the evidence in Type Ic SNe associated with Gamma-Ray Bursts (GRB-SNe). These SNe are thought to originate in very massive stars. They are particularly suited to study the details of the collapse process because they are not enshrouded in a thick hydrogen envelope, exposing the inner carbon-oxygen core, near

Favor de proporcionar un resumen en español. If you cannot provide a spanish abstract, the editors will do this. Binary stars are important for a full understanding of stellar evolution. We present a summary of how predictions of the relative supernova rates varies between single and binary stars

Abstract not found

Favor de proporcionar un resumen en español. If you cannot provide a spanish abstract, the editors will do this. X-ray emission from the supermassive star Eta Carinae (η Carinae) originates from hot shocked gas produced by current stellar mass loss as well as ejecta from prior eruptive events

Favor de proporcionar un resumen en español. If you cannot provide a spanish abstract, the editors will do this. Chandra High-Energy Transmission Grating (HETG) X-ray spectra are extracted from 17 bright, narrow regions of Cas A and provide unique measurements of their kinematic and plasma states. From the dominant emission lines, e.g. He-like Si, we derive accurate Doppler shifts in the range −2500 to +4000 kms −1; these agree well with transverse-velocity measurements and allow the features to be located in 3D. Plasma diagnostics of these regions indicate temperatures largely around 1keV with some above 3keV. Using as well the non-dispersed zeroth-order data, we determine NEI model parameters for the regions which lead to density estimates. Values of ne ≈ 100 cm −3 are likely the maximum of a range of densities in this X-ray emitting material. The common “oxygen-rich ” assumption is coarsely tested by comparing the integrated O VIII line flux and continuum levels. It appears that most of the continuum is due to another source, e.g., from He. Chandra High-Energy Transmission Grating (HETG) X-ray spectra are extracted from 17 bright, narrow regions of CasA and provide unique measurements of their kinematic and plasma states. From the dominant emission lines, e.g. He-like Si, we derive accurate Doppler shifts in the range −2500 to +4000 kms −1; these agree well with transverse-velocity measurements and allow the features to be located in 3D. Plasma diagnostics of these regions indicate temperatures largely around 1keV with some above 3keV. Using as well the non-dispersed zeroth-order data, we determine NEI model parameters for the regions which lead to density estimates. Values of ne ≈ 100 cm −3 are likely the maximum of a range of densities in this X-ray emitting material. The common “oxygen-rich ” assumption is coarsely tested by comparing the integrated O VIII line flux and continuum levels. It appears that most of the continuum is due to another source, e.g., from He.

La posibilidad de que las erupciones de rayos gamma (GRBs) no sean emisiones isotrópicas fue considerada teóricamente para atenuar el problema asociado a la gran cantidad de energía implicada por el modelo de bola de fuego estándar para estos potentes fenómenos. Sin embargo, el mecanismo por el cual, tras la deposión cuasiisotrópica de unos pocos 10 50 erg se origina una eyección colimada de plasma no pudo ser explicada de forma satisfactoria analíticamente. La razón de ello radica en que la colimación de un flujo saliente por su sistema progenitor depende de una dinámica no lineal muy compleja. Ello ha hecho necesario el uso de simulaciones numéricas para arrojar algo de luz sobre la viabilidad de algunos de los progenitores más probables de GRBs. En esta contribución revisaré los hechos más relevantes mostrados por tales simulaciones numéricas y cómo éstas han sido utilizadas para validar el modelos de estrella colapsante (para GRBs largos) y el modelo que implica la fusión de un sistema binario de objetos compactos (para GRBs cortos). The possibility that gamma-ray bursts (GRBs) were not isotropic emissions was devised theoretically as a way to ameliorate the huge energetic budget implied by the standard fireball model for these powerful phenomena. However, the mechanism by which after the quasy-isotropic release of a few 10 50 erg yields a collimated ejection of plasma could not be satisfactory explained analytically. The reason being that the collimation of an outflow by its progenitor system depends on a very complex and non-linear dynamics. That has made necessary the use of numerical simulations in order to shed some light on the viability of some likely progenitors of GRBs. In this contribution I will review the most relevant features shown by these numerical simulations and how they have been used to validate the collapsar model (for long GRBs) and the model involving the merger of compact binaries (for short GRBs).

and not within the interstellar medium. We explore the evolution of the medium around massive stars, and the expansion of the shock wave within this medium. We then apply these results to understanding the expansion of the shock wave in the ambient medium surrounding SN 1987A, and the evolution of the radio

in the form of stellar wind during their evolution. There are two possible ways to probe the CSM of long GRB progenitors. Firstly, the GRB afterglow consists of synchrotron radiation, emitted when the GRB jet sweeps up the surrounding medium. Therefore, the lightcurve is directly related to the density

Favor de proporcionar un resumen en español. If you cannot provide a spanish abstract, the editors will do this. Supernovae of type IIn possess spectral signatures that indicate an intense interaction between the supernova ejecta and surrounding dense circumstellar material cast off by the star in pre-explosion mass-loss episodes. Studying this interaction can yield clues to the nature of Type IIn progenitors and their mass loss history. In particular, polarization spectra of Type IIn’s show complex line polarization and position angle features that arise from a combination of geometrical and optical effects. I have constructed a Monte Carlo code that simulates the transfer of the Hα line through circumstellar shells with various geometrical configurations and optical characteristics. The superposition of broad and narrow line components produced in different regions of the circumstellar environment and modified by electron and line scattering, hydrogen absorption, thermal emission, and geometrical and viewing angle effects gives rise to a variety of polarized line shapes in the model spectra. Comparison of these results with recent high-quality spectropolarimetric observations of Type IIn supernovae suggests that a model “shock ” region between the supernova photosphere and the circumstellar shell is necessary to produce the narrow polarized emission features at the rest wavelength of Hα seen in some IIn’s. Further model results point toward other features in the polarized line profile that can be used to constrain the characteristics of the circumstellar material in these intriguing objects. The code’s

Favor de proporcionar un resumen en español. If you cannot provide a spanish abstract, the editors will do this. Radio observations of Type Ib/c supernovae suggest that circumstellar interaction takes place with a wide range of wind densities, comparable to that seen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in the shocked region is needed. The X-ray emission observed from some Type Ib/c supernovae is higher than would be expected by the thermal or inverse Compton mechanisms; a synchrotron interpretation requires a flattening of the electron energy spectrum at high energies, as might occur in a cosmic ray dominated shock wave. The wind density variations that are indicated in two supernovae may be due to a binary companion, although variable mass loss from a single star remains a possibility. Other than the optical supernova radiation, the emission from the nearby SN 2006aj/GRB 060218 appears to be powered by a central engine, while that from SN 1998bw/GRB 980425 could be powered by either a central engine or the outer supernova ejecta. Radio observations of Type Ib/c supernovae suggest that circumstellar interaction takes place with a wide range of wind densities, comparable to that seen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in the shocked region is needed. The X-ray emission observed from some Type Ib/c supernovae is higher than would be expected by the thermal or inverse Compton mechanisms; a synchrotron interpretation requires a flattening of the electron energy spectrum at high energies, as might occur in a cosmic ray dominated shock wave. The wind density variations that are indicated in two supernovae may be due to a binary companion, although variable mass loss from a single star remains a possibility. Other than the optical supernova radiation, the emission from the nearby SN 2006aj/GRB 060218 appears to be powered by a central engine, while that from SN 1998bw/GRB 980425 could be powered by either a central engine or the outer supernova ejecta.