Fine phase resolved spectroscopy of the X-ray emission of the Crab pulsar (PSR B0531+21) observed with BeppoSAX

The Crab Nebula and the Pulsar have been pointed several times by the Beppo SAX satellite. We analysed all these observations, summed together, to stud y the main spectral properties with a good phase resolution. A new accurate estimate of the hydrogen column density in the Crab direction N-H=3.23 x 1 0(21) cm(-2) is given as derived from the analysis of the off-pulse emissio n at low energies. We studied the changes of the spectral index with the pu lse phase and showed that in the interpeak region it is systematically hard er than in the main peaks of about 0.4. We observed also a significant spec tral steepening of the pulsed emission and showed that this distribution ca n be represented by a unique law with a linear variable log slope and apply it to the spectrum of the first peak. A two component model is proposed to explain the phase evolution of the spectrum. One component has the same pr ofile observed in the optical while the other presents a maximum at the pha se 0.4 with essentially the spectrum of the interpeak region. Two possible interpretations for the origin of the latter component are discussed.