Breaking the Blazar Sequence: A New View of Radio Loud AGN Unification

TL;DR

This paper proposes a new framework for understanding radio-loud AGN by identifying two jet structure-based sub-populations, challenging the traditional blazar sequence, and linking jet properties to accretion modes and gamma-ray emission mechanisms.

Contribution

It introduces a broken power sequence model for radio-loud AGN, emphasizing jet structure, accretion mode, and intrinsic power as key unification axes, and presents new insights into gamma-ray emission regions.

Findings

Identification of two AGN sub-populations based on jet structure.

A new unification scheme involving accretion mode and jet power.

Gamma-ray emission in powerful jets originates inside the BLR or torus.

Abstract

In recent work, we have identified two sub-populations of radio-loud AGN which appear to be distinguished by jet structure, where low-efficiency accreting systems produce `weak' jets which decelerate more rapidly than the `strong' jets of black holes accreting near the Eddington limit. The two classes are comprised of: (1) The weak jet sources, corresponding to FR I radio galaxies, having a decelerating or spine-sheath jet with velocity gradients, and (2) The strong jet sources, having fast, collimated jets, and typically displaying strong emission lines. The dichotomy in the \nu_peak-L_peak plane can be understood as a `broken power sequence' in which jets exist on one branch or the other based on the particular accretion mode. We suggest that the intrinsic kinetic power (as measured by low-frequency, isotropic radio emission), the orientation, and the accretion rate of the SMBH system are the the fundamental axes needed for unification of radio-loud AGN by studying a well-characterized sample of several hundred Fermi-detected jets. Finally, we present very recent findings that the most powerful strong jets produce gamma-rays by external Compton rather than SSC emission, placing the dissipation region in these strong jets at a radius inside the BLR and/or molecular torus.