Gamma-ray bursts (GRBs) that signal the explosive collapse of distant, very massive stars are detected almost daily by a variety of orbiting telescopes. But last April’s GRB 130427A, first spotted by NASA’s Fermi Gamma-Ray Space Telescope, was extraordinary in two respects. Its total radiant output ranks it among the half dozen most energetic GRBs ever recorded. And, more important, its surprisingly modest redshift (z = 0.34) places it a mere 5 billion light-years away. It was five times closer than a typical GRB and was, by far, the closest of the hyperenergetic ones.

That happy coincidence—estimated to occur only once or twice a century—has allowed only Fermi and a number of x-ray and optical telescopes to examine the initial burst and its afterglow in unprecedented detail. The observations, recently reported in five papers,1,2,3,4,5 suggest that GRB 130427A is not...

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