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New bright soft X-ray selected ROSAT AGN: I. Infrared-to-X-ray spectral energy distributions

D. Grupe·K. Beuermann·H. -C. Thomas·K. Mannheim·H. H. Fink
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Abstract

We present results of an infrared-to-X-ray study of 76 bright soft X-ray selected Seyfert galaxies discovered in the ROSAT All-Sky Survey. These objects are characterized by steep X-ray spectra in the 0.2-2.0 keV bandpass with power law energy spectral indices in the range of 1.3 to 8 and a lack of internal absorption by neutral hydrogen. Our sample selection based on hardness ratio yields a mean X-ray slope of alpha-X = 2.1, steeper than in any other known AGN population. At optical wavelengths, the soft AGN have significantly bluer spectra than a comparison sample of AGN with a canonical, harder X-ray spectrum, whereas the slope between 5500 Angstrom and 1 keV is the same. This is consistent with a more pronounced Big Blue Bump emission component in the soft X-ray selected AGN. The blueness of the optical spectra increases with the softness of the X-ray spectra and with the luminosity, saturating at an approximate F_nu proportional to nu^+0.3 spectrum. Such properties are expected if most of the Big Blue Bump emission originates in a (comptonized) accretion disk and accretion rate to mass ratio is higher than in AGN with a hard X-ray spectrum.

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D. Grupe, K. Beuermann, H. -C. Thomas, K. Mannheim, H. H. Fink. 1997-10-27. New bright soft X-ray selected ROSAT AGN: I. Infrared-to-X-ray spectral energy distributions. https://arxiv.org/abs/astro-ph/9710298

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