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Diffusive Shock Acceleration in Radiation Dominated Environments


Vannoni,  Giulia
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Vannoni, G. (2008). Diffusive Shock Acceleration in Radiation Dominated Environments. PhD Thesis, Ruprecht-Karls Universität, Heidelberg, Germany.

In this work I describe a numerical method developed, for the first time, for the study of Diffusive Shock Acceleration in astrophysical environments where the radiation pressure dominates over the magnetic pressure. This work is motivated by the overwhelming evidence of the acceleration of particles to high energy in astrophysical objects, traced by the non- thermal radiation they emit due to interactions with the gas, radiation fields and magnetic fields. The main objective of this work is to create a generic framework to study self--consistently the interaction of acceleration at shocks and radiative energy losses and the effect such an interplay has on the particle spectrum and on the radiation they emit, in the case when energy losses determine the maximum achievable energy. I apply the developed method to electrons accelerated in three different types of sources: a Supernova Remnant in the Galactic Centre region, a microquasar, and a galaxy cluster. In all three cases the energy losses due to the interaction of electrons with radiation dominate over synchrotron cooling. I demonstrate that there is a strong impact due to the changing features of the inverse Compton scattering from the Thomson to the Klein-Nishina regime, on both the spectrum of accelerated electrons and their broadband emission. I also consider proton acceleration in galaxy clusters, where the particles lose energy during acceleration due to the interaction with the Cosmic Microwave Background radiation. The secondary products from pair production and photomeson processes interact with the same photon field and the background magnetic field, producing broadband electromagnetic radiation from radio to gamma-rays.