The history of the iron K

This paper presents ASCA (July 1997), XMM-Newton (December 2000) and BeppoSAX (January 2001) observations of the Piccinotti Seyfert 1 galaxy ESO 198-G24. The BeppoSAX 0.1–200 keV spectrum exhibits reprocessing features, probably produced by an X-ray illuminated, relativistic accretion disk subtending a solid angle $\la$ $2 \pi$. During the XMM-Newton observation the fluorescent iron Kα line profile (centroid energy $E_{\rm c} \simeq 6.4$ keV) was broad and twice as bright as in the BeppoSAX observation. An additional emission feature ($E_{\rm c} \simeq 5.7$ keV), detected at the 96.3% confidence level, may be part of a relativistic, double-peaked profile. By contrast, in the earlier ASCA observation the line profile is dominated by a remarkably narrow “core” (intrinsic width, $\sigma < 50$ eV). If this component is produced by reflection off the inner surface of a molecular torus, its large Equivalent Width ($\simeq$ 300 eV) most likely represents the “echo” of a previously brighter flux state, in agreement with the dynamical range covered by the historical X-ray light curve in ESO 198-G24.