3,069 research outputs found
HIGH-ENERGY PHENOMENA STUDIED WITH X-RAY POLARIMETRY
No full textAfter more than 30 years since the last X-ray polarimetric measurements, performed in the 70's by the OSO-8 satellite, thanks to recent technological advances, polarimetry is considered again as a viable technique for studing X-ray sources. In this contribution the author briefly discusses a couple of astrophysical situations, related to the topics of this conference, where X-ray polarimetry can be extremely useful. The author also discusses the observational perspectives, listing the main future space missions (proposed or even already approved) carrying on-board an X-ray polarimeter
Seyfert galaxies and BeppoSAX
No full textThe contributions that BeppoSAX is expected to give and, after one and a half year of operation, has already given, to our knowledge of both type 1 and type 2 Seyfert galaxies are outlined and reviewed
Desativar o direito: um caminho a partir da obra de Giorgio Agamben
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Jurídicas, Programa de Pós-Graduação em Direito, Florianópolis, 2014O trabalho parte do problema de tentar pensar uma forma de resistência pelo Direito. A hipótese sustentada encontra amparo na noção de "desativar" o Direito, contida na obra de Giorgio Agamben. Neste sentido, o trabalho busca recompor os paradigmas jurídico-político e governamental dentro da obra do autor em questão, principalmente a partir dos livros "O poder soberano e a vida nua", "Estado de Exceção" e "O Reino e a Glória". Ao fim, a proposta de "desativar" o Direito e o conceito de inoperosidade defrontam-se com a máquina governamental agambeniana. Na conclusão, a filosofia do Direito é apresentada como alternativa para se pensar uma nova relação entre Direito e vida.Abstract: The work begins from the problem of trying to think of a way of resistance by Law. The hypothesis is supported by the notion of "deactivate" the law, contained in the work of Giorgio Agamben. In this sense, this dissertation seeks to reconstruct the legal-political and governmental paradigms within the work of the author in question, mostly from the books "The sovereign power and bare life", "State of Exception" and "The Kingdom and the Glory". At the end, the proposal to "deactivate" the Law and the concept of unindustriousness are confronted with Agamben's government machinery. In conclusion, the philosophy of law is presented as an alternative to think about a new relationship between law and life
General Relativity effects and line emission
No full textGeneral Relativity effects (gravitational redshift, light bending,...) strongly modify the characteristics of the lines emitted close to the Black Hole in Active Galactic Nuclei and Galactic Black Hole systems. These effects are reviewed and illustrated, with particular emphasis on line emission from the accretion disc. Methods, based on the iron line, to measure the two astrophysically relevant parameters of a Black Hole, the mass and spin, are briefly discussed
X-ray polarization properties of the accretion column in magnetic CVs
No full textThe accretion column in magnetic Cataclysmic Variables may have a non negligible Thomson optical depth. A fraction of the thermal radiation from the post-shock region may therefore be scattered - and then polarized - before escaping the column. Moreover, part of the thermal radiation is reflected - and again polarized - by the White Dwarf surface. We show that X-ray polarimetry can provide valuable and probably unique information on the geometry and physical parameters of the accretion column by calculating, by means of Monte Carlo simulations, the expected polarization properties of magnetic CVs as a function of the geometrical parameters (assuming a cylindrical geometry) and the Thomson optical depth of the column. We find that degrees of polarization as high as about 4% can be present, and apply our calculations to the archetypal magnetic CV, AM Herculis
X-RAY-POLARIZATION PROPERTIES OF A CENTRALLY ILLUMINATED ACCRETION DISK
No full textThe polarization of the X-rays reflected by a centrally illuminated, optically thick and geometrically thin accretion disc is calculated as a function of the source and disc parameters. The degree of polarization of the reflected radiation depends strongly on the disc inclination, and could be greater than 20 per cent; the polarization angle is 90-degrees, i.e. the polarization vector lies in the meridian plane. Due to the dilution of the primary source, assumed unpolarized, the net polarization depends strongly on photon energy, and could reach values as high as approximately 6 per cent at energies greater than a few tens of keV. When relativistic effects in the Schwarzschild metric are taken into account, the degree of polarization generally increases, and the polarization angle becomes greater than 90-degrees. The model could be tested by the SXRP experiment for several galactic X-ray binaries, and at least for one active galaxy, i.e. Centaurus A
The iron K alpha Compton shoulder in transmitted and reflected spectra
No full textWe calculate the equivalent width of the core, and the centroid energy and relative flux of the first-order Compton shoulder of the iron Kalpha emission line from neutral matter. The calculations are performed with Monte Carlo simulations. We explore a large range of column densities for both transmitted and reflected spectra, and study the dependence on the iron abundance. The Compton shoulder is now becoming observable in many objects thanks to the improved sensitivity and/or energy resolution of the XMM-Newton and Chandra satellites, and the present work aims to provide a tool to derive information on the geometry and element abundances of the line-emitting matter from Compton shoulder measurements
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