A weakening Compton hump and soft X-ray excess detected in the Seyfert-1 galaxy MCG-02-58-22

TL;DR

This study analyzes X-ray observations of Seyfert-1 galaxy MCG-02-58-22, revealing a weakening Compton hump and soft X-ray excess, suggesting dynamic, clumpy reprocessing media like a torus with multiple structures.

Contribution

It provides the first detailed comparison of multi-epoch X-ray spectra, proposing a dynamic, multi-structured torus as the cause of observed spectral changes.

Findings

The primary X-ray emission remained constant across observations.

The soft excess flux decreased by a factor of two in 2016.

The Compton hump weakened or vanished in 2016.

Abstract

We have carried out an extensive X-ray spectral study of the bare Seyfert-1 galaxy MCG--02--58--22 to ascertain the nature of the X-ray reprocessing media, using observations from Suzaku (2009) and simultaneous observations from XMM-Newton and NuSTAR (2016) . The most significant results of our investigation are: 1. The primary X-ray emission from the corona is constant in these observations, both in terms of the power law slope ($\Gamma=1.80$) and luminosity ($L_{2-10 \rm keV}= 2.55\times 10^{44} $ erg/s). 2. The soft excess flux decreased by a factor of two in 2016, the Compton hump weakened/vanished in 2016, and the narrow FeK$\alpha$ emission line became marginally broad ($\sigma=0.35\pm0.08$ keV) and its flux doubled in 2016. 3. From physical model fits we find that the normalization of the narrow component of the FeK$\alpha$ line does not change in the two epochs, although the Compton hump vanishes in the same time span. Since the primary X-ray continuum does not change, we presume that any changes in the reprocessed emission must arise due to changes in the reprocessing media. Our primary conclusions are: A. The vanishing of the Compton hump in 2016 can probably be explained by a dynamic clumpy torus which is infalling/outflowing, or by a polar torus wind. B. The torus in this AGN possibly has two structures: an equatorial toroidal disk (producing the narrow FeK$\alpha$ emission) and a polar component (producing the variable Compton hump), C. The reduction of the soft-excess flux by half and increase in the FeK$\alpha$ flux by a factor of two in the same period cannot be adequately explained by ionized disk reflection model alone.