BLAZARS IN THE FERMI ERA: THE OVRO 40 m TELESCOPE MONITORING PROGRAM
- Cahill Laboratory of Astronomy and Astrophysics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125 (United States)
- Max-Planck-Institut-fuer-Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)
- Department of Physics, Stanford University, Stanford, CA 94305 (United States)
- Astrophysics Group, Cavendish Laboratory, University of Cambridge, J J Thomson Ave, Cambridge CB3 0HE (United Kingdom)
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 ({delta} > -20{sup 0}) 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 (6{sigma}), 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 (3{sigma}) 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 3{sigma} significance. These findings represent an important step toward understanding why some blazars emit gamma-rays while others, with apparently similar properties, remain silent.
- OSTI ID:
- 21560375
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 194, Issue 2; Other Information: DOI: 10.1088/0067-0049/194/2/29; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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