Fast Radiative Shocks in Dense Media. III. Properties of the Emission

Evolution of fast, radiative shocks in high density medium is presented. Ionizing spectra and approximate broad band light curves of the shocked gas are calculated. Emergent shock spectra, as seen by a distant observer, are obtained from photoionization models. The emergent spectra have a power-law shape $F_{\nu}\propto{\nu}^{-\alpha}$ with mean spectral index $\alpha\sim0.6-1.0$ in the energy range $0.01-10$ keV, and have a high-energy cutoff corresponding to the original shock velocity. It is shown that the models exhibit promising features that may account for some photometric and spectral properties of Active Galactic Nuclei.Comment: 9 pages, 8 Postscript figures (not included), uses mn.sty, submitted to MNRAS, revised version. A complete version with figures (self-unpacking uuencoded archive) is available at http://www.astrouw.edu.pl/~plewa/papers/pap3/ps/pap3.u

Toward connecting core-collapse supernova theory with observations: I. Shock revival in a 15 Msun blue supergiant progenitor with SN 1987A energetics

We study the evolution of the collapsing core of a 15 Msun blue supergiant supernova progenitor from the core bounce until 1.5 seconds later. We present a sample of hydrodynamic models parameterized to match the explosion energetics of SN 1987A. We find the spatial model dimensionality to be an important contributing factor in the explosion process. Compared to two-dimensional simulations, our three-dimensional models require lower neutrino luminosities to produce equally energetic explosions. We estimate that the convective engine in our models is 4% more efficient in three dimensions than in two dimensions. We propose that the greater efficiency of the convective engine found in three-dimensional simulations might be due to the larger surface-to-volume ratio of convective plumes, which aids in distributing energy deposited by neutrinos. We do not find evidence of the standing accretion shock instability nor turbulence being a key factor in powering the explosion in our models. Instead, the analysis of the energy transport in the post-shock region reveals characteristics of penetrative convection. The explosion energy decreases dramatically once the resolution is inadequate to capture the morphology of convection on large scales. This shows that the role of dimensionality is secondary to correctly accounting for the basic physics of the explosion. We also analyze information provided by particle tracers embedded in the flow, and find that the unbound material has relatively long residency times in two-dimensional models, while in three dimensions a significant fraction of the explosion energy is carried by particles with relatively short residency times.Comment: accepted for publication in Astrophysical Journa

The Physics of Wind-Fed Accretion

We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global models of the radiatively-driven photoionized winds and accretion flows of HMXBs, with particular attention to the prototypical system Vela X-1. The models combine XSTAR photoionization calculations, HULLAC emission models appropriate to X-ray photoionized plasmas, improved models of the radiative driving of photoionized winds, FLASH time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo radiation transport. We present two- and three-dimensional maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of representative X-ray emission lines, as well as synthetic global Monte Carlo X-ray spectra. Such models help to better constrain the properties of the winds of HMXBs, which bear on such fundamental questions as the long-term evolution of these binaries and the chemical enrichment of the interstellar medium.Comment: 9 pages including 5 color encapsulated postscript figures; accepted for inclusion in the proceedings of "Cool Discs, Hot Flows: The Varying Faces of Accreting Compact Objects," ed. M. Axelsson (New York: AIP); minor revision which addresses the referee's comments; added Fig. 1 and removed Fig. 3 and the associated tex