Blazars are powerful, variable emitters from radio to gamma-ray wavelengths. Even though the general picture of synchrotron emission at low energies and inverse Compton at the high energy end is well established, many important aspects of these remarkable objects are still not well understood. For example even the location of the gamma-ray emission regions is still not clearly established, with some theories locating it close to the black hole/accretion disk, while others place it at parsec scales in the radio jet. Since mid-2007 we have carried out a large scale monitoring program at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope.
We are currently observing about 1700 blazars twice per week. The sample includes all the Fermi-LAT detected blazars north of declination -20 degrees. We study the existence of correlated variability between these two bands for 91 sources bright enough to be detected weekly by LAT. The existence of correlated variability can be interpreted as an indication of common spatial location for the radio and gamma-ray emission, making the evaluation of its statistical significance a key goal of our program.
A study of the statistical significance of these cross-correlations is presented along with a discussion of the Monte Carlo simulations used to evaluate them. More information about the conditions on the radio emission zone can be obtained through polarization monitoring which tells us about the configuration of the magnetic fields on this region. To study radio polarization variability we are building KuPol, a radio polarization receiver for the 12 to 18 GHz band. A description of its capabilities and progress report will be given.