Multifrequency monitoring of the Seyfert 1 galaxy NGC 4593 -1. Isolating the nuclear emission

We present data obtained within a campaign to monitor spectral variations in the low-luminosity Seyfert 1 galaxy NGC 4593, at X-ray, ultraviolet, optical and near-IR (/, H, K and L) frequencies. The different 'parasitic' contributions that contaminate the pure nuclear continuous emission have been isolated and modelled. The light from the composite stellar population and the dust in the bulge and disc of the underlying galaxy are characterized by a spectral energy distribution similar to that of the Sb spiral M31. Its surface brightness profile is modelled with two components and provides the luminosity through any given aperture. Stars are responsible for as much as 70-85 per cent of the 5600-Å flux through a 4 × 4 arcsec2 square aperture. The 'small bump' which characterizes the spectral energy distribution of active nuclei in the 2000-4000 Å range is well accounted for by many blended broad Fe n lines plus Balmer continuum emission. On average ~ 64 per cent of the total 2710-Å flux is due to Fe ii plus Balmer emission. Almost half of the broad-line cooling is due to Fe n line emission/The pattern of variability of the pure nuclear continuum, as well as the broad lines and their implications, is discussed in an accompanying paper.