  Second Chandra observation of 1E 1207.4-5209, the central source of the
supernova remnant 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, Pdot (0.7-3)e-14 s/s. The corresponding characteristic age of the
pulsar, P/2Pdot~200-900 kyr, is much larger than the estimated age of the SNR,
\~7 kyr. The values of the spin-down luminosity, Edot (0.4-1.6)e34 erg/s, and
conventional magnetic field, B (2-4)e12 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 supernova remnant, but the probability of
such a coincidence is very low.
