Obscured Active Nucleus of NGC 7172 as Seen by NuSTAR

Аннотация

Abstract—The properties of X-ray emission of the active nucleus of the Seyfert 2 galaxy NGC 7172 detected by the NuSTAR space observatory in 2014 are analyzed. This source exhibits constant obscuration N_H ≈ 8 × 10²² cm^–2, which is similar to that determined by XMM-Newton, Suzaku, ASCA, and BeppoSAX in the past 30 years. Spectral analysis reveals the presence of a moderate reflection component with \(\left\langle R \right\rangle \) = 0.44 and a narrow FeK_α line with EW = \(67_{{ - 14}}^{{ + 13}}\) eV. Numerical torus models confirm that the Seyfert nucleus of NGC 7172 is of a Compton-thin type and provide estimates of the torus inclination (Θ_i ≈ 61° and its opening angle (Θ_t ≈ 59°). The data of earlier observations reveal approximately order-of-magnitude variations of intrinsic luminosity L_intr(2–10 keV) and fourfold variations of equivalent width EW FeK_α on a timescale of 12 years, which corresponds to distance d ≈ 3.7 pc. This behavior of L_intr(2–10 keV) is indicative of variability of the central source. The results of spectral analysis, the lag between variations of the intrinsic luminosity and EWFeK_α, and the variation of intensity \({{I}_{{{\text{Fe}}{{K}_{\alpha }}}}}\) agree best with the scenario of production of the observed FeK_α line in a distant gas-dust torus.