2006A&A...451L..17H

The XMM-Newton spectra of the isolated neutron star RXJ0720.4-3125 obtained over 4.5-years can be described by sinusoidal variations in the inferred blackbody temperature, the size of the emitting area and the depth of the absorption line with a period of 7.1±0.5-years, which we suggest to be the precession period of the neutron star. Precession of a neutron star with two hot spots of different temperature and size, probably not located exactly in antipodal positions, may account for the variations in the X-ray spectra, changes in the pulsed fraction, shape of the light curve and the phase-lag between soft and hard energy bands observed from RXJ0720.4-3125. An independent sinusoidal fit to published and new pulse timing residuals from a coherent analysis covering ∼12-years yields a consistent period of 7.7±0.6-years supporting the precession model.