3,253 research outputs found

    Disc outbursts in various types of binary systems

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    I discuss some aspects of the Disc Instability Model applied to outbursts in various types of binary systems. I lament the general lack of interest in the subject.Comment: The Golden Age of Cataclysmic Variables and Related Objects, F. Giovannelli & L. Sabau-Graziati (eds.), Mem. SAIt. (2012) 83 N.2 (in press

    X-rays from Quiescent Low-Mass X-ray Binary Transients

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    I argue that it is very unlikely that X-rays from quiescent black-hole low-mass X-ray binary transients are emitted by coronae of companion stars. I show that in a simple model in which these X-rays are emitted by an ADAF filling the inner part of an unsteady, dwarf-nova type disc, the X-ray luminosity is correlated with the orbital period. I predict what values of X-ray luminosities from black-hole transient systems should be observed by Chandra and XMM-Newton.Comment: 9 pages, 2 figures, Astronomy and Astrophysics, in press. Slightly revised versio

    Black hole accretion discs

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    This is an introduction to models of accretion discs around black holes. After a presentation of the non-relativistic equations describing the structure and evolution of geometrically thin accretion discs we discuss their steady-state solutions and compare them to observation. Next we describe in detail the thermal-viscous disc instability model and its application to dwarf novae for which it was designed and its X-ray irradiated-disc version which explains the soft X--ray transients, i.e. outbursting black-hole low-mass X-ray binaries. We then turn to the role of advection in accretion flows onto black holes illustrating its action and importance with a toy model describing both ADAFs and slim discs. We conclude with a presentation of the general-relativistic formalism describing accretion discs in the Kerr space-time.Comment: 41 pages, 11 figures, Chapter 1 in: "Astrophysics of Black Holes - From fundamental aspects to latest developments", Ed. Cosimo Bambi, Springer: Astrophysics and Space Science Library 440 (2016). Minor errors correcte

    Mechanisms for Dwarf Nova Outbursts and Soft X-Ray Transients

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    I review models trying to explain dwarf-nova outbursts and soft X-ray transients. The disc-instability model for dwarf-novae is still in its preliminary state of development: its predictions depend very strongly on the unknown viscosity mechanism. It is also doubtful that a {\sl pure} disc-instability phenomenon will be able to describe {\sl all} types of dwarf-nova outbursts, in particular superoutbursts. The disc-instability model for SXTs suffers from the same difficulties but in addition its predictions are contradicted by observations of transient sources in quiescence. The illuminated mass-transfer model cannot describe correctly the time-scales of SXT events for main-sequence secondaries with masses less than 1M‚äôM_{\odot}. The existence of at least three systems with Porb<10P_{\rm orb} < 10 hr seems to rule it out as an explanation of the SXT phenomenon.Comment: 13 pages, no figures, (available as uuencoded compressed tar file). Invited review at IAU Symposium 165 "Compact Stars in Binaries", Den Haag, 15-19 August 199

    Why Do Black--Hole X-ray Binaries Tend to Be Transient?

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    Black hole X-ray binaries are transient probably because their discs are subject to the same thermal-viscous instability which is present in dwarf nova binary systems. I discuss applications of the dwarf-nova instability model to transient, low-mass, X-ray binary systems. When disc truncation and X-ray irradiation are taken into account this model is capable of reproducing the basic properties of X-ray binary outbursts (Dubus et al. 2000).Comment: 6 pages, 2 figures; Proceedings of the ESO Workshop on "Black Holes in Binaries and Galactic Nuclei: Diagnostics, Demography and Formation", in honour of Prof. R. Giacconi, in pres
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