Towards locating the ultra-high energy cosmic ray accelerators

  • Date October 26, 2017
  • Hour 3 pm
  • Room GSSI Main Lecture Hall
  • Speaker Oliver Deligny (Institut de Physique Nucléaire d'Orsay IPN-France)


Since the first detection of a cosmic ray with energy in excess of 10^20 eV by J. Linsley in 1963, the origin of these particles, the most energetic produced in nature, is an enduring problem in astroparticle physics. These particles carry the information on the most extreme phenomena in the Universe. At these energies, even charged particles could be magnetically rigid enough to keep track of the original positions of their sources on the sky. Recent analyses of data recorded at the Pierre Auger Observatory provide evidence that these particles originate from far away galaxies. The evidence is twofold. First, by studying the distribution of the arrival directions above 8x10^18 eV, an anisotropy at 5.2 standard deviations has been revealed. The pattern of this anisotropy, well described by a dipole with an amplitude of ~6.5%, is incompatible with any structure suggestive of an origin from the Milky Way. Second, a new analysis of the cumulative dataset has captured an anisotropy above ~4x10^19 eV on an intermediate angular scale through comparison to the flux pattern of nearby star-forming galaxies, which are strong gamma ray emitters. In this seminar, the consequences of these recent findings will be discussed, together with prospects for future more sensitive studies.