ar X iv : a st ro - p h / 97 04 11 2 v 1 1 2 A pr 1 99 7 Evidence for Ordered Magnetic Fields in the Quasar Environment

At a distance of 20 pc from the purported supermassive black hole powering quasars, temperatures and densities are inferred from optical observations (Osterbrock 1989) to be ∼ 10 4 K and ∼ 10 4 cm −3. Here we present Very Long Baseline Interferometry radio observations revealing organized magnetic fields on the parsec scale in the hot plasma surrounding the quasar OQ 172 (1442+101). These magnetic fields rotate the plane of polarization of the radio emission coming from the core and inner jet of the quasar. The derived rotation measure (RM) is 40,000 rad m −2 in the rest frame of the quasar. Only 10 mas (a projected distance of 68 pc) from the nucleus the jet absolute values of RM fall to less than 100 rad m −2 .