A multi-wavelength study of super soft X-ray sources in the Magellanic Clouds

English: Supersoft X-ray Sources (SSS) form Cl, highly luminous class of objects that emit more Than ~ 90% of their energy in the supersoft X-ray band, i.e. below 0.5 keV. They are generally believed to consist of a white dwarf with a more massive binary companion, resulting in thermal time-scale mass transfer to the white dwarf and associated accretion. The high accretion rate of material onto the white dwarf is sufficient to drive nuclear burning and accompanying soft X-ray emission on the white dwarf surface, and may imply the presence of an accretion disc and significant mass outflow from some of these sources. However, SSS do not form a homogeneous class and also include objects like planetary nebulae, symbiotic novae and cataclysmic variables exhibiting nova outbursts. To investigate the phenomenon of accretion and the nature of possible mass outflow in SSS. a sample of 3 candidate sources in the Magellanic Clouds were identified for optical spectroscopic and X-ray studies: CAL 83, N67 and SMC 13. The galactic symbiotic nova RR Tel was also included in the study due to the evidence for an accretion disc implied by the double-peaked Raman-scattered 0 VI emission. Signatures of disc accretion and mass ejection in close binary supersoft sources (CBSS) like CAL 83, may provide evidence that such systems can evolve towards another class of binary system, namely the cataclysmic variables. Optical spectroscopic studies of CAL 83, NG7 and RR Tel were performed with the Southern African Large Telescope (SALT) and the SAAO l.9-m Telescope, and archived Chandm and XMM-Newton observations of the sources SMC 13 and CAL 83 were also analysed. The optical spectra of CAL 83 exhibit evidence of line broadening due to radial motion in an accretion disc, and a signature of possible disc outflows is also present. A search for periodicity in the X-ray data of CAL 83 revealed indication of consistent periodic modulations at P ~ 67 s, which could possibly be associated with the rotation period of a spun-up white dwarf. The presence of a fast rotating WD could provide a mechanism to explain the outflow inferred from the optical spectrum. The widths of nebular emission lines of the planetary nebula N67, as well as that of typical nebular lines in RR Tel are consistent with the known expansion velocities of nebulae surrounding the central objects in these systems.