Structure of the Circumnuclear Region of Seyfert 2 Galaxies Revealed by   RXTE Hard X-ray Observations of NGC 4945
  We report the Rossi X-ray Timing Explorer observations of the heavily absorbed Seyfert 2 galaxy NGC 4945, which confirm the large column density of the absorber, corresponding to the optical depth to Thomson scattering of about 2.4. The hard X-ray flux (8-30 keV) measured by us is rapidly variable with a large amplitude, on time scales of a day or less. This implies that the bulk of the extreme absorption does not originate in a parsec-size, geometrically thick molecular torus: limits on the amount of scattered flux require that the optically thick material on parsec scales must be rather geometrically thin, subtending a half-angle of less than 10 degrees as seen from the nucleus. This presents a problem in accounting for the Cosmic X-ray Background primarily with AGN possessing such geometry. 
G.M. Madejski (NASA/GSFC), P.T. Zycki (Copernicus Ctr.), C. Done   (Durham Univ.), A. Valinia (NASA/GSFC), P. Blanco (UCSD),...