  We have discovered heavy obscuration in the dual active galactic nucleus
(AGN) in the Swift/Burst Alert Telescope (BAT) source SWIFT J2028.5+2543 using
Nuclear Spectroscopic Telescope Array (NuSTAR). While an early XMM-Newton study
suggested the emission was mainly from NGC 6921, the superior spatial
resolution of NuSTAR above 10 keV resolves the Swift/BAT emission into two
sources associated with the nearby galaxies MCG +04-48-002 and NGC 6921 (z =
0.014) with a projected separation of 25.3 kpc (91"). NuSTAR's sensitivity
above 10 keV finds both are heavily obscured to Compton-thick levels (N
H=(1-2)x10^24 cm-2) and contribute equally to the BAT detection ({L}10-50
{keV}{{int}}= 6x10^42 erg s-1). The observed luminosity of both sources is
severely diminished in the 2-10 keV band, illustrating the importance of >10
keV surveys like those with NuSTAR and Swift/BAT. Compared to archival X-ray
data, MCG +04-48-002 shows significant variability (>3) between observations.
Despite being bright X-ray AGNs, they are difficult to detect using optical
emission-line diagnostics because MCG +04-48-002 is identified as a
starburst/composite because of the high rates of star formation from a luminous
infrared galaxy while NGC 6921 is only classified as a LINER using line
detection limits. SWIFT J2028.5+2543 is the first dual AGN resolved above 10
keV and is the second most heavily obscured dual AGN discovered to date in the
X-rays other than NGC 6240.
