The knee at cosmic ray spectra is explained due to interactions at the sources

Abstract

In some CR acceleration sources the photon background is very dense. The high energy charged CR particles will interact with the background inevitably. For the visible light with energy of about 1 eV, the reaction for the electron-positron pair produced can only take place when the CRs energy reaches PeV, which is just the energy of the knee. When the interaction takes place, the high energy CR particles will loss a part of its energy and lead the CR spectra fall down more rapidly. Therefore two different power law indices are present in the CR spectra before and after the energy where the pair production takes place. This behavior just accounts for the knee of the CR spectra. At the same time the produced electron-positron pairs can also explain the electron/positron excesses by recent measures. According to a detailed simulation of the collision process the analysis in this work further shows that the model can well explain the sharp knee due to rapid energy loss once the reaction channel is opened. More interestingly the fine structures near the knee are also reproduced in this interaction model since different CR components have different threshold energies for pair production. Finally the so-called “component B” of Galactic CRs is also explained since the reaction of pair production becomes weak for much higher energy than the threshold energy. It is proposed in the work that the intense nuclei-photon interaction can be achieved in young supernova remnants. The present work is a new attempt to explain two long-term puzzles, the origin of cosmic rays and the knee of the spectra. The relation between the knee and the recent observation of the electron-positron excess is another interesting feature of the model. The authors are affiliated at Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences in Beijing and Department of Physics, Shandong University in Jinan. The authors are conducting research mainly in high energy cosmic ray fields. Funding from the Ministry of Science and Technology of China, the National Natural Sciences Foundation of China (Grant Nos. 10725524 and 10773011), and the Chinese Academy of Sciences (Grant Nos. KJCX2-YW-N13, KJCX3-SYW-N2 and GJHZ1004).