Precise Timing of the X-ray Pulsar 1e 1207.4−5209: a Steady Neutron Star Weakly Magnetized at Birth

We analyze all X-ray timing data on 1E 1207.4−5209 in supernova remnant PKS 1209−51/52 gathered in 2000–2005, and find a highly stable rotation with P = 424.130751(4) ms and Ṗ = (9.6±9.4)×10 s s. This refutes previous claims of large timing irregularities in these data. In the dipole spin-down formalism, the 2σ upper limit on Ṗ implies an energy loss rate Ė < 1.5×10 ergs s, surface magnetic field strength Bp < 3.5× 10 11 G, and characteristic age τc ≡ P/2Ṗ > 24 Myr. This τc exceeds the remnant age by 3 orders of magnitude, requiring that the pulsar was born spinning at its present period. The X-ray luminosity of 1E 1207.4−5209, Lbol ≈ 2 × 10 33 (d/2 kpc) ergs s, exceeds its Ė, implying that Lbol derives from residual cooling, and perhaps partly from accretion of supernova debris. The upper limit on Bp is small enough to favor the electron cyclotron model for at least one of the prominent absorption lines in its soft X-ray spectrum. This is the second demonstrable case of a pulsar born spinning slowly and with a weak B-field, after PSR J1852+0040 in Kesteven 79. Subject headings: ISM: individual (PKS 1209−51/52) — pulsars: individual (1E 1207.4−5209, PSR J1852+0040) — stars: neutron — supernova remnants