A strong $\ddot{\nu} - \dot{\nu}$ correlation in radio pulsars with implications for torque variations

We present an analysis of the spin-down parameters for 131 radio pulsars for which $\ddot\nu$ has been well determined. These pulsars have characteristic ages ranging from $10^{3} - 10^{8}$ yr and spin periods in the range 0.4--30 s; nearly equal numbers of pulsars have $\ddot\nu>0$ as $\ddot\nu<0$. We find a strong correlation of $\ddot\nu$ with $\dot{\nu}$, {\em independent of the sign of} $\ddot\nu$. We suggest that this trend can be accounted for by small, stochastic deviations in the spin-down torque that are directly proportional (in magnitude) to the spin-down torque.