@article{GonzalezDornerBretzetal.2019, author = {Gonz{\´a}lez, Mar{\´i}a Magdalena and Dorner, Daniela and Bretz, Thomas and Garc{\´i}a-Gonz{\´a}lez, Jos{\´e} Andr{\´e}s}, title = {Unbiased long-term monitoring at TeV energies}, series = {Galaxies}, volume = {7}, journal = {Galaxies}, number = {2}, issn = {2075-4434}, doi = {10.3390/galaxies7020051}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-197389}, year = {2019}, abstract = {For the understanding of the variable, transient and non-thermal universe, unbiased long-term monitoring is crucial. To constrain the emission mechanisms at the highest energies, it is important to characterize the very high energy emission and its correlation with observations at other wavelengths. At very high energies, only a limited number of instruments is available. This article reviews the current status of monitoring of the extra-galactic sky at TeV energies.}, language = {en} } @phdthesis{Lange2012, author = {Lange, Sebastian}, title = {Turbulenz und Teilchentransport in der Heliosph{\"a}re - Simulationen von inkompressiblen MHD-Plasmen und Testteilchen -}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-74012}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2012}, abstract = {Die Herkunft hochenergetischer solarer Teilchen konnte in den vergangenen Jahren eindeutig auf Schockbeschleunigung an koronalen Masseausw{\"u}rfen zur{\"u}ckgef{\"u}hrt werden. Durch resonante Interaktionen zwischen Wellen und Teilchen werden zum einen geladene Teilchen unter Ver{\"a}nderung ihrer Energie gestreut, zum anderen wird die Dynamik der Plasmawellen in solchen Beschleunigungsregionen durch diese Prozesse von selbstgenerierten Wellenmoden maßgeblich beeinflusst. Mittels numerischer Modellierungen wurden im Rahmen dieser Arbeit die grundlegenden physikalischen Regimes der Turbulenz und des Teilchentransports beschrieben. Die Simulation der Plasmadynamik bedient sich der Methodik der Magnetohydrodynamik, wohingegen kinetische Einzelteilchen durch die elementaren Bewegungsgleichungen der Elektrodynamik berechnet werden. Es konnten die Turbulenztheorien von Goldreich und Sridhar unter heliosph{\"a}rischen Bedingungen bei drei solaren Radien best{\"a}tigt werden. Vor allem zeigten sich Hinweise f{\"u}r das Erreichen der kritischen Balance, einem Schl{\"u}sselparameter dieser Theorien. Weiterhin werden Ergebnisse der dynamischen Entwicklung angeregter Wellenmoden pr{\"a}sentiert, in denen die Bedeutsamkeit f{\"u}r die gesamte Turbulenz gezeigt werden konnte. Als zentraler Prozess bei hohen Energien hat sich das wave-steepening herausgestellt, das als effizienter Energietransportmechanismus in paralleler Richtung zum Hintergrundmagnetfeld identifiziert wurde und somit turbulente Strukturen bei hohen parallelen Wellenzahlen erkl{\"a}rt, deren Entstehung das Goldreich-Sridhar Modell nicht beschreiben kann. Dar{\"u}ber hinaus wurden grundlegende Erkenntnisse {\"u}ber die quasilineare Theorie des Teilchentransports erzielt. Im Speziellen konnte ein tieferes Verst{\"a}ndnis f{\"u}r die Interpretation der Diffusionskoeffizienten von Welle-Teilchen Wechselwirkungen erlangt werden. Simulationen zur Streuung an angeregten Wellenmoden zeigten erstmals komplexe resonante Strukturen die im Rahmen analytischer Modelle nicht mehr ad{\"a}quat beschrieben werden k{\"o}nnen.}, subject = {Heliosph{\"a}re}, language = {de} } @phdthesis{Deppisch2004, author = {Deppisch, Frank}, title = {Towards a reconstruction of the SUSY seesaw model}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-12757}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2004}, abstract = {In this work, we studied in great detail how the unknown parameters of the SUSY seesaw model can be determined from measurements of observables at or below collider energies, namely rare flavor violating decays of leptons, slepton pair production processes at linear colliders and slepton mass differences. This is a challenging task as there is an intricate dependence of the observables on the unknown seesaw, light neutrino and mSUGRA parameters. In order to separate these different influences, we first considered two classes of seesaw models, namely quasi-degenerate and strongly hierarchical right-handed neutrinos. As a generalisation, we presented a method that can be used to reconstruct the high energy seesaw parameters, among them the heavy right-handed neutrino masses, from low energy observables alone.}, subject = {Supersymmetrie}, language = {en} } @article{RoelofsBlackburnLindahletal.2023, author = {Roelofs, Freek and Blackburn, Lindy and Lindahl, Greg and Doeleman, Sheperd S. and Johnson, Michael D. and Arras, Philipp and Chatterjee, Koushik and Emami, Razieh and Fromm, Christian and Fuentes, Antonio and Knollm{\"u}ller, Jakob and Kosogorov, Nikita and M{\"u}ller, Hendrik and Patel, Nimesh and Raymond, Alexander and Tiede, Paul and Traianou, Efthalia and Vega, Justin}, title = {The ngEHT analysis challenges}, series = {Galaxies}, volume = {11}, journal = {Galaxies}, number = {1}, issn = {2075-4434}, doi = {10.3390/galaxies11010012}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-304976}, year = {2023}, abstract = {The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased uv-coverage, sensitivity, and frequency coverage allow a wide range of new science opportunities to be explored. The ngEHT Analysis Challenges have been launched to inform the development of the ngEHT array design, science objectives, and analysis pathways. For each challenge, synthetic EHT and ngEHT datasets are generated from theoretical source models and released to the challenge participants, who analyze the datasets using image reconstruction and other methods. The submitted analysis results are evaluated with quantitative metrics. In this work, we report on the first two ngEHT Analysis Challenges. These have focused on static and dynamical models of M87* and Sgr A* and shown that high-quality movies of the extended jet structure of M87* and near-horizon hourly timescale variability of Sgr A* can be reconstructed by the reference ngEHT array in realistic observing conditions using current analysis algorithms. We identify areas where there is still room for improvement of these algorithms and analysis strategies. Other science cases and arrays will be explored in future challenges.