The Complex Soft X-Ray Excess in NGC 4151

Details The Complex Soft X-Ray Excess in NGC 4151 The Complex Soft X-Ray Excess in NGC 4151

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...423..621w&link_type=abstract

Astrophysical Journal v.423, p.621

Astronomy and Astrophysics

Astronomy

37

Galaxies: Individual Ngc Number: Ngc 4151, Galaxies: Nuclei, Galaxies: Seyfert, X-Rays: Galaxies

Scientific paper

We present Broad-Band X-ray Telescope (BBXRT) observations (˜0.4-11.0 keV) of the Seyfert 1.5 galaxy NGC 4151, with emphasis placed upon modeling the low-energy X-ray spectrum. A prominent soft X-ray "excess" below the ˜2 keV cutoff due to a high absorbing column is known to exist in NGC 4151. This excess has been variously discussed in terms of "leakage" through a patchy absorber, the reduced opacity of an ionized absorber, and/or a distinct and possibly spatially extended component. BBXRT, with its combination of moderate resolution and a large bandpass, has allowed the origin of this excess to be tested for the first time over a 2 day period. We find that the ˜0.4-1.5 keV flux remains essentially constant while the 2-10 keV continuum flux decreases by ˜40%. We also see no evidence of strong spectral features at energies of less than 1.5 keV. This implies that the excess is neither continuum "leakage" nor is it dominated by emission from a 106-107 K equilibrium plasma. The best single-component description of the soft excess is scattering of the central continuum into our line of sight by an "electron scattering zone" similar to that in the Seyfert 2 galaxy NGC 1068. However, a more likely description of the lack of strong spectral features and the lack of correlated soft-to-hard X-ray variability is that at least two spectral components comprise the soft excess.

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