In the period between 2007 and 2010, a new polarimetric calibration procedure, that allows the contemporary measurement of linear (LP) and circular polarization (CP), has been implemented at the Effelsberg radio telescope. Stokes V, which measures CP by means of the ratio V/I, has often been discarded from polarimetric observation strategies and calibrations, due to its typically low value.
The study of circular polarization and accurate multifrequency observations of linear polarization provide probes of AGN magnetic field properties. Spectral information, CP and LP, can be used to constrain the low energy end of the relativistic particle distribution, derive the magnetic field order, strength, and geometry, and infer the particle content of the AGN jets.
To date, several studies of CP from AGN have been carried out with interferometers: ATCA at 5 GHz, VLBA at 5.0 GHz and 15.0 GHz, and the VLA at 8.4 GHz. On the other hand the Michigan 26-metre radio telescope at 4.8 GHz and 8.0 GHz has been used to perform single-dish CP observations.
After a 1-year test phase of the new calibration procedure, the Effelsberg antenna has been used to perform a Full Stokes survey at 5 GHz, targeted on the Northern 1-Jy catalogue, and to obtain the first full Stokes spectra, in the range 2.5-10.5 GHz, from a sample of AGNs.
This Science Collaboration has the goal of proposing and investigating new science questions that can be addressed by means of a full Stokes study, to be performed by single-dish antennas and including following investigation at interferometric resolutions.
The tasks and opportunities of this Science Collaboration include:
The collaboration is for investigators who wish to participate in science which will stress the accuracy of contemporary linear and circular polarimetric observations, and who in turn, agree to contribute substantially to the efforts to realize the defined key-projects.