Population synthesis of isolated Neutron Stars with magneto--rotational evolution

TL;DR

This study enhances population synthesis models of isolated neutron stars by integrating recent magneto-thermal evolution insights, removing the need for a death line, and favoring realistic magnetospheric models with specific initial magnetic field distributions.

Contribution

It introduces a novel population synthesis approach that incorporates recent magnetic and magnetosphere evolution models without assuming a death line, and identifies parameter regions consistent with observations.

Findings

Broad initial spin period distributions fit observational data.

Realistic magnetospheric models are favored over classical models.

Optimal initial magnetic field strength has a mean log value around 13.0-13.2 G.

Abstract

We revisit the population synthesis of isolated radio-pulsars incorporating recent advances on the evolution of the magnetic field and the angle between the magnetic and rotational axes from new simulations of the magneto-thermal evolution and magnetosphere models, respectively. An interesting novelty in our approach is that we do not assume the existence of a death line. We discuss regions in parameter space that are more consistent with the observational data. In particular, we find that any broad distribution of birth spin periods with $P_0\lesssim 0.5$ s can fit the data, and that if the alignment angle is allowed to vary consistently with the torque model, realistic magnetospheric models are favoured compared to models with classical magneto-dipolar radiation losses. Assuming that the initial magnetic field is given by a lognormal distribution, our optimal model has mean strength $\langle\log B_0{\rm [G]}\rangle \approx 13.0-13.2$ with width $\sigma (\log B_0) = 0.6-0.7$. However, there are strong correlations between parameters. This degeneracy in the parameter space can be broken by an independent estimate of the pulsar birth rate or by future studies correlating this information with the population in other observational bands (X-rays and $\gamma$-rays).