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

Abstract

We present the results of seven years of multicolour photometric monitoring of a sample of 31 ${\hat{I}}^3$-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 ${\hat{I}}^3$-ray data in order to explore the radiation mechanisms and particle populations in blazar jets. We find significant correlations between optical and ${\hat{I}}^3$-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 ${\hat{I}}^3$-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.

32 pages, 35 figures