Broadband X-Ray Observation of Broad-line Radio Galaxy 3C 109

Abstract

We present a study of the central engine in the broad-line radio galaxy 3C 109. To investigate the immediate surrounding of this accreting, supermassive black hole, we perform a multiepoch broadband spectral analysis of a joint NuSTAR/XMM observation (2017), an archival XMM observation (2005) and the 105 month averaged Swift-BAT data. We are able to clearly separate the spectrum into a primary continuum, neutral and ionized absorption, and a reflection component. The photon index of the primary continuum has changed since 2005 ( ${\rm{\Gamma }}={1.61}_{-0.01}^{+0.02}\to 1.54\pm 0.02$ ), while other components remain unchanged, indicative of minimal geometric changes to the central engine. We constrain the high-energy cutoff of 3C 109 (E ${}_{\mathrm{cut}}={49}_{-5}^{+7}$ keV ) for the first time. The reflector is found to be ionized (log ξ = ${2.3}_{-0.2}^{+0.1}$ ) but no relativistic blurring is required by the data. Spectral energy distribution (SED) analysis confirms the super-Eddington nature of 3C 109 initially (λ_Edd > 2.09). However, we do not find any evidence for strong reflection (R = ${0.18}_{-0.03}^{+0.04}$ ) or a steep power-law index, as expected from a super-Eddington source. This puts the existing virial mass estimate of 2 ×10⁸M_⊙ into question. We explore additional ways of estimating the Eddington ratio, some of which we find to be inconsistent with our initial SED estimate. We obtain a new black hole mass estimate of 9.3 ×10⁸M_⊙, which brings all Eddington ratio estimates into agreement and does not require 3C 109 to be super-Eddington.