Showing papers by "Eliot Quataert published in 1999"
TL;DR: In this paper, the authors calculate spectral models of advection-dominated accretion flows, taking into account the possibility that significant mass may be lost to an outflow/wind, and apply the models to the soft X-ray transient V404 Cyg in quiescence, the Galactic center source Sgr A*, and the nucleus of NGC 4649.
Abstract: We calculate spectral models of advection-dominated accretion flows, taking into account the possibility that significant mass may be lost to an outflow/wind. We apply the models to the soft X-ray transient V404 Cyg in quiescence, the Galactic center source Sgr A*, and the nucleus of NGC 4649. We show that there are qualitative degeneracies between the mass-loss rate in the wind and parameters characterizing the microphysics of the accretion flow; of particular importance is δ, the fraction of the turbulent energy which heats the electrons. For small δ, current observations suggest that at most 90% of the mass originating at large radii is lost to a wind, so that at least ~10% reaches the central object. For large δ ~ 0.3, however, models with significantly more mass loss are in agreement with the observations. We conclude by highlighting future observations which may clarify the importance of mass loss in sub-Eddington accretion flows.
268 citations
TL;DR: M81 and NGC 4579 are two of the few low-luminosity active galactic nuclei that have an estimated mass for the central black hole, detected hard X-ray emission, and detected optical/UV emission.
Abstract: M81 and NGC 4579 are two of the few low-luminosity active galactic nuclei that have an estimated mass for the central black hole, detected hard X-ray emission, and detected optical/UV emission. In contrast to the canonical "big blue bump," both have optical/UV spectra that decrease with increasing frequency in a nuLnu plot. Barring significant reddening by dust and/or large errors in the black hole mass estimates, the optical/UV spectra of these systems require that the inner edge of a geometrically thin, optically thick accretion disk lies at approximately 100 Schwarzschild radii. The observed X-ray radiation can be explained by an optically thin, two-temperature, advection-dominated accretion flow at smaller radii.
164 citations
01 Jan 1999
TL;DR: In binary star systems, consisting of two stars revolving around each other under the influence of their mutual gravitational attraction, black holes with masses of order several solar masses (M ~ 5 − 20M⊙) are thought to exist as the dead remnant of the initially more massive of the two stars as discussed by the authors.
Abstract: Astronomers have identified potential black holes in a variety of astrophysical objects. In binary star systems, consisting of two stars revolving around each other under the influence of their mutual gravitational attraction, black holes with masses of order several solar masses (M ~ 5 – 20M⊙) are thought to exist as the dead remnant of the initially more massive of the two stars.
20 citations
TL;DR: In this article, the authors calculate the proton distribution function due to heating by subsonic, Alfvenic turbulence in a weakly magnetized collisionless plasma and show that the distribution function is nonthermal.
Abstract: We calculate the proton distribution function due to heating by subsonic, Alfvenic turbulence in a weakly magnetized collisionless plasma. The distribution function is nonthermal. For nonrelativistic energies it is an exponential of the magnitude of the proton velocity. For ultrarelativistic energies, it can be characterized as a power law with a momentum-dependent slope. We briefly discuss the implications of this work for gamma-ray emission (via pion decay) from hot accretion flows.
17 citations
01 Jan 1999
TL;DR: In binary star systems, consisting of two stars revolving around each other under the influence of their mutual gravitational attraction, black holes with masses of order several solar masses (M ~ 5 − 20M⊙) are thought to exist as the dead remnant of the initially more massive of the two stars.
Abstract: Astronomers have identified potential black holes in a variety of astrophysical objects. In binary star systems, consisting of two stars revolving around each other under the influence of their mutual gravitational attraction, black holes with masses of order several solar masses (M ~ 5 – 20M⊙) are thought to exist as the dead remnant of the initially more massive of the two stars.
2 citations