Astrophys. J., Suppl. Ser., 194, 29 (2011/June-0)
Blazars in the Fermi era: the OVRO 40 m telescope monitoring program.
RICHARDS J.L., MAX-MOERBECK W., PAVLIDOU V., KING O.G., PEARSON T.J., READHEAD A.C.S., REEVES R., SHEPHERD M.C., STEVENSON M.A., WEINTRAUB L.C., FUHRMANN L., ANGELAKIS E., ANTON ZENSUS J., HEALEY S.E., ROMANI R.W., SHAW M.S., GRAINGE K., BIRKINSHAW M., LANCASTER K., WORRALL D.M., TAYLOR G.B., COTTER G. and BUSTOS R.
Abstract (from CDS):
The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope provides an unprecedented opportunity to study gamma-ray blazars. To capitalize on this opportunity, beginning in late 2007, about a year before the start of LAT science operations, we began a large-scale, fast-cadence 15 GHz radio monitoring program with the 40 m telescope at the Owens Valley Radio Observatory. This program began with the 1158 northern (δ > -20°) sources from the Candidate Gamma-ray Blazar Survey and now encompasses over 1500 sources, each observed twice per week with about 4 mJy (minimum) and 3% (typical) uncertainty. Here, we describe this monitoring program and our methods, and present radio light curves from the first two years (2008 and 2009). As a first application, we combine these data with a novel measure of light curve variability amplitude, the intrinsic modulation index, through a likelihood analysis to examine the variability properties of subpopulations of our sample. We demonstrate that, with high significance (6σ), gamma-ray-loud blazars detected by the LAT during its first 11 months of operation vary with almost a factor of two greater amplitude than do the gamma-ray-quiet blazars in our sample. We also find a significant (3σ) difference between variability amplitude in BL Lacertae objects and flat-spectrum radio quasars (FSRQs), with the former exhibiting larger variability amplitudes. Finally, low-redshift (z < 1) FSRQs are found to vary more strongly than high-redshift FSRQs, with 3σ significance. These findings represent an important step toward understanding why some blazars emit gamma-rays while others, with apparently similar properties, remain silent.
BL Lacertae objects: general - galaxies: active - methods: statistical - quasars: general - radio continuum: galaxies
VizieR on-line data:
<Available at CDS (J/ApJS/194/29): table4.dat table5.dat>
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