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G.M. Madejski (NASA/GSFC), C. Done, P. Zycki (Univ. of Durham), R. E. Rothschild, P. Blanco (UCSD), A. Valinia (NASA/GSFC), B. Turek (Stanford Univ.)
The Seyfert~2 / megamaser galaxy NGC~4945 is a unique example of an object where the obscuration allows only the X--ray flux above ~8 keV to penetrate the absorber, implying \tau\rm Thomson ~3: in the 10 - 100 keV range, it is among the brightest Seyferts on the sky. The details of the hard X-ray spectrum and X--ray variability of such an object can help validate the currently popular picture of Seyfert nuclei where the nucleus (i.e. black hole, accretion disc and broad line region) is embedded within an optically thick absorber, but importantly, they can reveal the details of its structure. The shape of the hard X--ray spectrum, as well as the detection of rapid hard X--ray variability in this object detected by us in the RXTE data argue that indeed the nucleus is intrinsically Seyfert~1 - like, but they also imply that bulk of the optical depth arises in a structure subtending a relatively small solid angle with respect to the nucleus, such as an accretion disk rather than a geometrically and optically thick torus.