IMPLICATIONS OF A CONSTANT OBSERVED BRAKING INDEX FOR YOUNG PULSARS SPIN-DOWN

The observed braking index n(obs), which has been determined for a few young pulsars, has been found to differ from the expected value for a rotating magnetic dipole model. In addition, the observed jerk parame ter, determined for two of these pulsars, disagrees with the theoretic al prediction m(obs) = 15 in both cases. We propose a simple model abl e to account for these differences, based on a growth of the ''torque function'' K = - (Ohm) over dot /Ohm(n), under the constraint that n(o bs) is a constant. We show that there is observational evidence suppor ting the latter hypothesis and derive initial values for several physi cal quantities for the four pulsars whose n(obs) has been measured.