The Central Engine Structure of 3C120: Evidence for a Retrograde Black Hole or a Refilling Accretion Disk

TL;DR

This study reanalyzed Suzaku X-ray data of 3C120, revealing a truncated accretion disk and suggesting the black hole may be retrograde or the disk recently refilled after instabilities.

Contribution

It provides new spectral analysis indicating a truncated disk and constrains black hole spin, proposing a possible retrograde or refilled disk scenario.

Findings

Inner disk radius of approximately 11.7 r_g

Black hole spin constrained to a < -0.1

Rapid prograde spin (a > 0.8) ruled out at 99% confidence

Abstract

The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160 ks of Suzaku data taken in 2006, previously examined by Kataoka et al. (2007). Spectral fits to the XIS and HXD/PIN data over a range of 0.7-45 keV reveal a well-defined iron K line complex with a narrow Ka core and relativistically broadened features consistent with emission from the inner regions of the accretion disk. Furthermore, the inner region of the disk appears to be truncated with an inner radius of r_in = 11.7^{+3.5}_{-5.2} r_g. If we assume that fluorescent iron line features terminate at the inner-most stable circular orbit (ISCO), we measure a black hole spin of a < -0.1 at a 90% confidence level. A rapidly spinning prograde black hole (a > 0.8) can be ruled out at the 99% confidence level. Alternatively, the disk may be truncated well outside of the ISCO of a rapid prograde hole. The most compelling scenario is the possibility that the inner regions of the disk were destroyed/ejected by catastrophic instabilities just prior to the time these observations were made.