Blazar sequence - an artefact of Doppler boosting

TL;DR

This paper demonstrates that the observed blazar sequence, characterized by an anticorrelation between synchrotron peak frequency and luminosity, is an artifact caused by Doppler boosting effects, which, when corrected, reveal no such intrinsic correlation.

Contribution

The study provides a new Doppler correction method for blazar spectral data, showing the blazar sequence is not an intrinsic property but an observational artifact.

Findings

Doppler correction removes the negative correlation in the blazar sequence.

Intrinsic synchrotron peak frequencies and luminosities are positively correlated.

Doppler boosting varies with synchrotron peak frequency, affecting observed properties.

Abstract

The blazar sequence is a scenario in which the bolometric luminosity of the blazar governs the appearance of its spectral energy distribution. The most prominent result is the significant negative correlation between the synchrotron peak frequencies and the synchrotron peak luminosities of the blazar population. Observational studies of the blazar sequence have, in general, neglected the effect of Doppler boosting. We study the dependence of both the synchrotron peak frequency and luminosity with Doppler-corrected quantities. We determine the spectral energy distributions of 135 radio-bright AGN and find the best-fit parabolic function for the distribution to quantify their synchrotron emission. The corresponding measurements of synchrotron peak luminosities and frequencies are Doppler-corrected with a new set of Doppler factors calculated from variability data. The relevant correlations for the blazar sequence are determined for these intrinsic quantities. The Doppler factor depends strongly on the synchrotron peak frequency, the lower energy sources being more boosted. Applying the Doppler correction to the peak frequencies and luminosities annuls the negative correlation between the two quantities, which becomes positive. For BL Lacertae objects, the positive correlation is particularly strong. The blazar sequence, when defined as the anticorrelation between the peak frequency and luminosity of the synchrotron component of the spectral energy distribution, disappears when the intrinsic, Doppler-corrected values are used. It is an observational phenomenon created by variable Doppler boosting across the synchrotron peak frequency range.