First high-resolution Chandra LETGS spectrum of the transient supersoft X-ray source RX J0513.9-6951 Original Research Article

The transient luminous soft X-ray source RX J0513.9-6951 in the large magellanic cloud is a key object within the class of accreting binary supersoft X-ray sources. In this system, mass-transfer is thought to occur close to the Eddington limit of a solar mass white dwarf. The source switches quasi-periodically between two physically distinct states with anti-correlated X-ray and optical luminosities. We have obtained the first high-resolution X-ray spectrum of RX J0513.9-6951 on December 24, 2003 during an X-ray bright state as a 48 ks target of opportunity observation with the low energy transmission grating spectrograph (LETGS) on board Chandra. The X-ray observations were triggered using optical monitoring data obtained with ANDICAM on the 1.3-m telescope at Cerro Tololo, Chile of the SMARTS consortium. The X-ray spectrum deviates strongly from a smooth continuum and reveals complex structures which are probably a mixture of absorption and emission line patterns. Such features can be understood as a superposition of X-ray emission from a hot high-gravity stellar atmosphere and from an optically thin corona-like plasma enshrouding the system. Here, we present first results of our spectral analysis of the LETGS data using white dwarf atmosphere codes.