Implications of a constant observed braking index for young pulsar’s spindown

The observed braking index nobs which had been determined for a few young pulsars, had been found to differ from the expected value for a rotating magnetic dipole model. In addition, the observational jerk parameter, determined for two of these pulsars, disagrees with the theoretical prediction mobs = 15 in both cases. We propose a simple model able to account for these differences, based on a growth of the ”torque function” K = −Ω̇/Ω, under the constraint that nobs is a constant. We show that there is observational evidence supporting the latter hypotesis, and derive initial values for several physical quantities for the four pulsars whose nobs have been measured. Subject headings: Pulsars : general — Pulsars : individual : (PSR B0531+21, PSR B0540-69, PSR B0833-45, PSR B1509-58)