The needle in the haystack - Where to look for more isolated cooling neutron stars

TL;DR

This study uses population synthesis modeling to identify promising sky regions, especially near OB associations and the Gould Belt, to improve detection of isolated cooling neutron stars in X-ray surveys.

Contribution

It introduces a comprehensive model considering progenitor and interstellar medium inhomogeneities to predict neutron star distributions and guide future searches.

Findings

Cooling neutron stars are most abundant near OB associations.

New candidates likely behind the Gould Belt, especially in Cygnus-Cepheus.

Younger, hotter neutron stars are expected to be discovered.

Abstract

Context: Isolated cooling neutron stars with thermal X-ray emission remain rarely detected objects despite many searches investigating the ROSAT data. Aims: We simulate the population of close-by young cooling neutron stars to explain the current observational results. Given the inhomogeneity of the neutron star distribution on the sky it is particularly interesting to identify promising sky regions with respect to on-going and future searches. Methods: Applying a population synthesis model the inhomogeneity of the progenitor distribution and the inhomogeneity of the X-ray absorbing interstellar medium are considered for the first time. The total number of observable neutron stars is derived with respect to ROSAT count rates. In addition, we present sky maps of neutron star locations and discuss age and distance distributions of the simulated neutron stars. Implications for future searches are discussed. Results: With our advanced model we can successfully explain the observed logN - logS distribution of close-by neutron stars. Cooling neutron stars will be most abundant in the directions of rich OB associations. New candidates are expected to be identified behind the Gould Belt, in particular in the Cygnus-Cepheus region. They are expected to be on average younger and then hotter than the known population of isolated cooling neutron stars. In addition, we propose to use data on runaway stars to search for more radio-quiet cooling neutron stars.