ESO Telescopes Observe Swift Satellite’s 1000th Gamma-ray Burst
6 November 2015
On 27 October 2015, at 22:40 GMT, the NASA/ASI/UKSA Swift satellite discovered its 1000th gamma-ray burst (GRB). This landmark event was subsequently observed and characterised by ESO telescopes at the La Silla Paranal Observatory in northern Chile, which revealed that this GRB was an especially interesting object.
Gamma-ray bursts are intense flashes of gamma radiation that occur randomly throughout the distant Universe. They are thought to be caused by an extremely energetic stellar explosion and believed to signal the birth of a new black hole.
Swift is dedicated to searching the skies for these mysterious and fascinating events and, after more than ten vigilant years, the satellite has now discovered its 1000th GRB. GRB 151027B occurred on 27 October 2015, in the direction of the constellation of Eridanus (The River) .
ESO telescopes have a long and successful tradition of performing follow-up observations of GRB events (eso0318 and eso0533), and they did not falter for this milestone. The Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) mounted on the MPG/ESO 2.2-metre telescope at the La Silla Observatory and the X-shooter spectrograph on the Very Large Telescope (VLT) at ESO’s Paranal Observatory began observations as soon as the GRB became visible from Chile — around five hours after its detection .
By splitting the faint and rapidly fading light from GRBs up into their component colours the X-shooter spectrograph is one of the most powerful tools in existence for probing their nature. More than half of all distance measurements of GRBs since X-shooter started operations were made with this instrument.
The ESO observations revealed that the GRB 151027B explosion occurred when the Universe was just 1.5 billion years old (10% of its present age) and its light had travelled for 12.3 billion years before reaching the Earth. This result was announced just three hours after the data were taken and eight hours after the GRB was first detected by Swift. Further analysis also allowed astronomers to determine that the galaxy in which GRB 151027B occurred has an unusually high abundance of heavier chemical elements.
These intriguing conclusions from GRB 151027B demonstrate the success of the partnership between the Swift mission and ESO’s telescopes, which have provided critical follow-up observations for hundreds of gamma-ray bursts. The X-shooter and GROND instruments have been systematically observing these elusive events from the Atacama Desert since 2009 and 2007, respectively, providing valuable insights into the most powerful explosions in the Universe.
 The X-shooter/GRB collaboration consists of: L.A. Antonelli (INAF/OA Roma), M. Arabsalmani (ESO), Z. Cano (Univ. Iceland), L. Christensen (DARK/NBI Copenhagen), S. Covino (INAF/OA Brera), A. De Cia (ESO), P. D'Avanzo (INAF/OA Brera), V. D'Elia (INAF/OA Roma and ASI/ASDC), F. Fiore (INAF/OA Roma), H. Flores (Paris Obs./GEPI), M. Friis (Univ. Iceland), J. P. U. Fynbo (DARK/NBI Copenhagen), P. Goldoni (APC/Irfu - CEA), A. Gomboc (Univ. Nova Gorica), P. Groot (Nijmegen), O. E. Hartoog (Amsterdam), F. Hammer (Paris Obs./GEPI), J. Hjorth (DARK/NBI Copenhagen), P. Jakobsson (Univ. Iceland), J. Japelj (INAF/OA Trieste), L. Kaper (API/Amsterdam), T. Krühler (MPE, Munich), C. Ledoux (ESO, Santiago), A. J. Levan (Univ. Warwick), G. Leloudas (Weizmann and DARK/NBI Copenhagen), E. Maiorano (INAF/IASF Bologna), D. Malesani (DARK/NBI Copenhagen), A. Melandri (INAF/OA Brera), B. Milvang-Jensen (DARK/NBI Copenhagen), P. Møller (ESO), E. Palazzi (INAF/IASF Bologna), D. A. Perley (DARK/NBI Copenhagen), E. Pian (SNS Pisa), S. Piranomonte (INAF/OA Roma), G. Pugliese (API/Amsterdam), R. Sánchez-Ramírez (IAA-CSIC, Granada), S. Savaglio (University of Calabria), P. Schady (MPE), J. Schaye (Leiden), S. Schulze (Pontificia Universidad Católica de Chile and MAS), J. Selsing (DARK/NBI Copenhagen), J. Sollerman (OKC Stockholm), M. Sparre (MPA, Heidelberg), G. Tagliaferri (INAF/OA Brera), N. R. Tanvir (Univ. Leicester), C. C. Thöne (IAA-CSIC, Granada), A. de Ugarte Postigo (IAA-CSIC Granada), S. D. Vergani (CNRS, Paris Obs./GEPI), P. M. Vreeswijk (WIS), D. J. Watson (DARK/NBI Copenhagen), K. Wiersema (Univ. Leicester), R. A. M. J. Wijers (API/Amsterdam) and D. Xu (NAOC, Beijing).
The GROND collaboration consists of: P. Afonso (American River College), J. Bolmer (MPE), C. Delvaux (MPE), J. Elliott (CfA), R. Filgas (Techn. Univ. Prague), J. Graham (MPE), J. Greiner (MPE), D.A. Kann (TLS Tautenburg), S. Klose (TLS Tautenburg), F. Knust (MPE), T. Krühler (MPE), A. Nicuesa Guelbenzu (TLS Tautenburg), P. Schady (MPE), S. Schmidl (TLS Tautenburg), T. Schweyer (MPE), M. Tanga (MPE), K. Varela (MPE) and P. Wiseman (MPE).
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