Connecting radio variability to the characteristics of gamma-ray blazars
We present results from four years of twice-weekly 15 GHz radio monitoring of about 1500 blazars with the Owens Valley Radio Observatory 40 m telescope. Using the intrinsic modulation index to measure variability amplitude, we find that, with >6σ significance, the radio variability of radio-selected gamma-ray-loud blazars is stronger than that of gamma-ray-quiet blazars. Our extended data set also includes at least 21 months of data for all AGN with 'clean' associations in the Fermi Large Area Telescope First AGN Catalog, 1LAC. With these additional data, we examine the radio variability properties of a gamma-ray-selected blazar sample. Within this sample, we find no evidence for a connection between radio variability amplitude and optical classification. In contrast, for our radio-selected sample we find that the BL Lac object subpopulation is more variable than the flat-spectrum radio quasar (FSRQ) subpopulation. Radio variability is found to correlate with the synchrotron peak frequency, with low- and intermediate-synchrotron-peaked blazars varying more than high-synchrotron-peaked ones. We find evidence for a significant negative correlation between redshift and radio variability among bright FSRQs.
Additional Information© 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2013 December 12. Received 2013 December 9; in original form 2013 October 25. First published online: January 14, 2014. JLR would like to thank Matthew L. Lister for several helpful discussions. The OVRO 40m monitoring programme is supported in part by National Science Foundation (NSF) grants AST-0808050 and AST-1109911 and NASA grants NNX08AW31G and NNX11AO43G. TH was supported by the Jenny and Antti Wihuri foundation. VP acknowledges support from the 'RoboPol' project, which is implemented under the 'Aristeia' Action of the 'Operational Programme Education and Lifelong Learning' and is co-funded by the European Social Fund (ESF) and Greek National Resources; and from the European Commission Seventh Framework Programme (FP7) through grants PCIG10-GA-2011-304001 'JetPop' and PIRSES-GA-2012-31578 'EuroCal.' The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. 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.
Published - MNRAS-2014-Richards-3058-69.pdf
Submitted - 1312.3634v1.pdf
Supplemental Material - table1.csv
Supplemental Material - table2.csv