Supermassive Black Hole Spins in Seyfert I AGN via Principal Component Analysis

The general-relativistic frame-dragging caused by a spinning supermassive black hole (SMBH) has geometric effects on the inner accretion disk, which can be traced in the X-rays reflected from the disk. Modeling the relativistically broadened X-ray emission reflected from the innermost accretion flows at the centers of active galactic nuclei (AGN) allows us to measure the SMBH spins. Since the supermassive black hole's spin is constant over the course of human history, changes in X-ray sources in AGN should not have an impact on our spin measurement. To evaluate the reliability of our spin constraint, we perform principal component analysis (PCA) on time-segmented XMM-Newton and Suzaku observations of a sample of Seyfert I AGN that have been found to contain the relativistically widened iron lines at 6.4 keV, such as NGC 3783, NGC 4051, and MCG-6-30-15. Our PCA analyses of all the available multi-epoch archival data show that the main component mostly causing X-ray variations is linked to the continuum of a power-law emitting source. The higher-order PCA components involve the trivial contributions from a relativistically redshifted, blurred reflection (<2%). The minimal variations in the relativistic X-ray reflection could potentially result from light-bending phenomena near the event horizon and have no impact on the spin constraints made by using all multi-epoch data.