Broadband X-Ray Spectral Analysis of the Double-nucleus Luminous Infrared Galaxy Mrk 463

Abstract

We present a broadband (0.4–70 keV) X-ray spectral analysis of the luminous infrared galaxy (LIRG) system Mrk 463 observed with Nuclear Spectroscopic Telescope Array ( NuSTAR ), Chandra , and XMM-Newton , which contains double active galactic nuclei (AGNs; Mrk 463E and Mrk 463W) with a separation of ∼3.8 kpc. Detecting their transmitted hard X-ray >10 keV continua with NuSTAR , we confirm that Mrk 463E and Mrk 463W have AGNs with intrinsic luminosities of (1.6–2.2) × 10 43 and (0.5–0.6) × 10 43 erg s −1 (2–10 keV) obscured by hydrogen column densities of 8 × 10 23 and 3 × 10 23 cm −2 , respectively. Both nuclei show strong reflection components from cold matter. The luminosity ratio between X-ray (2–10 keV) and [O iv ] 25.89 μ m of Mrk 463E is ∼5 times smaller than those of normal Seyfert galaxies, suggesting that the intrinsic SED is X-ray weak relative to the UV luminosity. In fact, the bolometric AGN luminosity of Mrk 463E estimated from L ′-band (3.8 μ m), [O iv ] 25.89 μ m, and [Ne v ] 14.32 μ m lines indicate a large bolometric-to-X-ray luminosity ratio, κ 2–10 keV  ≈ 110–410, and a high Eddington ratio, λ Edd  ∼ 0.4–0.8. We suggest that the merger triggered a rapid growth of the black hole in Mrk 463E, which is not yet deeply “buried” by circumnuclear dust. By contrast, the L ′-band luminosity of Mrk 463W is unusually small relative to the X-ray luminosity, suggesting that the Eddington ratio is low (<10 −3 ) and it might be still in an early phase of merger-driven AGN activity.