THE PULSED SOFT-X-RAY EMISSION FROM PSR-0656+14

We present the results of a spectral and timing analysis of PSR 0656+1 4 based on the complete set of ROSAT observations carried out with the PSPC instrument in 1991 and 1992. The present analysis confirms the t hermal origin of the bulk of the emission in the soft X-ray band (Finl ey et al. 1992). In addition, we find strong evidence of a harder comp onent, described equally well with a blackbody at T similar or equal t o 2 x 10(6) K, or with a steep power law with photon index Gamma simil ar or equal to 4.5. This bimodal emission is also supported by an anal ysis of the light curve shape as a function of the energy. The 0.1-2.4 keV light curve of PSR 0656+14, with a pulsed fraction of about 9%, i s interpreted with a simple model for the temperature distribution on the neutron star surface, coupled with the geometrical information der ived from radio data. In this model, which includes the effects of rel ativistic light bending and gravitational redshift, the X-rays origina te from two thermal components resulting from neutron star cooling and blackbody emission released in the hotter polar cap regions. The obse rved modulation can be reproduced only if PSR 0656+14 has a relatively high dipole inclination (similar to 30 degrees) and (1+z) less than o r similar to 1.15. The overall pulsed fraction cannot be significantly increased by including the polar cap contribution, if its temperature and intensity are to be consistent with the observed spectra.