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

Abstract

We present a new Suzaku observation of the obscured active galactic nucleus 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 timescales 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 covers >80% of the source with a column density N H ∼ 3-4×1024 cm-2. An alternative explanation is the presence of a double active nucleus in the center of NGC 1365. © 2009. The American Astronomical Society.