Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004head....8.3203p&link_type=abstract
American Astronomical Society, HEAD meeting #8, #32.03; Bulletin of the American Astronomical Society, Vol. 36, p.969
Astronomy and Astrophysics
Astronomy
Scientific paper
The X-ray variability properties of AGN have been long used in attempts to infer the black-hole masses by comparing break frequencies in their power spectra to those of galactic sources. This is based on the underlying assumption that all characteristic frequencies correlate with mass and do not change over time. However, because of the different nature of processes that produce the X-ray light curves in these objects in opposite sides of the mass spectrum, it is yet to be demonstrated that X-ray variability can indeed be used to compare them. Moreover, with the advent of RXTE, it has been shown that the power spectra of galactic sources are not broken power laws but can be decomposed into a sum of Lorentzians with different centroid frequencies. It is now evident that the different centroid frequencies of a given galactic source vary in time over 1 to 2 orders of magnitude making a comparison to AGN variability highly uncertain. The fractional power under the lowest Lorentzian, however, remains constant; this is the so called Belloni-Hasinger effect. If present in AGN, an analogy of the Belloni-Hasinger effect will be an excellent candidate to provide a solid basis for inferring properties of AGN by comparison against galactic sources. I show that preliminary studies of AGN variability are consistent with the presence of this effect and discuss the potential implications for measuring masses of AGN using the properties of their X-ray variability.
Pessah Martin E.
Psaltis Dimitrios
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