A history of the gamma-ray burst flux at the Earth from Galactic
  globular clusters
  Nearby gamma-ray bursts (GRBs) are likely to have represented a significant
threat to life on the Earth. Recent observations suggest that a significant
source of such bursts is compact binary mergers in globular clusters. This link
between globular clusters and GRBs offers the possibility to find time
intervals in the past with higher probabilities of a nearby burst, by tracing
globular cluster orbits back in time. Here we show that the expected flux from
such bursts is not flat over the past 550 Myr but rather exhibits three broad
peaks, at 70, 180 and 340 Myr ago. The main source for nearby GRBs for all
three time intervals is the globular cluster 47 Tuc, a consequence of its large
mass and high stellar encounter rate, as well as the fact that it is one of the
globular clusters which comes quite close to the Sun. Mass extinction events
indeed coincide with all three time intervals found in this study, although a
chance coincidence is quite likely. Nevertheless, the identified time intervals
can be used as a guide to search for specific signatures of GRBs in the
geological record around these times.
