We present multiple spectropolarimetric observations of the nearby Type. Ia supernova (SN) 2011fe in M101, obtained before, during, and after the time of maximum apparent visual brightness. The excellent time coverage of our spectropolarimetry has allowed better monitoring of the evolution of polarization features than is typical, which has allowed us new insight into the nature of normal SNe. Ia. SN. 2011fe exhibits time-dependent polarization in both the continuum and strong absorption lines. At early epochs, red wavelengths exhibit a degree of continuum polarization of up to 0.4%, likely indicative of a mild asymmetry in the electron-scattering photosphere. This behavior is more common in subluminous SNe. Ia than in normal events, such as SN. 2011fe. The degree of polarization across a collection of absorption lines varies dramatically from epoch to epoch. During the earliest epoch, lambda 4600-5000 angstrom complex of absorption lines shows enhanced polarization at a different position angle than the continuum. We explore the origin of these features, presenting a few possible interpretations, without arriving at a single favored ion. During two epochs near maximum, the dominant polarization feature is associated with the Si lambda 6355 angstrom absorption line. This is common for SNe. Ia, but for SN. 2011fe the polarization of this feature increases after maximum light, whereas for other SNe. Ia, that polarization feature was strongest before maximum light.

This manuscript presents information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) during 2015, its second full year of operations. The same information is presented for bright (m(V) <= 17), spectroscopically confirmed supernovae discovered by other sources in 2015. As with the first ASAS-SN bright supernova catalogue, we also present redshifts and near-ultraviolet through infrared magnitudes for all supernova host galaxies in both samples. Combined with our previous catalogue, this work comprises a complete catalogue of 455 supernovae from multiple professional and amateur sources, allowing for population studies that were previously impossible. This is the second of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team.

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 Ni-56 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.

High-mass X-ray binaries (HMXRBs), such as Cygnus X-1, host some of the most rapidly spinning black holes (BHs) known to date, reaching spin parameters a greater than or similar to 0.84. However, there are several effects that can severely limit the maximum BH spin parameter that could be obtained from direct collapse, such as tidal synchronization, magnetic core-envelope coupling, and mass loss. Here, we propose an alternative scenario where the BH is produced by a failed supernova (SN) explosion that is unable to unbind the stellar progenitor. A large amount of fallback material ensues, whose interaction with the secondary naturally increases its overall angular momentum content, and therefore the spin of the BH when accreted. Through SPH hydrodynamic simulations, we studied the unsuccessful explosion of an 8 M-circle dot pre-SN star in a close binary with a 12 M-circle dot companion with an orbital period of approximate to 1.2 days, finding that it is possible to obtain a BH with a high spin parameter a greater than or similar to 0.8 even when the expected spin parameter from direct collapse is a less than or similar to 0.3. This scenario also naturally explains the atmospheric metal pollution observed in HMXRB stellar companions.

We present photometry and spectroscopy of PS1-14bj, a hydrogen-poor superluminous supernova (SLSN) at redshift z = 0.5215 discovered in the last months of the Pan-STARRS1 Medium Deep Survey. PS1-14bj stands out because of its extremely slow evolution, with an observed rise of greater than or similar to 125 rest-frame days, and exponential decline out to similar to 250 days past peak at a measured rate of 0.01 mag day(-1), consistent with fully trapped Co-56 decay. This is the longest rise time measured in an SLSN to date, and the first SLSN to show a rise time consistent with pair-instability supernova (PISN) models. Compared to other slowly evolving SLSNe, it is spectroscopically similar to the prototype SN 2007bi at maximum light, although lower in luminosity (L-peak similar or equal to 4.6 x 10(43) erg s(-1) ) and with a flatter peak than previous events. PS1-14bj shows a number of peculiar properties, including a near-constant color temperature for > 200 days past peak, and strong emission lines from [O III] lambda 5007 and [O III] lambda 4363 with a velocity width of similar to 3400 km s(-1) in its late-time spectra. These both suggest there is a sustained source of heating over very long timescales, and are incompatible with a simple Ni-56-powered/PISN interpretation. A modified magnetar model including emission leakage at late times can reproduce the light curve, in which case the blue continuum and [O III] features are interpreted as material heated and ionized by the inner pulsar wind nebula becoming visible at late times. Alternatively, the late-time heating could be due to interaction with a shell of H-poor circumstellar material.

We present spectropolarimetric observations of the nearby Type Ia supernova SN 2014J in M82 over six epochs: +0, +7, +23, +51, +77, +109, and +111 days with respect to B-band maximum. The strong continuum polarization, which is constant with time, shows a wavelength dependence unlike that produced by linear dichroism in Milky Way dust. The observed polarization may be due entirely to interstellar dust or include a circumstellar scattering component. We find that the polarization angle aligns with the magnetic field of the host galaxy, arguing for an interstellar origin. Additionally, we confirm a peak in polarization at short wavelengths that would imply R-V < 2 along the light of sight, in agreement with earlier polarization measurements. For illustrative purposes, we include a two-component fit to the continuum polarization of our +51-day epoch that combines a circumstellar scattering component with interstellar dust where scattering can account for over half of the polarization at 4000 angstrom. Upon removal of the interstellar polarization signal, SN 2014J exhibits very low levels of continuum polarization. Asymmetries in the distribution of elements within the ejecta are visible through moderate levels of time-variable polarization in accordance with the Si II lambda 6355 absorption line. At maximum light, the line polarization reaches similar to 0.6% and decreases to similar to 0.4% 1 week later. This feature also forms a loop on theqRSP-uRSP plane, illustrating that the ion does not have an axisymmetric distribution. The observed polarization properties suggest that the explosion geometry of SN 2014J is generally spheroidal with a clumpy distribution of silicon.

