Left: posterior distribution estimated for the reference spectrum with 2000 counts (red). The posterior distributions inferred from Bayesian fits with BXA and XSPEC are also shown in blue and green, respectively. Right: emission spectrum and residuals corresponding to the reference Model A with 2000 counts, together with the folded best-fit model from the GRU (solid green line) and XSPEC (dashed blue line) with a frequentist approach.