Chandra X-ray Observation of NGC 4151

Abstract

We present Chandra X-ray observations of the nearby Seyfert 1.5 galaxy NGC 4151. The images show the extended soft X-ray emission on the several hundreds of pc scale with better sensitivity than previously obtained. The spectrum of the unresolved nuclear source may be described by a heavily absorbed (N_{H} \simeq 3 \times 10^{22} cm^-2), hard power-law (Γ\simeq 0.3) plus soft emission from either a power-law (Γ\simeq 2.6) or a thermal (kT \simeq 0.6 keV) component. The flux of the high energy component has decreased from that observed by ASCA in 1993 and the spectrum is much harder.The large difference between the soft and hard spectral shapes does not favor the partial covering or scattering model of the ``soft excess''. Instead, it is likely that the hard and soft nuclear components represent intrinsically different X-ray sources. Spectra of the extended emission to almost 1 kpc NE and SW of the nucleus have also been obtained. The spectra of these regions may be described by either thermal bremsstrahlung (kT \simeq 0.4-0.7 keV) or power-law (Γ\simeq 2.5-3.2) continua plus 3 emission lines. There is an excellent correlation between the extended X-ray and [O III]λ5007 line emissions. We discuss the nature of the extended X-ray emission. Upper limit to the electron scattering column was obtained. This upper limit is much too low for the soft X-rays to be electron scattered nuclear radiation.