Comparison of the Angles between the Magnetic Moment and Rotation Axis for Two Groups of Radio Pulsars

Abstract

Angles $\beta$ between the rotation axis and the magnetic moment are calculated in two groups of radio pulsars with different periods ($P > 2$ s and $0.1{\text{ s}} < P < 2$ s). Two methods have been used. The first method is based on the observed pulse widths and provides the minimum values of angle ${{\beta }_{1}}$. The distributions of these angles differ significantly for these groups of objects. The second method uses polarization data to calculate more accurate values ${{\beta }_{2}}$. There is a trend for bimodality in the distribution of ${{\beta }_{2}}$ values for pulsars with $P > 2$ s. The closeness of the mean ${{\beta }_{2}}$ values ($47.6^\circ$ for long-period pulsars and $35.6^\circ$ for sources with shorter periods) does not allow us to explain the previously discovered difference in the behavior of these two groups in the $(dP{\text{/}}dt){-} (P)$ diagram by a decrease in the role of magnetic dipole radiation due to a decrease in $\beta$. Our analysis showed that the observed difference can be explained by the different dependence of the pulsar wind and magnetic dipole braking on the period of the pulsar. The deceleration of pulsars with $P > 2$ s is mainly caused by the pulsar wind.