The Unusual Super-Luminous Supernovae SN 2011kl and ASASSN-15lh

Two recently discovered very luminous supernovae (SNe) present stimulating cases to explore the extents of the available theoretical models. SN 2011kl represents the first detection of a supernova explosion associated with an ultra-long duration gamma ray burst. ASASSN-15lh was even claimed as the most luminous SN ever discovered, challenging the scenarios so far proposed for stellar explosions. Here we use our radiation hydrodynamics code in order to simulate magnetar powered SNe. To avoid explicitly assuming neutron star properties we adopt the magnetar luminosity and spin-down timescale as free parameters of the model. We find that the light curve (LC) of SN 2011kl is consistent with a magnetar power source, as previously proposed, but we note that some amount of 56^Ni (> 0.08 M_sun) is necessary to explain the low contrast between the LC peak and tail. For the case of ASASSN-15lh we find physically plausible magnetar parameters that reproduce the overall shape of the LC provided the progenitor mass is relatively large (a mass of the ejecta approx 6 M_sun). The ejecta hydrodynamics of this event is dominated by the magnetar input, while the effect is more moderate for SN 2011kl. We conclude that a magnetar model may be used for the interpretation of these events and that the hydrodynamic modeling is necessary to derive the properties of powerful magnetars and their progenitors.Comment: Accepted by Astrophysical Journal Letters, 5 pages, 5 figure

Double-peaked SuperNovae

Fil: Bersten, M. CCT-CONICET-UNLP. Instituto de Astrofísica de La Plata (IALP), La Plata, Argentina.Fil: Orellana, Mariana. CONICET; Argentina.Fil: Orellana, Mariana. Universidad Nacional de Río Negro. Río Negro, Argentina.Se adjunta versión aceptada para su publicaciónThrough hydrodynamical 1D simulations we explore two of the more promissing physical scenarios invoked to explain peculiar double-peaked supenovae. One consists of a double radioactive nickel distribution formed when some of this material is pushed out by a putative jet that is related to the supernova explosion. The other scenario has only outer nickel, but the main peak is powered by a newly born magnetar. We present the whole evolution of the bolometric light curve for a helium-rich progenitor. The main goal is to compare the resulting bolometric light curves (LCs) and to confirm the fact that, for some parameters, the two peaks are clearly departed, being the latter a brigther and broader main peak.A través de simulaciones hidrodinámicas 1D, exploramos dos de los escenarios físicos más prometedores invocados para explicar las peculiares supernovas de doble pico. Uno consiste en una doble distribución de níquel radiactivo que se forma cuando parte de este material es expulsado por un supuesto chorro que está relacionado con la explosión de la supernova. El otro escenario solo tiene níquel exterior, pero el pico principal es impulsado por una magnetar recientemente formado. Presentamos toda la evolución de la curva de luz bolométrica para un progenitor rico en helio. El objetivo principal es comparar las curvas de luz bolométricas resultantes y confirmar el hecho de que, para algunos parámetros, los dos picos están claramente separados, siendo este último un pico principal más ancho y brillante

Early UV/Optical Emission of The Type Ib SN 2008D

We propose an alternative explanation for the post-breakout emission of SN 2008D associated with the X-ray transient 080109. Observations of this object show a very small contrast of 0.35 dex between the light-curve minimum occurring soon after the breakout, and the main luminosity peak that is due to radioactive heating of the ejecta. Hydrodynamical models show that the cooling of a shocked Wolf-Rayet star leads to a much greater difference (> 0.9 dex). Our proposed scenario is that of a jet produced during the explosion which deposits 56Ni-rich material in the outer layers of the ejecta. The presence of high-velocity radioactive material allows us to reproduce the complete luminosity evolution of the object. Without outer 56Ni it could be possible to reproduce the early emission purely from cooling of the shocked envelope by assuming a larger progenitor than a Wolf-Rayet star, but that would require an initial density structure significantly different from what is predicted by stellar evolution models. Analytic models of the cooling phase have been proposed reproduce the early emission of SN 2008D with an extended progenitor. However, we found that the models are valid only until 1.5 days after the explosion where only two data of SN 2008D are available. We also discuss the possibility of the interaction of the ejecta with a binary companion, based on published analytic expressions. However, the binary separation required to fit the early emission should be < 3 Rsun which is too small for a system containing two massive stars.Comment: 10 pages, 10 figures, Accepted for publication in Ap

