Properties of discrete X-ray sources in the starburst spiral galaxy M83

We have identified 127 discrete sources in a Chandra ACIS observation of M83, with a detection limit of approximate to3 x 10(36) erg s(-1) in the 0.3-8.0 keV band. We discuss the individual X-ray spectral and time-variability properties of approximate to20 bright sources with luminosities greater than or similar to10(38) erg s(-1), and the statistical properties of the whole sample. About one third of the bright sources show X-ray spectra with a blackbody component at temperatures less than or similar to1 keV, plus a powerlaw component with Gamma approximate to 2.5, typical of X-ray binaries in a soft state; another third have powerlaw spectra with Gamma approximate to 1.5, consistent with X-ray binaries in a hard state. Two bright sources show emission lines on a hard powerlaw continuum, and are probably X-ray binaries surrounded by a photo-ionized nebula or stellar wind. Among the other bright sources, we also identified two supernova remnant candidates, with optically-thin thermal plasma spectra at temperatures similar to0.5 keV. The two brightest supersoft sources have blackbody temperatures kT approximate to 70 eV and luminosities similar to10(38) erg s(-1). Two candidate X-ray pulsars are detected with periods approximate to200 s. One X-ray source corresponds to the core of a background FRII radio galaxy. The discrete sources can be divided into three groups, based on their spatial, color and luminosity distributions. The first group comprises supersoft sources with no detected emission above 1 keV and blackbody spectra at temperatures <100 eV. The second group consists of soft sources with little or no detected emission above 2 keV. They are strongly correlated with H alpha emission in the spiral arms and starburst nucleus, tracing a young population. Their relative abundance depends on the current level of star-forming activity in the galaxy. Most of them are likely to be supernova remnants. The sources in the third group are mostly X-ray binaries, reaching higher X-ray luminosities than sources in the other two groups. Being a mixture of old low-mass and young high-mass systems, the whole group appears to be of intermediate age when correlated with the H alpha emission. The color-color diagrams allow us to distinguish between sources in a soft and hard state.