@phdthesis{HoehneMoench2010,
  author    = {H{\"o}hne-M{\"o}nch, Daniel},
  title     = {Steady-state emission of blazars at very high energies},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-53700},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {One key scientific program of the MAGIC telescope project is the discovery and detection of blazars. They constitute the most prominent extragalactic source class in the very high energy (VHE) Gamma-ray regime with 29 out of 34 known objects (as of April 2010). Therefore a major part of the available observation time was spent in the last years on high-frequency peaked blazars. The selection criteria were chosen to increase the detection probability. As the X-ray flux is believed to be correlated to the VHE Gamma-ray flux, only X-ray selected sources with a flux F(X) > 2 μJy at 1 keV were considered. To avoid strong attenuation of the Gamma-rays in the extragalactic infrared background, the redshift was restricted to values between z < 0.15 and z < 0.4, depending on the declination of the objects. The latter determines the zenith distance during culmination which should not exceed 30° (for z < 0.4) and 45° (for z < 0.15), respectively. Between August 2005 and April 2009, a sample of 24 X-ray selected high-frequency peaked blazars has been observed with the MAGIC telescope. Three of them were detected including 1ES 1218+304 being the first high-frequency peaked BL Lacertae object (HBL) to be discovered with MAGIC in VHE Gamma-rays. One previously detected object was not confirmed as VHE emitter in this campaign by MAGIC. A set of 20 blazars previously not detected will be treated more closely in this work. In this campaign, during almost four years ~ 450 hrs or ~ 22\% of the available observation time for extragalactic objects were dedicated to investigate the baseline emission of blazars and their broadband spectral properties in this emission state. For the sample of 20 objects in a redshift range of 0.018 < z < 0.361 integral flux upper limits in the VHE range on the 99.7\% confidence level (corresponding to 3 standard deviations) were calculated resulting in values between 2.9\% and 14.7\% of the integral flux of the Crab Nebula. As the distribution of significances of the individual objects shows a clear shift to positive values, a stacking method was applied to the sample. For the whole set of 20 objects, an excess of Gamma-rays was found with a significance of 4.5 standard deviations in 349.5 hours of effective exposure time. For the first time a signal stacking in the VHE regime turned out to be successful. The measured integral flux from the cumulative signal corresponds to 1.4\% of the Crab Nebula flux above 150 GeV with a spectral index α = -3.15±0.57. None of the objects showed any significant variability during the observation time and therefore the detected signal can be interpreted as the baseline emission of these objects. For the individual objects lower limits on the broad-band spectral indices αX-Gamma between the X-ray range at 1 keV and the VHE Gamma-ray regime at 200 GeV were calculated. The majority of objects show a spectral behaviour as expected from the source class of HBLs: The energy output in the VHE regime is in general lower than in X-rays. For the stacked blazar sample the broad-band spectral index was calculated to αX-Gamma = 1.09, confirming the result found for the individual objects. Another evidence for the revelation of the baseline emission is the broad-band spectral energy distribution (SED) comprising archival as well as contemporaneous multi-wavelength data from the radio to the VHE band. The SEDs of known VHE Gamma-ray sources in low flux states matches well the SED of the stacked blazar sample.},
  subject      = {MAGIC-Teleskop},
  language  = {en}
}
@phdthesis{Paul2010,
  author    = {Paul, Surajit},
  title     = {Evolution of shocks and turbulence in major galaxy-cluster mergers},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-47266},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {Mergers between rich clusters of galaxies represent the most violent events in the Universe. The merger events initiate a complex chain of processes that leads to the dissipation of the collisional energy. This phase of violent relaxation is accompanied by turbulence and shock waves as well as non-thermal particle acceleration. This thesis aims at the interpretation of multi-wavelength observations of the merging cluster of galaxies Abell 3376 in the framework of a theoretical model of the involved effects. Observations with the Very Large Array radio interferometer were carried out and analyzed to clarify the morphology of the non-thermal particle distribution in Abell 3376, in particular about the shocked regions. The dissipation in the hot intra-cluster gas was studied using archival X-ray observations with ROSAT and XMM. Results were compared with constrained numerical simulations of the evolution of the merger process in the framework of cosmological structure formation. For this purpose, the ENZO-Code was employed for the computation of the gas dynamics and self-gravity of the colliding mass distribution. The non-thermal properties of the intra-cluster gas could be indirectly inferred from the local Mach number and the strength of the turbulence.},
  subject      = {Galaxienhaufen},
  language  = {en}
}
@phdthesis{Maier2008,
  author    = {Maier, Andreas},
  title     = {Adaptively Refined Large-Eddy Simulations of Galaxy Clusters},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-32274},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {It is aim of this work to develop, implement, and apply a new numerical scheme for modeling turbulent, multiphase astrophysical flows such as galaxy cluster cores and star forming regions. The method combines the capabilities of adaptive mesh refinement (AMR) and large-eddy simulations (LES) to capture localized features and to represent unresolved turbulence, respectively; it will be referred to as Fluid mEchanics with Adaptively Refined Large-Eddy SimulationS or FEARLESS.},
  subject      = {Turbulenz},
  language  = {en}
}
@phdthesis{Hupp2008,
  author    = {Hupp, Markus},
  title     = {Simulating Star Formation and Turbulence in Models of Isolated Disk Galaxies},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-34510},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {We model Milky Way like isolated disk galaxies in high resolution three-dimensional hydrodynamical simulations with the adaptive mesh refinement code Enzo. The model galaxies include a dark matter halo and a disk of gas and stars. We use a simple implementation of sink particles to measure and follow collapsing gas, and simulate star formation as well as stellar feedback in some cases. We investigate two largely different realizations of star formation. Firstly, we follow the classical approach to transform cold, dense gas into stars with an fixed efficiency. These kind of simulations are known to suffer from an overestimation of star formation and we observe this behavior as well. Secondly, we use our newly developed FEARLESS approach to combine hydrodynamical simulations with a semi-analytic modeling of unresolved turbulence and use this technique to dynamically determine the star formation rate. The subgrid-scale turbulence regulated star formation simulations point towards largely smaller star formation efficiencies and henceforth more realistic overall star formation rates. More work is necessary to extend this method to account for the observed highly supersonic turbulence in molecular clouds and ultimately use the turbulence regulated algorithm to simulate observed star formation relations.},
  subject      = {Astrophysik},
  language  = {en}
}