2005A&A...430L..53L

We report the results of an observation of the galactic black-hole binary 4U 1543-475 performed by XMM-Newton on 2002 August 18, about two months after the start of an outburst detected by RXTE. Despite the relatively low flux of the source, corresponding to a luminosity L_X∼4x10³⁴erg/s∼10^–5 L_EDD, we could obtain a good quality spectrum thanks to the high throughput of the XMM-Newton EPIC instrument. The spectrum is well fit by a power law with photon index Γ=1.9-2 without any evidence for iron emission lines or for thermal emission from an accretion disk. We could estimate an upper-limit on the disk bolometric luminosity as a function of the colour temperature: it is always lower than ∼10³³erg/s, i.e. less than 10% of the source total luminosity. Finally, we evaluated that the disk colour temperature must satisfy the condition kT_col<0.25keV in order to obtain an acceptable value for the disk inner radius.