Abstract:
We select a sample of 10 radio-quiet quasars with confirmed intranight optical variability and
with available X-ray data. We compare the variability properties and the broad-band spectral
constraints to the predictions of intranight variability by three models: (i) irradiation of an
accretion disc by a variable X-ray flux, (ii) an accretion disc instability, (iii) the presence of a
weak blazar component. We concluded that the third model, e.g. the blazar component model,
is the most promising if we adopt a cannonball model for the jet variable emission. In this case,
the probability of detecting the intranight variability is within 20–80 per cent, depending on
the ratio of the disc to the jet optical luminosity. Variable X-ray irradiation mechanism is also
possible but only under additional requirement: either the source should have a very narrow
Hβ line or occasional extremely strong flares should appear at very large disc radii.
