A new X-ray spectral observation of NGC 1068

Citations Over TimeTop 10% of 1993 papers

Abstract

The first moderate-resolution (FWHM ~ 100 eV) X-ray spectrum of a Seyfert 2 galaxy was obtained with the BBXRT experiment aboard Astro-1. The observed X-ray continuum of NGC 1068 from 0.3 to 10 keV is well fitted as the sum of two power-law spectra with no evidence for absorption intrinsic to the source. Strong Fe K emission lines with a total equivalent width of 2700 eV were detected due to iron less ionized than Fe XX and to iron more ionized than Fe XXIII. Unresolved Fe L lines with a total equivalent width of 340 eV were also seen. No evidence was seen for lines due to the recombination of highly ionized oxygen with an upper limit for the O Lyα emission line of 40 eV. The discovery of multiple Fe K and Fe L emission lines clearly indicates a broad range of ionization states for this gas. The X-ray emission from NGC 1068 is thought to be due to radiation from the obscured nucleus of the galaxy that is Compton-scattered by warm (T ~2 x 10^5^ K) electrons above the obscuring material. We associate the cooler, less ionized Fe with the warm electrons producing the polarized optical light, and the hotter (T ~ 4 x 10^6^ K), highly ionized Fe with a previously unseen component. The two components may share the same volume, or the hot component may be located closer to the nucleus. The X-ray emission from the two components is modeled for various geometries using a photoionization code that calculates the temperature and ionization state of the gas. We present models consistent with the X-ray, UV, and optical observations. Typical model parameters are a total Compton depth of a few percent, an inner boundary of the hot component of about 1 pc, and an inner boundary of the warm component of about 20 pc. All the successful models require that oxygen be under-abundant compared with solar by a factor of at least 5, while Fe is most likely overabundant. We show that the observed optical and UV line strengths from the NLR are consistent with these abundances.

Related Papers

• → The effect of gravity darkening on spectral lines in a rotating star(2000)3 cited
• → Markarian 478: A Second Seyfert Galaxy with 1 Micron FeiiEmission Lines(2001)9 cited
• → The Effect of Gravity Darkening on the Spectral Lines Produced of Rotating Stars(1999)
• → Observations of Fe II in Active Galactic Nuclei(1988)