Active Galactic Nuclei:  Then
	* Proportional counter observations of AGNs had generally shown that their spectra were dominated by power law continua, attenuated at low energies by interstellar and/or circumsource absorption. * The first weak evidence for Fe K line emission came from higher statistics observations obtained with OSO 8 and HEAO 1 in the late 1970’s. * NGC 4151 was one of the most intensively studied sources. Mushotzky et al. were the first to report the Fe K line, although it was only a 2s detection.
					Mushotzky, Holt & Serlemitsos, 1978, Ap. J., 225, L115.