  We propose that radio-quiet quasars and Seyfert galaxies have central black
holes powering outflows and jets which propagate only for a short distance,
because the velocity of the ejected material is smaller than the escape
velocity. We call them "aborted" jets. If the central engine works
intermittently, blobs of material may be produced, which can reach a maximum
radial distance and then fall back, colliding with the blobs produced later and
still moving outwards. These collisions dissipate the bulk kinetic energy of
the blobs by heating the plasma, and can be responsible (entirely or at least
in part) for the generation of the high energy emission in radio-quiet objects.
This is alternative to the more conventional scenario in which the X-ray
spectrum of radio-quiet sources originates in a hot (and possibly patchy)
corona above the accretion disk. In the latter case the ultimate source of
energy of the emission of both the disk and the corona is accretion. Here we
instead propose that the high energy emission is powered also by the extraction
of the rotational energy of the black hole (and possibly of the disk). By means
of Montecarlo simulations we calculate the time dependent spectra and light
curves, and discuss their relevance to the X-ray spectra in radio-quiet AGNs
and galactic black hole sources. In particular, we show that time variability
and spectra are similar to those observed in Narrow Line Seyfert 1 galaxies.
