Akn 564: an unusual component in the X-ray spectra of NLSy1 galaxies

Details Akn 564: an unusual component in the X-ray spectra of NLSy1 galaxies Akn 564: an unusual component in the X-ray spectra of NLSy1 galaxies

1999-06-17

arxiv.org/abs/astro-ph/9906294v1

Astronomy and Astrophysics

Astrophysics

15 pages, 5 figures. LaTeX with encapsulated postscript. Accepted for publication in the Astrophysical Journal

Scientific paper

10.1086/307995

We present an ASCA observation of the NLSy1 Ark 564. The X-ray light curve shows rapid variability, but no evidence for energy-dependence to these variations, within the 0.6 -- 10 keV bandpass. A strong (EW ~ 70 eV) spectral feature is observed close to 1 keV. A similar feature has been observed in TON S180 (another NLSy1) but has not been observed in broad-line Seyfert galaxies. The feature energy suggests a large contribution from Fe L-shell lines but its intensity is difficult to explain in terms of emission and/or absorption from photoionized gas. Models based on gas in thermal equilibrium with kT ~1 keV provide an alternative parameterization of the soft spectrum. The latter may be interpreted as the hot intercloud medium, undergoing rapid cooling and producing strong Fe L-shell recombination lines. In all cases the physical conditions are rather different from those observed in broad-line Seyferts. The hard X-ray spectrum shows a broad and asymmetric Fe Kalpha line of large equivalent width (~550 eV) which can be explained by a neutral disk viewed at ~ 60 degrees to the line-of-sight, contrary to the hypothesis that NLSy1s are viewed pole-on. The large EW of this line, the strong 1 keV emission and the strong optical Fe emission lines all suggest an extreme Fe abundance in this and perhaps other NLSy1s.

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