Brightest gamma-ray burst ever

The most energetic gamma-ray burst ever detected was announced this week by the team at the Fermi Gamma-Ray Space Telescope.  The gamma-ray burst (or GRB) event was triggered on Saturday 27 April 2013, and so the GRB has the name GRB 130427A.  The Fermi Large Area Telescope (LAT) recorded energies up to 94 GeV, almost 3 times higher the energy of the previous LAT record of GRBs.  The GeV emission lasted for several hours and remained detectable by LAT for most of the day. As well as the most energetic,  GRB 130427A also set the record for the longest gamma-ray emission from a GRB measured to date.

The gamma-ray sky as see by the Fermi Gamma-ray Space Telescope before (left) and after (right) the record-setting gamma-ray burst GRB 130427A. Each frame covers 3 hours of time, with the left frame including the first 30 minutes of the GRB event. The map includes all gamma-ray sources with energies above 1 MeV. (Credit: NASA/DOE/Fermi LAT Collaboration)

When Fermi triggered the GRB event, the Swift satellite quickly determined its position towards the constellation Leo. With the position tied down, follow-up observations were immediately made by ground-based optical, infrared and radio telescopes, including finding an optical counter-part in the Catalina Real-time Transient Survey. The GRB is now know to have originated in a distant galaxy about 3.6 billion light years away.

Swift’s X-Ray Telescope image of of GRB 130427A, taken at 3:50am EDT on 27 April 2013. The image, made with a 0.1-second exposure, is 6.5 arcminutes across. (Credit: NASA/Swift/Stefan Immler)

GRBs are brief but very intense bursts of gamma radiation. There are two types of GRBs defined by the length of their burst. Long bursts (longer than two seconds) are thought to be associated with supernova explosions that result when massive stars run out of nuclear fuel and undergo sudden collapse, and short bursts (shorter than two second) are thought to originate from the merger of two compact objects such as neutron stars. Both types are GRBs are likely signal the birth of a black hole. In the case of  GRB 130427A, the long-period burst likely resulted from core collapse of a massive star.

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[Sarah Maddison]

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