Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae, so-called, "SN impostors", but the distinction is not always straightforward. Here we present observations of a luminous blue variable (LBV) in NGC 2770 in outburst over more than 20 yr that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN (or "main event") had a precursor peaking ∼40 days before maximum. The total energy release of the main event is ∼1.8 × 10 49 erg, consistent with a <0.5 M shell plunging into a dense CSM. The emission lines show a single narrow P Cygni profile during the LBV phase and a double P Cygni profile post maximum suggesting an association of the second component with the possible SN. Since 1994 the star has been redder than an LBV in an S-Dor-like outburst. SN 2015bh lies within a spiral arm of NGC 2770 next to several small star-forming regions with a metallicity of ∼0.5 solar and a stellar population age of 7-10 Myr. SN 2015bh shares many similarities with SN 2009ip and may form a new class of objects that exhibit outbursts a few decades prior to a "hyper eruption" or final core-collapse. If the star survives this event it is undoubtedly altered, and we suggest that these "zombie stars" may evolve from an LBV to a Wolf-Rayet star over the timescale of only a few years. The final fate of these stars can only be determined with observations a decade or more after the SN-like event.

We present early mid-ultraviolet and optical observations of Type IIn supernovae (SNe IIn) observed from 2007 to 2013. Our results focus on the properties of UV light curves: peak absolute magnitudes, temporal decay, and color evolution. During early times, this sample demonstrates that UV light decays faster than optical, and each event transitions from a predominantly UV-bright phase to an optically bright phase. In order to understand early UV behavior, we generate and analyze the sampleʼs blackbody luminosity, temperature, and radius as the SN ejecta expand and cool. Since most of our observations were detected post maximum luminosity, we introduce a method for estimating the date of peak magnitude. When our observations are compared based on filter, we find that even though these SNe IIn vary in peak magnitudes, there are similarities in UV decay rates. We use a simple semianalytical SN model in order to understand the effects of the explosion environment on our UV observations. Understanding the UV characteristics of nearby SNe IIn during an early phase can provide valuable information about the environment surrounding these explosions, leading us to evaluating the diversity of observational properties in this subclass.

Core-collapse supernovae (CCSNe) have very distinct observational properties that depend on the composition of the progenitor star, the dynamics of the explosion mechanism, and the surrounding stellar wind environment. In recent years, due to the uncertainty behind the type of massive star that evolves into different types of core-collapse events, there has been an increase in core-collapse supernova surveys aiding the advancement of numerical supernova simulations that explore the properties of the star before the explosion. Observationally, the unpredictable nature of these events makes it difficult to identify the type of star from which the CCSNe subtype evolves, but the issue from a theoretical standpoint relies on a gap in our current understanding of the explosion mechanism. The general light curve properties of CCSNe (rise, peak, and decay) by subtype are diverse, but appear to be homogeneous within each subtype, with the exception of Type IIn.Simplified SN models can be processed quickly in order to explore the properties of the progenitor star along with the explosion mechanism and circumstellar medium. Here, we present a suite of SN light curve models presented using a 1-temperature, homologous outflow light curve code. The SN explosion is modeled from shock breakout through the ultimate uncovering of the nickel core. We are able to rapidly explore the diversity of the SN light curves by studying the effects of various explosion and progenitor star parameters, including ejecta mass, explosion energy, shock temperature, and stellar radii using this "simple" calculation technique. Furthermore, we compare UV and optical modeled light curves to Swift UVOT IIn observations to identify the general initial conditions that enable the difference between SN 2009ip and SN 2011ht light curve properties. Our results indicate that the peak light curve is dominated by the shock temperature and explosion energy, whereas the shape depends on the mass of the ejecta and the explosion energy. Based on this modeling approach, the comparison SN light curves are a product of processes occurring after shock breakout, but before 56 Ni decay. Therefore, the energy from nickel decay does not play a major role in the light curves of these explosions. In general, the diversity between SN 2009ip and SN 2011ht can be explained by the differences in the outer ejecta mass and the explosion energy.

The SuperNovae Analysis aPplication (SNAP) is a new tool for the analysis of SN observations and validation of SN models. SNAP consists of an open source relational database with (a) observational light curve, (b) theoretical light curve, and (c) correlation table sets, statistical comparison software, and a web interface available to the community. The theoretical models are intended to span a gridded range of parameter space. The goal is to have users to upload new SN models or new SN observations and run the comparison software to determine correlations via the web site. There are looming problems on the horizon that SNAP begins to solve. Namely, large surveys will discover thousands of SNe annually. Frequently, the parameter space of a new SN event is unbounded. SNAP will be a resource to constrain parameters and determine if an event needs follow-up without spending resources to create new light curve models from scratch. Secondly, there is not a rapidly available, systematic way to determine degeneracies between parameters or even what physics is needed to model a realistic SNe. The correlations made within the SNAP system begin to solve these problems.