A Suzaku observation of Mkn 590 reveals a vanishing soft excess

Abstract

We have analyzed a long-look Suzaku observation of the Seyfert 1.2 Mkn 590. We aimed to measure the Compton reflection strength, Fe K complex properties, and soft excess emission as had been observed previously in this source. The Compton reflection strength was measured to be in the range 0.2-1.0 depending on the model used. A moderately strong Fe Kα emission line was detected with an equivalent width of ∼120 ± 25eV and an Fe Kβ line was identified with an equivalent width of ∼30 ± 20eV, although we could not rule out contribution from ionized Fe emission at this energy. Surprisingly, we found no evidence for soft excess emission. Comparing our results with a 2004 observation from XMM-Newton we found that either the soft excess has decreased by a factor of 20-30 in 7years or the photon index has steepened by 0.10 (with no soft excess present) while the continuum flux in the range 2-10keV has varied only minimally (10%). This result could support recent claims that the soft excess is independent of the X-ray continuum. © 2012. The American Astronomical Society. All rights reserved.