Reflection at large distance from the central engine in Seyferts

We consider the possibility that most of the reflection component, observed in the hard X-ray spectra of Seyfert galaxies, could be formed on an extended medium, at large distance from the central source of primary radiation (e.g. on a torus). Then, the reflector cannot respond to the rapid fluctuations of the primary source. The observed reflected flux is controlled by the time-averaged primary spectrum rather than the instantaneous (observed) one. We show that this effect strongly influence the spectral fits parameters derived under the assumption of a reflection component consistent with the primary radiation. We find that a pivoting primary power-law spectrum with a nearly constant Comptonised luminosity may account for the reported correlation between the reflection amplitude $R$ and the spectral index $\Gamma$.Comment: Proceeding of the meeting "X-ray emission from accretion onto black hole" 20-23 June 2001, Hopkins University, Baltimore, USA (style file jhuwkshp.sty included

Diagnostic prénatal

National audienc

Prédiction (médecine prédictive)

National audienc

Génétique (tests et conseil génétique)

National audienc

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

The emission of Cygnus X-1: observations with INTEGRAL SPI from 20 keV to 2 MeV

We report on Cyg X-1 observations performed by the SPI telescope onboard the INTEGRAL mission and distributed over more than 6 years. We investigate the variability of the intensity and spectral shape of this peculiar source in the hard X-rays domain, and more particularly up to the MeV region. We first study the total averaged spectrum which presents the best signal to noise ratio (4 Ms of data). Then, we refine our results by building mean spectra by periods and gathering those of similar hardness. Several spectral shapes are observed with important changes in the curvature between 20 and 200 keV, even at the same luminosity level. In all cases, the emission decreases sharply above 700 keV, with flux values above 1 MeV (or upper limits) well below the recently reported polarised flux (Laurent et al. 2011), while compatible with the MeV emission detected some years ago by CGRO/COMPTEL (McConnell et al., 2002). Finally, we take advantage of the spectroscopic capability of the instrument to seek for spectral features in the 500 keV region with negative results for any significant annihilation emission on 2 ks and days timescales, as well as in the total dataset.Comment: 14 pages, 10 figures, accepted for publication in Ap

O gálio e a patologia óssea.

Estima-se que mais de 200.000 cirurgias para fusão da coluna vertebral são realizadas a cada ano nos EUA. Artrodese lombar posterolateral intertransversalis é o procedimento mais comum realizado, ainda que a falha para obter uma sólida união óssea ocorre em 10% a 40% dos pacientes com único nível envolvido e mais freqüentemente em múltiplos níveis. Esta alta taxa de pseudoartrose indica que eventos fisiológicos, biológicos e químicos, cruciais para este processo, não são adequadamente compreendidos. A não união óssea frequentemente leva a uma resolução insatisfatória dos sintomas clínicos e usualmente resulta em maior custo médico e morbidade, bem como a necessidade de intervenções adicionais(1). Infelizmente, o efeito dos íons metálicos no processo de mineralização não tem recebido considerável atenção até recentemente, entretanto dados interessantes da participação do alumínio e gálio no metabolismo ósseo foram publicados há mais de 15 anos(2). Atualmente, o número de publicações dedicadas ao papel do gálio na patologia óssea está crescendo rapidamente, todavia, revisões abrangentes não estão disponíveis. A intenção do presente estudo é preencher esta lacuna, considerando a formação, crescimento e solubilidade da hidroxiapatita na presença de sais de gálio, a incorporação do gálio dentro do tecido ósseo e o mecanismo de atividade terapêutica deste elemento

Spectral variability modes of GX 339-4 in a hard-to-soft state transition

We report on INTEGRAL observations performed during the 2004 outburst of the bright black hole transient GX 339-4. We analysed IBIS and JEM-X public data starting on 9th August and lasting about one month. During this period GX 339-4 showed spectral state transitions. In order to seek for variability patterns, a principal component analysis (PCA) has been used.Comment: 5 pages, 6 figures, accepted for publication in the proceedings of VI Microquasar workshop: Microquasar and Beyond, 18-22 September 2006 in Como (Italy), eds: T. Belloni et al. (2006