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An international team of astronomers, including researchers at the University of Amsterdam, have managed to track the onset of a gamma-ray burst. An hour and a half after the gamma-ray burst was detected on 5 December 2017, the astronomers began to monitor the accompanying supernova SN 2017iuk through a range of telescopes. Never before had a supernova signal been registered as soon after the gamma-ray burst, nor as extensively. The renowned journal Nature will publish the study results on Thursday, 17 January.

Burst Alert

When the so-called Burst Alert Telescope (BAT) on the Swift Observatory issued a warning on 5 December 2017, the astronomers started their investigations. The gamma-ray burst detected by the BAT lasted approximately three minutes. An additional X-ray telescope on the Swift Observatory identified the source of the gamma radiation as an exploding star near the periphery of a large spiral galaxy at a distance from the earth of around 500 million light years, which is rather nearby as far as gamma-ray bursts go. Following the initial signal, it only took an hour and a half to turn various telescopes in Spain, the United States, Poland and Chile towards the supernova. Among others, the X-shooter spectrograph on the Very Large Telescope of the European Southern Observatory in Chile diverted its attention to SN 2017iuk/GRB 171205A.

Jet of matter

Under the direction of Luca Izzo and Antonio de Ugarte Postigo at the Instituto de Astrofísica de Andalucía (Spain), an international research group analysed the data emerging from the exploding star. The explosion appeared to propel a jet of matter on the first day at a pace of 115,000 kilometres a second, which is about one third the speed of light. This so-called relativistic jet subsequently diminished in energy and pace. A cocoon with elements including silicon, calcium, iron, titanium, chromium and nickel meanwhile started coating the jet. These elements had been thrust outwards after their creation in the star's collapsing core. While it used to weigh as much as dozens of suns, it is likely that this star will ultimately become a black hole.

Early

Only once a decade or so is a supernova detected this early after the gamma-ray burst, says Lex Kaper, an astronomer at the University of Amsterdam who co-authored the study. The detailed analysis of the supernova's spectra was made possible by the X-shooter that Kaper helped develop in 2009.

Further contributors to the investigation were postdoctoral researchers Jure Japelj and Vanna Pugliese at the UvA. As part of a team on permanent alert, they are ready day and night to track gamma-ray bursts with the X-shooter.

Powerful

Gamma-ray bursts constitute the galaxy's most powerful explosions. Three military satellites witnessed the first burst in 1970. It took a team of astronomers headed by Jan van Paradijs and Paul Groot at the University of Amsterdam until 1997 to identify a smouldering gamma-ray burst in visible light as proof that these explosions originated outside of our Milky Way. PhD candidates Titus Galama and Paul Vreeswijk at the UvA observed the first gamma-ray burst to accompany a supernova in the next year. As of today, astronomers at the University of Amsterdam have analysed hundreds of gamma-ray bursts together with colleagues around the globe.

Publication details

L. Izzo et al., Signatures of a jet cocoon in early spectra of a supernova associated with a γ-ray burst, in: Nature volume 565, pages 324–327 (2019), DOI: 10.1038/s41586-018-0826-3