Radiation processes around accreting black holes

Accreting sources such as AGN, X-ray binaries or gamma-ray bursts are known to be strong, high energy emitters. The hard emission is though to originate from plasmas of thermal and/or non-thermal high energy particles. Not only does this emission allow to probe the unique properties of the matter in an extreme environment, but it also has a crucial backreaction on the energetics and the dynamics of the emitting medium itself. Understanding interactions between radiation and matter has become a key issue in the modelling of high energy sources. Although most cross sections are well known, they are quite complex and the way all processes couple non-linearly is still an open issue. We present a new code that solves the local, kinetic evolution equations for distributions of electrons, positrons and photons, interacting by radiation processes such as self-absorbed synchrotron and brems-strahlung radiation, Compton scattering, pair production/annihilation, and by Coulomb collisions. The code is very general and aimed to modelled various high energy sources. As an application, we study the spectral states of X-ray binaries, including thermalization by Coulomb collisions and synchrotron self-absorption. It is found that the low-hard and high-soft states can be modelled with different illumination but the same non-thermal acceleration mechanism.Comment: 4 pages, 2 figures, proceedings of the SF2A conference 200

The x-ray corona and jet of cygnus x-1

Evidence is presented indicating that in the hard state of Cygnus X-1, the coronal mag- netic field might be below equipartition with radiation (suggesting that the corona is not powered by magnetic field dissipation) and that the ion temperature in the corona is significantly lower than what predicted by ADAF like models. It is also shown that the current estimates of the jet power set interesting contraints on the jet velocity (which is at least mildly relativistic), the accretion efficiency (which is large in both spectral states), and the nature of the X-ray emitting region (which is unlikely to be the jet).Comment: 8 pages, 1 figure. Accepted for publication in Journal of Modern Physics D, Proceedings of HEPRO II conference, Buenos Aires, Argentina, October 26-30, 200

A Critical Examination of Oil Wealth Management Strategies and Their Effects on Economic Growth in the Gulf Cooperation Council Countries

Despite their natural resources, the countries of the Gulf Cooperation Council (Kuwait, the United Arab Emirates, Saudi Arabia, Bahrain, Qatar, and Oman) have failed to live up to their economic potential, primarily due to their dependence on a revenue source with volatile prices and political significance in an unstable region. This thesis argues that the best way to convert oil wealth into consistent long term growth is through diversification, both by investing in foreign assets and by growing domestic sectors that are independent from oil and gas prices. The research further investigates the primary tool these countries have used to do so – sovereign wealth funds – and how their implementation and structures have impacted their effectiveness in achieving economic diversification and growth

The existence of warm and optically thick dissipative coronae above accretion disks

In the past years, several observations of AGN and X-ray binaries have suggested the existence of a warm T around 0.5-1 keV and optically thick, \tau ~ 10-20, corona covering the inner parts of the accretion disk. These properties are directly derived from spectral fitting in UV to soft-X-rays using Comptonization models. However, whether such a medium can be both in radiative and hydrostatic equilibrium with an accretion disk is still uncertain. We investigate the properties of such warm, optically thick coronae and put constraints on their existence. We solve the radiative transfer equation for grey atmosphere analytically in a pure scattering medium, including local dissipation as an additional heating term in the warm corona. The temperature profile of the warm corona is calculated assuming it is cooled by Compton scattering, with the underlying dissipative disk providing photons to the corona. Our analytic calculations show that a dissipative thick, (\tau_{cor} ~ 10-12) corona on the top of a standard accretion disk can reach temperatures of the order of 0.5-1 keV in its upper layers provided that the disk is passive. But, in absence of strong magnetic fields, the requirement of a Compton cooled corona in hydrostatic equilibrium in the vertical direction sets an upper limit on the Thomson optical depth \tau_{cor} < 5 . We show this value cannot be exceeded independently of the accretion disk parameters. However, magnetic pressure can extend this result to larger optical depths. Namely, a dissipative corona might have an optical depth up to ~ 20 when the magnetic pressure is 100 times higher that the gas pressure. The observation of warm coronae with Thomson depth larger than ~ 5 puts tights constraints on the physics of the accretion disk/corona systems and requires either strong magnetic fields or vertical outflows to stabilize the system.Comment: 9 pages 6 figure, submitted to A&A, comments are welcom

