X-ray Absorption and Optical Extinction in the Partially Obscured Seyfert Nucleus in Mrk 1393

TL;DR

This study investigates the variable partial obscuration of the active nucleus in Seyfert galaxy Mrk 1393 through X-ray and optical spectra, revealing changes in dust extinction and suggesting debris from the dusty torus as the obscuring material.

Contribution

It provides the first detailed multi-epoch analysis linking X-ray and optical variability to the location and nature of obscuring material near the active nucleus.

Findings

Variable dust extinction occurs on timescales of years.

The dust-to-gas ratio can be as high as the Galactic value.

Obscuring material may be debris from the dusty torus.

Abstract

We present a detailed study of the X-ray and optical spectra of the luminous Seyfert galaxy Mrk 1393, which revealed variable partial obscuration of the active nucleus. The X-ray spectra obtained by XMM-Newton and Swift show moderate absorption with a column density around 3x10^21 cm^-2, consistent with a dust-reddening interpretation of the steep Balmer decrement seen in recent optical spectra. The X-ray flux in the 0.5 to 2 keV band during the XMM-Newton observation in 2005 and Swift observation in 2006 was a factor 6 brighter than that of the ROSAT All Sky Survey in 1991. In the past 4 years, the broad H\alpha line brightened by a factor of 4 accompanied by a decrease in the Balmer decrement. A comparison with literature spectra reveals variations in the dust extinction on time scales of several years, suggesting that the obscuring material is very close to the active nucleus. These observations indicate that a dust-to-gas ratio as high as the Galactic value can be present in moderately thick gas in the vicinity of the central engine within a few parsecs. We suggest that the obscuring material may be debris disrupted from the dusty torus.