Microlensing signatures in spectra of quasars: X-ray radiation

Gravitational microlensing is a very useful tool for investigating the innermost part of quasars, especially for studying a relativistic accretion disk around a massive black hole (BH) supposed to exist in the center of every quasar. Here we present a short overview of our recent investigations of the gravitational microlensing influence on detected X-ray radiation from accretion disks of quasars. We set our focus to the analysis of the Fe K alpha spectral line and the X-ray continuum variations due to gravitational microlensing. The disk emission was analyzed by numerical simulations, based on a ray-tracing method in a Kerr metric, taking into account only photon trajectories reaching the observer's sky plane. The influence of microlensing on a standard accretion disk was studied using three types of a microlensing model: point-like microlens, straight-fold caustic and quadruple microlens (microlensing pattern). Our results show that gravitational microlensing can produce significant variations and amplifications of the Fe Ka line and X-ray continuum flux and that even very small mass objects could produce such changes. These deformations of the X-ray radiation depend on both the disk and microlens parameters and they are significantly larger than the corresponding effects on the optical and UV emission lines and continua, due to the smaller dimensions of the X-ray emitting region. Although gravitational microlensing is an achromatic effect, it can induce wavelength dependent variations of the X-ray continuum.