X-ray continuum and line emission of the Seyfert galaxy MCG - 5-23-16

Abstract

We report observations of X-ray continum and line emission from the highly absorbed and variable Seyfert galaxy MCG-5-23-16, using the low-energy and the medium-energy detectors of the Exosat Observatory.The galaxy was observed in 1983 December and 1984 May. The X-ray intensity of the source is observed to vary by ~25% in the hard (2-10 keV) and by ~40 percent in the soft (0.1-2.0 keV) energy bands over a period of 6 months. The 0.1-10 keV X-ray spectrum is adequately explained by a simple power law. The measured energy index lies in the range 0.42-0.89 and shows a dependence on the intensity. Line emission at 6.4 keV is detected in the 1984 observations when the X-ray spectrum is relatively harder. The equivalent width of the line is measured to be 346 ± 146 eV. The presence of line emission is also indicated in the 1983 data. The line-of-sight absorption is much higher than the 21-cm value, suggesting a very high obscuration of the nuclear source. The present observations are well explained by the reflection of X-rays by cold material in an accretion disk around the nuclear source. It is suggested that as the absorption(due to the disk) of the direct component increases with time, so does the amount of the reflected component, thus hardening the spectrum and also producing more line emission.