Adam Rogers

Frequency-dependent effects of gravitational lensing within plasma

The interaction between refraction from a distribution of inhomogeneous plasma and gravitational lensing introduces novel effects to the paths of light rays passing by a massive object. The plasma contributes additional terms to the equations of motion, and the resulting ray trajectories are frequency–dependent. Lensing phenomena and circular orbits are investigated for plasma density distributions N / 1/r h with h � 0 in the Schwarzschild space–time. For rays passing by the mass near the plasma frequency refractive effects can dominate, effectively turning the gravitational lens into a mirror. We obtain the turning points, circular orbit radii, and angular momentum for general h. Previous results have shown that light rays behave like massive particles with an effective mass given by the plasma frequency for a constant density h = 0. We study the behaviour for general h and show that when h = 2 the plasma term acts like an additional contribution to the angular momentum of the passing ray. When h = 3 the potential and radii of circular orbits are analogous to those found in studies of massless scalar fields on the Schwarzschild background. As a physically motivated example we study the pulse profiles of a compact object with antipodal hotspots sheathed in a dense plasma, which shows dramatic frequency–dependent shifts from the behaviour in vacuum. Finally, we consider the potential observability and applications of such frequency–dependent plasma effects in general relativity for several types of neutron star.

Escape and trapping of low-frequency gravitationally lensed rays by compact objects within plasma

We consider the gravitational lensing of rays emitted by a compact object (CO) within a distribution of plasma with power-law density

Two families of astrophysical diverging lens models

\propto r^{-h}

On the diversity of compact objects within supernova remnants – I. A parametric model for magnetic field evolution

. For the simplest case of a cloud of spherically symmetric cold non-magnetized plasma, the diverging effect of the plasma and the converging effect of gravitational lensing compete with one another. When

Global Optimization Methods for Gravitational Lens Systems with Regularized Sources

h<2

STRONG GRAVITATIONAL LENS MODELING WITH SPATIALLY VARIANT POINT-SPREAD FUNCTIONS

, the plasma effect dominates over the vacuum Schwarzschild curvature, potentially shifting the radius of the unstable circular photon orbit outside the surface of the CO. When this occurs, we define two relatively narrow radio-frequency bands in which plasma effects are particularly significant. Rays in the escape window have

The inertia tensor of a magic cube

\omega_{0} < \omega \leq \omega_{+}

The electric multipole expansion for a magic cube

and are free to propagate to infinity from the CO surface. To a distant observer, the visible portion of the CO surface appears to shrink as the observed frequency is reduced, and vanishes entirely at

GRAVITATIONAL LENS MODELING WITH GENETIC ALGORITHMS AND PARTICLE SWARM OPTIMIZERS

\omega_{0}

On the Diversity of Compact Objects within Supernova Remnants II: Energy Loss Mechanisms

, in excess of the plasma frequency at the CO surface. We define the anomalous propagation window for frequencies