EDP Sciences
Free access
Volume 397, Number 1, January I 2003
Page(s) 249 - 256
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20021477

A&A 397, 249-256 (2003)
DOI: 10.1051/0004-6361:20021477

X-ray properties of 4U 1543-624

J. Schultz

Observatory, PO Box 14, 00014 University of Helsinki, Finland
(Received 4 July 2002 / Accepted 8 October 2002 )

4U 1543-624 is a relatively bright persistent low-mass X-ray binary. Analysis of archival data from ASCA, SAX and RXTE is presented. The X-ray continuum be can modeled with the standard low-mass X-ray binary spectrum, an isothermal blackbody and a Comptonized component. Variations in the luminosity and flux ratio of the continuum components are seen. An increase in luminosity is accompanied by a decrease in the blackbody luminosity and a hardening of the spectrum. Most low-mass X-ray binaries have softer spectra and higher blackbody luminosities in high luminosity states. The Fe ${\rm K}_\alpha$ line is seen only in the high luminosity spectra. A narrow feature near 0.7 keV, previously detected in the ASCA data, is also seen in the SAX data. A qualitative model of the system is presented. The X-ray observations can be explained by a low inclination system (face-on disk) containing a slowly ( $P \gg $ ms) rotating neutron star. A slowly rotating neutron star would imply either that the system is a young low-mass X-ray binary, or that the accretion rate is unusually low. The empirical relation between optical and X-ray luminosity and orbital period suggests a relatively short period.

Key words: binaries: close -- stars: individual: 4U 1543-624 -- X-rays: binaries

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