Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005astl...31..645l&link_type=abstract
Astronomy Letters, vol. 31, Issue 10, p.645-662
Astronomy and Astrophysics
Astronomy
6
Active Galactic Nuclei - Ngc 4151 - Ubv Photometry - Variability - Ultraviolet Variability - Color Analysis - Accretion Disk - Accretion Disk Instabilities
Scientific paper
We have analyzed the optical (U BV) and ultraviolet (λ1000 2700 Å) observations of the nuclear variability of the Seyfert galaxy NGC 4151 in the period 1987 2001 (the second cycle of activity). The fast (tens of days) and slow (˜10 years) components of the nuclear variability, F and S, respectively, are shown to be completely different, but thermal in nature. We associate the S component with the formation and evolution of an accretion disk and the F component (flares) with instabilities in the accretion disk and their propagation over the disk in the form of a shock wave. The S component is present not only in the optical, but also in the ultraviolet range, with its amplitude being comparable over the entire range λ1000 5500 Å under study. The amplitude of the average flare (the F component) doubles as the wavelength decreases from 5500 to 1000 Å, while the rise time of the brightness to its maximum Δt (the variability time scale) decreases from
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