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Register a new userWhere are the X-ray QPOs in active galaxies?
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S. Vaughan
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In this paper we address the question of whether existing X-ray observations of Seyfert galaxies are sufficiently sensitive to detect quasi-periodic oscillations (QPOs) similar to those observed in the X-ray variations of Galactic Black Holes (GBHs). We use data from XMM-Newton and simulated data based on the best RXTE long-term monitoring light curves, to show that if X-ray QPOs are present in Seyfert X-ray light curves - with similar shapes and strengths to those observed in GBHs, but at lower frequencies commensurate with their larger black hole masses - they would be exceedingly difficult to detect. Our results offer a simple explanation for the present lack of QPO detections in Seyferts. We discuss the improvements in telescope size and monitoring patterns needed to make QPO detections feasible. The most efficient type of future observatory for searching for X-ray QPOs in AGN is an X-ray All-Sky Monitor (ASM). A sufficiently sensitive ASM would be ideally suited to detecting low frequency QPOs in nearby AGN. The detection of AGN QPOs would strengthen the AGN-GBH connection and could serve as powerful diagnostics of the black hole mass, and the structure of the X-ray emitting region in AGN.
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Since EXOSAT produced the first good quality X-ray light curves of Seyfert galaxies there have been several claims of quasi-periodic oscillations (QPOs). None of these have withstood repeated analyses and observations. We review some problems concerning the detection of QPOs.
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