1E 1207.4-5209: The puzzling pulsar at the center of the supernova remnant PKS 1209-51/52

A second Chandra observation of 1E 1207.4-5209, the central source of the supernova remnant (SNR) PKS 1209-51/52, allowed us to confirm the previously detected period of 424 ms and, assuming a uniform spin-down, estimate the period derivative, Ṗ ∼ (0.7-3) × 10^-14 s s ^-1. The corresponding characteristic age of the pulsar, P/2Ṗ ∼ 200-900 kyr, is much larger than the estimated age of the SNR, ∼ 7 kyr. The values of the spin-down luminosity, Ė ∼ (0.4-1.6) × 10³⁴ ergs s^-1, and conventional magnetic field, B ∼ (2-4) × 10¹² G, are typical for a middle-aged radio pulsar, although no manifestations of pulsar activity have been observed. If 1E 1207.4-5209 is indeed the neutron star formed in the same supernova explosion that created PKS 1209-51/52, such a discrepancy in ages could be explained either by a long initial period, close to its current value, or, less likely, by a very large braking index of the pulsar. Alternatively, the pulsar could be a foreground object unrelated to the SNR, but the probability of such a coincidence is very low.