Orientations of spin and magnetic dipole axes of pulsars in the J0737-3039 binary based on polarimetry observations at the green bank telescope

We report here the first polarimetric measurements of the pulsars in the J0737-3039 binary neutron star system using the Green Bank Telescope. The data suggest that the primary star (pulsar A) has a wide hollow cone of emission, which is an expected characteristic of the relatively open magnetosphere given its short spin period, and that pulsar A has a small angle between its spin and magnetic dipole axes, 4° ± 3°. This geometry suggests that pulsar A's wind pressure on pulsar B's magnetosphere will depend on orbital phase. This variable pressure is one mechanism for the variation of flux and profile shape of pulsar B with respect to the orbital phase that has been reported. The response of pulsar B to the pulsar A wind pressure will also depend on the particular side of its magnetosphere facing the wind at the spin phase when pulsar B is visible. This is a second possible mechanism for variability. We suggest that pulsar B may have its spin axis aligned with the orbital angular momentum owing to pulsar A's wind torque that contributes to its spin-down. Monitoring the pulsars while geodetic precession changes spin orientations will provide essential evidence to test detailed theoretical models. We determine the rotation measures of the two stars to be -112.3 ± 1.5 and -118 ± 12 rad m^-2.