A critical comparison of estimates for the rates of hypernovae ( HNe ) and gamma-ray bursts ( GRBs ) is presented .
Within the substantial uncertainties , the estimates are shown to be quite comparable and give a Galactic rate of 10 ^ { -6 } – 10 ^ { -5 } yr ^ { -1 } for both events .
These rates are several orders of magnitude lower than the rate of core-collapse supernovae , suggesting that the evolution leading to a HN/GRB requires special circumstances , very likely due to binary interactions .
Various possible binary channels are discussed , and it is shown that these are generally compatible with the inferred rates .