I understand that the LIGO experiment was very lucky to find a very strong signal of a very energetic event (binary black hole merger). Having into account the non-negligible possibility that the signal may be spurious or some problem in the data adquisition, how much time must pass before we can confirm (with a second event) that the result was likely genuine, or that could be spurious (for example, if months pass without other detection). In other words, what is the average rate of expected discoveries similar to the event on 11th December? I have also heard that there has been independent confirmation of Gamma-ray burst coincident in time with the event (0.4 seconds shift). How trusty are those news?