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

Abstract

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.

Accepted for publication in The Monthly Notices of the Royal Astronomical Society

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