Optical polarization of 52 radio-loud QSOs and BL Lacertae objects

Polarization measurements are presented for 52 radio-loud QSOs and BL Lac objects. For nine highly polarized (p > 3%) active galactic nuclei (AGNs), these are the first published polarization measurements. Of these nine, seven are highly polarized QSOs (HPQs), one is a BL Lac object, and another is a likely BL Lac object. Polarization variability is confirmed for some of these new and previously known highly polarized AGNs. While six of the HPQs have flat radio spectra and are almost certainly blazars, PKS 1452-217 is probably a new member of the rare class of radio-loud QSOs that show high polarization by scattering, and it is therefore important for testing orientation unified schemes. In competition for the highest redshift HPQ are the well-observed QSO PKS 0438-43 at z = 2.85, with maximum p similar to 4.7%, and PKS 0046 - 315 at z = 2.72, for which we find p similar to 13%.