High-Energy pulse profile of the Transient X-ray Pulsar SAX J2103.5+4545

Two recent INTEGRAL papers report a timing and spectral analysis of the transient Be/X-ray pulsar SAX J2103.5+4545 at high energies (5-200 keV). In this work we present for the first time a study of the pulse profile at energies above 20 keV using INTEGRAL data. The spin-pulse profile shows a prominent (with a duty cycle of 14%) and broad (with a FWHM of similar to 51 s) peak and a secondary peak which becomes more evident above 20 keV. The pulsed fraction increases with energy from similar to 45% at 5-40 keV to similar to 80% at 40-80 keV. The morphology of the pulse profile also changes as a function of energy, consistent with variations in the spectral components that are visible in the pulse phase resolved spectra. A study of the double peaked profile shows that the difference in the two peaks can be modeled by a different scattering fraction between the radiation from the two magnetic poles.