Astron. Astrophys. 355, 1041-1048 (2000)

RX J0537.7-7034: The shortest-period supersoft X-ray source ^*

J. Greiner ¹, M. Orio ² and R. Schwarz <sup>1

1</sup> Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10125 Pino Torinese (TO), Italy

Received 18 October 1999 / Accepted 13 December 1999

Abstract

We present new photometric and spectroscopic observations of the transient supersoft X-ray source RX J0537.7-7034 and find a periodicity of approximately 3.5 hrs. This establishes RX J0537.7-7034 as the supersoft X-ray source with the shortest orbital period. We furthermore derive an inclination of the binary system of 45^o 70^o, and the masses of the two binary components: , . This implies that the standard scenario of supersoft X-ray sources, in which the donor is thought to be more massive than the accreting white dwarf to ensure high mass transfer rates on a thermal timescale (van den Heuvel et al. 1992), is not applicable for this system. We discuss alternative interpretations of this source as a former nova in which the thermonuclear flashes have become mild and most accreted mass is retained by the white dwarf (so-called SMC 13 type systems), or as a self-sustained wind-driven system.

Key words: stars: binaries: close stars: binaries: general stars: individual: RX J0537.7 7034 X-rays: stars

* Based on observations (60.H-0682 and 62.H-0839) obtained at the European Southern Observatory, La Silla, Chile.

Send offprint requests to: J. Greiner (jgreiner@aip.de)

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Contents

• 1. Introduction
• 2. Optical photometry
• 3. Spectroscopy
• 4. Update of the X-ray light curve of RX J0537.7-7034
• 5. Discussion
  • 5.1. Orbital variations and binary parameters
  • 5.2. On the nature of RX J0537.7-7034
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: March 21, 2000
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