The blazar's divide and the properties of Fermi blazars

TL;DR

This paper analyzes Fermi satellite blazar observations, confirming the blazar sequence, and proposes that the division into FSRQs and BL Lacs is due to a change in accretion mode at a critical rate.

Contribution

It provides a comprehensive physical analysis of Fermi blazars and links blazar subclasses to accretion mode changes based on observational data.

Findings

Jets are matter dominated with large total power.

Blazar subclasses are linked to accretion mode changes.

The division occurs at a critical accretion rate of ~1% Eddington luminosity.

Abstract

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.