Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.275.1003w&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 275, Issue 4, pp. 1003-1016.
Astronomy and Astrophysics
Astronomy
29
Galaxies: Individual: Ngc 4151, Galaxies: Seyfert, X-Rays: Galaxies
Scientific paper
In a deep (~30 ks) ROSAT PSPC observation, the Seyfert galaxy NGC 4151 is detected as a bright unresolved X-ray source in a very rich field. There is no clear evidence for soft X-ray variability during the 1-d ROSAT observation. In order to investigate further the very complex soft X-ray spectrum of NGC 4151, we combine the ROSAT PSPC data with near-simultaneous Ginga measurements to obtain wide-band (0.1-20 keV) spectral coverage. We find that the X-ray emission observed below ~1 keV has a rather steep spectrum, consistent, in these low-resolution data, with either a thermal bremsstrahlung (kT~0.5 keV) or power-law (photon index Gamma~2.8) form. This soft X-ray emission can be attributed to a blend of thermal and electron-scattered components, although the exact contribution of each is uncertain. We also reassess the possible origin of the complex variable absorption which is most apparent between 1 and 4keV in the X-ray spectrum of NGC 4151. The evidence now favours an absorbing medium subject to a modest level of photoionization, which we describe as a `lukewarm' absorber. In this scenario it is possible to reconcile the column densities measured in the soft X-ray regime with those inferred from ultraviolet absorption-line studies.
Done Christine
Smith Alastair D.
Warwick Robert S.
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