Noisy Timing Behavior is a Feature of Central Compact Object Pulsars

TL;DR

The paper investigates why Central Compact Object pulsars exhibit exceptionally slow spin-down and weak surface magnetic fields, which challenge standard pulsar evolution and the origin of their X-ray hot spots. By combining two decades of X-ray timing from Chandra, XMM-Newton, and NICER and performing phase-connected timing analyses, the authors test whether the observed timing irregularities arise from glitches or timing noise and explore alternatives such as strong internal crustal fields and magnetothermal evolution, or low-level accretion. They find that timing irregularities in 1E 1207.4-5209 and PSR J0821-4300 are extreme for their spin-down rates and can be modeled as glitches in $f$ and $ abla f$ or by significant timing noise, while PSR J1852+0400 remains inconclusive due to data gaps. These results link CCO timing behavior to internal temperature, buried magnetic fields, and superfluid dynamics, while keeping open the possibility that accretion from fallback material contributes to timing noise, with implications for the evolutionary paths of CCOs and their magnetic-field reemergence.

Abstract

We present a timing study of the three known central compact object (CCO) pulsars, isolated cooling neutron stars in supernova remnants, using Chandra, XMM-Newton and NICER observations spanning two decades. Relative to canonical young pulsars, CCOs are spinning down at a very slow rate $|\dot f| <10^{-15}$ s$^{-2}$, implying a surface dipole magnetic field strength $B_s < 10^{11}$ G that is too weak to account for their X-ray emitting hot spots. Two CCO pulsars with sufficiently long monitoring, 1E 1207.4$-$5209 and PSR J0821$-$4300, are seen to deviate from steady spin-down; their timing residuals can be modeled by one or more glitches in $f$ and $\dot f$, or alternatively by extreme timing noise. For the third CCO pulsar, PSR J1852+0400, the sparse temporal coverage was insufficient to detect such effects. Glitch activity and timing noise in large samples of rotation-powered pulsars correlate best with $\dot f$, while the timing irregularities of the first two CCOs are extreme compared to pulsars of the same $\dot f$. Nevertheless, timing activity in CCOs may arise from properties that they share with other young but more energetic pulsars: high internal temperature, strong buried magnetic field and superfluid behavior. Alternatively, continuing low-level accretion of supernova debris is not ruled out as a source of timing noise in CCOs.