The soft X-ray spectrum of NGC 4151 revisited
Abstract
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 1995
- DOI:
- 10.1093/mnras/275.4.1003
- Bibcode:
- 1995MNRAS.275.1003W
- Keywords:
-
- GALAXIES: INDIVIDUAL: NGC 4151;
- GALAXIES: SEYFERT;
- X-RAYS: GALAXIES