Aller, Hugh

Circular Polarization Measurements at Centimeter Wavelengths.

Authors list:  Hugh D. Aller & Margo F. Aller

The University of Michigan 26-Meter paraboloid was used to monitor the integrated emissions of over a dozen active extragalactic objects at 4.8, 8.0, and 14.5 GHz in all four Stokes parameters for more than a decade. The low level of instrumental polarization in Stokes V (less than 0.1 percent) is verified by repeated observations of galactic HII regions such as M17 and M42. We present light curves and spectra in all 4 Stokes parameters for the bright QSOs 3C 279, 3C 345, and OV-236, and for the radio galaxy 3C 84. 3C 279 and OV-236 have exhibited V as high as 1% with variability time scales of months to years. The polarity of V has been observed in our source sample to reverse with time, and we have observed simultaneous opposite polarities of V within our frequency range of 5 to 15 GHz. The variability observed includes temporal changes in polarity at a single frequency, frequency-dependent differences in polarity at a single epoch, and long-term ordered changes in amplitude. This research was supported in part by funds from NSF grant AST-0607523.