We present optical/near-infrared spectroscopy and photometry of the supernova (SN) PS15si. This object was originally identified as a Type IIn SN, but here we argue that it should be reclassified as a Type Ia SN with narrow hydrogen lines originating from interaction with circumstellar matter (CSM; i.e. SN Ia/IIn or SN Ia-CSM). Based on deep non-detections 27 d before discovery, we infer that this SN was discovered around or slightly before optical maximum, and we estimate the approximate time that it reached R-band maximum based on comparison with other SNe Ia/IIn. In terms of spectral morphology, we find that PS15si can be matched to a range of SN Ia spectral types, although SN 1991T-like SNe Ia provides the most self-consistent match. While this spectral classification agrees with analysis of most other SNe Ia/IIn, we find that the implied CSM-interaction luminosity is too low. We infer that the similarity between PS15si and the hot, overluminous, high-ionization spectrum of SN 1991T is a consequence of a spectrum that originates in ejecta layers that are heated by ultraviolet/X-ray radiation from CSM interaction. In addition, PS15si may have rebrightened over a short time-scale in the B and V bands around 85 d after discovery, perhaps indicating that the SN ejecta are interacting with a local enhancement in CSM produced by clumps or a shell at large radii.

Due to its proximity, SN. 1987A offers a unique opportunity to directly observe the geometry of a stellar explosion as it unfolds. Here we present spectral and imaging observations of SN. 1987A obtained similar to 10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths. These observations allow us to produce the most detailed 3D map of Ha to date, the first 3D maps for [Ca II] lambda lambda 7292, 7324, [O I] lambda lambda 6300, 6364, and Mg. II lambda lambda 9218, 9244, as well as new maps for [Si I]+[Fe II] 1.644 mu m and He I 2.058 mu m. A comparison with previous observations shows that the [Si I]+[Fe II] flux and morphology have not changed significantly during the past ten years, providing evidence that this line is powered by Ti-44. The time evolution of Ha shows that it is predominantly powered by X-rays from the ring, in agreement with previous findings. All lines that have sufficient signal show a similar large-scale 3D structure, with a north-south asymmetry that resembles a broken dipole. This structure correlates with early observations of asymmetries, showing that there is a global asymmetry that extends from the inner core to the outer envelope. On smaller scales, the two brightest lines, Ha and [Si I]+[Fe II] 1.644 mu m, show substructures at the level of similar to 200-1000 km s(-1) and clear differences in their 3D geometries. We discuss these results in the context of explosion models and the properties of dust in the ejecta.

We present optical and near-IR photometry and spectroscopy of SN 2013L for the first 4 yr post-explosion. SN 2013L was a moderately luminous (M-r = -19.0) Type IIn supernova (SN) that showed signs of strong shock interaction with the circumstellar medium (CSM). The CSM interaction was equal to or stronger to SN 1988Z for the first 200 d and is observed at all epochs after explosion. Optical spectra revealed multicomponent hydrogen lines appearing by day 33 and persisting and slowly evolving over the next few years. By day 1509, the Ha emission was still strong and exhibiting multiple peaks, hinting that the CSM was in a disc or torus around the SN. SN 2013L is part of a growing subset of SNe IIn that shows both strong CSM interaction signatures and the underlying broad lines from the SN ejecta photosphere. The presence of a blue Ha emission bump and a lack of a red peak does not appear to be due to dust obscuration since an identical profile is seen in Pa beta. Instead this suggests a high concentration of material on the near-side of the SN or a disc inclination of roughly edge-on and hints that SN 2013L was part of a massive interactive binary system. Narrow Ha P-Cygni lines that persist through the entirety of the observations measure a progenitor outflow speed of 80-130 km s(-1), speeds normally associated with extreme red supergiants, yellow hypergiants, or luminous blue variable winds. This progenitor scenario is also consistent with an inferred progenitor mass-loss rate of 0.3-8.0 x 10(-3) M-circle dot yr(-1).

The SuperNovae Analysis aPplication (SNAP) is a new tool for the analysis of SN observations and validation of SN models. SNAP consists of a publicly available relational database with observational light curve, theoretical light curve, and correlation table sets with 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 upload new SN models or new SN observations and run the comparison software to determine correlations via the website. There are problems looming on the horizon that SNAP is beginning to solve. For example, 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. Second, there is no rapidly available, systematic way to determine degeneracies between parameters, or even what physics is needed to model a realistic SN. The correlations made within the SNAP system are beginning to solve these problems.