Astronomers Observe Two Distinct Gamma-Ray Bursts Occurring Four Minutes Apart

Astronomers have identified a pair of gamma-ray bursts (GRBs) that occurred only four minutes apart, a configuration that has not been observed before. The event, designated GRB 160425A, was captured on April 25, 2016, by the Neil Gehrels Swift Observatory, with subsequent observations of the afterglow made by ground-based telescopes. The bursts originated from a galaxy, possibly a merging system, whose light has traveled about 5.5 billion years to reach Earth.

The first burst, lasting 1.7 seconds, exhibits characteristics of a short-duration GRB, typically linked to mergers of compact objects such as neutron stars or black holes. The second burst, lasting 51.2 seconds, aligns with long-duration GRBs, which are usually associated with the core collapse of massive stars. Together, the two bursts released energy far exceeding the total output of the Sun over its lifetime, even after accounting for the directional nature of GRB emissions.

"This is so far the only event with such a property," said corresponding author Bing Zhang, an astrophysicist at the University of Hong Kong. "I’d think that these are two independent GRBs, but the chance of having them happen together in the same direction and around the same time is so low that we have to admit that the pair has the same origin."

The research team outlined five possible explanations, each presenting significant challenges. Scenarios range from a rare coincidence of two unrelated bursts pointing toward Earth, to both bursts originating in different locations within the same galaxy, to a single astrophysical system producing both emissions through an as-yet-unknown mechanism. Zhang noted that all proposed models face substantial difficulties and that the event pushes the limits of current GRB theories.