The BeppoSAX spectrum of the composite galaxy Mrk 609

We present BeppoSAX observations of the starburst/Seyfert composite galaxy Mrk 609. This enigmatic object has an optical spectrum dominated by the features of starburst galaxies, yet its X-ray luminosity (6.3 x 10 4 2 erg s - 1 ) is typical of an active galactic nucleus (AGN). The X-ray spectrum of Mrk 609 can be parametrized by a single-power-law model with a photon index Γ ∼ 1.6 ′ 0.1 and no evidence for significant absorption above the Galactic value. Long-term variability in both the 0.1-2 and 2-10 keV energy bands is detected, again suggesting that the X-ray emission is dominated by an AGN. The observed broad Ha component is a factor of 40 below that predicted by the X-ray flux, implying a deficit of ionizing ultraviolet photons.