A high resolution radio continuum survey of Messier 31. I : Observations at 610 MHz, data reduction, and the 36W catalogue of radio sources

High resolution observations of M31 at 610 MHz (49.2 cm), made with the Westerbork Synthesis Radio Telescope, are described. The observations and reduction of three full synthesis fields which, after combination, cover M31 are presented. Maps at full resolution, 54arcsec×82arcsec, and maps at lower resolutions are discussed. The continuum emission of M31 comes mainly from the central region and from an annulus at 10 kpc distance from the nucleus. Further the 36W catalogue of 392 discrete radio sources in the area of M31, having flux densities S610 > 3 mJy, i.e. above the 4σ level is given. Of these sources 224 are new detections. There are indications for a slight excess of sources with low flux densities in the M31 area; this could be due to sources related to M31.