Detection of a Record-Breaking Gamma-Ray Burst
Artistic depiction of a Gamma-ray with Jet. | © ICRR UTokyo / Naho Wakabayashi

Detection of a Record-Breaking Gamma-Ray Burst

29. November 2019 | by Gunnar Bartsch / Julius-Maximilians-Universität Würzburg

Astronomers have observed the most energetic gamma-ray burst ever recorded, which originated in a galaxy some 5 billion light-years away. The international team that detected the event included researchers from Würzburg University. 

The observations that characterized the event depended on a high degree of precision. On the 14th of January 2019, the Burst Alert Telescope on board NASA’s Neil Gehrels SWIFT Observatory detected a sudden increase in luminosity in the constellation Eridanus. Just 22 seconds later, the estimated celestial coordinates had been posted on the Internet. The reaction on the Earth was only marginally less swift. Within 25 seconds of the reception of the coordinates, the two 17-m MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) optical telescopes (each weighing around 65 tons) on the island of La Palma in the Canaries had been automatically targeted to the corresponding position. 

Record-breaking energies

The data gathered by the two telescopes in the aftermath of the alert has thrilled astronomers and resulted in two publications by an multinational team that includes astronomers from the Julius-Maximilian University (JMU) in Würzburg. The reports appear in the latest issue of the journal Nature. The observations revealed that the event flagged by SWIFT was a gamma-ray burst (GRB) that took place in a galaxy more than 5 billion light-years away. But what makes this event so spectacular is that it emitted photons with energies that have never before been recorded. While previous measurements of GRBs have recorded peak energies on the order of 100 gigaelectronvolts (GeV), the emission from GRB 190114C contained photons in the teraelectronvolt (TeV) range. Moreover, GRB 190114C was 100 hundred times brighter than the brightest gamma-ray source in the sky as seen from Earth – the supernova remnant Messier 1 in the Crab Nebula (which is only 3600 light-years away).

“Gamma radiation is an extremely powerful form of electromagnetic radiation, akin to X-rays but even more powerful, indeed so energetic that very few materials can effectively shield us from it. It was discovered by Paul Villard in Strasbourg in the course of an investigation of samples of radioactive material only a few years after Wilhelm Conrad Röntgen first detected X-radiation in Würzburg,” explains Professor Karl Mannheim, who holds the Chair of Astronomy at the JMU and is a co-author of both papers in Nature. Gamma radiation is emitted during certain types of nuclear decay, in matter/anti-matter annihilation and in collisions between very high-energy elementary particles. The Earth’s atmosphere is constantly bombarded by high-energy particles from outer space. Otherwise known as cosmic rays, these account for about half of the ionizing radiation that reaches the planet’s surface. The MAGIC telescopes register the light (Cherenkov radiation) that is produced when very high-energy gamma-rays collide with Earth’s atmosphere and generate what is known as an air shower.