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Astron. Astrophys. 354, L37-L40 (2000)


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Letter to the Editor

A limit-cycle model for the binary supersoft X-ray source RX J0513.9-6951

K. Reinsch 1, A. van Teeseling 1, A.R. King 2 and K. Beuermann 1

1 Universitäts-Sternwarte, Geismarlandstrasse 11, 37083 Göttingen, Germany (reinsch@uni-sw.gwdg.de)
2 University of Leicester, Astronomy Group, Leicester LE1 7RH, U.K.

Received 29 November 1999 / Accepted 3 January 2000

Abstract

We present new results of our X-ray monitoring of the transient binary supersoft X-ray source RX J0513.9-6951 in the LMC and of our re-analysis of optical light curves obtained during the MACHO project. We have covered a complete X-ray outburst cycle with the ROSAT HRI detector. From the amplitude and timescale of the soft X-ray variability, tight limits are derived for the temporal behaviour of the white-dwarf radius and the effective temperature of its envelope. A limit-cycle model is proposed to explain the observed optical and X-ray variability, the characteristic timescales of the durations of the X-ray on and off states, and those of the transitions between both states. Our observations confirm that the radius changes of the white-dwarf envelope occur on the Kelvin-Helmholtz timescale. The duration of the X-ray on and off states is compatible with the viscous timescales of the inner and outer accretion disk, respectively.

Key words: accretion, accretion disks – stars: binaries: close – stars: binaries: spectroscopic – stars: individual: RX J0513.9 – 6951 – stars: novae, cataclysmic variables – X-rays: stars


© European Southern Observatory (ESO) 2000

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