3,227 research outputs found
Disc outbursts in various types of binary systems
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
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
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
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 1.
The existence of at least three systems with 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?
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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