The Progenitor of the Type IIb SN 2008ax Revisited

Hubble Space Telescope observations of the site of the supernova (SN) 2008ax obtained in 2011 and 2013 reveal that the possible progenitor object detected in pre-explosion images was in fact multiple. Four point sources are resolved in the new, higher-resolution images. We identify one of the sources with the fading SN. The other three objects are consistent with single supergiant stars. We conclude that their light contaminated the previously identified progenitor candidate. After subtraction of these stars, the progenitor appears to be significantly fainter and bluer than previously measured. Post-explosion photometry at the SN location indicates that the progenitor object has disappeared. If single, the progenitor is compatible with a supergiant star of B to mid-A spectral type, while a Wolf-Rayet (WR) star would be too luminous in the ultraviolet to account for the observations. Moreover, our hydrodynamical modelling shows the pre-explosion mass was $4-5$ $M_\odot$ and the radius was $30-50$ $R_\odot$, which is incompatible with a WR progenitor. We present a possible interacting binary progenitor computed with our evolutionary models that reproduces all the observational evidence. A companion star as luminous as an O9-B0 main-sequence star may have remained after the explosion.Comment: ApJ accepted, 14 pages, 7 figure

Supernovas superluminosas de Tipo II Plateau

Fil: Orellana, Mariana D. Universidad Nacional de Río Negro; ArgentinaFil: Orellana, Mariana D. CONICET; ArgentinaFil: Bersten, Melina C. Universidad Nacional de La Plata. Instituto de Astrofísica de La Plata (IALP), CCT-CONICET; ArgentinaFil: Bersten, Melina C. CONICET; ArgentinaCorresponde a una presentación oral en la reunión anual de la AAA.We have incorporated the effect of the energy injection provided by a magnetar as an additional source to power the light curve of superlumine supernovae, that is, supernovae that shine between ten and one hundred times more than usual. We study in greater detail the case of hydrogen-rich progenitor stars. We present results of our exploration of the space of physical parameters that lead to different morphologies of the light curves. We identified cases that develop a quasi-constant luminosity phase, and would preserve the plateau classification defined for normal supernovae.Hemos incorporado el efecto de la inyección de energía proporcionada por un magnetar como fuente adicional para alimentar la curva de luz de las supernovas superluminas, es decir, las supernovas que brillan entre diez y cien veces más de lo habitual. Estudiamos con mayor detalle el caso de las estrellas progenitoras ricas en hidrógeno. Presentamos los resultados de nuestra exploración del espacio de parámetros físicos que conducen a diferentes morfologías de las curvas de luz. Identificamos casos que desarrollan una fase de luminosidad casi constante y preservarían la clasificación de meseta definida para supernovas normales

