Left: Survival functions of the fluence distributions from the FAST and Onsala observations during the S21 activity window, together with MLE PL fits. The vertical lines mark the optimal minimum fluence as found by the powerlaw package, after modification according to Eqs. (A.2)–(A.3) in Appendix A. Top right: Posterior distributions of α_t|α_m. The gray lines indicate gamma distributions from Eq. (2). Bottom right: Probability of α_t(Onsala)−α_t(FAST) being smaller than the threshold value.