Power density spectrum of NGC 5548 and the nature of its variability

We derive power density spectra in the optical and X-ray band in the timescale range from several years down to $\sim$ a day. We suggest that the optical power density spectrum consists of two separate components: long timescale variations and short timescale variations, with the dividing timescale around 100 days. The shape of the short timescale component is similar to X-ray power density spectrum which is consistent with the interpretation of short timescale optical variations being caused by X-ray reprocessing. We show that the observed optical long timescale variability is consistent with thermal pulsations of the accretion disc.Comment: Accepted for publication in The Monthly Notices of the Royal Astronomical Societ

Slim accretion disks: theory and observational consequences

Slim accretion disks idea emerged over 30 years ago as an answer to several unsolved problems. Since that time there was a tremendous increase in the amount of observational data where this model applies. However, many critical issues on the theoretical side remain unsolved, as they are inherently difficult. This is the issue of the disk stability under the radiation pressure, the role of the magnetic field in the energy transfer inside the disk and the formation (or not) of a warm corona, and outflows. Thus the progress has to be done both through further developments of the model and through the careful comparison to the observational data.Comment: Universe, in pres

The relationship between Mg II broad emission and quasar inclination angle

Several observed spectral properties of quasars are believed to be influenced by quasar orientation. In this investigation we examine the effect of orientation on the Mg II line located at 2798 {\AA} in a sample of 36 radio-loud quasars, with orientation angles having been obtained in a previous study using radio observations. We find no significant relationship between orientation angle and either Mg II line full-width at half-maximum or equivalent width. The lack of correlation with inclination angle contradicts previous studies which also use radio data as a proxy for inclination angle and suggests the Mg II emission region does not occupy a disk-like geometry. The lack of correlation with Mg II equivalent width, however, is reported in at least one previous study. Although the significance is not very strong (86 percent), there is a possible negative relationship between inclination angle and Fe II strength which, if true, could explain the Fe II anti-correlation with [O III ] strength associated with Eigenvector 1. Interestingly, there are objects having almost edge-on inclinations while still exhibiting broad lines. This could be explained by a torus which is either clumpy (allowing sight lines to the central engine) or mis-aligned with the accretion disk.Comment: Proceedings from the conference 'Quasars at all cosmic epochs' held in Padova, Italy (2-7 April 2017

Price-cap regulation of airports: single-till versus dual-till

This paper takes up the debate whether price-cap regulation of airports should take the form of single-till or dual-till regulation. The contribution is to model single- and dual-till regulation, evaluate their welfare implications, and compare them to Ramsey prices. We show that the single-till dominates the dual-till regulation at non-congested airports with regard to welfare maximization. However, none of them provides an airport with the incentives to implement Ramsey prices. A perfect price-cap regulation, which achieves this goal, is also presented. -- Eine übliche Form der Flughafen-Regulierung ist die Price-Cap-Regulierung. Hierbei ist zwischen einer Single-Till- und einer Dual-Till-Regulierung zu unterscheiden. In dieser Arbeit analysieren wir, welche der beiden Regulierungsvarianten aus Sicht eines Wohlfahrtsmaximierers vorteilhaft ist. Dazu wird ein Vergleich der Regulierungsergebnisse mit denen von Ramsey-Preisen vorgenommen. Es zeigt sich, dass bei nicht kapazitätsbeschränkten Flughäfen die Single-Till- Regulierung zu besseren Wohlfahrtsergebnissen führt als die Dual-Till- Regulierung. Dennoch, keine der beiden Regulierungsformen kann das Ramsey- Ergebnis erreichen. Aus diesem Grund wird zusätzlich eine perfekte Price-Cap- Regulierung vorgestellt, die zu einer Implementierung des Ramsey-Ergebnisses führt.