Broad Band X-ray Constraints on the Accreting Black Hole in Quasar 4C 74.26

TL;DR

This study models broadband X-ray spectra of quasar 4C 74.26 using MYTORUS, revealing a Compton thick environment and suggesting the X-ray emission does not originate from the inner accretion disk, challenging SMBH spin measurements.

Contribution

First comprehensive broadband X-ray modeling of 4C 74.26 with MYTORUS, demonstrating the dominance of distant matter in X-ray emission and questioning the use of relativistic lines for SMBH spin.

Findings

Global column density in the Compton thick regime (~1.5-2.9×10^{24} cm^{-2})

Line-of-sight column density is Compton thin in all observations

No evidence for relativistic broadening or truncated accretion disk

Abstract

X-ray data for quasar 4C 74.26 have previously been modeled with a broad Fe K$\alpha$ emission line and reflection continuum originating in the inner part of the accretion disk around the central supermassive black hole (SMBH), i.e. the strong gravity regime. We modeled broadband X-ray spectra from $Suzaku$ and $NuSTAR$ with MYTORUS, self-consistently accounting for Fe K$\alpha$ line emission, as well as direct and reflected continuum emission, from finite column density matter. A narrow Fe K$\alpha$ emission line originating in an X-ray reprocessor with solar Fe abundance far from the central SMBH is sufficient to produce excellent fits for all spectra. For the first time, we are able to measure the global, out of the line-of-sight column density to be in the range $\sim$$1.5$ to $\sim$$2.9\times10^{24}$ cm$^{-2}$, i.e. in the Compton thick regime, while the line-of-sight column density is Compton thin in all observations. The Fe K$\alpha$ emission line is unresolved in all but one observations. The Compton scattered continuum from distant matter removes the need for relativistic broadening of the Fe K$\alpha$ emission line, which is required for SMBH spin measurements. The resolved line observation can alternatively be modeled with a relativistic model but we do not find evidence for a truncated accretion disk model. We conclude that the X-ray emission in these 4C 74.26 data is unlikely to originate in the inner accretion disk region and thus cannot be used to measure SMBH spin.