Active Galactic Nucleus Pairs from the Sloan Digital Sky Survey. III.
  Chandra X-ray Observations Unveil Obscured Double Nuclei
  We present Chandra ACIS-S X-ray imaging spectroscopy for five dual active
galactic nucleus (AGN) candidates. Our targets were drawn from a sample of 1286
[O III]-selected AGN pairs systematically selected from the Sloan Digital Sky
Survey Seventh Data Release. Each of the targets contains two nuclei separated
by $\sim$3-9 kpc in projection, both of which are optically classified as Type
2 (obscured) AGNs based on diagnostic ratios of the narrow emission lines.
Combined with independent, empirical star formation rate estimates based on the
host-galaxy stellar continua, the new Chandra X-ray observations allow us to
evaluate the dual-AGN hypothesis for each merging system. We confirm two (SDSS
J0907+5203 and SDSS J1544+0446) of the five targets as bona-fide dual AGNs. For
the other three targets, the existing data are consistent with the dual-AGN
scenario, but we cannot rule out the possibility of stellar/shock heating
and/or one AGN ionizing both gaseous components in the merger. The average
X-ray-to-[O III] luminosity ratio in our targets seems to be systematically
smaller than that observed in single AGNs but is higher than that seen in dual
AGNs selected from AGNs with double-peaked narrow emission lines. We suggest
that the systematically smaller X-ray-to-[O III] luminosity ratio observed in
dual AGNs than in single AGNs is due to a high nuclear gas column likely from
strong merger-induced inflows. Unlike double-peaked-[O III]-selected dual AGNs,
the new sample selected from resolved galaxy pairs are not subject to the
orientation bias caused by the double-peak line-of-sight velocity splitting
selection, which also contributes to lowering the X-ray-to-[O III] luminosity
ratio.