}, language = {en} } @phdthesis{Nuernberger2004, author = {N{\"u}rnberger, Dieter}, title = {The Galactic Starburst Region NGC 3603 : exciting new insights on the formation of high mass stars}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-10440}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2004}, abstract = {One of the most fundamental, yet still unsolved problems in star formation research is addressed by the question "How do high mass stars form?". While most details related to the formation and early evolution of low mass stars are quite well understood today, the basic processes leading to the formation of high mass stars still remain a mystery. There is no doubt that low mass stars like our Sun form via accretion of gas and dust from their natal environment. With respect to the formation of high mass stars theorists currently discuss two possible scenarios controversely: First, similar to stars of lower masses, high mass stars form by continuous (time variable) accretion of large amounts of gas and dust through their circumstellar envelopes and/or disks. Second, high mass stars form by repeated collisions (coalescence) of protostars of lower masses. Both scenarios bear difficulties which impose strong constrains on the final mass of the young star. To find evidences for or against one of these two theoretical models is a challenging task for observers. First, sites of high mass star formation are much more distant than the nearby sites of low mass star formation. Second, high mass stars form and evolve much faster than low mass star. In particular, they contract to main sequence, hydrogen burning temperatures and densities on time scales which are much shorter than typical accretion time scales. Third, as a consequence of the previous point, young high mass stars are usually deeply embedded in their natal environment throughout their (short) pre-main sequence phase. Therefore, high mass protostars are rare, difficult to find and difficult to study. In my thesis I undertake a novel approach to search for and to characterize high mass protostars, by looking into a region where young high mass stars form in the violent neighbourhood of a cluster of early type main sequence stars. The presence of already evolved O type stars provides a wealth of energetic photons and powerful stellar winds which evaporate and disperse the surrounding interstellar medium, thus "lifting the courtains" around nearby young stars at a relatively early evolutionary stage. Such premises are given in the Galactic starburst region NGC 3603. Nevertheless, a large observational effort with different telescopes and instruments -- in particular, taking advantage of the high angular resolution and high sensitivity of near and mid IR instruments available at ESO -- was necessary to achieve the goals of my study. After a basic introduction on the topic of (high mass) star formation in Chapter 1, a short overview of the investigated region NGC 3603 and its importance for both galactic and extragalactic star formation studies is given in Chapter 2. Then, in Chapter 3, I report on a comprehensive investigation of the distribution and kinematics of the molecular gas and dust associated with the NGC 3603 region. In Chapter 4 I thoroughly address the radial extent of the NGC 3603 OB cluster and the spatial distribution of the cluster members. Together with deep Ks band imaging data, a detailed survey of NGC 3603 at mid IR wavelengths allows to search the neighbourhood of the cold molecular gas and dust for sources with intrinsic mid IR excess (Chapter 5). In Chapter 6 I characterize the most prominent sources of NGC 3603 IRS 9 and show that these sources are bona-fide candidates for high mass protostars. Finally, a concise summary as well as an outlook on future prospects in high mass star formation research is given in Chapter 7.}, subject = {Starburst-Galaxie}, language = {en} } @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{Wendel2022, author = {Wendel, Christoph}, title = {Spectral Imprints from Electromagnetic Cascades in Blazar Jets}, doi = {10.25972/OPUS-29007}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-290076}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2022}, abstract = {The extragalactic gamma-ray sky is dominated by blazars, active galactic nuclei (AGN) with a relativistic jet that is closely aligned with the line of sight. Galaxies develop an active nucleus if the central supermassive black hole (BH) accretes large amounts of ambient matter and magnetic flux. The inflowing mass accumulates around the plane perpendicular to the accretion flow's angular momentum. The flow is heated through viscous friction and part of the released energy is radiated as blackbody or non-thermal radiation, with luminosities that can dominate the accumulated stellar luminosity of the host galaxy. A fraction of the accretion flow luminosity is reprocessed in a surrounding field of ionised gas clouds. These clouds, revolving around the central BH, emit Doppler-broadened atomic emission lines. The region where these broad-line-emitting clouds are located is called broad-line region (BLR). About one in ten AGN forms an outflow of radiation and relativistic particles, called a relativistic jet. According to the Blandford-Znajek mechanism, this is facilitated through electromagnetic processes in the magnetosphere of a spinning BH. The latter induces a magnetospheric poloidal current circuit, generating a decelerating torque on the BH and inducing a toroidal magnetic field. Consequently, rotational energy of the BH is converted to Poynting flux streaming away mainly along the rotational axis and starting the jet. One possibility for particle acceleration near the jet base is realised by magnetospheric vacuum gaps, regions temporarily devoid of plasma, such that an intermittent electric field arises parallel to the magnetic field lines, enabling particle acceleration and contributing to the mass loading of the jets. Magnetised structures, containing bunches of relativistic electrons, propagate away from the galactic nucleus along the jets. Assuming that these electrons emit synchrotron radiation and that they inverse-Compton (IC) up-scatter abundant target photons, which can either be the synchrotron photons themselves or photons from external emitters, the emitted spectrum can be theoretically determined. Additionally taking into account that these emission regions move relativistically themselves and that the emission is Doppler-boosted and beamed in forward direction, the