Superbubbles and the origin of cosmic rays

The origin of PeV cosmic rays is a crucial issue in cosmic ray physics. The chemical composition of cosmic rays is dominated by protons below a particle energy of ~1 PeV, while heavier nuclei become important above it. This, together with the evidence that the transition between galactic and extragalactic cosmic rays takes place at particle energies largely exceeding the PeV, implies that the sources of galactic cosmic rays must be proton PeVatrons  

According to a popular (though not proven) hypothesis, galactic cosmic rays up to PeV energies are accelerated at supernova remnant shocks. However, no observational evidence for the acceleration of PeV cosmic rays at supernova remnents has ever been found, and theoretical predictions struggle in reaching such large energies. A variation of the hypothesis involves the acceleration of cosmic rays in superbubbles, the cavities inflated in the interstellar medium around stellar clusters as the result of multiple stellar explosions and winds. Though this scenario might explain PeV particles , until very recently it was considered virtually untestable due to the lack of observations able to reveal the presence of cosmic rays. The recent detection in gamma rays of two of such objects, the Cygnus region (by the FERMI satellite) and 30 Dor C (by the array of Cherenkov telesopes H.E.S.S.), opens new possibilities and urges to revive these studies, that can now be confronted with observations. In particular, very little work exists on the predictions of radiative signatures of cosmic ray acceleration in superbubbles, and the goal of the thesis is to fill this gap and obtain predictions to be tested against available and future observations. 


Stefano Gabici & Vincent Tatischeff (CSNSM)






Niveau demandé: 


Email du responsable: