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 components (i.e. point sources, extended emission from hot gas in the bulge, disk and halo). Within the D25 ellipse of M 83, 21 X-ray sources are detected with (0.1–2.4 keV band) fluxes ranging from 1.4 to 115 × 10−14 erg cm−2 s−1, corresponding to luminosities of (1.3–106)× 1038 erg s−1 for an assumed distance of 8.9 Mpc. The sources account for half (2.0 × 1040 erg s−1) of the total X-ray luminosity of the galaxy (4.1 × 1040 erg s−1). Using the high spatial resolution of the HRI instrument and applying a new technique to search for variable sources in the extended bulge region leads to the 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 represents <∼ 45% of the total bulge luminosity (1.0 × 1040 erg s−1). A variable (factor >∼ 2), super-Eddington (3.8 × 1039 erg s−1) X-ray source is found to coincide with a faint, extended optical counterpart. Based on the spectral indices opticalto-X-ray αOX = 1 and radio-to-optical αRO < 0, the source is unlikely to be a background galaxy, AGN or quasar and most likely represents a massive (∼ 30M ) accreting black hole binary, located in a compact Hii region or in a globular cluster in M 83. We also detect two luminous (3.7 and 6.7× 1038 erg s−1), previously unknown supernova remnant candidates, located in extended Hα emission complexes 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. Spectral analysis of the PSPC data gives evidence for the detection of gas flowing into the halo of the galaxy (soft 0.26 keV component, absorbed by the Galactic foreground only), and hot gas (0.95 keV) with additional intrinsic absorption, that is heated by the star-forming activity in the south-western spiral arm of M 83. Send offprint requests to: S. Immler ([email protected])