typical two-hump spectral energy distribution (SED) of blazars is recovered. There are however findings that challenge this well-established model. Short-time variability, reaching down to minute scales at very high energy gamma rays, is today known to be a widespread phenomenon of blazars, calling for very compact emission regions. In most models of such optically thick emission regions, the gamma-ray flux is usually pair-absorbed exponentially, without considering the cascade evolving from the pair-produced electrons. From the observed flux, it is often concluded that emission emanates from larger distances where the region is optically thin, especially from outside of the BLR. Only in few blazars gamma-ray attenuation associated with pair absorption in the BLR was clearly reported. With the advent of sophisticated high-energy or very high energy gamma-ray detectors, like the Fermi Large Area Telescope or the Major Atmospheric Gamma-ray Imaging Cherenkov telescopes, besides the extraordinarily fast variability spectral features have been found that cannot be explained by conventional models reproducing the two-hump SED. Two such narrow spectral features are discussed in this work. For the nearby blazar Markarian 501, hints to a sharp peak around 3 TeV have been reported from a multi-wavelength campaign carried out in July 2014, while for 3C 279 a spectral dip was found in 2018 data, that can hardly be described with conventional fitting functions. In this work it is examined whether these spectral peculiarities of blazar jet emission can be explained, if the full radiation reprocessing through an IC pair cascade is accounted for. Such a cascade is the multiple concatenation of IC scattering events and pair production events. In the cascades generally considered in this work, relativistic electrons and high-energy photons are injected into a fixed soft target photon field. A mathematical description for linear IC pair cascades with escape terms is delivered on the basis of preliminary works. The steady-state kinetic equations for the electrons and for the photons are determined, whereby it is paid attention to an explicit formulation and to motivating the correct integration borders of all integrals from kinematic constraints. In determining the potentially observable gamma-ray flux, both the attenuated injected flux and the flux evolving as an effect of IC up-scattering, pair absorption and escape are incorporated, giving the emerging spectra very distinct imprints. Much effort is dedicated to the numerical solution of the electrons' kinetic equation via iterative schemes. It is explained why pointwise iteration from higher to lower Lorentz factors is more efficient than iterating the whole set of sampling points. The algorithm is parallelised at two positions. First, several workers can perform pointwise iterations simultaneously. Second, the most demanding integral is cut into a number of part integrals which can be determined by multiple workers. Through these measures, the Python code can be readily applied to simulate steady-state IC pair cascades with escape. In the case of Markarian 501 the developed framework is as follows. The AGN hosts an advection-dominated accretion flow with a normalised accretion rate of several \(10^{-4}\) and an electron temperature near \(10^{10}\) K. On the one hand, the accretion flow illuminates the few ambient gas clouds with approximate radius \(10^{11}\) m, which reprocess a fraction 0.01 of the luminosity into hydrogen and helium emission lines. On the other hand, the gamma rays from the accretion flow create electrons and positrons in a sporadically active vacuum gap in the BH magnetosphere. In the active gap, a power of roughly 0.001 of the Blandford-Znajek power is extracted from the rotating BH through a gap potential drop of several \(10^{18}\) V, generating ultra-relativistic electrons, which subsequently are multiplied by a factor of about \(10^6\) through interaction with the accretion flow photons. This electron beam propagates away from the central engine and encounters the photon field of one passing ionised cloud. The resulting IC pair cascade is simulated and the evolving gamma-ray spectrum is determined. Just above the absorption troughs due to the hydrogen lines, the spectrum exhibits a narrow bump around 3 TeV. When the cascaded emission is added to the emission generated at larger distances, the observed multi-wavelength SED including the sharp peak at 3 TeV is reproduced, underlining that radiation processes beyond conventional models are motivated by distinct spectral features. The dip in the spectrum of 3C 279 is addressed by a similar cascade model. Three types of injection are considered, varying in the ratio of the photon density to the electron density and varying in the spectral shape. The IC pair cascade is assumed to happen either in the dense BLR photon field with a luminosity of several \(10^{37}\) W and a radial size of few \(10^{14}\) m or in the diluted photon field outside of the BLR. The latter scenario is however rejected as the spectral slope around several 100 MeV and the dip at few 10 GeV cannot be reconciled within this model. The radiation cascaded in the BLR can explain the observational data, irrespective of the assumed injected rate. It is therefore concluded that for this period of gamma-ray emission, the radiation production happens at the edge of the BLR of 3C 279. Both investigations show that IC pair cascades can account for fine structure seen in blazar SEDs. It is insufficient to restrict the radiation transport to pure exponential absorption of an injection term. Pair production and IC up-scattering by all generations of photons and electrons in the optically thick regime critically shape the emerging spectra. As the advent of future improved detectors will provide more high-precision spectra, further observations of narrow spectral features can be expected. It seems therefore recommendable to incorporate cascading into conventional radiation production models or to extend the model developed in this work by synchrotron radiation.