General Relativistic Geodetic Precession from the Double Pulsar Eclipses

The double pulsar system PSR J0737-3039 exhibits unique and spectacular radio eclipses when pulsar A passes behind its companion pulsar B. During these eclipses, we observe rapid modulation of pulsar A's flux that is synchronized with the rotation of pulsar B. Lyutikov and Thompson proposed that synchrotron absorption from relativistic plasma trapped in pulsar B's magnetosphere, which is assumed to be a truncated dipole, is the mechanism responsible for the eclipses. The change in geometry caused by the co-rotation of the magnetosphere with the pulsar leads to the observed flux modulation. We present 3.5 years of 820 MHz eclipse monitoring with the Green Bank Telescope. Successful modelling of the complex eclipse light curves using this simple model provides direct empirical evidence that the magnetic field of pulsar B is predominantly dipolar. Furthermore, eclipse fitting yields a very accurate constraint on the orientation of pulsar B in space. We observed significant changes in the eclipse profile that are well characterized by geodetic precession of pulsar B's spin axis about the orbital angular momentum. We found a precession rate that is in remarkable agreement with the value predicted by general relativity. This is the most precise measurement of geodetic precession in the strong-field regime made so far and it offers a promising new test of gravity theories that is independent of the pulsar timing.