Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-01-31
Astronomy and Astrophysics
Astrophysics
13 Latex pages, 15 figures, Accepted for publication in Astronomy & Astrophysics
Scientific paper
We present the results of a BeppoSAX observation of the nearby spiral galaxy NGC4945 in the 0.1-200 keV energy band. The nuclear X-ray emission emerges above ~7 keV, through an absorber with column density N_H ~ a few 10^24/cm/cm. Its remarkable variability (doubling/halving timescale ~10^4 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 K-ALPHA fluorescent emission line is likely to be produced by the same nuclear absorbing matter. Our estimate of the intrinsic nuclear power suggests that the active nucleus dominates the bolometric energy output of NGC4945, if its nucleus has a typical quasar L_X/L(bol) 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.
Antonelli Lucio Angelo
Barr Paul
Bassani Loredana
Brandt Wiliam N.
Guainazzi Matteo
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