}, subject = {Active galactic nucleus}, 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} } @phdthesis{Dorner2008, author = {Dorner, Daniela}, title = {Observations of PG 1553+113 with the MAGIC telescope}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-28196}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2008}, abstract = {Blazars are among the most luminous sources in the universe. Their extreme short-time variability indicates emission processes powered by a supermassive black hole. With the current generation of Imaging Air Cherenkov Telescopes, these sources are explored at very high energies. Lowering the threshold below 100 GeV and improving the sensitivity of the telescopes, more and more blazars are discovered in this energy regime. For the MAGIC telescope, a low energy analysis has been developed allowing to reach energies of 50 GeV for the first time. The method is presented in this thesis at the example of PG 1553+113 measuring a spectrum between 50 GeV and 900 GeV. In the energy regime observed by MAGIC, strong attenuation of the gamma-rays is expected from pair production due to interactions of gamma-rays with low-energy photons from the extragalactic background light. For PG 1553+113, this provides the possibility to constrain the redshift of the source, which is still unknown. Well studied from radio to x-ray energies, PG 1553+113 was discovered in 2005 in the very high energy regime. In total, it was observed with the MAGIC telescope for 80~hours between April 2005 and April 2007. From more than three years of data taking, the MAGIC telescope provides huge amounts of data and a large number of files from various sources. To handle this data volume and to provide monitoring of the data quality, an automatic procedure is essential. Therefore, a concept for automatic data processing and management has been developed. Thanks to its flexibility, the concept is easily applicable to future projects. The implementation of an automatic analysis is running stable since three years in the data center in W{\"u}rzburg and provides consistent results of all MAGIC data, i.e. equal processing ensures comparability. In addition, this database controlled system allows for easy tests of new analysis methods and re-processing of all data with a new software version at the push of a button. At any stage, not only the availability of the data and its processing status is known, but also a large set of quality parameters and results can be queried from the database, facilitating quality checks, data selection and continuous monitoring of the telescope performance. By using the automatic analysis, the whole data sample can be analyzed in a reasonable amount of time, and the analyzers can concentrate on interpreting the results instead. For PG 1553+113, the tools and results of the automatic analysis were used. Compared to the previously published results, the software includes improvements as absolute pointing correction, absolute light calibration and improved quality and background-suppression cuts. In addition, newly developed analysis methods taking into account timing information were used. Based on the automatically produced results, the presented analysis was enhanced using a special low energy analysis. Part of the data were affected by absorption due to the Saharan Air Layer, i.e. sanddust in the atmosphere. Therefore, a new method has been developed, correcting for the effect of this meteorological phenomenon. Applying the method, the affected data could be corrected for apparent flux variations and effects of absorption on the spectrum, allowing to use the result for further studies. This is especially interesting, as these data were taken during a multi-wavelength campaign. For the whole data sample of 54 hours after quality checks, a signal from the position of PG 1553+113 was found with a significance of 15 standard deviations. Fitting a power law to the combined spectrum between 75 GeV and 900 GeV, yields a spectral slope of 4.1 +/- 0.2. Due to the low energy analysis, the spectrum could be extended to below 50 GeV. Fitting down to 48 GeV, the flux remains the same, but the slope changes to 3.7 +/- 0.1. The determined daily light curve shows that the integral flux above 150 GeV is consistent with a constant flux. Also for the spectral shape no significant variability was found in three years of observations. In July 2006, a multi-wavelength campaign was performed. Simultaneous data from the x-ray satellite Suzaku, the optical telescope KVA and the two Cherenkov experiments MAGIC and H.E.S.S. are available. Suzaku measured for the first time a spectrum up to 30 keV. The source was found to be at an intermediate flux level compared to previous x-ray measurements, and no short time variability was found in the continuous data sample of 41.1 ksec. Also in the gamma regime, no variability was found during the campaign. Assuming a maximum slope of 1.5 for the intrinsic spectrum, an upper limit of z < 0.74 was determined by deabsorbing the measured spectrum for the attenuation of photons by the extragalactic background light. For further studies, a redshift of z = 0.3 was assumed. Collecting various data from radio, infrared, optical, ultraviolet, x-ray and gama-ray energies, a spectral energy distribution was determined, including the simultaneous data of the multi-wavelength campaign. Fitting the simultaneous data with different synchrotron-self-compton models shows that the observed spectral shape can be explained with synchrotron-self-compton processes. The best result was obtained with a model assuming a log-parabolic electron distribution.}, subject = {Aktiver galaktischer Kern}, language = {en} } @phdthesis{Meyer2008, author = {Meyer, Markus}, title = {Observations of a systematically selected sample of high frequency peaked BL Lac objects with the MAGIC telescope}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-28115}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2008}, abstract = {At the beginning of regular observations with the MAGIC telescope in December 2004, all but one extragalactic sources detected at very high energy (VHE) gamma-rays belonged to the class of high frequency peaked BL Lac (HBL) objects. This motivated a systematic scan of candidate sources to increase the number of known sources and to study systematically their spectral properties. As candidate sources for VHE emission, X-ray bright HBLs were selected from a compilation of active galactic nuclei. The MAGIC observations took place from December 2004 to March 2006. The declination of the objects was restricted to values between -1.2° and +58.8° corresponding to a maximum zenith distance lower than 30° at culmination. Since gamma-rays are absorbed by photo-pair