Pulse phase spectroscopy of 0115+63 and an observation of 4U1223-62

Ariel-6 observed 0115+63 during 1980 December 16-30. The source was in outburst with a mean flux of 150 + or - 20 mCrab, this value is consistant with the HEAO A-2 flux during the previously detected outburst. Throughout the observation there was no evidence for spectral variability on timescales greater than the pulse period. The large Ariel-6 data base has enabled a sensitive study of phase dependent spectral variability. The data were folded over the pulse period (after removal of orbital effects) and subdivided into 16 equal phase bins. As per the phase averaged spectrum the data were best represented by power law + h.e. cut off. The hardening of the pulse profile at pulse maximum is very evident and is similar to the effect observed in GX1+4. A reanalysis of the HEAO A-2 data shows an almost constant spectral index for 0115+63 and in general a tendency for pulsator spectra to harden at minimum is found. This discrepancy is clearly of importance in the modelling of neutron star emission. The variation in the high energy cut off is less significant.