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 s tar system. As part of our analysis, we model the motion of the binary in t he Galaxy after the second supernova explosion, and we derive constraints o n the unknown radial velocity. We also obtain limits on the magnitude and d irection of the kick velocity imparted to the pulsar companion during the s econd supernova explosion. We consider the complete set of possible cases, depending on the kinematic age of the system and the 180 degrees 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 n eutron star progenitor, independent of the specific presupernova configurat ion. Such a tight constraint on the kick direction has important implicatio ns for the physical mechanism responsible for the kick.