ROSAT high-resolution X-ray observations of M 83: detection of supernova remnant and black hole candidates

High-resolution X-ray observations of the face-on galaxy M 83 with the HRI onboard ROSAT are presented. The analysis aimed at studying the X-ray point source population inside the galaxy and disentangling the X-ray emission c omponents (i.e. point sources, extended emission from hot gas in the bulge, disk and halo). Within the D-25 ellipse of M 83, 21 X-ray sources are detected with (0.1-2. 4 keV band) fluxes ranging from 1.4 to 115 x 10(-14) erg cm(-2) s(-1), corr esponding to luminosities of (1.3-106) x 10(38) erg s(-1) for an assumed di stance of 8.9 Mpc. The sources account for half (2.0 x 10(40) erg s(-1)) of the total X-ray luminosity of the galaxy (4.1 x 10(40) erg s(-1)). Using t he high spatial resolution of the HRI. instrument and applying a new techni que to search for variable sources in the extended bulge region leads to th e detection of four variable X-ray sources within the bulge (< 1 kpc radius from the nucleus). The amount of truly diffuse emission from hot gas repre sents;less than or similar to 45% of the total bulge luminosity (1.0 x 10(4 0) erg s(-1)). A variable (factor greater than or similar to 2), super-Eddington (3.8 x 10 (39) erg s(-1)) X-ray source is found to coincide with a faint, extended op tical counterpart. Based on the spectral indices optical-to-X-ray alpha(OX) = 1 and radio-to-optical alpha(RO) < 0, the source is unlikely to be a bac kground galaxy, AGN or quasar and most likely represents a massive (similar to 30M.) accreting black hole binary, located in a compact HII region or i n a globular cluster in M 83. We also detect two luminous (3.7 and 6.7 x 10(38) erg s(-1)), previously un known supernova remnant candidates, located in extended Ha emission complex es and coinciding with compact 6 cm and 20 cm radio sources. Bright extended X-ray emission is discerned in the southwestern spiral arm from point sources and from the overall diffuse emission with the HRI. Spec tral analysis of the PSPC data gives evidence for the detection of gas flow ing into the halo of the galaxy (soft 0.26 keV component, absorbed by the G alactic foreground only), and hot gas (0.95 keV) with additional intrinsic absorption, that is heated by the star-forming activity in the south-wester n spiral arm of M 83.