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P. M. Ogle, H. L. Marshall, J. C. Lee, C. R. Canizares (MIT/CXC)
We report on the X-ray spectrum and structure of the Seyfert 1.5 active galaxy NGC 4151, observed with the Chandra High Energy Transmission Grating. We see over 50 emission lines from high-ionization species, including N VII, hydrogen-like and helium-like O, Ne, Mg, Al, Si, S, and Ar, and Fe XVII-XX. We confirm that the low-energy (E<2.5 keV) emission is extended (Morse et al. 1995) and further find a correspondence on arcsecond scales to the optical narrow-line region. The hard continuuum source (E>2.5 keV) is point-like and was in an unusually low state during our observation.
The dispersed spectrum is fit by highly absorbed non-thermal (power-law) emission from the central point source plus lines and continuum scattered by the extended photoionized nebula. Photoionization is clearly required by the large ratio of forbidden to resonance emission in O VII. Spatial broadening is seen in the X-ray emission lines, showing that they come from a region at least 2.5 arcsec in diameter. Differences in the the redshifts as well as ionization states of the X-ray and optical lines suggest that though the X-ray and optical line-emitting regions appear to be spatially coincident, they constitute two distinct components within the narrow-line region. This work was funded in part by contracts NAS8-38249 and SAO SV1-61010.
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