  We report individual dynamical masses for the brown dwarfs Epsilon Indi B and
C, which have spectral types of T1.5 and T6, respectively, measured from
astrometric orbit mapping. Our measurements are based on a joint analysis of
astrometric data from the Carnegie Astrometric Planet Search and the Cerro
Tololo Inter-American Observatory Parallax Investigation as well as archival
high resolution imaging, and use a Markov Chain Monte Carlo method. We find
dynamical masses of 75.0+-0.82 Mjup for the T1.5 B component and 70.1+-0.68
Mjup for the T6 C component. These masses are surprisingly high for substellar
objects and challenge our understanding of substellar structure and evolution.
We discuss several evolutionary scenarios proposed in the literature and find
that while none of them can provide conclusive explanations for the high
substellar masses, evolutionary models incorporating lower atmospheric
opacities come closer to approximating our results. We discuss the details of
our astrometric model, its algorithm implementation, and how we determine
parameter values via Markov Chain Monte Carlo Bayesian inference.
