2001/10/31 by B. Czerny, V. T. Doroshenko, M. Nikolajuk +3
Physics and Astronomy · #Accretion (finance) #Accretion disc #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Autocorrelation #Core (optical fiber) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Instability #Radiation #Radiation pressure #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2003.06623.x
published as Mon.Not.Roy.Astron.Soc. 342 (2003) 1222 · 21 pages, 19 figures, 4 tables, accepted for publication in MNRAS
arxiv created 2003/03/13 · openalex publication_date 2003/07/04 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We analyse observations of the Seyfert galaxy NGC 4151 covering 90 years in the optical band and 27 years in the 2–10 keV X-ray band. We compute the normalized power spectrum density, the structure function and the autocorrelation function for these data. The results show that the optical and X-ray variability properties are significantly different. X-ray variations are predominantly in the time-scale range of 5–1000 d. The optical variations also have a short time-scale component that may be related to X-ray variability, but the dominant effect is the long time-scale variability, with time-scales longer than ∼10 yr. We compare our results with observations of NGC 5548 and Cyg X-1. We conclude that the long time-scale variability may be caused by radiation pressure instability in the accretion disc, although the observed time-scale in NGC 4151 is by a factor of a few longer than expected. X-ray variability of this source is very similar to what is observed in Cyg X-1 but scaled with the mass of the black hole, which suggests that the radiation pressure instability does not affect the X-ray production considerably.