Phil Uttley, University of Southampton
Title: 'How the accretion disc found its voice'

Abstract: Accretion discs are a ubiquitous feature of accreting black
holes and neutron stars, and blackbody emission from the inner disc can
be seen in X-rays in stellar mass systems, through to the optical/UV in
AGN.   Continuum variability is another ubiquitous characteristic of
accreting compact objects, but for many years it has been difficult to
identify the role of the disc in generating the variability.  Part of
the problem is that power-law continuum emission - presumably from a hot
optically thin plasma - dominates the variability in the X-ray band, and
it is difficult to disentangle intrinsic disc blackbody variations from
variations due to heating of the disc by the variable X-ray power-law.
I will give a general introduction to the spectral evidence for discs in
accreting compact objects, as well as the nature of the X-ray
variability.  Then I will show new results from extensive optical/X-ray
monitoring campaigns on AGN, which show the effects of X-ray heating and
intrinsic variability of the disc.  Similar complex behaviour is seen in
hard-state X-ray binary systems, which also provide the first direct
evidence that characteristic features in the power-spectra of these
systems are generated by the disc.  Finally, I will discuss the
prospects for X-ray 'reverberation-mapping' of the inner discs in AGN
and X-ray binaries, which is only just becoming possible with the
current generation of X-ray observatories.