Magnetares como fuentes para potenciar supernovas peculiares

Fil: Bersten, Melina C. CONICET; ArgentinaFil: Orellana, Mariana D. CONICET; ArgentinaFil: Bersten, Melina C. Universidad Nacional de La Plata. Instituto de Astrofísica de La Plata (IALP), CCT-CONICET; ArgentinaFil: Orellana, Mariana D. Universidad Nacional de Río Negro. Laboratorio de Procesamiento de Señales Aplicado y Computación de Alto Rendimiento; ArgentinaAdjunto la versión que ha sido aceptada, está en prensa a la fecha (18/4)Hemos incorporado el efecto de la inyección de energía sostenida por un magnetar en las simulaciones hidrodinámicas de supernovas (SNe) de Bersten et al. (2011). La variación de las propiedades de la eyecta y del magnetar introducen cambios en la curva de luz (tiempo de aumento, luminosidad máxima, ancho). Mostramos los rasgos más importantes de las morfologías encontradas para las curvas de luz de una población sintética de SNe con y sin hidrógeno. Como parte del trabajo en curso, buscamos los parámetros que expliquen los datos observacionales de SN2018cow que es una SN brillante que a diferencia del general de las SNe superluminosas, fue muy cercana (60 Mpc). Ha llamado la atención dada la rápida evolución de su curva de luz. Ha sido objeto de numerosas campañas multifrecuencia y de debatidas ideas teóricas para explicarla. La propuesta de un magnetar no es nueva en este caso, pero sí el cálculo hidrodinámico, como mejora a propuestas más simplificadoras que se presentan en la literatura

iPTF13bvn: The First Evidence of a Binary Progenitor for a Type Ib Supernova

The recent detection in archival HST images of an object at the the location of supernova (SN) iPTF13bvn may represent the first direct evidence of the progenitor of a Type Ib SN. The object's photometry was found to be compatible with a Wolf-Rayet pre-SN star mass of ~11 Msun. However, based on hydrodynamical models we show that the progenitor had a pre-SN mass of ~3.5 Msun and that it could not be larger than ~8 Msun. We propose an interacting binary system as the SN progenitor and perform evolutionary calculations that are able to self-consistently explain the light-curve shape, the absence of hydrogen, and the pre-SN photometry. We further discuss the range of allowed binary systems and predict that the remaining companion is a luminous O-type star of significantly lower flux in the optical than the pre-SN object. A future detection of such star may be possible and would provide the first robust identification of a progenitor system for a Type Ib SN.Comment: Accepted to AJ on July 26. Slight changes from original, however delayed by slow refereeing proces

A Binary Progenitor for the Type IIb Supernova 2011dh in M51

We perform binary stellar evolutionary calculations following the simultaneous evolution of both stars in the system to study a potential progenitor system for the Type IIb supernova 2011dh. Pre-explosion photometry as well as light-curve modeling have provided constraints on the physical properties of the progenitor system. Here we present a close binary system that is compatible with such constraints. The system is formed by stars of solar composition with 16 Msun + 10 Msun on a circular orbit with an initial period of 125 days. The primary star ends its evolution as a yellow supergiant with a mass of ~4 Msun, a final hydrogen content of ~3-5E-03 Msun and with an effective temperature and luminosity in agreement with the HST pre-explosion observations of SN 2011dh. These results are nearly insensitive to the adopted accretion efficiency factor beta. At the time of explosion, the companion star has an effective temperature of 22 to 40 thousand Kelvin, depending on the value of beta, and lies near the zero age main sequence. Considering the uncertainties in the HST pre-SN photometry the secondary star is only marginally detectable in the bluest observed band. Close binary systems, as opposed to single stars, provide a natural frame to explain the properties of SN 2011dh.Comment: 12 pages, 15 figures, 3 tables. Accepted for publication in The Astrophysical Journal on October June 27, 201

Detection of the Gravitational Lens Magnifying a Type Ia Supernova

Objects of known brightness, like Type Ia supernovae (SNIa), can be used to measure distances. If a massive object warps spacetime to form multiple images of a background SNIa, a direct test of cosmic expansion is also possible. However, these lensing events must first be distinguished from other rare phenomena. Recently, a supernova was found to shine much brighter than normal for its distance, which resulted in a debate: was it a new type of superluminous supernova or a normal SNIa magnified by a hidden gravitational lens? Here we report that a spectrum obtained after the supernova faded away shows the presence of a foreground galaxy--the first found to strongly magnify a SNIa. We discuss how more lensed SNIa may be found than previously predicted.Comment: 32 pages, 10 figures. Accepted for publication in Scienc