We present results on the Omega baryon electromagnetic form factors using $N_f=2+1$ domain-wall fermion configurations for three pion masses in the range of about 350 to 300 MeV. We compare results obtained using domain wall fermions with those of a mixed-action (hybrid) approach, which combine domain wall valence quarks on staggered sea quarks, for a pion mass of about 350 MeV. We pay particular attention in the evaluation of the subdominant electric quadrupole form factor to sufficient accuracy to exclude a zero value, by constructing a sequential source that isolates it from the dominant form factors. The $Omega^-$ magnetic moment, $mu_{Omega^{-}}$, the electric charge and magnetic radius, $langle r^{2}_{E0/M1} rangle$, are extracted for these pion masses. The electric quadrupole moment is determined for the first time using dynamical quarks.
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