3.2. The nature of individual sources
In M83, detailed spectral analysis is possible for sources with an emitted luminosity 1038 erg s-1. We can easily distinguish (Fig. 6):
For a more extensive discussion of the spectral and temporal properties of the discrete sources in M83, see Soria & Wu (2003).
Figure 6. Spectral fits to a sample of bright X-ray sources in M83 show different classes of objects. First three rows, from top left: the galactic nucleus; an X-ray binary in a hard state; an X-ray binary in a soft state; a source with soft thermal plasma emission (a young SNR?); a source with a power-law continuum plus line emission (from a photo-ionized stellar wind?); a supersoft source. See Soria & Wu (2003) for further details on the sources and their fitted spectral models. Bottom row: the brightest X-ray source in M83 has an emitted luminosity in excess of 1039 erg s-1. A power-law spectral fit gives a photon index 2.5 ± 0.1. Its lightcurve shows an increase by 40% over the duration of the Chandra observation.
The brightest point source, located 5' south-east of the nucleus, is variable and has an emitted luminosity of 1039 erg s-1 (Fig. 6, bottom panels). Hence, it can be classified as an ultra-luminous source (ULX).