} L{sub sun} 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 an L{sub IR} {approx_equal} 3 x 10{sup 6} L{sub sun} 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{sub IR} {approx_equal} 10{sup 5} L{sub sun} and does not correspond tomore » 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 an SN or greater. We conclude that SN 1961V was a peculiar, but real, SN. 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, {approx}1/3 solar, high-mass, M{sub ZAMS} {approx}> 80 M{sub sun}, star, which means either that BH formation can be accompanied by an SN or that surprisingly high-mass stars can form an NS. We also report on the mid-IR properties of the two other SNe in NGC 1058, SN 1969L, and SN 2007gr.« less

The supernova impostor impostor sn 1961v: spitzer shows that zwicky was right (again)

The “supernova impostors” in nearby galaxies mimic the appearance of a true supernova, but rather than a terminal explosion, the impostors appear to be massive stars that have undergone a powerful eruption. Several of these have energetics comparable to true supernovae, and may, in fact, be analogous to the Great Eruption of η Carinae in the 1800s. We distinguish the observed characteristics of impostors from true supernovae. We discuss in detail the prototypical impostor, SN 1961V. We also discuss other known examples where available data imply that these are also impostors. Finally, we connect the impostors to true supernova events—in other words, several recent supernovae appear to have progenitors which experienced high mass-loss events immediately prior to explosion, with one case clearly having an impostor-like eruption only 2 years before discovery as a supernova. The supernova impostors represent rare instances of analogs to η Car and other known luminous blue variables from which we can acquire important insight into the final stages in the evolution of very massive stars.

The Supernova Impostors

We report VLA radio observations of 29 SNe with ages ranging from 10 days to about 90 years past explosion. These observations significantly contribute to the existing data pool on such objects. Included are detections of known radio SNe~1950B, 1957D, 1970G, 1983N, the suspected radio SN 1923A, and the possible radio SN 1961V. None of the remaining 23 observations resulted in detections, providing further evidence to support the observed trend that most SNe are not detectable radio emitters. To investigate the apparent lack of radio emission from the SNe reported here, we have followed standard practice and used Chevalier's ``standard model'' to derive (upper limits to) the mass-loss rates for the super nova progenitors. These upper limits to the fluxes are consistent with a lack of circumstellar material needed to provide detectable radio emission for SNe at these ages and distances. Comparison of the radio luminosities of these supernovae as a function of age past explosion to other well-observed radio SNe indicates that the Type II SNe upper limits are more consistent with the extrapolated light curves of SN 1980K than of SN 1979C, suggesting that SN 1980K may be a more typical radio emitter than SN 1979C. For completeness, we have included an appendix where the results of analyses of the non-SN radio sources are presented. Where possible, we make (tentative) identifications of these sources using various methods.

https://arxiv.org/pdf/astro-ph/0204466.pdf

A Search for Radio Emission from Supernovae With Ages from About One Week to More Than 80 Years

Reports of the death of the precursor of supernova (SN) 1961V in NGC 1058 are exaggerated. Consideration of the best astrometric data shows that the star, known as "Object 7," lies at the greatest proximity to SN 1961V and is the likely survivor of the "SN impostor" super-outburst. SN 1961V does not coincide with a neighboring radio source and is therefore not a radio SN. Additionally, the current properties of Object 7, based on data obtained with the Hubble Space Telescope, are consistent with it being a quiescent luminous blue variable (LBV). Furthermore, post-explosion non-detections by the Spitzer Space Telescope do not necessarily and sufficiently rule out a surviving LBV. We therefore consider, based on the available evidence, that it is still a bit premature to reclassify SN 1961V as a bona fide SN. The inevitable demise of this star, though, may not be too far off.

It's Alive! The Supernova Impostor 1961V

The VLA has been used at 20 cm to detect a 0.19 mJy point source at the site of the extraordinary supernova 1961v in NGC 1058. At the distance of NGC 1058, the absolute monochromatic luminosity of the source is comparable to that of Cas A. 20 references.

D. Branch

Papers

Radio emission from the site of supernova 1961v in NGC 1058