Zooming into γ-ray loud galactic nuclei: broadband emission and structure dynamics of the blazar PKS 1502+106 and the narrow-line Seyfert 1 1H 0323+342

Abstract

Blazars are accretion-powered systems representing the most extreme flavor of active galactic nuclei (AGN). This thesis focuses on the study of blazar PKS 1502+106 during a prominent broadband outburst using ultra-high resolution imaging and a broadband single-dish study. The former is accomplished through very-long-baseline interferometry (VLBI) down to short millimeter (mm) wavelengths, while the latter uses densely-sampled radio light curves at a wide frequency range. The same combination allows the detailed study of the galaxy 1H 0323+342. This is a prominent member of the narrow-line Seyfert 1 (NLS1) class of AGN, recently discovered to emit gamma-rays. General aspects of AGN along with an introduction to their discovery, phenomenology, and their constituent parts are discussed in Chapter 1. Here, specific aspects of blazars and concepts used in later chapters are also introduced. Chapter 2 introduces the technique of VLBI from a theoretical standpoint, while in Chapter 3 the practical aspects of VLBI calibration and imaging at mm wavelengths are discussed. The phenomenology and physical characteristics of PKS 1502+106 through a cm- to mm-VLBI study are presented in Chapter 4. The data set features Global Millimeter VLBI Array (GMVA) observations at 7 mm (43 GHz) and 3 mm (86 GHz) along with complementary observations at 2 cm (15 GHz) from the MOJAVE program. We also combine the analysis with F-GAMMA program data at frequencies matching the VLBI monitoring and with the Fermi/LAT gamma-ray light curve. From the rich data set we deduce its kinematical and spectral characteristics which allow the inference of physical parameters of the ultra-relativistic jet of PKS 1502+106. For the jet features identified across observing frequencies we deduce Doppler factors in the range ~10--50 at different positions within the flow. Magnetic field strengths and brightness temperatures along the jet are also deduced. The position-dependent differences in viewing angle and Lorentz factors, indicate a jet bending towards the observer that also accelerates. The kinematical model and radio flux density decomposition into distinct jet components in conjunction with the gamma-ray data indicate that the broadband flare, seen first at γ-rays and its delayed counterparts at radio wavelengths, can be attributed to one traveling jet feature (C3). Finally, the emission site of the gamma-ray emission is constrained to <10--15 pc from the jet base. The outburst of PKS 1502+106 seen through the dense, single-dish, F-GAMMA data set between 2.64--345 GHz is discussed in Chapter 5. By employing three different time series analysis techniques relevant light curve parameters, such as the flare amplitude, flare time scales, and time delays of maxima are extracted. Those exhibit dependencies on observing frequency that are well-described by power laws. The frequency-dependent light curve parameters are compared with the expectations of analytical simulations (see Chapter 5 for references) under the shock-in-jet scenario with which a good agreement is found. From the frequency-dependent time lags, equipartition magnetic field strengths are calculated and in combination with the VLBI findings from Chapter 4, the MeV/GeV emitting region is localized at the edge or slightly further from the bulk of the broad-line region (BLR) material of PKS 1502+106 with important consequences on the origin of photons available for inverse Compton up-scattering. In Chapter 6 the powerful combination of previous findings based on the F-GAMMA monitoring with VLBI images at 15 GHz allows the determination of the viewing angle towards the NLS1 galaxy 1H 0323+342. This is found to be θ = 12--13 degrees. A summary and concluding remarks arising from the thesis at hand are presented in Chapter 7.