The blazar sequence: a new perspective

TL;DR

This paper presents a new model linking blazar spectral energy distributions to black hole mass and accretion rate, explaining diverse blazar types and their evolution through a unified framework.

Contribution

It introduces a theoretical framework that connects blazar SEDs to fundamental accretion parameters, accounting for different blazar subclasses and their evolution.

Findings

The model explains the existence of blue quasars and low luminosity high-energy peaked BL Lacs.

It predicts the SEDs based on black hole mass and accretion rate.

The framework can be tested with upcoming satellite observations.

Abstract

We revisit the so called "blazar sequence", which connects the observed bolometric luminosity to the shape of the spectral energy distribution (SED) of blazars. We propose that the power of the jet and the SED of its emission are linked to the two main parameters of the accretion process, namely the mass of the black hole and the accretion rate. We assume: i) that the jet kinetic power is proportional to the mass accretion rate; ii) that most of the jet dissipation takes place at a distance proportional to the black hole mass; iii) that the broad line region exists only above a critical value of the disk luminosity, in Eddington units, and iv) that the radius of the broad line region scales as the square root of the ionising disk luminosity. These assumptions, motivated by existing observations or by reasonable theoretical considerations, are sufficient to uniquely determine the SED of all blazars. This framework accounts for the existence of "blue quasars", i.e. objects with broad emission lines but with SEDs resembling those of low luminosity high energy peaked BL Lac objects, as well as the existence of relatively low luminosity "red" quasars. Implications on the possible evolution of blazars are briefly discussed. This scenario can be tested quite easily once the AGILE and especially the GLAST satellite observations, coupled with information in the optical/X-ray band from Swift, will allow the knowledge of the entire SED of hundreds (and possibly thousands) blazars.