Showing papers by "Center for Theoretical Physics published in 2011"
TL;DR: In this paper, the authors discuss two important instability mechanisms that may lead to the limit-cycle oscillations of the luminosity of the accretion disks around compact objects: ionization instability and radiation pressure instability.
Abstract: We discuss two important instability mechanisms that may lead to the limit-cycleoscillations of the luminosity of the accretion disks around compact objects: ionizationinstability and radiation-pressure instability. Ionization instability is well establishedas a mechanism of X-ray novae eruptions in black hole binary systems but its ap-plicability to AGN is still problematic. Radiation pressure theory has still very weakobservational background in any of these sources. In the present paper we attempt toconfront the parameter space of these instabilities with the observational data. At thebasis of this simple survey of sources properties we argue that the radiation pressureinstability is likely to be present in several Galactic sources with the Eddington ratiosabove 0.15, and in AGN with the Eddington ratio above 0.025. Our results favor theparameterization of the viscosity through the geometrical mean of the radiation andgas pressure both in Galactic sources and AGN. More examples of the quasi-regularoutbursts in the timescales of 100 seconds in Galactic sources, and hundreds of yearsin AGN are needed to formulate firm conclusions. We also show that the disk sizes inthe X-ray novae are consistent with the ionization instability. This instability may alsoconsiderably influence the lifetime cycle and overall complexity in the supermassiveblack hole environment.Keywords: physical processes:accretion; X-rays:binaries; galaxies: active – galaxies:evolution – galaxies
75 citations
06 Jan 2011
TL;DR: The Pi of the Sky (Pi-Sky) project as discussed by the authors is a system of robotic telescopes designed for observations of short timescale astrophysical phenomena, e.g. prompt optical GRB emissions.
Abstract: Pi of the Sky is a system of robotic telescopes designed for observations of short timescale astrophysical phenomena, e.g. prompt optical GRB emissions. The apparatus is designed to monitor a large fraction of the sky with 12–13 m range and time resolution of the order of 1–10 seconds. In October 2010 the first unit of the new Pi of the Sky detector system was successfully installed in the INTA El Arenosillo Test Centre in Spain. We also moved our prototype detector from Las Campanas Observatory to San Pedro de Atacama Observatory in March 2011. The status and performance of both detectors is presented.
6 citations
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TL;DR: In this paper, the authors introduce a type of Riemannian geometry in nine dimensions, which can be viewed as the counterpart of selfduality in four dimensions, and show how to construct self-dual 4-manifolds with totally antisymmetric torsion.
Abstract: We introduce a type of Riemannian geometry in nine dimensions, which can be viewed as the counterpart of selfduality in four dimensions. This geometry is related to a 9-dimensional irreducible representation of ${\bf SO}(3) \times {\bf SO} (3)$ and it turns out to be defined by a differential 4-form. Structures admitting a metric connection with totally antisymmetric torsion and preserving the 4-form are studied in detail, producing locally homogeneous examples which can be viewed as analogs of self-dual 4-manifolds in dimension nine.
2 citations