Constraints on supernova kicks from the double neutron star system PSR B1913+16

We use recent information on geodetic precession of the binary pulsar B1913+16 along with measurements of its orbital parameters and proper motion to derive new constraints on the immediate progenitor of this double neutron star system. As part of our analysis, we model the motion of the binary in the Galaxy after the second supernova explosion, and we derive constraints on the unknown radial velocity. We also obtain limits on the magnitude and direction of the kick velocity imparted to the pulsar companion during the second supernova explosion. We consider the complete set of possible cases, depending on the kinematic age of the system and the 180° ambiguity in the pulsar spin orientation. Most interestingly, we find that the natal kick must have been directed almost perpendicular to the spin axis of the neutron star progenitor, independent of the specific presupernova configuration. Such a tight constraint on the kick direction has important implications for the physical mechanism responsible for the kick.