HEAO 1 observations of high-energy X-rays from the Seyfert I galaxy Mkn 509

The results of observations of the Seyfert I galaxy Mkn 509 at high X-ray energies (14-140 keV) with the UCSD/MIT instrument aboard HEAO 1 are reported. The source is detected at energies above 40 keV, and the spectrum is consistent with an extrapolation of the power-law spectrum obtained at lower X-ray energies. Observations on four separate days in 1978 October indicate that the source is varying on a time scale of days.