A New XMM-Newton Long Look of the Low-Luminosity Active Galactic Nucleus NGC 3226

Abstract

We present the results of a 99 ks XMM-Newton observation of NGC 3226, a low-luminosity active galactic nucleus. The long exposure has enabled us to critically test several models for the form of the 0.3-10 keV spectrum. We find the 0.3-10 keV spectrum is best fitted by a partial-covering model, consisting of a power-law continuum (Γ ≈ 1.87) absorbed at low energies by neutral material in excess of the Galactic column (N _H≈3 × 10²¹ cm^-2) with a covering fraction near 90%. We conclusively reject (1) a single-temperature thermal bremsstrahlung model and (2) a partial-covering model including absorption by moderately ionized material with a column density N _W > 1.1 × 10²⁰ cm^-2. We find no significant evidence for an Fe Kα emission line or any other strong emission or absorption features. The lack of a strong observed Fe K edge and the low accretion rate relative to Eddington, \dot{m} ∼ 2× 10^{-5}, suggest NGC 3226 hosts an optically thin, geometrically thick accretion disk consistent with radiatively inefficient accretion flow (RIAF) models. We find significant flux variation during the observation on timescales of lsim1 day. The fractional variability amplitude F _var is measured to be 11.7 ± 0.6%, which is comparable to values found for Seyferts of similar black hole mass. We also present spectral fits for 22 additional X-ray sources within the XMM-Newton EPIC camera field of view.