Hunting for Orphaned Central Compact Objects among Radio Pulsars

TL;DR

This study searches for orphaned central compact objects (CCOs) among weak-field radio pulsars and finds no X-ray evidence, suggesting such objects are either old pulsars or require different search strategies.

Contribution

It provides the first systematic X-ray survey of weak-field radio pulsars to identify potential orphaned CCOs, and discusses their evolutionary implications.

Findings

No X-ray detection of 12 weak-field pulsar candidates.

Weak surface fields in CCOs may re-emerge as young pulsars within 10,000 years.

Further searches should target pulsars with stronger magnetic fields.

Abstract

Central compact objects (CCOs) are a handful of young neutron stars found at the center of supernova remnants (SNRs). They show high thermal X-ray luminosities but no radio emission. Spin-down rate measurements of the three CCOs with X-ray pulsations indicate surface dipole fields much weaker than those of typical young pulsars. To investigate if CCOs and known radio pulsars are objects at different evolutionary stages, we carried out a census of all weak-field (<1e11 G) isolated radio pulsars in the Galactic plane to search for CCO-like X-ray emission. None of the 12 candidates is detected at X-ray energies, with luminosity limits of 1e32-1e34 erg/s. We consider a scenario in which the weak surface fields of CCOs are due to rapid accretion of supernova materials and show that as the buried field diffuses back to the surface, a CCO descendant is expected to leave the P-Pdot parameter space of our candidates at a young age of a few times 10kyr. Hence, the candidates are likely to be just old ordinary pulsars in this case. We suggest that further searches for orphaned CCO, which are aged CCOs with parent SNRs dissipated, should include pulsars with stronger magnetic fields.