Constraining Black Hole Spin via X-Ray Spectroscopy

• Published in: The Astrophysical journal Vol. 652; no. 2; pp. 1028 - 1043
• Main Authors: Brenneman, Laura W, Reynolds, Christopher S
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 01.12.2006; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; galaxies: Seyfert; X-ray galaxies; Black holes; accretion, accretion disks; X-rays: galaxies; Cosmic x-ray sources; galaxies: individual (MCG -6-30-15); X-ray spectroscopy; Accretion disks; Seyfert galaxies; black hole physics; Galaxy nuclei; Cosmology; galaxies: nuclei
• DOI: 10.1086/508146
• ISSN: 0004-637X

We present an analysis of the observed broad iron line feature and putative warm absorber in the long 2001 XMM-Newton observation of the Seyfert 1.2 galaxy MCG-06-30-15. The new kerrdisk model we have designed for simulating line emission from accretion disk systems allows black hole spin to be a free parameter in the fit, enabling the user to formally constrain the angular momentum of a black hole, among other physical parameters of the system. In an important extension of previous work, we derive constraints on the black hole spin in MCG-06-30-15 using a self-consistent model for X-ray reflection from the surface of the accretion disk while simultaneously accounting for absorption by dusty photoionized material along the line of sight (the warm absorber). Even including these complications, the XMM-Newton EPIC pn data require extreme relativistic broadening of the X-ray reflection spectrum; assuming no emission from within the radius of marginal stability, we derive a formal constraint on the dimensionless black hole spin parameter of a = 0.989 super(+0.009-0.002) at 90% confidence. The principal unmodeled effect that can significantly reduce the inferred black hole spin is powerful emission from within the radius of marginal stability. Although significant theoretical developments are required to fully understand this region, we argue that the need for a rapidly spinning black hole is robust to physically plausible levels of emission from within the radius of marginal stability. In particular, we show that a nonrotating black hole is strongly ruled out.