2024A&A...691A.279M

We report the discovery of the Fe K line emission at ∼6.62_–0.06^+0.06 keV with a width of ∼0.19_–0.05^+0.05 keV using two epochs of Chandra archival data for the nucleus of the galaxy 4C+37.11, which is known to host a binary supermassive black hole (BSMBH) system where the SMBHs are separated by ∼7 mas or ∼7pc. Our study reports the first detection of the Fe K line from a known binary AGN, which has an F-statistic value of 20.98 and a probability of 2.47 × 10^–12. Stacking two spectra reveals another Fe K line component at ∼7.87_–0.09^+0.19 keV. Different model scenarios indicate that the lines originate from the combined effects of accretion disk emission and circumnuclear collisionally ionized medium. The observed low column density favors a gas-poor merger scenario, where the high temperature of the hot ionized medium may be associated with the shocked gas in the binary merger and not with star formation activity. The estimated total BSMBH mass and disk inclination are ∼1.5 × 10¹⁰ M_⊙ and ≳75°, indicating that the BSMBH is probably a high-inclination system. We were not able to tightly constrain the spin parameter using the present data sets. Our results draw attention to the fact that detecting the Fe K line emissions from BSMBHs is important for estimating the individual SMBH masses and the spins of the binary SMBHs, as well as for exploring their emission regions.