Time delay induced by plasma in strong lens systems

Abstract

If the gravitational lens is surrounded by non-homoheneous plasma, in addition to the vacuum gravitational deflection, chromatic refraction occurs. Also, the speed of signal propagation decreases compared to vacuum. In this article, we investigate analytically the time delay in the case of gravitational lensing in plasma, focusing on strong lens systems. We take into account the following contributions: geometric delay due to trajectory bending in the presence of both gravity and plasma; potential delay of the ray in the gravitational field of the lens; dispersion delay in the plasma due to decrease of speed of light signal in the medium. We consider singular isothermal sphere as a model of gravitational lens, and arbitrary spherically symmetric distribution of surrounding plasma. For this scenario, plasma corrections for the time delay between two images are found in compact analytical form convenient for estimates.

Ray tracing through absorbing dielectric media in the Schwarzschild spacetime

“…The microlensing calculation proceeds generally following the approach outlined in the work of Tsupko and Bisnovatyi-Kogan [1,2,12,39,49,57,58]. We will review the general features of the calculation here.…”

“…Describing the path of rays through these regions requires an understanding of optics in both curved spacetime and dielectric materials [8][9][10]. On this front, there has been a substantial amount of investigation into relativistic ray tracing around massive objects such as black holes and neutron stars immersed within a cold plasma medium [2,[11][12][13]. There have also been studies on the optical effects of plasma on hypothetical exotic objects and within modified theories of gravity [14][15][16].…”