Astroparticle Physics:
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Project leader: Olaf Reimer
Institute of Astro and Particle Physics
We offer the following two thesis topics:
- Numerical modeling of galactic diffuse gamma-ray emission processes using a structured model of the Milky Way
- Particle cascades in air showers and imaging techniques for next-generation Cherekov telescopes
Astroparticle Physics:
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In this project it is expected (in collaboration with the Fermi working group DIFFUSE and the principal author of the GALPROP code, A.W. Strong, MPE Garching, Germany) to extend the widely-used cosmic ray propagation code GALPROP regarding a more realistic implementation of the geometrical model of our Milky Way. Whereas the numerical framework of the GALPROP-code could so far handle only a simple slab and halo approximation representing the geometry of our Galaxy, it is now realistic (in terms of computational resources) and indeed mandated (in terms of availability of more precise astrophysical data to confront the model prediction) to consider the spiral-arm geometry of our Galaxy when solving the diffusion-convection equation for the transport and propagation of charged and neutral cosmic rays. Particularly the incoming data from the Fermi Gamma-ray Space Telescope will constrain the propagation of the charged particles, making high-energy gamma-ray observations a most sensitive test for testing model predictions regarding cosmic ray spectra and abundances, secondary / primary ratios, and radio survey data to constrain the cosmic ray propagation problem. Additionally, given the recent success of detecting cosmic accelerators at TeV energies by instruments like H.E.S.S. and MAGIC, the so far only assumed distribution of galactic particle accelerators can be put to test with a realistic spatial model of SNR and / or PSR / PWN indeed seen to accelerate particles to energies up to 1015 eV in our Galaxy. Finally, the role of plasma physics for characterizing the transport of cosmic rays in presence of interstellar magnetic fields will be investigated. MHD turbulence will change the conditions of particle transport and introduce non-linear effects to the diffusion of charged cosmic rays – and warrants to incorporate plasma-wave interactions into the current framework of modelling cosmic ray propagation.
Astroparticle Physics:
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With ongoing refinement of the measurements of the charged particle and gamma-ray spectra, air shower Monte-Carlo codes are expected to be adapted for application to the new generation of Imaging Atmospheric Cherenkov telescopes (IACTs). In this project a contemporary air shower code (CORSICA) for applicability regarding gamma / hadron separation and imaging capabilities for low-threshold telescopes like H.E.S.S. 2 or CTA will be tested. Special emphasis will be given to new methods to distinguish air shower primary particles by their different first interaction point in the atmosphere, e.g. random forest techniques. This technique has been successfully used to study iron-like showers and for measuring the cosmic ray electron spectrum at TeV energies with H.E.S.S. Particularly challenging are advanced pattern recognition techniques in low-threshold IACTs camera images given the absence of fully-developed air shower signatures / footprints in highly pixelized Cherekov imaging cameras near energy threshold. This will be studied using state-of-the-art air shower cascading codes for particles entering the Earth atmosphere and realistic geometry models for, e.g. the soon-to-be-commissioned H.E.S.S. 2 telescope and camera as well as the telescopes studied for the next-generation CTA observatory. Adequate Monte-Carlo simulations correspond to a variety of possible systematic effects (statistical fluctuations in the shower development, different atmospheric conditions, partial shower images in the camera, and physics implementation limits in current high-energy particle interaction models), which are to be investigated. This will constitute a solid foundation for any subsequent investigation of cosmic particle accelerators up to 1015 eV with the new generation IACTs being built now and over the next years.