  The unitarity regime of the BCS-BEC crossover can be realized by diluting a
system of two-component lattice fermions with an on-site attractive
interaction. We perform a systematic-error-free finite-temperature simulations
of this system by diagrammatic determinant Monte Carlo. The critical
temperature in units of Fermi energy is found to be T_c / E_F = 0.152(7). We
also report the behavior of the thermodynamic functions, and discuss the issues
of thermometry of ultracold Fermi gases.
