We present an analysis of the linear polarization of six active galactic nuclei – 0415+379 ( 3C 111 ) , 0507+179 , 0528+134 ( OG+134 ) , 0954+658 , 1418+546 ( OQ+530 ) , and 1637+574 ( OS+562 ) .
Our targets were monitored from 2007 to 2011 in the observatory-frame frequency range 80–253 GHz , corresponding to a rest-frame frequency range 88–705 GHz .
We find average degrees of polarization m _ { L } \approx 2 - 7 % ; this indicates that the polarization signals are effectively averaged out by the emitter geometries .
From a comparison of the fluctuation rates in flux and degree of polarization we conclude that the spatial scales relevant for polarized emission are of the same order of , but probably not smaller than , the spatial scales relevant for the emission of the total flux .
We see indication for fairly strong shocks and/or complex , variable emission region geometries in our sources , with compression factors \lesssim 0.9 and/or changes in viewing angles by \gtrsim 10 ^ { \circ } .
An analysis of correlations between source fluxes and polarization parameter points out special cases : the presence of ( at least ) two distinct emission regions with different levels of polarization ( for 0415+379 ) as well as emission from a single , predominant component ( for 0507+179 and 1418+546 ) .
Regarding the evolution of flux and polarization , we find good agreement between observations and the signal predicted by “ oblique shock in jet ” scenarios in one source ( 1418+546 ) .
We attempt to derive rotation measures for all sources , leading to actual measurements for two AGN and upper limits for three sources .
We derive values of { RM } = ( -39 \pm 1 _ { stat } \pm 13 _ { sys } ) \times 10 ^ { 3 } rad m ^ { -2 } and { RM = ( 42 \pm 1 _ { stat } \pm 11 _ { sys } ) \times 10 ^ { 4 } } rad m ^ { -2 } for 1418+546 and 1637+574 , respectively ; these are the highest values reported to date for AGN .
These values indicate magnetic field strengths of the order \sim 10 ^ { -4 } G. For 0415+379 , 0507+179 , and 0954+658 we derive upper limits { |RM| } < 1.7 \times 10 ^ { 4 } rad m ^ { -2 } .
From the relation | { RM } | \propto \nu ^ { a } we find a = 1.9 \pm 0.3 for 1418+546 , in good agreement with a = 2 as expected for a spherical or conical outflow .