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X-ray signatures of a high accretion rate in AGN
Ken Pounds (Leicester)
Since first indicated in EXOSAT data 10 years ago the importance of
X-ray spectral features arising by scattering, absorption and fluorescence
(generically termed 'reflection') in dense matter has been well established
in the study of X-ray binaries and Active Galactic Nuclei. More recently
a sub-set of AGN, the so-called Narrow Line Seyferts, have been found to
have other distinguishing X-ray features, particularly a steep or 'soft'
spectrum and strong variability. By analogy with the 'high state' of
Galactic Black Hole Binaries the unusual properties of NLS1 have been
attributed to accretion onto the putative central black hole at a
significantly higher rate (than for 'normal' Seyferts).
New data from ASCA and RXTE have now been analysed to show that additional
spectral features in NLS1 can be understood in terms of 'reflection'
from dense matter lying close to the black hole (the putative accretion disc)
and which is highly ionised, providing further support for the high accretion
rate hypothesis.
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