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 × 1042 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 Hα component is a factor of 40 below that predicted by the X-ray flux, implying a deficit of ionizing ultraviolet photons.