Browsing by Subject "luminous supernovae"
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Item Analytical Light Curve Models Of Superluminous Supernovae: Chi(2)-Minimization Of Parameter Fits(2013-08) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef; Horvath, Z. L.; Nagy, A.; Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, JozsefWe present fits of generalized semi-analytic supernova (SN) light curve (LC) models for a variety of power inputs including Ni-56 and Co-56 radioactive decay, magnetar spin-down, and forward and reverse shock heating due to supernova ejecta-circumstellar matter (CSM) interaction. We apply our models to the observed LCs of the H-rich superluminous supernovae (SLSN-II) SN 2006gy, SN 2006tf, SN 2008am, SN 2008es, CSS100217, the H-poor SLSN-I SN 2005ap, SCP06F6, SN 2007bi, SN 2010gx, and SN 2010kd, as well as to the interacting SN 2008iy and PTF 09uj. Our goal is to determine the dominant mechanism that powers the LCs of these extraordinary events and the physical conditions involved in each case. We also present a comparison of our semi-analytical results with recent results from numerical radiation hydrodynamics calculations in the particular case of SN 2006gy in order to explore the strengths and weaknesses of our models. We find that CS shock heating produced by ejecta-CSM interaction provides a better fit to the LCs of most of the events we examine. We discuss the possibility that collision of supernova ejecta with hydrogen-deficient CSM accounts for some of the hydrogen-deficient SLSNe (SLSN-I) and may be a plausible explanation for the explosion mechanism of SN 2007bi, the pair-instability supernova candidate. We characterize and discuss issues of parameter degeneracy.Item Effects Of Rotation On The Minimum Mass Of Primordial Progenitors Of Pair-Instability Supernovae(2012-03) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Chatzopoulos, Emmanouil; Wheeler, J. CraigThe issue of which stars may reach the conditions of electron/positron pair-formation instability is of importance to understand the final evolution both of the first stars and of contemporary stars. The criterion to enter the pair-instability regime in density and temperature is basically controlled by the mass of the oxygen core. The main-sequence masses that produce a given oxygen core mass are, in turn, dependent on metallicity, mass loss, and convective and rotationally induced mixing. We examine the evolution of massive stars to determine the minimum main-sequence mass that can encounter pair-instability effects, either a pulsational pair-instability supernova (PPISN) or a full-fledged pair-instability supernova (PISN). We concentrate on zero-metallicity stars with no mass-loss subject to the Schwarzschild criterion for convective instability, but also explore solar metallicity and mass loss and the Ledoux criterion. As expected, for sufficiently strong rotationally induced mixing, the minimum main-sequence mass is encountered for conditions that induce effectively homogeneous evolution such that the original mass is converted almost entirely to helium and then to oxygen. For this case, we find that the minimum main-sequence mass is about 40 M-circle dot to encounter PPISN and about 65 M-circle dot to encounter a PISN. The implications of these results for the first stars and for contemporary supernovae are discussed.Item Emission From Pair-Instability Supernovae With Rotation(2015-01) Chatzopoulos, Emmanouil; van Rossum, Daniel R.; Wheeler, Craig J.; Whalen, Daniel J.; Smidt, Joseph; Wiggins, Brandon; Wheeler, Craig J.Pair-instability supernovae (PISNe) have been suggested as candidates for some superluminous supernovae, such as SN 2007bi, and as one of the dominant types of explosion occurring in the early universe from massive, zero-metallicity Population III stars. The progenitors of such events can be rapidly rotating, therefore exhibiting different evolutionary properties due to the effects of rotationally induced mixing and mass-loss. Proper identification of such events requires rigorous radiation hydrodynamics and radiative transfer calculations that capture not only the behavior of the light curve but also the spectral evolution of these events. We present radiation hydrodynamics and radiation transport calculations for 90-300M(circle dot) rotating PISNe covering both the shock breakout and late light curve phases. We also investigate cases of different initial metallicity and rotation rate to determine the impact of these parameters on the detailed spectral characteristics of these events. In agreement with recent results on non-rotating PISNe, we find that for a range of progenitor masses and rotation rates these events have intrinsically red colors in contradiction with observations of superluminous supernovae. The spectroscopic properties of rotating PISNe are similar to those of non-rotating events with stripped hydrogen and helium envelopes. We find that