Journal Article

Short time-scale AGN X-ray variability with <i>EXOSAT</i>: black hole mass and normalized variability amplitude

I. M. McHardy

in Monthly Notices of the Royal Astronomical Society: Letters

Published on behalf of The Royal Astronomical Society

Volume 430, issue 1, pages L49-L53
Published in print March 2013 |
Published online January 2013 | e-ISSN: 1745-3933 | DOI:

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The old EXOSAT medium energy measurements of high-frequency (HF) active galactic nuclei (AGN) power spectral normalization are re-examined in the light of accurate black hole mass determinations which were not available when these data were first published by Green et al. It is found that the normalized variability amplitude (NVA), measured directly from the power spectrum, is proportional to Mβ, where β ∼ −0.54 ± 0.08. As NVA is the square root of the power, these observations show that the normalization of the HF power spectrum for this sample of AGN varies very close to inversely with black hole mass. Almost the same value of β is obtained whether the quasar 3C 273 is included in the sample or not, suggesting that the same process that drives X-ray variability in Seyfert galaxies applies also to 3C 273. These observations support the work of Gierliński et al. who show that an almost exactly linear anticorrelation is required if the normalizations of the HF power spectra of AGN and X-ray binary systems are to scale similarly. These observations are also consistent with a number of studies showing that the short time-scale variance of AGN X-ray light curves varies approximately inversely with mass.

Keywords: black hole physics; galaxies: active; galaxies: Seyfert; X-rays: galaxies

Journal Article.  3802 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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