excesses and the knee of the cosmic ray spectra — hints of cosmic rays acceleration at young supernova remnants

Supernova remnants have long been regarded as sources of the Galactic cosmic rays up to petaelectronvolts, but convincing evidence is still lacking. In this work we explore the common origin of the subtle features of the cosmic ray spectra, such as the knee of cosmic ray spectra and the excesses of electron/positron fluxes recently observed by ATIC, H.E.S.S., Fermi-LAT and PAMELA. Numerical calculation shows that those features of cosmic ray spectra can be well reproduced in a scenario with ee pair production by interactions between high energy cosmic rays and background photons in an environment similar to the young supernova remnant. The success of such a coherent explanation serves in turn as an evidence that at least a portion of cosmic rays might be accelerated at young supernova remnants. Subject headings: cosmic rays — supernova remnants — acceleration of particles Ever since the discovery made by Kulikov & Kristiansen (1958), the knee of the cosmic ray (CR) spectra observed ∼ 4 PeV has remained a puzzle for half a century. The origin of the knee has become a key problem of CR physics, as it is closely related to the acceleration of the Galactic CRs. There have been extensive studies on the issue (e.g., see the review of Hörandel (2006) and references therein), however, no consensus has been reached yet due to the lack of high precision experimental information. Recently, the ATIC experiment measured the cosmic electron (electron and positron) spectrum up to several TeV (Chang et al. 2008) with high precision and showed evidence for an obvious excess of flux above tens of GeV. In addition, the ground based atmospheric Cerenkov telescope H.E.S.S. and the space satellite Fermi, which are dedicated to high energy γ-ray detection, also reported their results on the electron spectrum measurements (Abdo et al. 2009; Aharonian et al. 2008, 2009). Despite some discrepancies between the