Chandra Observations of Galaxy Zoo Mergers: Frequency of Binary Active
  Nuclei in Massive Mergers
  We present the results from a Chandra pilot study of 12 massive galaxy
mergers selected from Galaxy Zoo. The sample includes major mergers down to a
host galaxy mass of 10$^{11}$ $M_\odot$ that already have optical AGN
signatures in at least one of the progenitors. We find that the coincidences of
optically selected active nuclei with mildly obscured ($N_H \lesssim 1.1 \times
10^{22}$ cm$^{-2}$) X-ray nuclei are relatively common (8/12), but the
detections are too faint ($< 40$ counts per nucleus; $f_{2-10 keV} \lesssim 1.2
\times 10^{-13}$ erg s$^{-1}$ cm$^{-2}$) to reliably separate starburst and
nuclear activity as the origin of the X-ray emission. Only one merger is found
to have confirmed binary X-ray nuclei, though the X-ray emission from its
southern nucleus could be due solely to star formation. Thus, the occurrences
of binary AGN in these mergers are rare (0-8%), unless most merger-induced
active nuclei are very heavily obscured or Compton thick.
