In this work we apply the stacking technique to estimate the average fractional polarisation from 30 to 353 GHz of a primary sample of 1560 compact sources – essentially all radio sources – detected in the 30 GHz Planck all-sky map and listed in the second version of the Planck Catalogue of Compact Sources ( PCCS2 ) .
We divide our primary sample in two subsamples according to whether the sources lay ( 679 sources ) or not ( 881 sources ) inside the sky region defined by the Planck Galactic mask ( f _ { sky } \sim 60 per cent ) and the area around the Magellanic Clouds .
We find that the average fractional polarisation of compact sources is approximately constant ( with frequency ) in both samples ( with a weighted mean over all the channels of 3.08 per cent outside and 3.54 per cent inside the Planck mask ) .
In the sky region outside the adopted mask , we also estimate the \mu and \sigma parameters for the log-normal distribution of the fractional polarisation , finding a weighted mean value over all the Planck frequency range of 1.0 for \sigma and 0.7 for \mu ( that would imply a weighted mean value for the median fractional polarisation of 1.9 per cent ) .