production in low energy background radiation fields, the redshift of the investigated objects was limitetd to z < 0.3. Under the assumption that HBLs generally emit the same energy flux at 1keV as at 200GeV, only the brightest X-ray sources were observed, leading to a cut in the X-ray flux of F(1keV) > 2µJy}. Of the fourteen sources observed, four have been detected: 1ES 1218+304 (for the first time at very high energies), 1ES 2344+514 (strong detection in a state of low activity), Mrk 421 and Mrk 501. A hint of a signal on a 3-sigma-level from the direction of 1ES 1011+496 has been observed. In the meantime the object has been confirmed as a source of VHE gamma-rays by a second MAGIC observation campaign triggered by an optical outburst. For ten sources, upper limits on their integral fluxes above 200GeV have been calculated on a 99\% confidence level. To cross calibrate the different data samples, collected during 14 months, bright muon ring images have been used, recorded as background events by the MAGIC telescope. Based on the development by Meyer (2003), the method has been improved and implemented into the automatic data analysis as a continuous monitor of the calibration and the point spread function of the optical system. While the ring images are generated by muons with small impact parameters, it could be shown that the image parameter distributions for muons with large impact parameters and gamma showers completely overlap, revealing these muons as the dominant background for gamma-ray observations below energies of 150GeV. The sample of HBLs (including all HBLs detected at VHE so far) has been investigated for correlations between broad-band spectral indices as determined from simultaneous optical, archival X-ray and radio luminosities, finding that the VHE emitting HBLs do not differ from the non-detected ones. In general the absorption corrected HBL gamma-ray luminosities at 200GeV are not higher than their X-ray luminosities at 1keV. Based on a complete X-ray BL Lac sample, the Hamburg/ROSAT X-ray BL Lac sample, the number of expected VHE sources has been estimated for the performed scan, finding a consistent number under the assumption of a 37\% completeness of the investigated sample and a 1keV-to-200GeV luminosity ratio of 1.4. An upper limit on the omnidirectional flux at 200GeV has been calculated by interpolating the sum over the observed fluxes and upper limits. Within the uncertainties, the result is in agreement with the expectations derived from the X-ray luminosity function of BL Lacs. For 1ES 1218+304 and 1ES 2344+514 the lightcurves have been derived, showing evidence for flux variability on a time scale of 17 days and 24h, respectively. In the case of 1ES 1218+304 variability has been reported for the first time at VHEs. For both sources the energy spectra have been reconstructed and discussed in the context of their broad band spectral energy distribution (SED), using a single zone synchrotron self Compton model. The SEDs are well fitted by the simulation even though the very high peak frequencies at gamma-rays push the model to its limits. The parameters derived from the simulation are in good agreement with the parameters found for similar HBLs.}, 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} } @article{AdrianMartinezAgeronAharonianetal.2016, author = {Adri{\´a}n-Mart{\´i}nez, S. and Ageron, M. and Aharonian, F. and Aiello, S. and Albert, A. and Ameli, F. and Annasontzis, E. and Andre, M. and Androulakis, G. and Anghinolfi, M. and Anton, G. and Ardid, M. and Avgitas, T. and Barbarino, G. and Baret, B. and Barrios-Mart{\´i}, J. and Belhorma, B. and Belias, A. and Berbee, A. and van den Berg, A. and Bertin, V. and Beurthey, S. and van Beeveren, V. and Beverini, N. and Biagi, S. and Biagioni, A. and Billault, M. and Bond{\`i}, M. and Bormuth, R. and Bouhadef, B. and Bourlis, G. and Bourret, S. and Boutonnet, C. and Bouwhuis, M. and Bozza, C. and Bruijn, R. and Brunner, J. and Buis, E. and Busto, J. and Cacopardo, G. and Caillat, L. and Calmai, M. and Calvo, D. and Capone, A. and Caramete, L. and Cecchini, S. and Celli, S. and Champion, C. and Cherkaoui El Moursli, R. and Cherubini, S. and Chiarusi, T. and Circella, M. and Classen, L. and Cocimano, R. and Coelho, J. A. B. and Coleiro, A. and Colonges, S. and Coniglione, R. and Cordelli, M. and Cosquer, A. and Coyle, P. and Creusot, A. and Cuttone, G. and D'Amico, A. and De Bonis, G. and De Rosa, G. and De Sio, C. and Di Capua, F. and Di Palma, I. and D{\´i}az Garc{\´i}a, A. F. and Distefano, C. and Donzaud, C. and Dornic, D. and Dorosti-Hasankiadeh, Q. and Drakopoulou, E. and Drouhin, D. and Drury, L. and Durocher, M. and Eberl, T. and Eichie, S. and van Eijk, D. and El Bojaddaini, I. and El Khayati, N. and Elsaesser, D. and Enzenh{\"o}fer, A. and Fassi, F. and Favali, P. and Fermani, P. and Ferrara, G. and Filippidis, C. and Frascadore, G. and Fusco, L. A. and Gal, T. and Galat{\`a}, S. and Garufi, F. and Gay, P. and Gebyehu, M. and Giordano, V. and Gizani, N. and Gracia, R. and Graf, K. and Gr{\´e}goire, T. and Grella, G. and Habel, R. and Hallmann, S. and van Haren, H. and Harissopulos, S. and Heid, T. and Heijboer, A. and Heine, E. and Henry, S. and Hern{\´a}ndez-Rey, J. J. and Hevinga, M. and Hofest{\"a}dt, J. and Hugon, C. M. F. and Illuminati, G. and James, C. W. and Jansweijer, P. and Jongen, M. and de Jong, M. and Kadler, M. and Kalekin, O. and Kappes, A. and Katz, U. F. and Keller, P. and Kieft, G. and Kießling, D. and Koffeman, E. N. and Kooijman, P. and Kouchner, A. and Kulikovskiy, V. and Lahmann, R. and Lamare, P. and Leisos, A. and Leonora, E. and Lindsey Clark, M. and Liolios, A. and Llorenz Alvarez, C. D. and Lo Presti, D. and L{\"o}hner, H. and Lonardo, A. and Lotze, M. and Loucatos, S. and Maccioni, E. and Mannheim, K. and Margiotta, A. and Marinelli, A. and Mari{\c{s}}, O. and Markou, C. and Mart{\´i}nez-Mora, J. A. and Martini, A. and Mele, R. and Melis, K. W. and Michael, T. and Migliozzi, P. and Migneco, E. and Mijakowski, P. and Miraglia, A. and Mollo, C. M. and Mongelli, M. and Morganti, M. and Moussa, A. and Musico, P. and Musumeci, M. and Navas, S. and Nicoleau, C. A. and Olcina, I. and Olivetto, C. and Orlando, A. and Papaikonomou, A. and Papaleo, R. and Păvăla{\c{s}}, G. E. and Peek, H. and Pellegrino, C. and Perrina, C. and Pfutzner, M. and Piattelli, P. and Pikounis, K. and Poma, G. E. and Popa, V. and Pradier, T. and