TY - THES A1 - Wendel, Christoph T1 - Bestimmung des hochenergetischen Spektrums des Crab-Pulsars anhand eines Outer Gap-Modells T1 - Determining the Gamma-Ray Spectrum of the Crab Pulsar through an Outer Gap Model N2 - Im Rahmen eines selbst-konsistenten Outer-Gap-Modells der Pulsar-Magnetosphäre wurde die elektromagnetische sehr hochenergetische Strahlung des Crab-Pulsars simuliert. Dies wurde parallel anhand zweier verschiedener Fälle getan, die sich in den angenommenen Gleichungen für die elektrische Feldstärke und für den Krümmungsradius der magnetischen Feldlinien unterscheiden. Die Kinetik der geladenen Teilchen bei ihrer Propagation durch die Outer Gap wurde unter Einbeziehung von Krümmungsstrahlung, inverser Compton-Streuung und Triple Paarbildung betrachtet. Das theoretisch simulierte Spektrum wird mit von Fermi-LAT und von den MAGIC Teleskopen gemessenen Daten verglichen. N2 - In a self-consistent model of outer vacuum gaps of pulsar magnetospheres, the gamma-ray output of the Crab pulsar is determined and compared to observational data by the Fermi Large Area Telescope and the Major Atmospheric Gamma-ray Imaging Cherenkov telescopes. Incorporating curvature radiation, inverse-Compton scattering and triplet pair production, the kinetics of the accelerated electrons are considered, energy losses are compared and the emerging spectra are computed. It is found that losses are dominated by curvature radiation emission. Triplet pair production may be relevant concerning particle multiplication and inverse-Compton up-scattering of the curvature photons is forming the spectral energy distribution at very high energies. KW - Neutronenstern KW - Crab-Nebel KW - Pulsar KW - Magnetosphäre KW - Synchrotronstrahlung KW - Krümmungsstrahlung KW - outer gap KW - Triplet Paar-Erzeugung Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257191 ER - TY - THES A1 - Maier, Andreas T1 - Adaptively Refined Large-Eddy Simulations of Galaxy Clusters T1 - Adaptiv verfeinerte Grobstruktursimulationen von Galaxienhaufen N2 - 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. N2 - Ziel dieser Arbeit war, ein neues numerisches Modell zu entwickeln, welches es ermöglicht Grobstruktursimulationen auch mit adaptiven Gittercodes auszuführen, um Turbulenz über große Längenskalenbereiche konsistent zu simulieren. KW - Turbulenz KW - Galaxienhaufen KW - Hydrodynamik KW - Numerische Strömungssimulation KW - LES KW - Computersimulation KW - Astrophysik KW - AMR KW - FEARLESS Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32274 ER - TY - JOUR A1 - Chatterjee, Koushik A1 - Chael, Andrew A1 - Tiede, Paul A1 - Mizuno, Yosuke A1 - Emami, Razieh A1 - Fromm, Christian A1 - Ricarte, Angelo A1 - Blackburn, Lindy A1 - Roelofs, Freek A1 - Johnson, Michael D. A1 - Doeleman, Sheperd S. A1 - Arras, Philipp A1 - Fuentes, Antonio A1 - Knollmüller, Jakob A1 - Kosogorov, Nikita A1 - Lindahl, Greg A1 - Müller, Hendrik A1 - Patel, Nimesh A1 - Raymond, Alexander A1 - Traianou, Efthalia A1 - Vega, Justin T1 - Accretion flow morphology in numerical simulations of black holes from the ngEHT model library: the impact of radiation physics JF - Galaxies N2 - In the past few years, the Event Horizon Telescope (EHT) has provided the first-ever event horizon-scale images of the supermassive black holes (BHs) M87* and Sagittarius A* (Sgr A*). The next-generation EHT project is an extension of the EHT array that promises larger angular resolution and higher sensitivity to the dim, extended flux around the central ring-like structure, possibly connecting the accretion flow and the jet. The ngEHT Analysis Challenges aim to understand the science extractability from synthetic images and movies to inform the ngEHT array design and analysis algorithm development. In this work, we compare the accretion flow structure and dynamics in numerical fluid simulations that specifically target M87* and Sgr A*, and were used to construct the source models in the challenge set. We consider (1) a steady-state axisymmetric radiatively inefficient accretion flow model with a time-dependent shearing hotspot, (2) two time-dependent single fluid general relativistic magnetohydrodynamic (GRMHD) simulations from the H-AMR code, (3) a two-temperature GRMHD simulation from the BHAC code, and (4) a two-temperature radiative GRMHD simulation from the KORAL code. We find that the different models exhibit remarkably similar temporal and spatial properties, except for the electron temperature, since radiative losses substantially cool down electrons near the BH and the jet sheath, signaling