XMM-Newton and VLT observations of the isolated neutron star 1E 1207.4-5209

Abstract

In August 2002, XMM-Newton devoted two full orbits to the observation of IE 1207.4-5209, making this isolated neutron star the most deeply scrutinized galactic target of the mission. Thanks to the high throughput of the EPIC instrument, ∼360 000 photons were collected from the source, allowing a very sensitive study of the temporal and spectral behaviour of this object. The spectral data, both time-averaged and phase-resolved, yield one compelling interpretation of the observed features: cyclotron absorption from one fundamental (∼0.7 keV) and three harmonics, at ∼1.4, ∼2.1 and ∼2.8 keV. Possible physical consequences are discussed, also on the basis of the obvious phase variations of the features' shapes and depths. We also present deep VLT optical data which we have used to search for a counterpart, with negative results down to V ∼ 27.