Letter to the Editor
XMM-Newton observation of 4U 1543–475: The X-ray spectrum of a stellar-mass black-hole at low luminosity
Istituto di Astrofisica Spaziale e Fisica Cosmica – Sezione di Milano “G.Occhialini”, CNR, via Bassini 15, 20133 Milano, Italy e-mail: email@example.com
Accepted: 11 December 2004
We report the results of an observation of the galactic black-hole binary 4U 1543-475performed 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 erg s, 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 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 erg s-1, i.e. less than 10% of the source total luminosity. Finally, we evaluated that the disk colour temperature must satisfy the condition 0.25 keV in order to obtain an acceptable value for the disk inner radius.
Key words: accretion, accretion disks / black hole physics / stars: individual: 4U 1543-475, Il Lupi / X-rays: binaries
© ESO, 2005