No Signatures of Black-Hole Spin in the X-ray Spectrum of the Seyfert 1 Galaxy Fairall 9

• Published in: arXiv.org
• Main Authors: Yaqoob, Tahir, Turner, Tracey Jane, Tatum, Malachi M, Max, Trevor, Scholtes, Alexis
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 25.07.2016
• Subjects: Active galactic nuclei; Alpha iron; Alpha rays; Angular momentum; Black holes; Density; Deposition; Emission; Galaxies; Gravitation; Physics - High Energy Astrophysical Phenomena; Seyfert galaxies; Supermassive black holes; X ray reflection
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1607.07125

Fairall 9 is one of several type 1 active galactic nuclei for which it has been claimed that the angular momentum (or spin) of the supermassive black hole can be robustly measured, using the Fe K\(\alpha\) emission line and Compton-reflection continuum in the X-ray spectrum. The method rests upon the interpretation of the Fe K\(\alpha\) line profile and associated Compton-reflection continuum in terms of relativistic broadening in the strong gravity regime in the innermost regions of an accretion disc, within a few gravitational radii of the black hole. Here, we re-examine a Suzaku X-ray spectrum of Fairall 9 and show that a face-on toroidal X-ray reprocessor model involving only nonrelativistic and mundane physics provides an excellent fit to the data. The Fe K\(\alpha\) line emission and Compton reflection continuum are calculated self-consistently, the iron abundance is solar, and an equatorial column density of \(\sim 10^{24} \ \rm cm^{-2}\) is inferred. In this scenario, neither the Fe K\(\alpha\) line, nor the Compton-reflection continuum provide any information on the black-hole spin. Whereas previous analyses have assumed an infinite column density for the distant-matter reprocessor, the shape of the reflection spectrum from matter with a finite column density eliminates the need for a relativistically broadened Fe K\(\alpha\) line. We find a 90 per cent confidence range in the Fe K\(\alpha\) line FWHM of \(1895\)-\(6205 \ \rm km \ s^{-1}\), corresponding to a distance of \(\sim 3100\) to \(33,380\) gravitational radii from the black hole, or \(0.015\)-\(0.49\) pc for a black-hole mass of \(\sim 1-3 \times 10^{8} \ M_{\odot}\).