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Simultaneous X-ray and Ultraviolet spectroscopy of the Seyfert galaxy NGC 5548. III. X-ray time variability

J. S. Kaastra·K. C. Steenbrugge·D. M. Crenshaw·S. B. Kraemer·N. Arav·I. M. George·D. A. Liedahl·R. L. J. van der Meer·F. B. S. Paerels·T. J. Turner·T. Yaqoob
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Abstract

The Seyfert 1 galaxy NGC 5548 was observed for a week by Chandra using both the HETGS and LETGS spectrometers. In this paper we study the time variability of the continuum radiation. During our observation, the source showed a gradual increase in flux over four days, followed by a rapid decrease and flattening of the light curve afterwards. Superimposed upon these relatively slow variations several short duration bursts or quasi-periodic oscillations occured with a typical duration of several hours and separation between 0.6-0.9 days. The bursts show a delay of the hard X-rays with respect to the soft X-rays of a few hours. We interprete these bursts as due to a rotating, fluctuating hot spot at approximately 10 gravitational radii; the time delay of the hard X-rays from the bursts agree with the canonical picture of Inverse Compton scattering of the soft accretion disk photons on a hot medium that is relatively close to the central black hole.

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J. S. Kaastra, K. C. Steenbrugge, D. M. Crenshaw, S. B. Kraemer, N. Arav, I. M. George, D. A. Liedahl, R. L. J. van der Meer, F. B. S. Paerels, T. J. Turner, T. Yaqoob. 2004-04-23. Simultaneous X-ray and Ultraviolet spectroscopy of the Seyfert galaxy NGC 5548. III. X-ray time variability. https://doi.org/10.1051/0004-6361%3A20040291

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