Broad-band X-ray spectrum of the bright Seyfert galaxy Mkn 509

Summary One of the brightest X-ray Seyfert galaxies, Mkn 509, has been observed with the X-ray satellite EXOSAT. Wide-band ((0.05÷35) keV) spectral information is now available at the same time. Different filters have been rotated in front of the low-energy telescope. The overall spectrum is best fitted by a two-component power law. The intensity and the spectral index of the soft component are in agreement with the extrapotation of the UV spectrum; the high-energy component exhibits a spectral index harder than reported by previous observations and a correspondingly lower intensity. Therefore, at least for this source, the predicted low-energy spectral turnover is a smooth prolungation of the UV spectrum rather than a sharp discontinuity. Paper presented at the 2° Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May – 2 June 1984.