June 8, 2009J. Richards, 214th AAS, Pasadena1 15 GHz Monitoring of Gamma-ray Blazars with the OVRO 40 Meter Telescope in Support of Fermi-GST Joseph Richards, W. Max-Moerbeck, V. Pavlidou, T. J. Pearson, A. C. S. Readhead, M. A. Stevenson California Institute of Technology, Owens Valley Radio Observatory S. E. Healey, R. W. Romani, M. S. Shaw Department of Physics/KIPAC, Stanford University E. Angelakis, L. Fuhrmann, J. A. Zensus Max-Planck-Institut für Radioastronomie K. Grainge Astrophysics Group, Cavendish Laboratory, University of Cambridge G. B. Taylor Department of Physics and Astronomy, University of New Mexico This work is supported in part by NSF award AST and NASA award NNX08AW31G.

June 8, 2009J. Richards, 214th AAS, Pasadena2 Overview ● ~1200 blazars, ≥ 2x per week since mid-2007 ● Blazars: radio-loud AGNs ● viewed along jet ● extremely variable ● broad-band (radio to TeV) ● dominate γ-ray sky ● MWL Support for Fermi-GST ● correlate radio/γ-ray events ● discriminate blazar models Figure: From (see, e.g., Urry and Padovani, 1995, PASP, 107, 803.)

June 8, 2009J. Richards, 214th AAS, Pasadena3 CGRaBS Sources The Sample ● CGRaBS: 1625 total ● 1158 at dec > −20º ● ~70% of LAT 3-mo AGNs ● Updates from Fermi-LAT ● Other Sources ● e.g., VERITAS monitoring Healey et al. 2008, ApJS, 175, 97. Abdo et al. 2009, arXiv A.

June 8, 2009J. Richards, 214th AAS, Pasadena4 Instrument and Observations ● 500 Hz Dicke-switched cryogenic HEMT receiver ● 15 GHz center freq, 3 GHz BW ● Dual 2.5 arcmin FWHM beams ● Trx ~ 30 K, Tsky(za=0) ~ 5 K, Tgnd ~ 18 K ● Azimuth double-switched ● Switch between two ref. fields – 8 s integration per field ● Removes atmosphere, ground Readhead et al. 1989, ApJ, 346, 566. A B C D 13' M−R1 R2−M M−R1 S=((A+D)-(B+C))/4

June 8, 2009J. Richards, 214th AAS, Pasadena5 Data Filters and Calibration ● Remove Unreliable Measurements ● High wind, sun/moon elongation ● Bad atmosphere (rain/snow, “ABCD”) ● Flux density calibration ● Short timescale: noise diode ● Absolute scale: 3C 286 (Baars et al., 1977) ● Error estimation ● Measure thermal noise for each flux density: ● Estimate S-proportional term from calibrator scatter:

June 8, 2009J. Richards, 214th AAS, Pasadena6 Flux Calibrator

June 8, 2009J. Richards, 214th AAS, Pasadena7 Variability Results 1 Time Series Autocorrelation Function Structure Function

June 8, 2009J. Richards, 214th AAS, Pasadena8 Variability Results 2 Time Series Autocorrelation Function Structure Function

June 8, 2009J. Richards, 214th AAS, Pasadena9 Variability Results 3

June 8, 2009J. Richards, 214th AAS, Pasadena10 F-GAMMA Collaboration ● Monthly Radio Spectra for ~60 Sources ● Effelsberg 100 m Telescope (MPIfR, Germany) – 8 frequencies, 2.7–43 GHz ● Pico Veleta 30 m Telescope (IRAM, Spain) – 3, 2, 1 mm ● Also ● APEX 12 m Telescope (MPIfR, ESO, OSO, Chile) – 0.8 mm ● Skinakas 1.3 m Telescope (Crete) – Optical U, B, V, R, I Fuhrmann et al. 2007, Angelakis et al. 2008

June 8, 2009J. Richards, 214th AAS, Pasadena11 3C Effelsberg + IRAM OVRO

June 8, 2009J. Richards, 214th AAS, Pasadena12 Summary ● Now have 2 years of densely-sampled 15 GHz light curves ● Good coverage of Fermi LAT sources ● Variability studies under way ● Wide variety of behaviors, time scales ● Promising prospects from MWL collaborations ● Simultaneous SEDs from radio – γ ● Time-series analysis ● For more information: AAS Poster, Max-Moerbeck et al.

June 8, 2009J. Richards, 214th AAS, Pasadena13 Non-Variability Results Time Series Autocorrelation Function Structure Function