Optical/UV counterpart of the supersoft transient X-ray source RX J0513.9-6951 in the Large Magellanic Cloud.
Motch, C.; Bianchi, L.; Pakull, M. W.; Thomas, H. -C.; Guibert, J.; Beaulieu, J. P.; Grison, P.; Schaeidt, S.
France, Italy
Abstract
Optical and IUE observations of the ROSAT X-ray transient RX J0513.9-6951 show this object to be remarkably similar to Cal 83, the prototype of luminous supersoft sources which is also located in the LMC. The counterpart is a B ~ 17 mag blue star which apparently did not vary much around the time of the X-ray outburst. Spectrophotometry reveals narrow and broad emission lines of H, He II, NV, and O VI, whereas the λλ1548, 50 C IV resonance doublet is very weak. Radial velocity variations by ~100 km/s suggest binary nature and a systemic velocity close to the bulk motion of the LMC. We discuss the hypothesis that the source is mainly powered by nuclear burning on the surface of a white dwarf rather than by accretion, and we argue that the X-ray outburst was triggered by a reduced accretion rate.