@phdthesis{Glawion2014,
  author    = {Glawion, Dorit},
  title     = {Contemporaneous Multi-Wavelength Observations of the Gamma-Ray Emitting Active Galaxy IC 310 - New Clues on Particle Acceleration in Extragalactic Jets},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-113866},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {In this thesis, the broad band emission, especially in the gamma-ray and radio band, of the active galaxy IC 310 located in the Perseus cluster of galaxies was investigated. The main experimental methods were Cherenkov astronomy using the MAGIC telescopes and high resolution very long baseline interferometry (VLBI) at radio frequencies (MOJAVE, EVN). Additionally, data of the object in different energy bands were studied and a multi-wavelength campaign has been organized and conducted. During the campaign, an exceptional bright gamma-ray flare at TeV energies was found with the MAGIC telescopes. The results were compared to theoretical acceleration and emission models for explaining the high energy radiation of active galactic nuclei. Many open questions regarding the particle acceleration to very high energies in the jets of active galactic nuclei, the particle content of the jets, or how the jets are launched, were addressed in this thesis by investigating the variability of IC 310 in the very high energy band. It is argued that IC310 was originally mis-classified as a head-tail radio galaxy. Instead, it shows a variability behavior in the radio, X-ray, and gamma-ray band similar to the one found for blazars. These are active galactic nuclei that are characterized by flux variability in all observed energy bands and at all observed time scales. They are viewed at a small angle between the jet axis and the line-of-sight. Thus, strong relativistic beaming influences the variability properties of blazars. Observations of IC 310 with the European VLBI Network helped to find limits for the angle between the jet axis and the line-of-sight, namely 10 deg - 20 deg. This places IC 310 at the borderline between radio galaxies (larger angles) and blazars (smaller angles). During the gamma-ray outburst detected at the beginning of the multi-wavelength campaign, flux variability as short as minutes was measured. The spectrum during the flare can be described by a simple power-law function over two orders of magnitude in energy up to ~10 TeV. Compared to previous observations, no significant variability of the spectral shape was found. Together with the constraint on the viewing angle, this challenges the currently accepted models for particle acceleration at shock waves in the jets. Alternative models, such as stars moving through the jets, mini-jets in the jet caused, e.g., by reconnection events, or gap acceleration in a pulsar-like magnetosphere around the black hole were investigated. It was found that only the latter can explain all observational findings, which at least suggests that it could even be worthwhile to reconsider published investigations of AGN with this new knowledge in mind. The first multi-wavelength campaign was successfully been conducted in 2012/2013, including ground-based as well as space-based telescopes in the radio, optical, ultraviolet, X-ray, and gamma-ray energy range. No pronounced variability was found after the TeV flare in any energy band. The X-ray data showed a slightly harder spectrum when the emission was brighter. The long-term radio light curve indicated a flickering flux variability, but no strong hint for a new jet component was found from VLBI images of the radio jet. In any case, further analysis of the existing multi-wavelength data as well as complimentary measurements could provide further exciting insights, e.g., about the broad band spectral energy distribution. Overall, it can be stated that IC 310 is a key object for research of active galactic nuclei in the high-energy band due to its proximity and its peculiar properties regarding flux variability and spectral behavior. Such objects are ideally suited for studying particle acceleration, jet formation, and other physical effects and models which are far from being fully understood.},
  subject      = {Aktiver galaktischer Kern},
  language  = {en}
}
@phdthesis{Ruegamer2012,
  author    = {R{\"u}gamer, Stefan},
  title     = {Multi-Wavelength Observations of the high-peaked BL Lacertae objects 1ES 1011+496 and 1ES 2344+514},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-77846},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2012},
  abstract  = {BL Lacertae objects belong to the most luminous sources in the Universe. They represent a subclass of active galactic nuclei with a spectrum that is dominated by non-thermal emission, extending from radio wavelengths to tera electronvolt (TeV) energies. The emission is strongly variable on time scales of years down to minutes, and arises from relativistic jets pointing at small angles to the line of sight of the observer, which is the reason for naming them "blazars". Blazars are the dominant extragalactic source class in the radio, microwave and gamma-ray regime, are prime candidates for the origin of the Cosmic Rays and excellent laboratories to study black hole and jet physics as well as relativistic effects. Despite more than 20 years of observational efforts, the physical mechanisms driving their emission are not yet fully understood. So far, studies of their broad-band continuum emission were mostly concentrated on bright, flaring states. However, for a better understanding of the central engine powering the jets, the bias from flux-limited observations of the past must be overcome and their long-term average continuum spectral energy distributions (SEDs) must be determined. This work presents the first simultaneous multi-wavelength campaigns from the radio to the TeV regime of two high-frequency peaked BL Lacertae objects known to emit at TeV energies. The first source, 1ES 1011+496, was observed between February and May 2008, the second one, 1ES 2344+514, between September 2008 and February 2009. The extensive observational campaigns were organised independently from an external trigger for the presence of a flaring state. Since the duty cycle of major flux outbursts is known to be rather low, the campaigns were expected to yield SEDs representative of the long-term average emission. Central for this thesis is the analysis of data obtained with the MAGIC Cherenkov telescope, measuring energy spectra and light curves from ~0.1 to ~10 TeV. For the remaining instruments, observation time was proposed and additional data was organised by collaboration with the instrument teams by the author of this work. Such data was obtained mostly in a fully reduced state. Individual light curves are investigated as well as combined in a search for inter-band correlations. The data of both sources reveal a notable lack of a correlation between the emission at radio and optical wavelengths, indicating that the radio and short-wavelength emission arise in different regions of the jet. Quasi-simultaneous SEDs of two different flux states are observationally determined and described by a one-zone as well as a self-consistent two-zone synchrotron self-Compton model. First approaches to model the SEDs by means of a Chi2 minimisation technique are briefly discussed. The SEDs and the resulting model parameters, characterising the physical conditions in the emission regions, are compared to archival data. Though the models can describe the data well, for 1ES 1011+496 the model parameters indicate that in addition to the synchrotron and inverse-Compton emission of relativistic electrons, emission due to accelerated protons seems to be required. The SEDs of 1ES 2344+514 reveal one of the lowest activity states ever detected from the source. Despite that, the model parameters are not indicative of a distinct quiescent state, which may be caused by the degeneracy of the different parameters in one-zone models. Moreover, indications accumulate that the radiation can not be attributed to a single emission region. The results disfavour some of the current blazar classification schemes and the so-called "blazar sequence", emphasising the need for a more realistic explanation of the systematics of the blazar SEDs in terms of fundamental parameters.},
  subject      = {Blazar},
  language  = {en}
}