Pratolongo, F. and P{\"u}hlhofer, G. and Pulvirenti, S. and Quinn, L. and Racca, C. and Raffaelli, F. and Randazzo, N. and Rapidis, P. and Razis, P. and Real, D. and Resvanis, L. and Reubelt, J. and Riccobene, G. and Rossi, C. and Rovelli, A. and Salda{\~n}a, M. and Salvadori, I. and Samtleben, D. F. E. and S{\´a}nchez Garc{\´i}a, A. and S{\´a}nchez Losa, A. and Sanguineti, M. and Santangelo, A. and Santonocito, D. and Sapienza, P. and Schimmel, F. and Schmelling, J. and Sciacca, V. and Sedita, M. and Seitz, T. and Sgura, I. and Simeone, F. and Siotis, I. and Sipala, V. and Spisso, B. and Spurio, M. and Stavropoulos, G. and Steijger, J. and Stellacci, S. M. and Stransky, D. and Taiuti, M. and Tayalati, Y. and T{\´e}zier, D. and Theraube, S. and Thompson, L. and Timmer, P. and T{\"o}nnis, C. and Trasatti, L. and Trovato, A. and Tsirigotis, A. and Tzamarias, S. and Tzamariudaki, E. and Vallage, B. and Van Elewyk, V. and Vermeulen, J. and Vicini, P. and Viola, S. and Vivolo, D. and Volkert, M. and Voulgaris, G. and Wiggers, L. and Wilms, J. and de Wolf, E. and Zachariadou, K. and Zornoza, J. D. and Z{\´u}{\~n}iga, J.}, title = {Letter of intent for KM3NeT 2.0}, series = {Journal of Physics G-Nuclear and Particle Physics}, volume = {43}, journal = {Journal of Physics G-Nuclear and Particle Physics}, number = {8}, doi = {10.1088/0954-3899/43/8/084001}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-188050}, pages = {84001}, year = {2016}, abstract = {The main objectives of the KM3NeT Collaboration are (i) the discovery and subsequent observation of high-energy neutrino sources in the Universe and (ii) the determination of the mass hierarchy of neutrinos. These objectives are strongly motivated by two recent important discoveries, namely: (1) the high-energy astrophysical neutrino signal reported by IceCube and (2) the sizable contribution of electron neutrinos to the third neutrino mass eigenstate as reported by Daya Bay, Reno and others. To meet these objectives, the KM3NeT Collaboration plans to build a new Research Infrastructure consisting of a network of deep-sea neutrino telescopes in the Mediterranean Sea. A phased and distributed implementation is pursued which maximises the access to regional funds, the availability of human resources and the synergistic opportunities for the Earth and sea sciences community. Three suitable deep-sea sites are selected, namely off-shore Toulon (France), Capo Passero (Sicily, Italy) and Pylos (Peloponnese, Greece). The infrastructure will consist of three so-called building blocks. A building block comprises 115 strings, each string comprises 18 optical modules and each optical module comprises 31 photo-multiplier tubes. Each building block thus constitutes a three-dimensional array of photo sensors that can be used to detect the Cherenkov light produced by relativistic particles emerging from neutrino interactions. Two building blocks will be sparsely configured to fully explore the IceCube signal with similar instrumented volume, different methodology, improved resolution and}, language = {en} } @phdthesis{Ganse2012, author = {Ganse, Urs}, title = {Kinetische Simulationen solarer Typ II Radiobursts}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-73676}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2012}, abstract = {Die Emission solarer Typ II Radiobursts ist ein seit Jahrzehnten beobachtetes Ph{\"a}nomen der heliosph{\"a}rischen Plasmaphysik. Diese Radiobursts, die im Zusammenhang mit der Propagation koronaler Schockfronten auftreten, zeigen ein charakteristisches, zweibandiges Emissionsspektrum. Mit expandierendem Schock driften sie zu niedrigeren Frequenzen. Analytische Theorien dieser Emission sagen nichtlineare Plasmawellenwechselwirkung als Ursache voraus, doch aufgrund des geringen Sonnenabstands der Emissionsregion ist die in-situ Datenlage durch Satellitenmessungen {\"a}usserst schlecht, so dass eine endg{\"u}ltige Verifikation der vorhergesagten Vorg{\"a}nge bisher nicht m{\"o}glich war. Mit Hilfe eines kinetischen Plasma-Simulationscodes nach dem Particle-in-Cell Prinzip wurde in dieser Dissertation die Plasmaumgebung in der Foreshock-Region einer koronalen Schockfront modelliert. Das Propagations- und Kopplungsverhalten elektrostatischer und elektromagnetischer Wellenmoden wurde untersucht. Die vollst{\"a}ndige r{\"a}umliche Information {\"u}ber die Wellenzusammensetzung in der Simulation erlaubt es, die Kinematik nichtlinearer Wellenkopplungen genauestens zu untersuchen. Es zeigte sich ein mit der analytischen Theorie der Drei-Wellen-Wechselwirkung konsistentes Bild der Erzeugung solarer Radiobursts: durch elektromagnetischen Zerfall elektrostatischer Moden kommt es zur Erzeugung fundamentaler, sowie durch Verschmelzung gegenpropagierender elektrostatischer Moden zur Anregung harmonischer Radioemission. Kopplungsst{\"a}rken und Winkelabh{\"a}ngigkeit dieser Prozesse wurden untersucht. Mit dem somit zur Verf{\"u}gung stehenden, numerischen Laborsystem wurde die Parameter-Abh{\"a}ngigkeit der Wellenkopplungen und entstehenden Radioemissionen bez{\"u}glich St{\"a}rke des Elektronenbeams und des solaren Abstandes untersucht.}, subject = {Heliosph{\"a}re}, language = {de} } @article{JohnsonAkiyamaBlackburnetal.2023, author = {Johnson, Michael D. and Akiyama, Kazunori and Blackburn, Lindy and Bouman, Katherine L. and Broderick, Avery E. and Cardoso, Vitor and Fender, Rob P. and Fromm, Christian M. and Galison, Peter and G{\´o}mez, Jos{\´e} L. and Haggard, Daryl and Lister, Matthew L. and Lobanov, Andrei P. and Markoff, Sera and Narayan, Ramesh and Natarajan, Priyamvada and Nichols, Tiffany and Pesce, Dominic W. and Younsi, Ziri and Chael, Andrew and Chatterjee, Koushik and Chaves, Ryan and Doboszewski, Juliusz and Dodson, Richard and Doeleman, Sheperd S. and Elder, Jamee and Fitzpatrick, Garret and Haworth, Kari and Houston, Janice and Issaoun, Sara and Kovalev, Yuri Y. and Levis, Aviad and Lico, Rocco and Marcoci, Alexandru and Martens, Niels C. M. and Nagar, Neil M. and Oppenheimer, Aaron and Palumbo, Daniel C. M. and Ricarte, Angelo and Rioja, Mar{\´i}a  J. and Roelofs, Freek and Thresher, Ann C. and Tiede, Paul and Weintroub, Jonathan and Wielgus, Maciek}, title = {Key science goals for the next-generation Event Horizon Telescope}, series = {Galaxies}, volume = {11}, journal = {Galaxies}, number = {3}, issn = {2075-4434}, doi = {10.3390/galaxies11030061}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-313525}, year = {2023}, abstract = {The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide.