8th HEAD Meeting, 8-11 September, 2004
Session 26 AGN/Galactic Nuclei
Poster, Friday, September 10, 2004, 9:00am-10:00pm

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[26.06] The origin of X-ray variability in radio-quiet AGN

P. Uttley (NASA-GSFC)

For many years, the most commonly accepted (if not proven) explanation for X-ray variability in radio-quiet AGN has been that of the `flaring corona', where the X-ray variations are produced by flares due to magnetic reconnection in the X-ray emitting corona. Although such a picture is attractive, being based on a simple analogy with the Solar corona, it has not been informative, since the nature of magnetic fields in AGN is not even understood, let alone how they relate to spectral variability. Recently however, a new picture has emerged of the origin of X-ray variability in AGN (and X-ray binary systems), which rules out the flaring corona model and instead suggests that the X-ray variability is the result of fluctuations in the accretion flow which originate outside the emitting region. The propagation of these accretion fluctuations through the emitting region can simply explain many of the variability characteristics of the X-ray continuum, including the surprisingly small time-lags between energy bands, and the energy dependence of the variability, as well as the apparent non-linear variability observed in Narrow Line Seyfert 1s. Here, we review the evidence for this new picture for AGN variability and demonstrate with numerical simulations how this model can shed light on the size and structure of the X-ray emitting region, as well as the properties of the accretion flow.

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.