  T CrB is a symbiotic recurrent nova known to exhibit active phases,
characterised by apparent increases in the hot component temperature and the
appearance of flickering, i.e. changes in the observed flux on the time-scale
of minutes. Historical UV observations have ruled out orbital variability as an
explanation for flickering and instead suggest flickering is caused by variable
mass transfer. We have analysed optical and X-ray observations to investigate
the nature of the flickering as well as the active phases in T CrB. The
spectroscopic and photometric observations confirm that the active phases
follow two periods of ~1000d and ~5000d. Flickering in the X-rays is detected
and follows an amplitude-flux relationship similar to that observed in the
optical. The flickering is most prominent at harder X-ray energies, suggesting
that it originates in the boundary layer between the accretion disc and the
white dwarf. The X-ray radiation from the boundary layer is then reprocessed by
a thick accretion disc or a nebula into UV radiation. A more detailed
understanding of flickering would benefit from long-term simultaneous X-ray and
optical monitoring of the phenomena in symbiotic recurrent novae and related
systems such as Z And type symbiotic stars.
