1994A&A...288..791H

ROSAT observations of Vela X-1 confirm the existence of a low-absorbed soft component in the X-ray spectrum of wind accreting supergiant X-ray binaries which does not originate at the neutron star. This soft emission can be modeled by thermal Bremsstrahlung with a temperature around 0.5 keV. The exact determination of the temperature depends on the contribution from the highly absorbed hard powerlaw component from the neutron star as observed by instruments in the 1-20keV band. The low pulsed fraction in the 0.1-2.4keV energy band of 3% is consistent with the pulsations originating from the hard powerlaw component only, while the soft component is not pulsed. An upper limit of 4% was derived for a possible contribution of X-rays scattered on interstellar dust grains.