Discovery of a close pair of faint dwarf galaxies in the halo of
  Centaurus A
  As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) we
report the discovery of a pair of faint dwarf galaxies (CenA-MM-Dw1 and
CenA-MM-Dw2) at a projected distance of $\sim$90 kpc from the nearby elliptical
galaxy NGC5128 (CenA). We measure a tip of the red giant branch distance to
each dwarf, finding $D=3.63 \pm 0.41$ Mpc for CenA-MM-Dw1 and $D=3.60 \pm 0.41$
Mpc for CenA-MM-Dw2, both of which are consistent with the distance to NGC5128.
A qualitative analysis of the color magnitude diagrams indicates stellar
populations consisting of an old, metal-poor red giant branch ($\gtrsim 12$
Gyr, [Fe/H]$\sim-1.7$ to -1.9). In addition, CenA-MM-Dw1 seems to host an
intermediate-age population as indicated by its candidate asymptotic giant
branch stars. The derived luminosities ($M_V=-10.9\pm0.3$ for CenA-MM-Dw1 and
$-8.4\pm0.6$ for CenA-MM-Dw2) and half-light radii ($r_{h}=1.4\pm0.04$ kpc for
CenA-MM-Dw1 and $0.36\pm0.08$ kpc for CenA-MM-Dw2) are consistent with those of
Local Group dwarfs. CenA-MM-Dw1's low central surface brightness
($\mu_{V,0}=27.3\pm0.1$ mag/arcsec$^2$) places it among the faintest and most
extended M31 satellites. Most intriguingly, CenA-MM-Dw1 and CenA-MM-Dw2 have a
projected separation of only 3 arcmin ($\sim3$ kpc): we are possibly observing
the first, faint satellite of a satellite in an external group of galaxies.
