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American Astronomical Society, Astrophysical Journal, 2(584), p. L53-L56, 2003

DOI: 10.1086/373887

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Correlated long-term optical and x-ray variations in NGC 5548

Journal article published in 2003 by Phillip Uttley, Rick Edelson ORCID, Ian M. McHardy, Bradley M. Peterson, and Alex Markowitz
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We combine the long-term optical light curve of the Seyfert 1 galaxy NGC 5548 with the X-ray light curve measured by the Rossi X-Ray Timing Explorer over 6 years, to determine the relationship between the optical and X-ray continua. The X-ray light curve is strongly correlated with the optical light curve on long (~1 yr) timescales. The amplitude of the long-term optical variability in NGC 5548 is larger than that of the X-ray variability (after accounting for the host galaxy contribution), implying that X-ray reprocessing is not the main source of the optical/X-ray correlation. The correlated X-ray and optical variations in NGC 5548 may be caused by instabilities in the inner part of the accretion flow, where both the X-ray and the optical emission regions may be located.