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We have discovered a binary AGN in the galaxy Mrk 739 using Chandra and SwiftBAT. We find two luminous L_2-10 keV=1.1*10^43 and 1.0*10^42 erg/s, unresolvednuclei with a projected separation of 3.4 kpc (5.8\pm0.1) coincident with twobulge components in the optical image. The western X-ray source (Mrk 739W) ishighly variable (2.5x) during the 4-hour Chandra observation and has a veryhard spectrum consistent with an AGN. While the eastern component was alreadyknown to be an AGN based on the presence of broad optical recombination lines,Mrk 739W shows no evidence of being an AGN in optical, UV, and radioobservations, suggesting the critical importance of high spatial resolutionhard X-ray observations (>2 keV) in finding these binary AGN. A high level ofstar formation combined with a very low L_[O III]/L_2-10 keV ratio cause theAGN to be missed in optical observations. CO observations of the (3-2) and(2-1) lines indicate large amounts of molecular gas in the system that could bedriven towards the black holes during the violent galaxy collision and be keyto fueling the binary AGN. Mrk 739E has a high Eddington ratio of 0.71 and asmall black hole (log M_BH=7.05\pm0.3) consistent with an efficiently accretingAGN. Other than NGC 6240, this stands as the nearest case of a binary AGNdiscovered to date.

Chandra Discovery of a Binary Active Galactic Nucleus in Mrk 739