Evidence for Geodetic Spin Precession in the Binary Pulsar PSR 1913+16

Six years of careful observations have revealed a gradual secular evolution in the pulse profile of binary pulsar PSR 1913 + 16. At frequencies near 1400 MHz, the flux density in the first component of the double-peaked profile is decreasing relative to the second component at a rate slightly greater than 1 percent per year. The changes are consistent with the expected rate of general relativistic geodetic precession of the pulsar spin axis. In addition to its relativistic implications, the precessional motion is providing unique two-dimensional information on the structure of the pulsar emission zone.