An Unexpectedly Swift Rise in the Gamma-ray Burst Rate
Abstract
The association of long gamma-ray bursts with the deaths of massive stars naturally suggests that the cosmic GRB rate should trace the star formation history. Finding otherwise would provide important clues for the further development of our views concerning these rare, curious phenomena. Making use of a sample of 44 luminous Swift GRBs with redshifts in the range z=0-4, we find evidence of enhanced evolution in the GRB rate, with ~4 times as many GRBs being observed at z~4 than expected from star formation measurements. We discuss the origins of this observed trend, including several progenitor populations that the GRBs may actually be tracing.Keywords
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