MOND prediction of a new giant shell in the elliptical galaxy NGC3923
  Context. Stellar shells, which form axially symmetric systems of arcs in some
elliptical galaxies, are most likely remnants of radial minor mergers. They are
observed up a radius of $\sim$100 kpc. The stars in them oscillate in radial
orbits. The radius of a shell depends on the free-fall time at the position of
the shell and on the time since the merger. We previously verified the
consistency of shell radii in the elliptical galaxy NGC 3923 with its most
probable MOND potential. Our results implied that an as~yet undiscovered shell
exists at the outskirts of the galaxy.
  Aims. We here extend our study by assuming more general models for the
gravitational potential to verify the prediction of the new shell and to
estimate its position.
  Methods. We tested the consistency of the shell radial distribution observed
in NGC 3923 with a wide variety of MOND potentials of the galaxy. The
potentials differed in the mass-to-light ratio and in distance to the galaxy.
We considered different MOND interpolation functions, values of the
acceleration constant $a_0$, and density profiles of the galaxy. We verified
the functionality of our code on a Newtonian self-consistent simulation of the
formation of a shell galaxy.
  Results. Our method reliably predicts that exactly one new outermost shell
exists at a galactocentric radius of about 1900$^{\prime\prime}$ ($\sim$210
kpc) on the southwestern side of the galaxy. Its estimated surface brightness
is about 28 mag arcsec$^{-2}$ in $B$ - a value accessible by current
instruments. This prediction enables a rare test of MOND in an elliptical down
to an acceleration of $a_0/10$. The predictive power of our method is verified
by reconstructing the position of the largest known shell from the distribution
of the remaining shells.
