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Event correlation analysis of the Galactic Centre region


Marx,  Ramin
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;
Université Pierre et Marie Curie, Paris (UPMC);

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Marx, R. (2012). Event correlation analysis of the Galactic Centre region. Master Thesis, Université Pierre et Marie Curie, Paris, France.

In order to investigate cosmic particle accelerators, like fast rotating neutron stars or supernova remnants, the very-high-energy (VHE: E > 100 GeV) γ-radiation generated during these processes is detected by imaging atmospheric Cherenkov telescopes (IACTs). With the H.E.S.S. telescopes, which are an array of four such IACTs located in Namibia, many data sets have already been collected and particularly the Galactic plane has been observed extensively. In the Galactic Centre region, it has detected two strong point sources (G 0.9+0.1 and Sagittarius A*) and an extended band of diffuse emission, located at the position of the giant molecular cloud in the Galactic Centre. In this work H.E.S.S. data from the Galactic Centre region is analyzed with an event correlation method in order to find out if there are populations of weak sources that cannot be detected individually by classical methods. First, the event correlation method is compared to the ring background method and then, it is verified in Monte Carlo simulations. For the generation of the required null hypothesis maps different methods that randomize the data at small scales are explained and analyzed. The findings of the simulations then tell how strongly the data may be randomized without changing the large-scale distributions and how many point sources and how many events per source there would have to be in the data in order to get detected. According to the correlation analysis, there are no small-scale anisotropies in the event distribution, which means that the VHE γ-radiation from the Galactic Centre region (minus the emission from Sagittarius A* and G 0.9+0.1) is consistent with diffuse emission only.