Publication Date:
2016-03-05
Description:
Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 10(17)-10(18) electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate air showers--cascades of secondary particles in the atmosphere-and their masses can be inferred from measurements of the atmospheric depth of the shower maximum (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground. Current measurements have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 10(17)-10(17.5) electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 10(17.5) electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 10(17)-10(17.5) electronvolt range.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Buitink, S -- Corstanje, A -- Falcke, H -- Horandel, J R -- Huege, T -- Nelles, A -- Rachen, J P -- Rossetto, L -- Schellart, P -- Scholten, O -- ter Veen, S -- Thoudam, S -- Trinh, T N G -- Anderson, J -- Asgekar, A -- Avruch, I M -- Bell, M E -- Bentum, M J -- Bernardi, G -- Best, P -- Bonafede, A -- Breitling, F -- Broderick, J W -- Brouw, W N -- Bruggen, M -- Butcher, H R -- Carbone, D -- Ciardi, B -- Conway, J E -- de Gasperin, F -- de Geus, E -- Deller, A -- Dettmar, R-J -- van Diepen, G -- Duscha, S -- Eisloffel, J -- Engels, D -- Enriquez, J E -- Fallows, R A -- Fender, R -- Ferrari, C -- Frieswijk, W -- Garrett, M A -- Griessmeier, J M -- Gunst, A W -- van Haarlem, M P -- Hassall, T E -- Heald, G -- Hessels, J W T -- Hoeft, M -- Horneffer, A -- Iacobelli, M -- Intema, H -- Juette, E -- Karastergiou, A -- Kondratiev, V I -- Kramer, M -- Kuniyoshi, M -- Kuper, G -- van Leeuwen, J -- Loose, G M -- Maat, P -- Mann, G -- Markoff, S -- McFadden, R -- McKay-Bukowski, D -- McKean, J P -- Mevius, M -- Mulcahy, D D -- Munk, H -- Norden, M J -- Orru, E -- Paas, H -- Pandey-Pommier, M -- Pandey, V N -- Pietka, M -- Pizzo, R -- Polatidis, A G -- Reich, W -- Rottgering, H J A -- Scaife, A M M -- Schwarz, D J -- Serylak, M -- Sluman, J -- Smirnov, O -- Stappers, B W -- Steinmetz, M -- Stewart, A -- Swinbank, J -- Tagger, M -- Tang, Y -- Tasse, C -- Toribio, M C -- Vermeulen, R -- Vocks, C -- Vogt, C -- van Weeren, R J -- Wijers, R A M J -- Wijnholds, S J -- Wise, M W -- Wucknitz, O -- Yatawatta, S -- Zarka, P -- Zensus, J A -- England -- Nature. 2016 Mar 3;531(7592):70-3. doi: 10.1038/nature16976.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. ; Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands. ; ASTRON, Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands. ; Nikhef, Science Park Amsterdam, 1098 XG Amsterdam, The Netherlands. ; Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany. ; Institute for Nuclear Physics (IKP), Karlsruhe Institute of Technology (KIT), Postfach 3640, 76021 Karlsruhe, Germany. ; Department of Physics and Astronomy, University of California Irvine, Irvine, California 92697, USA. ; KVI Center for Advanced Radiation Technology, University of Groningen, 9747 AA Groningen, The Netherlands. ; Vrije Universiteit Brussel, Dienst ELEM, B-1050 Brussels, Belgium. ; Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum GFZ, Department 1, Geodesy and Remote Sensing, Telegrafenberg A17, 14473 Potsdam, Germany. ; Shell Technology Center, 560 048 Bangalore, India. ; SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands. ; Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands. ; CSIRO Australia Telescope National Facility, PO Box 76, Epping, New South Wales 1710, Australia. ; University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA. ; Square Kilometre Array (SKA) South Africa, 3rd Floor, The Park, Park Road, Pinelands 7405, South Africa. ; Institute for Astronomy, University of Edinburgh, Royal Observatory of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK. ; University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany. ; Leibniz-Institut fur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany. ; School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK. ; Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australian Capital Territory 2611, Australia. ; Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands. ; Max Planck Institute for Astrophysics, Karl Schwarzschild Strasse 1, 85741 Garching, Germany. ; Onsala Space Observatory, Department of Earth and Space Sciences, Chalmers University of Technology, SE-43992 Onsala, Sweden. ; SmarterVision BV, Oostersingel 5, 9401 JX Assen, The Netherlands. ; Astronomisches Institut der Ruhr-Universitat Bochum, Universitaetsstrasse 150, 44780 Bochum, Germany. ; Thuringer Landessternwarte, Sternwarte 5, D-07778 Tautenburg, Germany. ; Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg. ; Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK. ; Laboratoire Lagrange, Universite Cote d'Azur, Observatoire de la Cote d'Azur, CNRS, Boulevard de l'Observatoire, CS 34229, 06304 Nice Cedex 4, France. ; Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands. ; LPC2E - Universite d'Orleans/CNRS, 45071 Orleans Cedex 2, France. ; Station de Radioastronomie de Nancay, Observatoire de Paris - CNRS/INSU, USR 704 - Universite Orleans, OSUC, route de Souesmes, 18330 Nancay, France. ; National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, New Mexico 87801-0387, USA. ; Astro Space Center of the Lebedev Physical Institute, Profsoyuznaya street 84/32, Moscow 117997, Russia. ; Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK. ; National Astronomical Observatory of Japan, Tokyo 181-8588, Japan. ; Sodankyla Geophysical Observatory, University of Oulu, Tahtelantie 62, 99600 Sodankyla, Finland. ; STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK. ; Center for Information Technology (CIT), University of Groningen, PO Box 72, 9700 AB Groningen, The Netherlands. ; Centre de Recherche Astrophysique de Lyon, Observatoire de Lyon, 9 avenue Charles Andre, 69561 Saint Genis Laval Cedex, France. ; Fakultat fur Physik, Universitat Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany. ; Department of Physics and Electronics, Rhodes University, PO Box 94, Grahamstown 6140, South Africa. ; Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA. ; GEPI, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France. ; LESIA, Observatoire de Paris, CNRS, UPMC, Universite Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26935696" target="_blank"〉PubMed〈/a〉
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
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Chemistry and Pharmacology
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Medicine
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Natural Sciences in General
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Physics
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