Investigations of Intraday Variable Blazar Cores and the Connected Interstellar Medium

The work presented here is an attempt to shed further light upon the phenomenon of short-term radio variations (Intraday Variability, IDV) often observed in compact blazar cores. Three different new observational approaches were performed with particular emphasis on the connected scattering material in the local ISM. I present the results of a new Effelsberg 4.85 GHz IDV monitoring over the period of 2.5 years aiming the detection of seasonal cycles in the variability time scale of "classical" type-II IDV sources. While the most promising new candidate turned out to be BL Lac 0954+658, the annual cycle in quasar 0917+624 proposed earlier could not be confirmed due to the sudden death of rapid variability in this source since 2000. Here, additional 15 GHz VLBI observations were performed in parallel to our IDV monitoring suggesting an extremely quenched scattering scenario and a possible connection between intrinsic structural changes on (sub-) mas-scale and the dramatic changes in IDV characteristics. The attempt to detect an intrinsic contribution to the IDV pattern using high frequency IDV observations revealed no significant variations in three sources including BL Lac 0716+714 for which IDV in the mm-band was detected earlier. The results of a short multi-frequency observation of the 'rapid scintillator' J1819+3845 are in agreement with weak interstellar scintillation of a point source due to enhanced turbulence in the local bubble wall at a distance of about 15pc. Finally, the possibility of a direct detection of the scattering medium in front of IDV and extreme scattering event (ESE) sources is examined and discussed with emphasis on the various components of the (local) ISM, such as the WIM, local bubble, adjacent bubble/loop structures and their turbulent interaction zones. First spectral line observations led to the detection of a high latitude molecular cloud intervening the line of sight to 0954+658. Here, several findings suggest that the observed scattering effects (IDV and ESEs) are produced by the ionized CII component provided by the photo-dissociation region surrounding the CO-cloud

Hafenstädte in globaler Perspektive.: Einleitung

Port Cities in Global Perspective: An Introduction This volume examines the phenomena of mobility and migration in port cities at the height of the steamship era, ca. 1860-1930. The inherent contradiction that ports were the source of a city’s (or a country’s or an Empire’s) esteem in the world on the one hand and that on the other, the ports’ unwanted and uncontrollable processes prompted negative reactions, is the common thread of all articles. Our approach to the study of port cities focuses on the contact in ports between people of different origin. This contact situation has the potential to put into question one’s concept of the city, the nation, the religious community, civilization, or even time. By consequence, it can threaten existing power structures and has the capacity to alter or reaffirm urban and national identities

Physical Conditions and Variability Processes in AGN Jets through Multi-Frequency Linear and Circular Radio Polarization Monitoring

Radio polarimetry is an invaluable tool to investigate the physical conditions and variability processes in active galactic nuclei (AGN) jets. However, detecting their linear and circular polarization properties is a challenging endeavor due to their low levels and possible depolarization effects. We have developed an end-to-end data analysis methodology to recover the polarization properties of unresolved sources with high accuracy. It has been applied to recover the linear and circular polarization of 87 AGNs measured by the F-GAMMA program from July 2010 to January 2015 with a mean cadence of 1.3 months. Their linear polarization was recovered at four frequencies between 2.64 and 10.45 GHz and the circular polarization at 4.85 and 8.35 GHz. The physical conditions required to reproduce the observed polarization properties and the processes which induce their variability were investigated with a full-Stokes radiative transfer code which emulates the synchrotron emission of modeled jets. The model was used to investigate the conditions needed to reproduce the observed polarization behavior for the blazar 3C 454.3, assuming that the observed variability is attributed to evolving internal shocks propagating downstream.Comment: 6 pages, 2 figure

Radio QPO in the γ{\gamma}-ray-loud X-ray binary LS I +61∘{^\circ}303

LS I +61${^\circ}$303 is a $\gamma$-ray emitting X-ray binary with periodic radio outbursts with time scales of one month. Previous observations have revealed microflares superimposed on these large outbursts with periods ranging from a few minutes to hours. This makes LS I +61${^\circ}$303, along with Cyg X-1, the only TeV emitting X-ray binary exhibiting radio microflares. To further investigate these microflaring activity in LS I +61${^\circ}$303 we observed the source with the 100-m Effelsberg radio telescope at 4.85, 8.35, and 10.45 GHz and performed timing analysis on the obtained data. Radio oscillations of 15 hours time scales are detected at all three frequencies. We also compare the spectral index evolution of radio data to that of the photon index of GeV data observed by Fermi-LAT. We conclude that the observed QPO could result from multiple shocks in a jet.Comment: 5 pages, 4 figures, accepted for publication in MNRA

Filling in the Gaps in the 4.85 GHz Sky

We describe a 4.85 GHz survey of bright, flat-spectrum radio sources conducted with the Effelsberg 100 m telescope in an attempt to improve the completeness of existing surveys, such as CRATES. We report the results of these observations and of follow-up 8.4 GHz observations with the VLA of a subset of the sample. We comment on the connection to the WMAP point source catalog and on the survey's effectiveness at supplementing the CRATES sky coverage.Comment: 13 pages, 3 figures, 2 tables. Accepted for publication in the Astronomical Journal. Tables available in electronic form: http://astro.stanford.edu/gaps