Long-term Evolutionary Links Between the Isolated Neutron Star Populations

TL;DR

This study uses the fallback disc model to explore evolutionary links among various isolated neutron star populations, explaining their observed diversity through initial conditions and continuous magnetic dipole moment distributions.

Contribution

It demonstrates that different neutron star types can evolve from common initial conditions within a unified fallback disc framework, clarifying their relationships and addressing the birth-rate problem.

Findings

HBRPs can evolve into AXP/SGRs and then into LPPs.

AXP/SGRs are not evolutionarily linked to CCOs, XDINs, or RRATs.

Most RRATs pass through RP or HBRP phases early in their evolution.

Abstract

We have investigated the evolutionary connections of the isolated neutron star (NS) populations including radio pulsars (RPs), anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated NSs (XDINs), ``high-magnetic-field'' RPs (``HBRPs''), central compact objects (CCOs), rotating radio transients (RRATs), and long-period pulsars (LPPs) in the fallback disc model. The model can reproduce these NS families as a natural outcome of different initial conditions (initial period, disc mass, and dipole moment, $\mu$) with a continuous $\mu$ distribution in the $\sim 10^{27} - 5 \times 10^{30}$ G cm$^3$ range. Results of our simulations can be summarised as follows: (1) A fraction of ``HBRPs'' with relatively high $\mu$ evolve into the persistent AXP/SGR properties, and subsequently become LPPs. (2) Persistent AXP/SGRs do not have evolutionary links with CCOs, XDINs, and RRATs. (3) For a wide range of $\mu$, most RRATs evolve passing through RP or ``HBRP'' properties during their early evolutionary phases. (4) A fraction of RRATs which have the highest estimated birth rate seem to be the progenitors of XDINs. (5) LPPs, whose existence was predicted by the fallback disc model, are the sources evolving in the late stage of evolution before the discs become inactive. These results provide concrete support to the ideas proposing evolutionary connections between the NS families to account for the ``birth-rate problem'', the discrepancy between the cumulative birth rate estimated for these systems and the core-collapse supernova rate.