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A New Model of the Gravitational Lens 0957+561 and a Limit on the Hubble Constant
Norman A. Grogin, Ramesh Narayan
We present a simple mass model for the lensing galaxy in the gravitationally lensed quasar 0957+561. The model is a generalization of the singular isothermal sphere and includes a…
Are There MeV Gamma-Ray Bursts?
Tsvi Piran, Ramesh Narayan
It is often stated that gamma-ray bursts (GRBs) have typical energies of several hundred keV. Is this a real feature of GRBs or is it due to an observational bias? We consider the…
Advection-Dominated Accretion Flows: Optically Thin Solutions
Ramesh Narayan
General properties of advection-dominated accretion flows are discussed. Special emphasis is given to the optically thin branch of solutions, which has very high ion and electron t…
Advection-Dominated Models of Luminous Accreting Black Holes
Ramesh Narayan
It has been found that a class of optically-thin two-temperature advection-dominated accretion solutions explains many observations of low-luminosity accreting black holes. Here it…
Advection-Dominated Accretion Model of Sagittarius A and Other Accreting Black Holes
Ramesh Narayan, Insu Yi, Rohan Mahadevan
Viscous rotating accretion flows around black holes become advection-dominated when the accretion rate is sufficiently low. Most of the accretion energy in such flows is s…
Models of Quiescent Black Hole Neutron Star Soft X-Ray Transients
Insu Yi, Ramesh Narayan, Didier Barret +1
When the mass accretion rate onto a black hole (BH) falls below a critical rate, , accretion can occur via a hot optically thin flow where m…
Accretion Flows Around Black Holes
Ramesh Narayan
Most accreting black holes emit a substantial fraction of their luminosity in hard X-rays/soft -rays of up to keV. The observations suggest that the rad…
A New Model for Black Hole Soft X-ray Transients in Quiescence
Ramesh Narayan, Jeffrey E. McClintock, Insu Yi
We present models of the soft X-ray transients, A0620-00, V404 Cyg, and X-ray Nova Mus 1991, in quiescence. In each source, we postulate that there is an outer region, extending ou…
The lens parallax method: determining redshifts of faint blue galaxies through gravitational lensing
Matthias Bartelmann, Ramesh Narayan
We propose a new technique, which we call the lens parallax method, to determine simultaneously the redshift distribution of the faint blue galaxies and the mass distributions of f…
Unified Description of Accretion Flows Around Black Holes
Xingming Chen, Marek A. Abramowicz, Jean-Pierre Lasota +2
We provide a unified description of thermal equilibria of black hole accretion disks, including the newly-discovered advection-dominated solutions. We classify the solutions on the…
TURBULENCE IN MOLECULAR CLOUDS
John Dubinski, Ramesh Narayan, T. G. Phillips
We generate random Gaussian turbulent velocity fields with a Kolmogorov spectrum and use these to obtain synthetic line-of-sight velocity profiles. The profiles are found to be sim…