POLARIMETRY OF COMPACT SYMMETRIC OBJECTS

摘要

We present multifrequency VLBA observations of two polarized Compact Symmetric Objects (CSOs), J0000+ 4054 and J1826+1831, and a polarized CSO candidate, J1915+6548. Using the wavelength-squared dependence of Faraday rotation, we obtained rotation measures (RMs) of -180 ± 10 rad m~(-2) and 1540 ± 7 rad m~(-2) for the latter two sources. These are lower than what is expected of CSOs (several 1000 rad m~(-2)) and, depending on the path length of the Faraday screens, require magnetic fields from 0.03 to 6 μG. These CSOs may be more heavily affected by Doppler boosting than their unpolarized counterparts, suggesting that a jet-axis orientation more inclined toward the line of sight is necessary to detect any polarization. This allows for low RMs if the polarized components are oriented away from the depolarizing circumnuclear torus. These observations also add a fourth epoch to the proper-motion studies of J0000+4054 and J1826+1831, constraining their kinematic age estimates to > 610 and 2600 ± 490 yr, respectively. The morphology, spectrum, and component motions of J1915+6548 are discussed in light of its new classification as a CSO candidate, and its angle to the line of sight (～50°) is determined from relativistic beaming arguments.