}, language = {en} } @article{GedalinDroege2013, author = {Gedalin, Michael and Dr{\"o}ge, Wolfgang}, title = {Ion dynamics in quasi-perpendicular collisionless interplanetary shocks: a case study}, series = {Frontiers in Physics}, volume = {1}, journal = {Frontiers in Physics}, issn = {2296-424X}, doi = {10.3389/fphy.2013.00029}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-189407}, pages = {29}, year = {2013}, abstract = {Interplanetary shocks are believed to play an important role in the acceleration of charged particles in the heliosphere. While the acceleration to high energies proceeds via the diffusive mechanism at the scales exceeding by far the shock width, the initial stage (injection) should occur at the shock itself. Numerical tracing of ions is done in a model quasi-perpendicular shock front with a typical interplanetary shock parameters (Mach number, upstream ion temperature). The analysis of the distribution of the transmitted solar wind is used to adjust the cross-shock potential which is not directly measured. It is found that, for typical upstream ion temperatures, acceleration of the ions from the tail of the solar wind distribution is unlikely. Pickup ions with a shell distribution are found to be effectively energized and may be injected into further diffusive acceleration regime. Pre-accelerated ions are efficiently upscaled in energies. A part of these ions is returned to the upstream region where they can further be diffusively accelerated.}, language = {en} } @phdthesis{Elsaesser2011, author = {Els{\"a}sser, Dominik Martin}, title = {Indirect Search for Dark Matter in the Universe - the Multiwavelength and Multiobject Approach}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-69464}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2011}, abstract = {Dunkle Materie ist ein zentraler Bestandteil der modernen Kosmologie, und damit von entscheidender Bedeutung f{\"u}r unser Verst{\"a}ndnis der Strukturbildung im Universum. Das offensichtliche Fehlen von elektromagnetischer Wechselwirkung in Kombination mit unabh{\"a}ngigen Messungen der Energiedichte der baryonischen Materie {\"u}ber die H{\"a}ufigkeit der primordialen leichten Elemente weisen auf eine nicht-baryonische Natur der Dunklen Materie hin. Die Wirkung der Dunklen Materie bei der Strukturbildung zeigt weiterhin dass ihre Konstituenten kalt sind, also zum Zeitpunkt des Gleichgewichts zwischen Strahlung und Materie eine Temperatur kleine als ihre Ruhemasse aufwiesen. Generische Kandidaten f{\"u}r das Dunkelmaterie-Teilchen sind stabile, schwach wechselwirkende Teilchen mit Ruhemassen von der Gr{\"o}ßenordnung der Skala der elektroschwachen Symmetriebrechung, wie sie zum Beispiel in der Supersymmetrie bei erhaltener R-Parit{\"a}t vorkommen. Derartige Teilchen frieren auf nat{\"u}rliche Weise im fr{\"u}hen Universum mit kosmologisch relevanten Reliktdichten aus. Die fortschreitende Strukturbildung im Universum f{\"u}hrt dann zur Bildung von {\"u}berdichten Regionen, in denen die Dunkelmaterie-Teilchen wiederum in signifikantem Ausmaß annihilieren k{\"o}nnen. Dadurch w{\"u}rde ein potentiell detektierbarer Fluß von Hochenergie-Teilchen einschließlich Photonen aus den instabilen Zwischenprodukten der Annihilationsereignisse erzeugt. Die Spektren dieser Teilchen w{\"u}rden R{\"u}ckschl{\"u}sse auf die Masse und den Annihilations-Querschnitt als wichtige Gr{\"o}ßen zur mikrophysikalischen Identifikation der Dunkelmaterie-Teilchen erlauben. Darin liegt die zentrale Motivation f{\"u}r indirekte Suchen nach der Dunklen Materie. Zum gegenw{\"a}rtigen Zeitpunkt jedoch haben weder diese indirekten Suchen, noch direkte Methoden zur Suche nach elastischen Streuereignissen zwischen Dunkelmaterie-Teilchen und Atomkernen sowie Beschleunigerexperimente einen eindeutigen Nachweis von Dunkelmaterie-Teilchen erbracht. Das an sich stellt keine {\"U}berraschung dar, denn die zu erwartenden Signale sind aufgrund der schwachen Wechselwirkung der Teilchen nur von geringer Intensit{\"a}t. Im Falle der indirekten Suchen steht zu erwarten, dass selbst f{\"u}r die gr{\"o}ßten Massekonzentrationen im Universum die St{\"a}rke des Annihilationssignals der Dunklen Materie den durch astrophysikalische Quellen verursachten Untergrund nicht {\"u}berschreitet. Die M{\"o}glichkeit der sicheren Unterscheidung zwischen einem m{\"o}glichen Signal aus der Annihilation der Dunklen Materie und eben diesem Untergrund ist daher entscheidend f{\"u}r die Erfolgsaussichten der indirekten Suchen. In der vorliegenden Arbeit wird eine neuartige Suchstrategie ausgearbeitet und vorgestellt, deren zentrale Komponente die Auswahl von Beobachtungszielen aus einem breiten Massebereich, die Kontrolle der astrophysikalischen Untergr{\"u}nde, und die Einbeziehung von Daten aus mehreren Wellenl{\"a}ngenbereichen ist. Die durchgef{\"u}hrten Beobachtungen werden vorgestellt und interpretiert. Ein Ergebnis ist, dass die Unsicherheiten in Bezug auf die Verteilung der Dunklen Materie in Halos und deren individuelle Dichtestruktur, sowie in Bezug auf die m{\"o}gliche Verst{\"a}rkung des Annihilationssignales durch Substruktur, im Falle der massearmen Halos (wie zum Beispiel bei den Zwerggalaxien) gr{\"o}ßer ist als bei massereichen Halos, wie denen der Galaxienhaufen. Andererseits weisen die massereichen Halos gr{\"o}ßere Unsicherheiten in Hinblick auf die zu erwartenden rein astrophysikalischen Untergr{\"u}nde auf. Die Unsicherheiten in Bezug auf die bisher unbekannte Teilchenphysik jenseits des Standardmodells schließlich sind unabh{\"a}ngig von der Masse der beobachteten Halos. Im Zusammenspiel erm{\"o}glichen es diese unterschiedlichen Skalierungsverhalten, die globale Unsicherheit durch eine kombinierte Analyse der Beobachtungen von Halos mit verschiedenen Massen, die einen bedeutenden Teil der Masseskala abdecken, nennenswert zu reduzieren. Diese Strategie wurde im Rahmen des wissenschaftlichen Beobachtungsprogrammes des MAGIC Teleskopsystems implementiert. Es wurden Beobachtungen von Zwerggalaxien sowie des Virgo- und des Perseus-Galaxienhaufens durchgef{\"u}hrt. Die resultierenden Grenzen auf Gammastrahlung aus der Annihilation von schwach wechselwirkenden, massereichen Teilchen geh{\"o}ren zum Zeitpunkt dieser Niederschrift zu den st{\"a}rksten Grenzen aus indirekten Suchen nach der Dunklen Materie. Die so gewonnenen Grenzen auf die Annihilations-Fl{\"u}sse schr{\"a}nken einige in der Literatur diskutierte und durch aussergew{\"o}hnlich große Annihilations-Fl{\"u}sse gekennzeichnete Szenarien stark ein.