The Extraordinary Timing Behavior of Central Compact Objects

We present a timing study of central compact object (CCO) pulsars, isolated young neutron stars in supernova remnants, using Chandra, XMM-Newton, and NICER observations spanning the two decades since their discoveries. Relative to a canonical radio pulsar, these X-ray-only pulsars are spinning down at a very slow rate, with an inferred magnetic field (B_s < 1E11 G) too weak to account for the observed hot spots as evident by their pulse modulation. For the two CCOs with sufficiently long monitoring, PSR J0821-4300 in SNR Puppis-A and 1E 1207.4-520 in SNR PKS 1209-51/52, their timing behavior can be well-modeled by one or more small glitches, or by extreme timing noise, unprecedented for a pulsar with their spin-down rates; no pulsar with their timing properties are otherwise known to display glitches. Unexpectedly, in the glitch scenario, the measured frequency derivative implies a decrease in the surface dipole magnetic field. Alternatively, a small rate of mass accretion of the supernova ejecta, in the propeller regime, may account for timing noise. Although coverage of the third CCO pulsar PSR J1852+0040 in SNR Kes 79 is insufficient to detect a glitch, a new timing campaign independently confirms its reported temporal properties.