STUDY OF A SINGLE-CHARGED IONS ECR SOURCE MATCHING OF THE EXTRACTED BEAM TO AN ISOTOPE SEPARATOR

A new ECR ion-source has been designed and studied for single-charged ion beams. A very stable regime has been obtained with an ion-source made of two identical stages in cascade. The RF power supplies consist of two 2.45 GHz magnetrons. The discharge chamber is made of two coaxial Pyrex tubes. The external one ensures vacuum and HT insulation. The tubes are aligned inside the two multimode cavities axially limited by three magnetic coils. The ion beam is extracted at 20 kV and focused with electric lenses. For argon and xenon, 1 mA single-charged ion currents have been extracted. The influence of various parameters has been progressively achieved with a set-up including a 60° analyzing magnet and with the 120° on-line isotope separator at SARA. From emittances and images observed it appears difficult to compensate charge space effects. Suggestions and future developments are proposed to improve qualities of the isotopic separation

Simulating acceleration and radiation processes in X-ray binaries

The high energy emission of microquasars is thought to originate from high energy particles. Depending on the spectral state, the distribution of these particles can be thermal with a high temperature (typically 100 keV) or non-thermal and extending to even higher energy. The properties of high energy plasmas are governed by a rich microphysics involving particle-particle collisions and particles-photons interactions. We present a new code developed to address the evolution of relativistic plasmas. This one-zone code focuses on the microphysics and solves the coupled kinetic equations for particles and photons, including Compton scattering, synchrotron emission and absorption, pair production and annihilation, bremsstrahlung emission and absorption, Coulomb interactions, and prescriptions for additional particle acceleration and heating. It can in particular describe mechanisms such a thermalisation by synchrotron self-absorption and Coulomb collisions. Using the code, we investigate whether various acceleration processes, namely thermal heating, non-thermal acceleration and stochastic acceleration, can reproduce the different spectral states of microquasars. Premilinary results are presented.Comment: 9 pages, 6 figures, proceedings of the VII Microquasar Workshop: Microquasars and Beyond, September 1-5 2008, Foca, Izmir, Turkey; accepted for publication in Po

Sur la présence de Mylesinus paraschomburgkii Jégu et al., 1989 (Characiformes, Serrasalmidae) dans le bassin du rio Jari (Brésil, Amapa)

Des récoltes postérieures à la description de #Mylesinus paraschomburgkii permettent d'étendre son aire de distribution au bassin du Jari et au principal affluent du Uatuma. Une analyse en composantes principales sur 18 descripteurs morphologiques montrent que la morphologie générale de la population du Jari est différente de celle des populations du Trombetas et du Uatuma. L'isolement de la population du Jari serait donc plus ancien que la séparation des populations du Trombetas et du Uatuma. La dispersion de #Mylesinus paraschomburgkii le long de la marge sud du plateau des Guyanes serait reliée aux transgressions marines du Quaternaire. (Résumé d'auteur

Absorption lines from magnetically-driven winds in X-ray binaries

High resolution X-ray spectra of black hole X-ray binaries (BHBs) show blueshifted absorption lines from disk winds which seem to be equatorial. Winds occur in the Softer (disk-dominated) states of the outburst and are less prominent or absent in the Harder (power-law dominated) states. We use self-similar magneto-hydrodynamic (MHD) accretion-ejection models to explain the disk winds in BHBs. In our models, the density at the base of the outflow from the accretion disk is not a free parameter, but is determined by solving the full set of dynamical MHD equations. Thus the physical properties of the outflow are controlled by the global structure of the disk. We studied different MHD solutions characterized by different values of (a) the disk aspect ratio ($\varepsilon$) and (b) the ejection efficiency ($p$). We use two kinds of MHD solutions depending on the absence (cold solution) or presence (warm solution) of heating at the disk surface. Such heating could be from e.g. dissipation of energy due to MHD turbulence in the disk or from illumination. We use each of these MHD solutions to predict the physical parameters of an outflow; put limits on the ionization parameter ($\xi$), column density and timescales, motivated by observational results; and thus select regions within the outflow which are consistent with the observed winds. The cold MHD solutions cannot account for winds due to their low ejection efficiency. But warm solutions can explain the observed physical quantities in the wind because they can have sufficiently high values of $p$ ($\gtrsim 0.1$, implying larger mass loading at the base of the outflow). Further from our thermodynamic equilibrium curve analysis for the outflowing gas, we found that in the Hard state a range of $\xi$ is thermodynamically unstable, and had to be excluded. This constrain made it impossible to have any wind at all, in the Hard state.Comment: 16 Pages, 10 figures in the main body and 4 figures in the appendix. Accepted for publication in A&