A broad-band X-ray view of NGC 4945

M. Guainazzi, G. Matt, W. N. Brandt, L. A. Antonelli, P. Barr, L. Bassani

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78 Scopus citations


We present the results of a BeppoSAX observation of the nearby spiral galaxy NGC 4945 in the 0.1-200 keV energy band. The nuclear X-ray emission emerges above ≲7 keV, through an absorber with column density NH ∼ a few 1024 cm-2. Its remarkable variability (doubling/halving timescale ∼104 s) is not associated with any appreciable spectral changes, ruling out variations of the interposed absorber or changes in the primary continuum shape. The intense iron Kα fluorescent emission line is likely to be produced by the same nuclear absorbing matte. Our estimate of the intrinsic nuclear power suggests that the active nucleus dominates the bolometric energy output ofNGC 4945, if its nucleus has a typical quasar LX/Lbol ratio. This supports the idea that X-rays are the best energy band to search for absorbed AGN. The 0.1-5 keV emission is extended along the plane of the galaxy, and most likely due to a population of unresolved binaries, as believed to happen in several early-type galaxies. Alternatively, hot gas associated with a starburst-driven superwind outflow could substantially contribute to the extended emission above 1 keV.

Original languageEnglish (US)
Pages (from-to)463-474
Number of pages12
JournalAstronomy and Astrophysics
Issue number2
StatePublished - 2000

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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