The Spin-down of PSR J0821-4300 and PSR J1210-5226: Confirmation of Central Compact Objects as Anti-magnetars

Using XMM-Newton and Chandra, we measure period derivatives for the second and third known pulsars in the class of central compact objects (CCOs) in supernova remnants, proving that these young neutron stars have exceptionally weak dipole magnetic field components. For the 112 ms PSR J0821-4300 in Puppis A, \dot{P} = (9.28 +/- 0.36) \times 10^{-18}. Its proper motion, μ = 61 ± 9 mas yr^-1, was also measured using Chandra. This contributes a kinematic term to the period derivative via the Shklovskii effect, which is subtracted from \dot{P} to derive dipole B_s = 2.9 × 10¹⁰ G, a value similar to that of the first measured CCO, PSR J1852+0040 in Kes 79, which has B_s = 3.1 × 10¹⁰ G. Antipodal surface hot spots with different temperatures and areas are deduced from the X-ray spectrum and pulse profiles. Paradoxically, such nonuniform surface temperature appears to require strong crustal magnetic fields, probably toroidal or quadrupolar components much stronger than the external dipole. A spectral feature, consisting of either an emission line at ≈0.75 keV or an absorption line at ≈0.46 keV, is modulated in strength with the rotation. It may be due to a cyclotron process in a magnetic field on the surface that is slightly stronger than the dipole deduced from the spin-down. We also timed anew the 424 ms PSR J1210-5226, resolving previous ambiguities about its spin-down rate. Its \dot{P} is (2.22 ± 0.02) × 10^-17, corresponding to B_s = 9.8 × 10¹⁰ G. This is also compatible with a cyclotron resonance interpretation of its prominent absorption line at 0.7 keV and its harmonics. These results deepen the mystery of the origin and evolution of CCOs: Why are their numerous descendants not evident?