The Magellanic Clouds (MCs) are excellent laboratories for studying discrete sources owing to their proximity to our own Galaxy. Most discrete radio sources in spiral and irregular galaxies are SNRs and HII regions. SNRs are usually observed as strong X-ray sources, whereas HII regions are generally weak X-ray emitters. It is well known that SNRs and X-ray binaries often occur in large HII regions and hence HII regions sometimes appear in X-ray surveys.
The first high-frequency radio detection of discrete sources in the MCs was made by McGee & Milton (1966) at 1.4 GHz, which opened a new era in extra galactic research. Pioneering X-ray surveys of the LMC have been presented in Long et al. (1981) (LHG catalogue) and in Wang et al. (1991) (W catalogue). The SMC X-ray surveys can be found in Seward & Mitchell (1981) (1E catalogue), Inoue et al. (1983) (IKT catalogue), Bruhweiler et al. (1987) and in Wang & Wu (1992). All these surveys are based on observations made with the Einstein satellite.
Almost half of the X-ray sources in the LMC field catalogued by Wang et al. (1991) were confirmed as SNRs, HII regions or X-ray binaries. The other half are foreground stars or background objects (e.g. clusters of galaxies, radio galaxies, quasars). In the Wang & Wu (1992) survey, 24 out of 70 sources towards the SMC are intrinsic to the SMC.
These earlier studies provided a good basis for a new generation of radio and X-ray surveys of the MCs. Recent Parkes radio surveys of the MCs are now available: Haynes et al. (1991), Filipovic et al. (1995; hereafter Paper IV), Filipovic et al. (1996, hereafter Paper IVa), Filipovic et al. (1997a, hereafter Paper V) and Filipovic (1996). At X-ray frequencies, Pietsch et al. (in preparation) have prepared a list of sources towards the LMC from the X-ray ROSAT All-Sky Survey (RASS; Pietsch & Kahabka 1993) and Kahabka et al. (in preparation) presented a list of sources towards the SMC from the ROSAT Position Sensitive Proportional Counter (PSPC).
There are several other high-resolution surveys of the MCs in progress. At radio frequencies, a neutral-hydrogen survey at 1.4 GHz and continuum surveys at 1.4 and 2.3 GHz have been made with the Compact Array of the Australia Telescope National Facility (Staveley-Smith et al. 1997). At X-ray frequencies there are the ROSAT PSPC and HRI pointed observations (Snowden & Petre 1994) and the ASCA X-ray observations of some MCs SNRs (Hughes et al. 1995).
In this paper we compare sources common to the available radio and X-ray surveys using primarily the radio data of Papers IV, IVa and V and X-ray data of Pietsch et al. (in preparation) and Kahabka et al. (in preparation). We classify each source as either SNR, HII region, X-ray binary, background object or foreground star. In Sect. 2 (click here) we briefly discuss discrete radio and X-ray sources. In Sects. 3 (click here) and 4 we analyse and discuss all discrete sources common to the radio surveys and the ROSAT X-ray surveys. Finally, in Sect. 5 (click here) we discuss the radio-to-X-ray source-intensity relationships for all sources in common towards the MCs, with special emphasis on the LMC SNRs.