the progenitor metallicity and rotation rate properties are erased after the explosion and cannot be identified in the resulting model spectra. It is the combined effects of pre-supernova mass-loss and the basic properties of the supernova ejecta such as mass, temperature, and velocity that have the most direct impact in the model spectra of PISNe.Item Generalized Semi-Analytical Models Of Supernova Light Curves(2012-02) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef; Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, JozsefWe present generalized supernova (SN) light curve (LC) models for a variety of power inputs including the previously proposed ideas of radioactive decay of Ni-56 and Co-56 and magnetar spin-down. We extend those solutions to include finite progenitor radius and stationary photospheres as might be the case for SN that are powered by interaction of the ejecta with circumstellar matter (CSM). We provide an expression for the power input that is produced by self-similar forward and reverse shocks that efficiently convert their kinetic energy into radiation. We find that this ejecta-CSM interaction luminosity that we derive is in agreement with results from multi-dimensional radiation hydrodynamics simulations in the case of an optically thin CSM. We develop a semi-analytical model for the case of an optically thick CSM by invoking an approximation for the effects of radiative diffusion similar to that adopted by Arnett for SN II and compare this model to the results of numerical radiation hydrodynamics models. This model can give complex LCs, but for monotonically declining shock input, the LCs have a smooth rise, peak, and decline. In the context of this model, we provide predictions of the shock breakout of the forward shock from the optically thick part of the CSM envelope. We also introduce a hybrid LC model that incorporates ejecta-CSM interaction plus Ni-56 and Co-56 radioactive decay input. We fit this hybrid model to the LC of the super-luminous supernova (SLSN) 2006gy. We find that shock heating produced by ejecta-CSM interaction plus some contribution from radioactive decay provides a better fit to the LC of this event than previously presented models. We also address the relation between SN IIL and SN IIn with ejecta-CSM interaction models. The faster decline of SN IIL can be reproduced by the diffusion of previously deposited shock power if the shock power input to the diffusive component vanishes when the reverse shock sweeps up the whole ejecta and/or the forward shock propagates through the optically thick CSM. A CSM interaction with forward and reverse shock power input can produce the LCs of SN IIn in terms of duration, shape, and decline rate, depending on the properties of the CSM envelope and the progenitor star. This model can also produce LCs that are symmetric in shape around peak luminosity, which is the case for the observed LCs of some recently discovered peculiar transient events. We conclude that the observed LC variety of SN IIn and of some SLSNe is likely to be a byproduct of the large range of conditions relevant to significant ejecta-CSM interaction as a power source.Item Hydrogen-Poor Circumstellar Shells From Pulsational Pair-Instability Supernovae With Rapidly Rotating Progenitors(2012-12) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Chatzopoulos, Emmanouil; Wheeler, J. CraigIn certain mass ranges, massive stars can undergo a violent pulsation triggered by the electron/positron pair instability that ejects matter, but does not totally disrupt the star. After one or more of these pulsations, such stars are expected to undergo core-collapse to trigger a supernova (SN) explosion. The mass range susceptible to this pulsational phenomena may be as low as 50-70 M-circle dot if the progenitor is of very low metallicity and rotating sufficiently rapidly to undergo nearly homogeneous evolution. The mass, dynamics, and composition of the matter ejected in the pulsation are important aspects for determining the subsequent observational characteristics of the explosion. We examine the dynamics of a sample of stellar models and rotation rates and discuss the implications for the first stars, for LBV-like phenomena, and for superluminous SNe. We find that the shells ejected by pulsational pair-instability events with rapidly rotating progenitors (>30% the critical value) are hydrogen-poor and helium- and oxygen-rich.Item Multi-Dimensional Simulations Of Rotating Pair-Instability Supernovae(2013-10) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Couch, Sean M.; Chatzopoulos, Emmanouil; Wheeler, J. CraigWe study the effects of rotation on the dynamics, energetics, and Ni-56 production of pair instability supernova (PISN) explosions by performing rotating two-dimensional ("2.5D") hydrodynamics simulations. We calculate the evolution of eight low-metallicity (Z = 10(-3), 10(-4) Z(circle dot)) massive (135-245 M-circle dot) PISN