Skip to content

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

Research output: Contribution to journalArticle

  • Joseph L. Richards
  • Walter Max-Moerbeck
  • Vasiliki Pavlidou
  • Oliver G. King
  • Timothy J. Pearson
  • Anthony C. S. Readhead
  • Rodrigo Reeves
  • Martin C. Shepherd
  • Matthew A. Stevenson
  • Lawrence C. Weintraub
  • Lars Fuhrmann
  • Enimanouil Angelakis
  • J. Anton Zensus
  • Stephen E. Healey
  • Roger W. Romani
  • Michael S. Shaw
  • Keith Grainge
  • Mark Birkinshaw
  • Katy Lancaster
  • Diana M. Worrallhttp://orcid.org/0000-0002-1516-0336
  • Gregory B. Taylor
  • Garret Cotter
  • Ricardo Bustos
Original languageEnglish
Article number29
Pages (from-to)29
Number of pages22
JournalAstrophysical Journal Supplement Series
Volume194
Issue number2
DOIs
DatePublished - Jun 2011

Abstract

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 degrees) 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.

Additional information

23 pages, 24 figures. Submitted to ApJS

    Research areas

  • BL Lacertae objects: general, galaxies: active, methods: statistical, quasars: general, radio continuum: galaxies, EXTRAGALACTIC RADIO-SOURCES, GAMMA-RAY EMISSION, LINEAR-POLARIZATION PROPERTIES, READHEAD SURVEY SOURCES, LARGE-AREA TELESCOPE, BL LACERTAE OBJECTS, BLACK-HOLES, RELATIVISTIC JET, TOTAL FLUX, VARIABILITY

Documents

View research connections

Related faculties, schools or groups