The blazar's divide and the properties of Fermi blazars
  The LAT instrument, onboard the Fermi satellite, in its first three months of
operation detected more than 100 blazars at more than the 10 sigma level. This
is already a great improvement with respect to its predecessor, the instrument
EGRET onboard the Compton Gamma Ray Observatory. Observationally, the new
detections follow and confirm the so-called blazar sequence, relating the
bolometric observed non-thermal luminosity to the overall shape of the spectal
energy distribution. We have studied the general physical properties of all
these bright Fermi blazars, and found that their jets are matter dominated,
carrying a large total power that correlates with the luminosity of their
accretion disks. We suggest that the division of blazars into the two
subclasses of broad line emitting objects (Flat Spectrum Radio Quasars) and
line-less BL Lacs is a consequence of a rather drastic change of the accretion
mode, becoming radiatively inefficient below a critical value of the accretion
rate, corresponding to a disk luminosity of ~1 per cent of the Eddington one.
The reduction of the ionizing photons below this limit implies that the broad
line clouds, even if present, cannot produce significant broad lines, and the
object becomes a BL Lac.