the importance of radiative cooling even for slowly accreting BHs such as M87*. We restrict ourselves to standard torus accretion flows, and leave larger explorations of alternate accretion models to future work. KW - black holes KW - general relativity KW - accretion KW - relativistic jets KW - very-long-baseline interferometry Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-304084 SN - 2075-4434 VL - 11 IS - 2 ER - TY - JOUR A1 - Kraus, Daniela A1 - Moucha, Annika A1 - Roth, Oliver T1 - A sharp Bernstein–type inequality and application to the Carleson embedding theorem with matrix weights JF - Analysis and Mathematical Physics N2 - We prove a sharp Bernstein-type inequality for complex polynomials which are positive and satisfy a polynomial growth condition on the positive real axis. This leads to an improved upper estimate in the recent work of Culiuc and Treil (Int. Math. Res. Not. 2019: 3301–3312, 2019) on the weighted martingale Carleson embedding theorem with matrix weights. In the scalar case this new upper bound is optimal. KW - Bernstein-type inequality KW - complex polynomials KW - Carleson embedding theorem Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-270485 SN - 1664-235X VL - 12 IS - 1 ER - TY - THES A1 - Schulz, Robert Frank T1 - A radio view of high-energy emitting AGNs T1 - Eine radioastronomische Betrachtung von hochenergetisch emittierenden AGNs N2 - The most energetic versions of active galactic nuclei (AGNs) feature two highly-relativistic plasma outflows, so-called jets, that are created in the vicinity of the central supermassive black hole and evolve in opposite directions. In blazars, which dominate the extragalactic gamma-ray sky, the jets are aligned close to the observer's line of sight leading to strong relativistic beaming effects of the jet emission. Radio observations especially using very long baseline interferometry (VLBI) provide the best way to gain direct information on the intrinsic properties of jets down to sub-parsec scales, close to their formation region. In this thesis, I focus on the properties of three AGNs, IC 310, PKS 2004-447, and 3C 111 that belong to the small non-blazar population of gamma-ray-loud AGNs. In these kinds of AGNs, the jets are less strongly aligned with respect to the observer than in blazars. I study them in detail with a variety of radio astronomical instruments with respect to their high-energy emission and in the context of the large samples in the monitoring programmes MOJAVE and TANAMI. My analysis of radio interferometric observations and flux density monitoring data reveal very different characteristics of the jet emission in these sources. The work presented in this thesis illustrates the diversity of the radio properties of gamma-ray-loud AGNs that do not belong to the dominating class of blazars. N2 - Die energetischsten Versionen von aktiven Galaxienkernen (AGNs) weisen zwei hoch-relativistische Plasmaausflüsse, sogenannte Jets auf, welche in der Nähe des zentralen supermassiven schwarzen Lochs entstehen und sich in entgegengesetzte Richtungen ausbreiten. In Blazaren, die die extragalaktische Gamma-Strahlung dominieren, sind diese Jets nahe zur Sichtlinie des Beobachters orientiert, das zu starkem relativistischen Beaming der Jetemission führt. Radiobeobachtungen vor allem mit Very Long Baseline Interferometry (VLBI) bieten die beste Möglichkeit direkt Informationen über die intrinsischen Eigenschaften von Jets in der Nähe ihrer Entstehungsregion auf sub-parsec Skalen zu sammeln. Der Fokus dieser Dissertation liegt auf den Eigenschaften von drei AGNs, IC 310, PKS 2004-447, and 3C 111, die zur kleinen Population von gamma-lauten AGNs abseits von Blazaren gehören. Diese Jets weisen einen etwas größeren Winkel zur Sichtlinie des Beobachters auf als Blazare. Ich untersuche diese AGNs im Detail mit Hilfe verschiedener radioastronomischer Instrumente in Bezug auf deren hochenergetischer Emission und im Vergleich der großen Samples der Langzeitbeobachtungsprogramme MOJAVE und TANAMI. Meine Analyse von Radiointerferometrie-Beobachtungen und Flussdichte-Messungen zeigen sehr unterschiedliche Eigenschaften der Jets. Damit verdeutlicht diese Arbeit anschaulich die vielfältigen Radioeigenschaften von gamma-lauten AGNs, die nicht zur dominierenden Klasse von Blazaren gehören. KW - Aktiver galaktischer Kern KW - Radioastronomie KW - Very long baseline interferometry KW - High-energy emission KW - Astrophysical Jet KW - Active galactic nucleus KW - Radio astronomy Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-137358 ER -