The Rotation Measure of Radio Galaxy ESO 328-13 Through the Shock Front of SN1006

PAC

In a radio polarization study of the supernova remnant (SNR) of SN1006, we found evidence for variable Faraday rotation toward a FR-I (double-lobed jet) radio source associated with ESO 328-13, a group of interacting galaxies. The background source lies on the eastern edge of the SNR, and the jet traverses from inside the remnant to outside. The rotation measure (RM) of the eastern jet's lobe experiences a shift of 20 rad/m2 as it crosses the shell, and exhibits a gradient whose magnitude decreases toward the interior so that the RM is the same for the edges of the radio galaxy’s eastern and western lobes. After rotating the polarization vectors to zero wavelength, we found that the magnetic field orientation of the SNR is nearly radial with respect to the shell, while the magnetic vectors of the radio jets are perpendicular to their axes, a typical trait of FR-I sources. These results suggest the variation in RM is not intrinsic to the radio galaxy; rather, the variation is a direct effect of SN1006’s post-shock environment. This discovery presents us with a unique opportunity to constrain the post-shock magnetic field strength of the SNR.