Distinguishing radiation mechanisms and particle populations in blazar jets through long-term multi-band monitoring with RINGO3 and Fermi

TL;DR

This study analyzes seven years of multi-band optical and gamma-ray data from 31 blazars, revealing correlations and spectral behaviors that shed light on the emission mechanisms and particle populations in their jets.

Contribution

It provides the first long-term multi-band monitoring of blazars combining optical polarimetry and gamma-ray data to distinguish radiation mechanisms.

Findings

Optical and gamma-ray fluxes are significantly correlated with no time lag.

Spectral behavior often fits a logarithmic model, indicating complex flux-spectral relationships.

High activity states show a transition from bluer- or redder-when-brighter to stable-when-brighter behaviors.

Abstract

We present the results of seven years of multicolour photometric monitoring of a sample of 31 $\gamma$-ray bright blazars using the RINGO3 polarimeter on the Liverpool Telescope from 2013--2020. We explore the relationships between simultaneous observations of flux in three optical wavebands along with Fermi $\gamma$-ray data in order to explore the radiation mechanisms and particle populations in blazar jets. We find significant correlations between optical and $\gamma$-ray flux with no detectable time lag, suggesting leptonic emission processes in the jets of these sources. Furthermore, we find the spectral behaviour against optical and $\gamma$-ray flux for many sources is best fit logarithmically. This is suggestive of a transition between bluer-/redder-when-brighter into stable-when-brighter behaviour during high activity states; a behaviour that might be missed in poorly sampled data, resulting in apparent linear relationships.