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Anisotropic and polarization-dependent gamma-ray absorption in relativistic jets

Blazars, a peculiar class of active galactic nuclei, are the most numerous class of gamma-ray sources detected by, e.g., Fermi-LAT and H.E.S.S. They emit across the entire electromagnetic spectrum, from radio waves to gamma-rays, and their emission is dominated by radiation originating from a relativistic jet, in which material is moving at an angle close to our line of sight, at a speed close to the speed of light. Gamma-rays emitted by these sources (as all gamma-rays) can be absorbed by interacting with lower-energy photons, producing an electron-positron pair (the inverse process of electron-positron pair annihilation). When considering this effect in blazars, it is usually assumed that, in the co-moving frame of the emission region moving along the jet, the distributions of radiating particles and their emission is isotropic, and polarization is ignored. However, the low-energy emission (which is the target on which gamma-rays can be absorbed) is synchrotron emission, which is (a) anisotropic if the magnetic field is orered, and (b) polarized. The task of this theoretical project to estimate the effects of this synchrotron anisotropy and polarization on the internal gamma-gamma absorption in blazar jets. The results will also be applicable to other relativistic jet sources, such as gamma-ray bursts.
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