A ug 1 99 7 Implications of a constant observed braking index for young pulsar ’ s spindown

The observed braking index n obs 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 m obs = 15 in both cases. We propose a simple model able to account for these differences, based on a growth of the " torque function " K = − ˙ Ω/Ω n , under the constraint that n obs 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 n obs have been measured.