Gamma-ray bursts, the explosions of extremely massive stars, are some of the most violent phenomena in the Universe. Early in the morning of April 27, 2013, an exceptionally bright gamma-ray burst (GRB) triggered the automatic detection system aboard the orbiting Fermi Gamma Ray Telescope. The system located the explosion within the constellation Leo. Observations by Fermi, the Swift X-ray observatory, and ground-based visible-light observatories determined the GRB was about 3.6 billion light-years away—relatively close for such an incident.

The event, labeled GRB 130427A, was the most energetic gamma-ray burst yet seen, and also had the longest duration. (The label of a GRB simply indicates its date.) The highest energy photon recorded by Fermi was about three times more energetic than the previous record-holder, a GRB discovered in 2009. The output from GRB 130427A was visible in gamma ray light for nearly half a day, while typical GRBs fade within a matter of minutes or hours. To the best of our knowledge, the supernova producing a GRB beams much of its energy along twin jets; we see a GRB when Earth lies along the path of one of those beams.

Unfortunately, GRB 130427A was never bright enough in visible light to be seen by the unaided eye or small telescopes. However, the event triggered the Catalina Real-Time Transient Survey (CRTS) automatic detection system independently of the Fermi and Swift observatories, which is the first time an independent optical discovery was made of a GRB. This provides hope that some unidentified bursts of visible light could be associated with gamma-ray bursts.

Thanks to its relative proximity, the long duration of the burst, and the large amount of data from different sources, astronomers hope to find the supernova remnant from GRB 130427A within the month. That will provide an unprecedented view of the environment of a GRB, and it will allow large telescopes to study what is left of the system in the explosion's aftermath.