Correlation between Compton reflection and X-ray slope in Seyferts and X-ray binaries

Abstract

A B S T R A C TWe find a very strong correlation between the intrinsic spectral slope in X-rays and the amount of Compton reflection from a cold medium in Seyfert AGNs and in the hard state of X-ray binaries with either black holes or weakly magnetized neutron stars. Objects with soft intrinsic spectra show much stronger reflection than those with hard spectra. We find that, at a given spectral slope, black hole binaries have similar reflection to or more reflection than Seyferts, whereas neutron star binaries in our sample have reflection consistent with that in Seyferts. The existence of the correlation implies a dominant role of the reflecting medium as a source of seed soft photons for thermal Comptonization in the primary X-ray source.

X-ray power law spectra in active galactic nuclei

“…A difference in the power law slope was observed in different AGN classes, in particular Seyfert 2 galaxies are found to have harder spectra than Seyfert 1 galaxies (Zdziarski et al 1995(Zdziarski et al , 2000. Furthermore, Zdziarski et al (1999) reported a significant correlation between reflection component and power law slope in Seyfert galaxies. More recently, a "spectral-timing" correlation was discovered in AGNs (Papadakis et al 2009), suggesting a close connection between X-ray spectral and variability properties.…”

“…In addition, the importance of the reflection component seems to be related to the X-ray spectral shape: a significant correlation between power law slope and amount of reflection has been observed in Seyfert galaxies (Zdziarski et al 1999). Softer spectra are associated with a strong reflection component, while less reflection is observed in objects with harder spectra.…”

Fluorescent iron lines as a probe of astrophysical black hole systems

“…It was suggested that there is a certain amount of overlap between the quasi-spherical corona and the outer, thin accretion disk. As this disk moves inward, the corona becomes more effectively Compton cooled and produces softer spectra, while the increase of overlap between disk and corona yields stronger lines and reflection features [282]. As for the case of NGC 5548, however, the details of the overall correlation are more complicated than any simple model.…”

“…Recently, Andrzej Zdziarski and collaborators have claimed such a correspondence between the two classes. Specifically, they describe a correlation between the spectral slope of a fitted power law with the amplitude of reflection, with softer spectra yielding greater reflection fractions [282]. The observations that made up this correlation consisted of both AGN and GBHC, mostly observed in relatively hard spectral states.…”

X-ray spectral parameters for a sample of 95 active galactic nuclei

“…For the first time the relationship between relative reflection R and photon index was found and described by Zdziarski et al (1999). This work used the X-ray Ginga satellite data for 23 radioquiet Seyfert galaxies of type 1, 1.2, 1.5 and several X-ray binary systems.…”