Precise Timing of the X-ray Pulsar 1E 1207.4-5209: A Steady Neutron Star Weakly Magnetized at Birth

Abstract

We analyze all X-ray timing data on 1E 1207.4-5209 in supernova remnant PKS 1209-51/52 gathered from 1993-2005 and find a highly stable rotation with P=424.130749(4) ms and P˙=(6.6+/-9.0)×10^-17 (1 σ errors). This refutes previous claims of large timing irregularities in these data. In the dipole spin-down formalism, the 2 σ upper limit on P˙ implies a spin-down luminosity E˙<1.3×10³² ergs s^-1, surface magnetic field strength B_p<3.3×10¹¹ G, and characteristic age τ_c≡P/2P˙>27 Myr. This τ_c 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, L_bol~2×10³³(d/2 kpc)² ergs s^-1, exceeds its E˙, implying that L_bol derives from residual cooling and perhaps partly from accretion of supernova debris. The upper limit on B_p 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. We suggest that these properties define the class of central compact objects.