Classification of Young Pulsars and Empirical Evolution of Regular Braking Index

Abstract

Abstract—The distribution of young pulsars in the log(dP/dt)–log(tc) diagram that have a characteristic age tc ~10–16 is analyzed. Six clusters-stripes are revealed for the first time, along which the long-term evolution tracks of individual pulsars pass. The mean track in a stripe corresponds to the long-term regular evolution for a typical pulsar of this stripe. The clusters-stripes population composition is analyzed by object types. Rotating radio transients (RRATs) are present in all clusters-stripes at tc > 105 yr. It turns out that three stripes contain objects of only one of the three numerous (≥10) known types: magnetars, pulsars with a high magnetic field, and Vela-like pulsars. In three other clusters-stripes, objects of the indicated three types are not found. The following object classification in the composition of six clusters-stripes is proposed: magnetars (M), pulsars with a high magnetic field (HB), pulsars with a sub-high magnetic field (S-HB), Vela-type pulsars (V), sub-Vela pulsars (SV), and low magnetic field pulsars (LB). Four pulsars that are outside the stripes are referred to peculiar. Analytical formulas are presented for calculating evolution parameters in the log(dP/dt)–log(tc) diagram. As a result of the optimal fitting of the mean clusters-stripes track by the appropriate empirical function, long-term regular values of the braking index and the second derivative of the period are estimated for 327 pulsars for the first time. As a consequence of the clusters-stripes presence, the “striped” distribution of the dipole magnetic field at pulsar birth indicates the intervality in the mass distribution of pulsar progenitor stars. The recent supernovae explosion models (Pejcha & Thomson, 2015) also produce an interval mass distribution of progenitors generating neutron stars, which confirm that pulsar clusters-stripes do exist and their origin can be naturally explained.