Pulse phase variations of the X-ray spectral features in the radio-quiet neutron star 1E 1207-5209

We present the results of an XMM-Newton observation of the radio-quiet X-ray pulsar 1E 1207-5209 located at the center of the shell-like supernova remnant G296.5+10.0. The X-ray spectrum is characterized by the presence of two phase- dependent absorption lines at energies of similar to0.7 and similar to1.4 keV. Moreover, these broad spectral features have significant substructure, suggesting that they are caused by the blending of several narrower lines. We interpret such features as evidence for an atmosphere containing metals and a magnetic field value of a few 10(12) G, consistent with the observed spin-down rate (P) over dot = (1.98 +/- 0.83) x 10(- 14) s s(-1). Since 1E 1207-5209 is the only X-ray-emitting pulsar showing evidence of such features, we tentatively link them to the unique combination of age and energetics that characterize this object. We suggest that a young age and a low level of magnetospheric activity are favorable conditions for the detection of atomic spectral features from Z > 1 elements in neutron star atmospheres, which would be either blanketed by a thin layer of accreted hydrogen in older objects or masked by nonthermal processes in young energetic pulsars