Iron and nickel line properties in the X-ray-reflecting region of the Circinus galaxy

Abstract

We discuss the iron and nickel properties in the nuclear X-ray-reflecting region of the Circinus galaxy, studied with XMM-Newton. The main results are as follows, (i) From the depth of the Fe Ka edge, a value of AFe = 1.7 in number with respect to the cosmic value (as for Anders & Grevesse) is measured, if the (not directly visible) illuminating spectrum is assumed to be that measured by BeppoSAX. If the slope of the primary power law is left free to vary, a steeper spectrum and a lower iron abundance (about 1.2) are found, (ii) From the Ni to Fe Ka line flux ratio, a nickel-to-iron abundance ratio of 0.055-0.075 is found, (iii) The Fe Kβ/Kα flux ratio is slightly lower than expected, possibly due to a mild ionization of iron (which, however, cannot be much more ionized than x). (iv) The presence of the Fe Ka Compton shoulder, already discovered by Chandra, is confirmed, its relative flux implying Compton-thick matter. This further supports the identification of the reflecting region with the absorber.