The X-ray reflector in NGC 4945: a time and space resolved portrait

TL;DR

This study uses multi-epoch X-ray observations to map the structure of the reflector around the AGN in NGC 4945, revealing a large, clumpy, flattened circumnuclear gas structure at 30-50 pc.

Contribution

It provides the first detailed spatial and temporal analysis of the X-ray reflector in NGC 4945, combining spectral, imaging, and variability data to characterize its geometry and physical state.

Findings

The reflector is located 30-50 pc from the nucleus.

The structure is a resolved, flattened, 150 pc-long clumpy gas complex.

The reflector's spectrum is dominated by cold reflection, with low covering factor.

Abstract

We present a time, spectral and imaging analysis of the X-ray reflector in NGC 4945, which reveals its geometrical and physical structure with unprecedented detail. NGC 4945 hosts one of the brightest AGN in the sky above 10 keV, but it is only visible through its reflected/scattered emission below 10 keV, due to absorption by a column density of ~4\times10^24 cm-2. A new Suzaku campaign of 5 observations spanning ~6 months, together with past XMM-Newton and Chandra observations, show a remarkable constancy (within <10%) of the reflected component. Instead, Swift-BAT reveals strong intrinsic variability on time scales longer than one year. Modeling the circumnuclear gas as a thin cylinder with the axis on the plane of the sky, we show that the reflector is at a distance >30-50 pc, well within the imaging capabilities of Chandra at the distance of NGC 4945 (1"~18 pc). Accordingly, the Chandra imaging reveals a resolved, flattened, ~150 pc-long clumpy structure, whose spectrum is fully due to cold reflection of the primary AGN emission. The clumpiness may explain the small covering factor derived from the spectral and variability properties.