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Blazars in the Fermi Era: The OVRO 40 m Telescope Monitoring Program

Richards, Joseph L. and Max-Moerbeck, Walter and Pavlidou, Vasiliki and King, Oliver G. and Pearson, Timothy J. and Readhead, Anthony C. S. and Reeves, Rodrigo and Shepherd, Martin C. and Stevenson, Matthew A. and Weintraub, Lawrence C. and Fuhrmann, Lars and Angelakis, Emmanouil and Zensus, J. Anton and Healey, Stephen E. and Romani, Roger W. and Shaw, Michael S. and Grainge, Keith and Birkinshaw, Mark and Lancaster, Katy and Worrall, Diana M. and Taylor, Gregory B. and Cotter, Garret and Bustos, Ricardo (2011) Blazars in the Fermi Era: The OVRO 40 m Telescope Monitoring Program. Astrophysical Journal Supplement Series, 194 (2). Art. No. 29. ISSN 0067-0049. doi:10.1088/0067-0049/194/2/29.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Max-Moerbeck, Walter0000-0002-5491-5244
Pavlidou, Vasiliki0000-0002-0870-1368
King, Oliver G.0000-0002-6271-0062
Pearson, Timothy J.0000-0001-5213-6231
Readhead, Anthony C. S.0000-0001-9152-961X
Reeves, Rodrigo0000-0001-5704-271X
Angelakis, Emmanouil0000-0001-7327-5441
Zensus, J. Anton0000-0001-7470-3321
Romani, Roger W.0000-0001-6711-3286
Grainge, Keith0000-0002-6780-1406
Birkinshaw, Mark0000-0002-1858-277X
Worrall, Diana M.0000-0002-1516-0336
Taylor, Gregory B.0000-0001-6495-7731
Bustos, Ricardo0000-0001-8468-9391
Additional Information:© 2011 American Astronomical Society. Received 2010 November 12; accepted 2011 March 22; published 2011 May 23. We are grateful to Russ Keeney for his tireless efforts in support of observations at the Owens Valley Radio observatory. The OVRO 40 m monitoring program is supported in part by NASA grants NNX08AW31G and NNG06GG1G and NSF grant AST-0808050. Support from the Max-Planck Institut für Radioastronomie for upgrading the OVRO 40 m telescope receiver is also acknowledged. O.G.K. acknowledges the support of a Keck Institute for Space Studies Fellowship. W.M. acknowledges support from the US Department of State and the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) in Chile for a Fulbright-CONICYT scholarship. V.P. acknowledges support for this work provided by NASA through Einstein Postdoctoral Fellowship grant number PF8-90060 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060, and thanks the Department of Physics at the University of Crete for their hospitality during the completion of part of this work. Facilities: OVRO:40m
Group:Keck Institute for Space Studies
Funding AgencyGrant Number
Keck Institute for Space Studies (KISS)UNSPECIFIED
Department of StateUNSPECIFIED
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)UNSPECIFIED
NASA Einstein FellowshipPF8- 90060
Subject Keywords:BL Lacertae objects: general; galaxies: active; methods: statistical; quasars: general; radio continuum: galaxies
Issue or Number:2
Classification Code:PACS: 98.54.Cm; 98.62.Qz; 98.54.Aj; 95.85.Bh; 98.62.Py
Record Number:CaltechAUTHORS:20110705-142641499
Persistent URL:
Official Citation:Blazars in the Fermi Era: The OVRO 40 m Telescope Monitoring Program Joseph L. Richards et al. 2011 ApJS 194 29
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24301
Deposited On:06 Jul 2011 14:44
Last Modified:09 Nov 2021 16:22

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