Posterior probability density function for as derived from sample B. The thick and thin lines refer to the PDF as derived considering a control time of 13 years and N_CC = 13 and an extended control time, summing the control times of the past searches for the galaxy in common, and N_CC = 21.3, respectively. The dashed line accounts for a statistical prior inferred from the local rate from Cappellaro et al. (1999).