  By means of Quantum Monte Carlo methods we calculate the binding energy of an
impurity immersed in a Bose-Einstein condensate at T = 0. The focus is on the
attractive branch of the Bose polaron and on the role played by the mass
imbalance between the impurity and the surrounding particles. For an impurity
resonantly coupled to the bath, we investigate the dependence of the binding
energy on the mass ratio and on the interaction strength within the medium. In
particular, we determine the equation of state in the case of a static
(infinite mass) impurity, where three-body correlations are irrelevant and the
result is expected to be a universal function of the gas parameter. For the
mass ratio corresponding to $^{40}$K impurities in a gas of $^{87}$Rb atoms we
provide an explicit comparison with the experimental findings of a recent study
carried out at JILA.
