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The XMM-Newton survey of the Small Magellanic Cloud (SMC) was performed tostudy the population of X-ray sources in this neighbouring galaxy. During oneof the observations, the symbiotic binary SMC3 was found at its highest X-rayluminosity observed until now. In SMC3 wind accretion from a giant donor staronto a white dwarf is believed to cause steady hydrogen burning on the whitedwarf surface, making such systems candidates for supernova type Iaprogenitors. It was suggested that the X-ray source is eclipsed every ~4.5years by the companion star and its stellar wind to explain the large X-rayvariability seen in ROSAT data. We use the available X-ray data to test thisscenario. We present the ~20 year X-ray light curve of SMC3 and study thespectral evolution as seen with XMM-Newton/EPIC-pn to investigate possiblescenarios which can reproduce the high X-ray variability. We did not findsignificant variations in the photo-electric absorption, as it would beexpected during eclipse ingress and egress. Instead, the X-ray spectra fromdifferent intensity levels, when modelled by black-body emission, can be betterexplained by variations either in normalisation (by a factor of ~50) or intemperature (kT between 24 eV and 34 eV). The light curve shows maxima andminima with slow transitions between them. To explain the gradual variations inthe X-ray light curve and to avoid changes in absorption by neutral gas, apredominant part of the stellar wind must be ionised by the X-ray source.Compton scattering with variable electron column density (of the order of 5 x10^24 cm^-2) along the line of sight could then be responsible for theintensity changes. The X-ray variability of SMC3 could also be caused bytemperature changes in the hydrogen burning envelope of the white dwarf, aneffect which could even dominate if the stellar wind density is notsufficiently high.

The XMM-Newton survey of the Small Magellanic Cloud: A new X-ray view of the symbiotic binary SMC3