Hadronic models of blazars require a change of the accretion paradigm

TL;DR

Hadronic models of blazar emission imply super-Eddington jet powers and low magnetic fluxes, challenging current accretion paradigms and suggesting the need for a significant revision of AGN accretion theories.

Contribution

This paper demonstrates that hadronic models of blazars require extremely high accretion rates and low magnetic fluxes, contradicting standard accretion and jet formation mechanisms.

Findings

Jet powers in hadronic models are highly super-Eddington.

Radio core shift measurements imply low magnetic fluxes.

The accretion efficiency is extremely low (~4×10⁻⁵).

Abstract

We study hadronic models of broad-band emission of jets in radio-loud active galactic nuclei, and their implications for the accretion in those sources. We show that the models that account for broad-band spectra of blazars emitting in the GeV range in the sample of Boettcher et al. have highly super-Eddington jet powers. Furthermore, the ratio of the jet power to the radiative luminosity of the accretion disc is $\sim 3000$ on average and can be as high as $\sim 10^5$. We then show that the measurements of the radio core shift for the sample imply low magnetic fluxes threading the black hole, which rules out the Blandford-Znajek mechanism to produce powerful jets. These results require that the accretion rate necessary to power the modelled jets is extremely high, and the average radiative accretion efficiency is $\sim 4 \times 10^{-5}$. Thus, if the hadronic model is correct, the currently prevailing picture of accretion in AGNs needs to be significantly revised. Also, the obtained accretion mode cannot be dominant during the lifetimes of the sources, as the modelled very high accretion rates would result in too rapid growth of the central supermassive black holes. Finally, the extreme jet powers in the hadronic model are in conflict with the estimates of the jet power by other methods.