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 similar or equal to 7 keV, through an absorber with column density N-H similar to a few 10(24) cm(-2) Its remarkable variability (doubling/halving timescale similar to 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 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 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.
Guainazzi, M., Matt, G., Brandt, W.n., Antonelli, L.a., Barr, P., Bassani, L. (2000). A broad-band X-ray view of NGC 4945. ASTRONOMY & ASTROPHYSICS, 356(2), 463-474.
A broad-band X-ray view of NGC 4945
MATT, Giorgio;
2000-01-01
Abstract
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 similar or equal to 7 keV, through an absorber with column density N-H similar to a few 10(24) cm(-2) Its remarkable variability (doubling/halving timescale similar to 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 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 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
