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

[摘要] English: Supersoft X-ray Sources (SSS) form Cl, highly luminous class of objects that emit moreThan ~ 90% of their energy in the supersoft X-ray band, i.e. below 0.5 keV. They aregenerally 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 associatedaccretion. The high accretion rate of material onto the white dwarf is sufficient todrive nuclear burning and accompanying soft X-ray emission on the white dwarfsurface, and may imply the presence of an accretion disc and significant mass outflowfrom some of these sources. However, SSS do not form a homogeneous classand also include objects like planetary nebulae, symbiotic novae and cataclysmicvariables exhibiting nova outbursts. To investigate the phenomenon of accretionand the nature of possible mass outflow in SSS. a sample of 3 candidate sources inthe 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 includedin the study due to the evidence for an accretion disc implied by the double-peakedRaman-scattered 0 VI emission. Signatures of disc accretion and mass ejection inclose binary supersoft sources (CBSS) like CAL 83, may provide evidence that suchsystems can evolve towards another class of binary system, namely the cataclysmicvariables. Optical spectroscopic studies of CAL 83, NG7 and RR Tel were performedwith 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 andCAL 83 were also analysed. The optical spectra of CAL 83 exhibit evidence of linebroadening due to radial motion in an accretion disc, and a signature of possibledisc outflows is also present. A search for periodicity in the X-ray data of CAL 83revealed indication of consistent periodic modulations at P ~ 67 s, which could possiblybe associated with the rotation period of a spun-up white dwarf. The presenceof a fast rotating WD could provide a mechanism to explain the outflow inferredfrom the optical spectrum. The widths of nebular emission lines of the planetarynebula N67, as well as that of typical nebular lines in RR Tel are consistent withthe known expansion velocities of nebulae surrounding the central objects in thesesystems.

[发布机构] University of the Free State