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A broad-band X-ray view of NGC 4945
We present the results of a BeppoSAX observation of the nearby spiralgalaxy NGC 4945 in the 0.1-200 keV energy band. The nuclear X-rayemission emerges above =~ 7 keV, through an absorber with column densityN_H ~ a few 1024 cm-2. Its remarkable variability(doubling/halving timescale ~ 104 s) is not associated withany appreciable spectral changes, ruling out variations of theinterposed absorber or changes in the primary continuum shape. Theintense iron Kalpha fluorescent emission line is likely tobe produced by the same nuclear absorbing matte. Our estimate of theintrinsic nuclear power suggests that the active nucleus dominates thebolometric energy output ofNGC 4945, if its nucleus has a typical quasarL_X/Lbol ratio. This supports the idea that X-rays are thebest energy band to search for absorbed AGN. The 0.1-5 keV emission isextended along the plane of the galaxy, and most likely due to apopulation of unresolved binaries, as believed to happen in severalearly-type galaxies. Alternatively, hot gas associated with astarburst-driven superwind outflow could substantially contribute to theextended emission above 1 keV.
| The spiral structure of galaxies.
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