A strong excess in the 20-100 keV emission of NGC 1365

TL;DR

This study reports an unexpected excess of high-energy X-ray emission in NGC 1365, indicating complex circumnuclear structures or a possible double active nucleus, based on new Suzaku, Swift-BAT, and Integral-IBIS observations.

Contribution

The paper presents the first detection of a significant excess in 20-100 keV X-ray emission in NGC 1365, suggesting complex nuclear structures or dual AGN activity.

Findings

Excess X-ray emission above 20 keV is at least twice the extrapolated model.

The high-energy emission is concentrated within 1.5 arcmin and is not significantly variable.

The circumnuclear medium likely has at least two components with different properties.

Abstract

We present a new Suzaku observation of the obscured AGN in NGC 1365, revealing an unexpected excess of X-rays above 20 keV of at least a factor ~2 with respect to the extrapolation of the best-fitting 3-10 keV model. Additional Swift-BAT and Integral-IBIS observations show that the 20-100 keV is concentrated within ~1.5 arcmin from the center of the galaxy, and is not significantly variable on time scales from days to years. A comparison of this component with the 3-10 keV emission, which is characterized by a rapidly variable absorption, suggests a complex structure of the circumnuclear medium, consisting of at least two distinct components with rather different physical properties, one of which covering >80% of the source with a column density NH~3-4x10^24 cm^(-2). An alternative explanation is the presence of a double active nucleus in the center of NGC 1365.