Radio beam of the relativistic binary pulsar B1534 + 12

We present high-resolution polarimetric observations and low-noise integrated profiles of the relativistic binary radio pulsar B1534 + 12. Roughly 20% of the main pulse emission is linearly polarized at 430 MHz. Our measurements are sensitive to low-level off-pulse emission and trace the variation in polarization angle through a substantial fraction of the pulse period. Within the rotating-vector model, two distinct sets of geometric parameters fit the data reasonably well. Both geometries imply that the pulsar is nearly an orthogonal rotator. We use this information to select one of the two equally likely values of orbital inclination obtained separately, from pulse timing measurements, and find that the misalignment between spin and orbital angular momentum is probably small. In addition to establishing the geometry of the system and providing clues to the relevant emission physics, our results form a pulse polarization template against which future observations can be compared in order to constrain or detect relativistic precession of the pulsar's spin axis.