Abstract
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 earlier 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 Hβ line profile and [Fe X]λ6374 line intensity variations correlate with the observed X-ray covering dip in 1990 (Yaqoobet al., 1993).
We discuss briefly the implications of these results.
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Oknyanskij, V.L. Connection between X-ray and optical variability in NGC 4151. Astrophys Space Sci 222, 157–169 (1994). https://doi.org/10.1007/BF00627090
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DOI: https://doi.org/10.1007/BF00627090