Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994ap%26ss.222..157o&link_type=abstract
Astrophysics and Space Science (ISSN 0004-640X), vol. 222, no. 1-2, p. 157-169
Astronomy and Astrophysics
Astrophysics
8
Active Galactic Nuclei, Electromagnetic Spectra, Gamma Rays, H Beta Line, Optical Emission Spectroscopy, Seyfert Galaxies, Ultraviolet Radiation, Variability, X Rays, Exosat Satellite, Fourier Transformation, Ginga Satellite, Light Curve
Scientific paper
We have used long light curves in the X-ray (ARIEL V, EXOSAT, Ginga and others), UV (IUE), and optical (data of intensive ground-based monitoring) ranges of NGC 4151 to investigate connections between variations in these spectral fields. Applying Fourier (CLEAN algorithm) and modern cross-correlation analysis, we revealed the different character of the variability and the cross-correlation between 'high' and 'low' states of the nucleus. In contrast to ealier results, we found that X-ray and optical fluxes correlate in the 'active'state without any apparent delay. In the power spectrum of the optical and X-ray light curves in the 'high state' we found the existence of the same 'period' of about 65 days, which disappeared in the 'low state'. We confirmed previous data that X-ray variations correlate more strongly with UV and optical continuum variability during the 'low state', but it is possible that the optical variations appear to lag behind those involving X-rays by several tens of days. Strong variations in H beta line profile and (Fe X) Lambda 6374 line intensity variations correlate with the observed X-ray covering dip in 1990 (Yaqoob et al., 1993). We discuss briefly the implications of these results.
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