The history of the iron K_alpha line profile in the Piccinotti AGN ESO 198-G24

Abstract

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 K_alpha line profile (centroid energy E_c =~ 6.4 keV) was broad and twice as bright as in the BeppoSAX observation. An additional emission feature (E_c =~ 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 ( =~ 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.