1,003 research outputs found
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 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
The role of the central stellar cluster in active galactic nuclei. I. Semi-analytical model
The subject of the paper is the role of the massive stellar cluster in the
activity phenomenon and in the structure of active galactic nuclei. We
introduce a simple model of stellar dynamics in the internal part of the
cluster, which allows us to include both the star-disk and the star-star
interactions. It is shown that the properties of the distribution of stars in
the vicinity of the black hole are determined both by the interaction of the
stars with the accretion disk and by the pair gravitational and contact
interaction between the stars. We calculate the distribution of stars in the
central parts of the cluster and we discuss possible effects of stellar
mass-loss due to the star-disk interaction. Finally, we study the implications
of the central cluster for active galactic nuclei activity. We model the broad
line region assuming that the gaseous wakes, following stars after each disk
crossing, play the role of the broad line region clouds, and we calculate the
corresponding line profiles. We also analyze the contribution of star-star and
star-disk collisions to active galactic nuclei variability.Comment: Accepted for publication in Astronomy and Astrophysic
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