Engineering topics

Kovner, Israel

Publications and source records attributed to Kovner, Israel.

3 records

NASA NTRS1991

Bounds on intergalactic compact objects from observations of compact radio sources

The constraints that can be imposed on the cosmic density of uniformly distributed intergalactic compact objects in the mass range of 10 million to 1 billion solar masses, using VLBI observations of compact radio sources. A compact object at a sufficiently small angular separation from a compact radio source produces a deamplified and inverted secondary image. No such cases are known. Using published maps of compact radio sources and assuming an Einstein-de Sitter cosmology, a density parameter for mass in this range greater than 0.4 is excluded at the 99.7 percent confidence level. Observations using the VLBA should allow one to exclude or discover a density parameter greater than about 0.001 for compact objects in the mass range of 0.1-100 solar masses.

Kassiola, Aggeliki↗

NASA NTRS1988

Supernovae in luminous arcs

The giant luminous arcs seem to be images of galaxies distorted by foreground clusters acting as gravitational lenses, with galaxies close to the cusps of gravitational lens caustic. The part of a galaxy located inside a cusp has three images of itself within an arc. The arcs are very blue, so the galaxies may be in a stage of active star formation with supernovae exploding every few years. If a supernova goes off inside a cusp it will be observed thrice, at three positions. The apparent magnitudes of the supernovae images may be M(R) roughly 20-23. The arrival time differences between the images can be as short as a few weeks or even days, whereas for ordinary lenses on a cluster scale the differences can be decades to centuries. Simple relations between the ratios of the arrival time differences, magnifications, and image separations are predicted.

Kovner, Israel↗

NASA NTRS1987

The quadrupole gravitational lens

An asymmetric lens made of a spherically symmetric galaxy and a quadrupole tidal part allows a very simple pictorial examination of the multiplicity and positions of the images, for any mass density profile. The lens equations can be reduced to one equation in one variable. In the special case of a singular isothermal sphere with a tide (SIST), the lens properties are described by five parameters. Two parameters determine the angular scale and orientation, while three determine the configuration of the images. A comprehensive investigation of the SIST lens is performed, including the variation of the configurations with the parameter values, the critical surfaces in the parameter space, and the extremal solutions. Analytic expressions are derived for the SIST parameters, and additional image positions, in the case when the intensity ratio and positions relative to the galaxy for two of the images are given as input. Quadrupole lenses with a point mass and a pseudoisothermal sphere as the main part are also described in terms of direction diagrams. A direct relation between deflection profile and rotational velocity is derived.

Kovner, Israel↗