Bimodal radio variability in OVRO-40 m-monitored blazars

: I. Liodakis, V. Pavlidou, T. Hovatta, W. Max-Moerbeck, T. J. Pearson, J. L. Richards, A. C. S. Readhead

Publisher: OXFORD UNIV PRESS

: 2017

: Monthly Notices of the Royal Astronomical Society

: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

: MON NOT R ASTRON SOC

: 467

: 4

: 4565

: 4576

: 12

: 0035-8711

: 1365-2966

DOI: https://doi.org/10.1093/mnras/stx432

: https://research.utu.fi/converis/portal/detail/Publication/20506620

Blazars are known to show periods of quiescence followed by outbursts visible throughout the electromagnetic spectrum. We present a novel maximum likelihood approach to capture this bimodal behaviour by examining blazar radio variability in the flux-density domain. We separate quiescent and flaring components of a source's light curve by modelling its flux-density distribution as a series of 'off'- and 'on'-states. Our modelling allows us to extract information regarding the flaring ratio, duty cycle, and the modulation index in the 'off'state, in the 'on'- state, as well as throughout the monitoring period of each blazar. We apply our method to a flux-density-limited subsample from the Owens Valley Radio Observatory's 15 GHz blazar monitoring programme, and explore differences in the variability characteristics between BL Lacs and FSRQs as well as between gamma-ray detected and non-detected sources. We find that (1) BL Lacs are more variable and have relatively larger outbursts than the FSRQs; (2) unclassified blazar candidates in our sample show similar variability characteristics as the FSRQs and (3) gamma-ray detected differ from the gamma-ray non-detected sources in all their variability properties, suggesting a link between the production of gamma-rays and the mechanism responsible for the radio variability. Finally, we fit distributions for blazar flaring ratios, duty cycles, and on- and off-modulation indices that can be used in population studies of variability-dependent blazar properties.

stx432.pdf