Jonathan Biteau (IPNO): Anisotropies at ultra-high energies: an indication and a discovery

vendredi 27 avr. 2018, 14:00 → 16:00 Europe/Paris

The Earth's atmosphere is constantly hit by charged particles from                                                                 
 outer-space that carry individual energies of more than a Joule                                                                    
 (~6x10^18 eV or 6 EeV): ultra-high energy cosmic rays. The constancy of                                                            
 their flux, their scarcity - a few per kilometer square every year -,                                                              
 and the uniformity - or isotropy - of their arrival directions over the                                                            
 sky could have made the quest for their origin illusory...                                                                         
                                                                                                                                    
 Because of their tremendous energies, ultra-high energy cosmic rays were                                                           
 often believed to be accelerated in extragalactic astrophysical sources.                                                           
 We report in this talk on the first significant observational evidence                                                             
 confirming this hypothesis: the discovery by the Pierre Auger                                                                      
 Collaboration of a few-percent-amplitude deviation from cosmic-ray                                                                 
 isotropy on large angular scales.                                                                                                  
                                                                                                                                    
 At higher energies, presumably higher rigidities (energy/charge), the                                                              
 deflections of cosmic rays within Galactic and extragalactic magnetic                                                              
 fields are expected to be reduced, possibly leaving an imprint of the                                                              
 sources at intermediate angular scales. We report on an indication of                                                              
 cosmic-ray anisotropy above ~40 EeV obtained through a comparison with                                                             
 the flux pattern of extragalactic gamma-ray sources, in particular that                                                            
 of starburst galaxies.                                                                                                             
                                                                                                                                    
 After a discussion of these exciting results, and necessary caveats in                                                             
 their interpretation, we depict some of the new opportunities                                                                      
 observations bring to the revived quest for the origin of the most                                                                 
 extreme particles known in the Universe.