arXiv subjects

P. Mazzali

Publications and source records attributed to P. Mazzali.

58 records · Page 4Linked to original sources

arXiv2002

Optical Spectropolarimetry of SN 2002ap: High Velocity Asymmetric Explosion

We present spectropolarimetry of the Type Ic supernova SN 2002ap and give a preliminary analysis: the data were taken at two epochs, close to and one month later than the visual maximum (2002 February 8). In addition we present June 9 spectropolarimetry without analysis. The data show the development of linear polarization. Distinct polarization profiles were seen only in the O I λ7773 multiplet/Ca II IR triplet absorption trough at maximum light and in the Ca II IR triplet absorption trough a month later, with the latter showing a peak polarization as high as ~2 %. The intrinsic polarization shows three clear position angles: 80 degs for the February continuum, 120 degs for the February line feature, and 150 degs for the March data. We conclude that there are multiple asymmetric components in the ejecta. We suggest that the supernova has a bulk asymmetry with an axial ratio projected on the sky that is different from 1 by of order 10 %. Furthermore, we suggest very speculatively that a high velocity ejecta component moving faster than ~0.115c (e.g., a jet) contributes to polarization in the February epoch.

astro-ph↗

arXiv2002

Peculiar, Low Luminosity Type II Supernovae: Low Energy Explosions in Massive Progenitors?

A number of supernovae, classified as Type II, show remarkably peculiar properties such as an extremely low expansion velocity and an extraordinarily small amount of $^{56}$Ni in the ejecta. We present a joint analysis of the available observations for two of these peculiar Type II supernovae, SN 1997D and SN 1999br, using a comprehensive semi-analytic method that can reproduce the light curve and the evolution of the line velocity and continuum temperature. We find that these events are under-energetic with respect to a typical Type II supernova and that the inferred mass of the ejecta is relatively large. We discuss the possibility that these supernovae originate from the explosion of a massive progenitor in which the rate of early infall of stellar material on the collapsed core is large. Events of this type could form a black hole remnant, giving rise to significant fallback and late-time accretion.

astro-ph↗

arXiv2001

Formation of the Black Hole in Nova Scorpii

Israelian et al. (1999) showed that the stellar companion of the black-hole binary Nova Sco is polluted with material ejected in the supernova that accompanied the formation of the black-hole primary. Here we systematically investigate the implications of these observations for the black-hole formation process. Using a variety of supernova models, including both standard as well as hypernova models (for different helium-star masses, explosion energies, and explosion geometries) and a simple model for the evolution of the binary and the pollution of the secondary, we show that most of the observed abundance anomalies can be explained for a large range of model parameters (apart from the abundance of Ti). The best models are obtained for He star masses of 10 to 16 Msun, where spherical hypernova models are generally favoured over standard supernova ones. Aspherical hypernova models also produce acceptable fits, provided there is extensive lateral mixing. All models require substantial fallback and that the fallback material either reached the orbit of the secondary or was mixed efficiently with material that escaped. The black hole therefore formed in a two-step process, where the initial mass of the collapsed remnant was increased substantially by matter that fell back after the initial collapse. This may help to explain the high observed space velocity of Nova Sco either because of a neutrino-induced kick (if a neutron star was formed first) or by asymmetric mass ejection in an asymmetric supernova explosion.

astro-ph↗

arXiv1998

Discovery of the peculiar supernova 1998bw in the error box of GRB980425

The discovery of X-ray, optical and radio afterglows of gamma-ray bursts (GRBs) and the measurements of the distances to some of them have established that these events come from Gpc distances and are the most powerful photon emitters known in the Universe, with peak luminosities up to 10^52 erg/s. We here report the discovery of an optical transient, in the BeppoSAX Wide Field Camera error box of GRB980425, which occurred within about a day of the gamma-ray burst. Its optical light curve, spectrum and location in a spiral arm of the galaxy ESO 184-G82, at a redshift z = 0.0085, show that the transient is a very luminous type Ic supernova, SN1998bw. The peculiar nature of SN1998bw is emphasized by its extraordinary radio properties which require that the radio emitter expand at relativistical speed. Since SN1998bw is very different from all previously observed afterglows of GRBs, our discovery raises the possibility that very different mechanisms may give rise to GRBs, which differ little in their gamma-ray properties.

astro-ph↗