progenitors with initial surface rotational velocities of 50% of the critical Keplerian value using the stellar evolution code MESA. We allow for both the inclusion and the omission of the effects of magnetic fields in the angular momentum transport and in chemical mixing, resulting in slowly rotating and rapidly rotating final carbon-oxygen cores, respectively. Increased rotation for carbon-oxygen cores of the same mass and chemical stratification leads to less energetic PISN explosions that produce smaller amounts of Ni-56 due to the effect of the angular momentum barrier that develops and slows the dynamical collapse. We find a non-monotonic dependence of Ni-56 production on rotational velocity in situations when smoother composition gradients form at the outer edge of the rotating cores. In these cases, the PISN energetics are determined by the competition of two factors: the extent of chemical mixing in the outer layers of the core due to the effects of rotation in the progenitor evolution and the development of angular momentum support against collapse. Our 2.5D PISN simulations with rotation are the first presented in the literature. They reveal hydrodynamic instabilities in several regions of the exploding star and increased explosion asymmetries with higher core rotational velocity.Item Polarimetry of the Superluminous Supernova LSQ14mo: No Evidence for Significant Deviations from Spherical Symmetry(2015-12) Leloudas, Giorgos; Patat, Ferdinando; Maund, Justyn R.; Hsiao, Eric; Malesani, Daniele; Schulze, Steve; Contreras, Carlos; De Ugarte Postigo, Antonio; Sollerman, Jesper; Stritzinger, Maximilian D.; Taddia, Francesco; Wheeler, J. Craig; Gorosabel, Javier; Wheeler, J. CraigWe present the first polarimetric observations of a Type I superluminous supernova (SLSN). LSQ14mo was observed with VLT/FORS2 at five different epochs in the V band, with the observations starting before maximum light and spanning 26 days in the rest frame (z. = 0.256). During this period, we do not detect any statistically significant evolution (<2 sigma) in the Stokes parameters. The average values we obtain, corrected for interstellar polarization in the Galaxy, are Q = -0.01% (+/- 0.15%) and U = -0.50% (+/- 0.14%). This low polarization can be entirely due to interstellar polarization in the SN host galaxy. We conclude that, at least during the period of observations and at the optical depths probed, the photosphere of LSQ14mo does not present significant asymmetries, unlike most lower-luminosity hydrogen-poor SNe Ib/c. Alternatively, it is possible that we may have observed LSQ14mo from a special viewing angle. Supporting spectroscopy and photometry confirm that LSQ14mo is a typical SLSN I. Further studies of the polarization of Type I SLSNe are required to determine whether the low levels of polarization are a characteristic of the entire class and to also study the implications for the proposed explosion models.Item Precursors Prior To Type IIn Supernova Explosions Are Common: Precursor Rates, Properties, And Correlations(2014-07) Ofek, Eran O.; Sullivan, Mark; Shaviv, Nir J.; Steinbok, Aviram; Arcavi, Iair; Gal-Yam, Avishay; Tal, David; Kulkarni, Shrinivas R.; Nugent, Peter E.; Ben-Ami, Sagi; Kasliwal, Mansi M.; Cenko, S. Bradley; Laher, Russ; Surace, Jason; Bloom, Joshua S.; Filippenko, Alexei V.; Silverman, Jeffrey M.; Yaron, Ofer; Silverman, Jeffrey M.There is a growing number of Type IIn supernovae (SNe) which present an outburst prior to their presumably final explosion. These precursors may affect the SN display, and are likely related to poorly charted phenomena in the final stages of stellar evolution. By coadding Palomar Transient Factory (PTF) images taken prior to the explosion, here we present a search for precursors in a sample of 16 Type IIn SNe. We find five SNe IIn that likely have at least one possible precursor event (PTF 10bjb, SN 2010mc, PTF 10weh, SN 2011ht, and PTF 12cxj), three of which are reported here for the first time. For each SN we calculate the control time. We find that precursor events among SNe IIn are common: at the one-sided 99% confidence level, >50% of SNe IIn have at least one pre-explosion outburst that is brighter than 3 x 10(7) L-circle dot taking place up to 1/3 yr prior to the SN explosion. The average rate of such precursor events during the year prior to the SN explosion is likely greater than or similar to 1 yr(-1), and fainter precursors are possibly even more common. Ignoring the two weakest precursors in our sample, the precursors rate we find is still on the order of one per year. We also find possible correlations between the integrated luminosity of the precursor and the SN total radiated energy, peak luminosity, and rise time. These correlations are expected if the precursors are mass-ejection events, and the early-time light curve of these SNe is powered by interaction of the SN shock and ejecta with optically thick circumstellar material.