}, subject = {Gammastrahlung}, language = {en} } @article{DornerMostafaSatalecka2021, author = {Dorner, Daniela and Mostaf{\´a}, Miguel and Satalecka, Konstancja}, title = {High-energy alerts in the multi-messenger era}, series = {Universe}, volume = {7}, journal = {Universe}, number = {11}, issn = {2218-1997}, doi = {10.3390/universe7110393}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-248496}, year = {2021}, abstract = {The observation of electromagnetic counterparts to both high energy neutrinos and gravitational waves marked the beginning of a new era in astrophysics. The multi-messenger approach allows us to gain new insights into the most energetic events in the Universe such as gamma-ray bursts, supernovas, and black hole mergers. Real-time multi-messenger alerts are the key component of the observational strategies to unravel the transient signals expected from astrophysical sources. Focusing on the high-energy regime, we present a historical perspective of multi-messenger observations, the detectors and observational techniques used to study them, the status of the multi-messenger alerts and the most significant results, together with an overview of the future prospects in the field.}, language = {en} } @phdthesis{Langejahn2022, author = {Langejahn, Marcus}, title = {Hard X-ray Properties of Relativistically Beamed Jets from Radio- and Gamma-Ray-Bright Blazars}, doi = {10.25972/OPUS-28200}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-282009}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2022}, abstract = {In this work I characterize the hard X-ray properties of blazars, active galactic nuclei with highly beamed emission, which are notoriously hard to detect in this energy range. I employ pre-defined samples of beamed AGN: the radio-selected MOJAVE and TANAMI samples, as well as the most recent gamma-ray-selected Fermi/LAT 4LAC catalog. The hard X-ray data is extracted from the 105-month all-sky survey maps of the Swift/BAT (Burst Alert Telescope) in the energy band of 20 keV to 100 keV. A great majority of both the MOJAVE and TANAMI samples are significantly detected, with signal-to noise ratios of the sources often just below the X-ray catalog signal thresholds. All blazar sub-types (FSRQs, BL Lacs) and radio galaxies show characteristic ranges of X-ray flux, luminosity, and photon index. Their properties are correlated with the corresponding SED's shape / peak frequency. The LogN-LogS distributions of the samples show a scarcity of blazars in the middle and lower X-ray flux range, indicating differing evolutionary paths between radio and X-ray emission, which is also suggested by the corresponding luminosity functions. Compared to the radio samples, the 4LAC sources are on average significantly less bright in the BAT band since this range often coincides with the spectral gap region between the two big SED emission bumps. Also, the spectral shapes differ notably, especially for the sub-type of BL Lacs. Using the parameter space of X-ray and gamma-ray photon indices, 35 blazar candidate sources can be assigned to either the FSRQ or BL Lac type with high certainty. The reason why many blazars are weak in this energy band can be traced back to a number of factors: the selection bias of the initial sample, differential evolution of the X-rays and the wavelengths in which the sample is defined, and the limited sensitivity of the observing instruments.}, subject = {Aktiver galaktischer Kern}, language = {en} } @article{MoraisPasechnikPorod2021, author = {Morais, Ant{\´o}nio P. and Pasechnik, Roman and Porod, Werner}, title = {Grand Unified origin of gauge interactions and families replication in the Standard Model}, series = {Universe}, volume = {7}, journal = {Universe}, number = {12}, issn = {2218-1997}, doi = {10.3390/universe7120461}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-250237}, year = {2021}, abstract = {The tremendous phenomenological success of the Standard Model (SM) suggests that its flavor structure and gauge interactions may not be arbitrary but should have a fundamental first-principle explanation. In this work, we explore how the basic distinctive properties of the SM dynamically emerge from a unified New Physics framework tying together both flavor physics and Grand Unified Theory (GUT) concepts. This framework is suggested by a novel anomaly-free supersymmetric chiral E\(_6\)×SU(2)\(_F\)×U(1)\(_F\) GUT containing the SM. Among the most appealing emergent properties of this theory is the Higgs-matter unification with a highly-constrained massless chiral sector featuring two universal Yukawa couplings close to the GUT scale. At the electroweak scale, the minimal SM-like effective field theory limit of this GUT represents a specific flavored three-Higgs doublet model consistent with the observed large hierarchies in the quark mass spectra and mixing already at tree level.}, language = {en} } @article{RomoliChakrabortyDorneretal.2018, author = {Romoli, Carlo and Chakraborty, Nachiketa and Dorner, Daniela and Taylor, Andrew and Blank, Michael}, title = {Flux Distribution of Gamma-Ray Emission in Blazars: The Example of Mrk 501}, series = {Galaxies}, volume = {6}, journal = {Galaxies}, number = {4}, organization = {FACT and H.E.S.S. Collaborations}, issn = {2075-4434}, doi = {10.3390/galaxies6040135}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-197580}, year = {2018}, abstract = {Flux distribution is an important tool to understand the variability processes in activegalactic nuclei. We now have available a great deal of observational evidences pointing towards thepresence of log-normal components in the high energy light curves, and different models have beenproposed to explain these data. Here, we collect some of the recent developments on this topic usingthe well-known blazar Mrk 501 as example of complex and interesting aspects coming from its fluxdistribution in different energy ranges and at different timescales. The observational data we refer toare those collected in a complementary manner by Fermi-LAT over multiple years, and by the FirstG-APD Cherenkov Telescope (FACT) telescope and the H.E.S.S. array in correspondence of the brightflare of June 2014}, language = {en} }