A Suzaku Observation of Mkn 590 Reveals a Vanishing Soft Excess

TL;DR

This study analyzes Suzaku observations of Mkn 590, revealing a significant decrease or disappearance of the soft excess emission over seven years, while other X-ray properties remained relatively stable.

Contribution

It provides the first detailed Suzaku measurement showing the vanishing soft excess in Mkn 590 and compares it with previous XMM-Newton data to explore its variability.

Findings

Soft excess emission was not detected in Suzaku data.

The Fe K emission lines were detected with specific equivalent widths.

The soft excess decreased by a factor of 20-30 or the photon index steepened significantly.

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 \ka emission line was detected with an equivalent width of ~120+/-25 eV and an Fe Kb line was identified with an equivalent width of ~30+/-20 eV, 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 7 years or the photon index has steepened by 0.10 (with no soft excess present) while the continuum flux in the range 2-10 keV has varied only minimally (10%). This result could support recent claims that the soft excess is independent of the X-ray continuum.