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Published September 2016 | Published + Submitted
Journal Article Open

Optical and radio variability of the northern VHE gamma-ray emitting BL Lacertae objects


We compare the variability properties of very high energy gamma-ray emitting BL Lac objects in the optical and radio bands. We use variability information to distinguish multiple emission components in the jet, to be used as a guidance for spectral energy distribution modelling. Our sample includes 32 objects in the northern sky for which we have data for at least two years in both bands. We use optical R-band data from the Tuorla blazar monitoring program and 15 GHz radio data from the Owens Valley Radio Observatory blazar monitoring program. We estimate the variability amplitudes using the intrinsic modulation index, and study the time-domain connection by cross-correlating the optical and radio light curves assuming power law power spectral density. Our sample objects are in general more variable in the optical than radio. We find correlated flares in about half of the objects, and correlated long-term trends in more than 40% of the objects. In these objects we estimate that at least 10−50% of the optical emission originates in the same emission region as the radio, while the other half is due to faster variations not seen in the radio. This implies that simple single-zone spectral energy distribution models are not adequate for many of these objects.

Additional Information

© 2016 ESO. Article published by EDP Sciences. Received 2 March 2016; Accepted 4 June 2016; Published online 29 September 2016. T.H. was supported by the Academy of Finland project number 267324. The OVRO 40-m monitoring program is supported in part by NASA grants NNX08AW31G and NNX11A043G, and NSF grants AST-0808050 and AST-1109911. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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Published - aa28420-16.pdf

Submitted - 1606.06431v1.pdf


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August 20, 2023
October 23, 2023