On the nature of the X-ray source 1E 1024.0--5732/Wack 2134

Two different models have been put forward to explain the origin of the X-ray emission of the unusual X-ray source 1E 1024.0-5732/Wack 2134: a high-mass X-ray binary system (HMXB) and a colliding wind binary (CWB). We present new optical and X-ray data in an attempt to clarify the nature of this system. The data seem to favour the colliding wind model since the optical spectra show characteristics of both, a Wolf-Rayet and an O-type star, implying that these two type of stars may be present in the system. The lack of coherent modulation (pulsations) and the relatively soft and low luminosity X-ray emission seems to exclude the presence of a neutron star as the body generating the X-ray emission. We present the first X-ray energy spectrum of this source at energies above 3 keV and discuss the implications of the spectral parameters obtained from the model fitting. We comment on the fact that the iron lines in CWB are centred at higher energies, ~ 6.6 keV, than those detected in supergiant HMXB, where a value of 6.4 keV is found, implying that the degree of ionisation of iron is higher in CWB.