We present Chandra and optical observations of a candidate dual AGN discovered serendipitously while searching for recoiling black holes via a cross-correlation between the serendipitous XMM source catalog ( 2XMMi ) and SDSS-DR7 galaxies with a separation no larger than ten times the sum of their Petrosian radii .
The system has a stellar mass ratio M _ { 1 } /M _ { 2 } \approx 0.7 .
One of the galaxies ( Source 1 ) shows clear evidence for AGN activity in the form of hard X-ray emission and optical emission-line diagnostics typical of AGN ionisation .
The nucleus of the other galaxy ( Source 2 ) has a soft X-ray spectrum , bluer colours , and optical emission line ratios dominated by stellar photoionisation with a ‘ ‘ composite '' signature , which might indicate the presence of a weak AGN .
When plotted on a diagram with X-ray luminosity vs [ OIII ] luminosity both nuclei fall within the locus defined by local Seyfert galaxies .
From the optical spectrum we estimate the electron densities finding n _ { 1 } < 27 e ^ { - } cm ^ { -3 } and n _ { 2 } \approx 200 e ^ { - } cm ^ { -3 } .
From a 2D decomposition of the surface brightness distribution we infer that both galaxies host rotationally supported bulges ( Sersic index < 1 ) .
While the active nature of Source 1 can be established with confidence , whether the nucleus of Source 2 is active remains a matter of debate .
Evidence that a faint AGN might reside in its nucleus is , however , tantalising .