Origin of the break in the cosmic-ray electron plus positron spectrum at ~ 1 TeV

Abstract

Recent measurements of the cosmic-ray electron plus positron spectrum by several experiments have confirmed the presence of a break at $\sim\,1$ TeV. The origin of the break is still not clearly understood. In this work, we explore different possibilities for the origin which include an electron source spectrum with a broken power-law, a power-law with an exponential or super-exponential cut-offs and the absence of potential nearby cosmic-ray sources. Based on the observed electron plus positron data from the DAMPE and the H.E.S.S experiments, and considering supernova remnants as the main sources of cosmic rays in the Galaxy, we find statistical evidence in favour of the scenario with a broken power-law source spectrum with the best-fit source parameters obtained as $\Gamma=2.39$ for the source spectral index, $E_0\approx 1.6$ TeV for the break energy and $f=1.59\times 10^{48}$ ergs for the amount of supernova kinetic energy injected into cosmic-ray electrons. Such a power-law break in the spectrum has been predicted for electrons confined inside supernova remnants after acceleration via diffusive shock acceleration process, and also indicated by the multi-wavelength study of supernova remnants. All these evidences have shown that the observed spectral break provides a strong indication of a direct link between cosmic-ray electrons and their sources. Our findings further show that electrons must undergo spectral changes while escaping the source region in order to reconcile the difference between the spectral index of electrons observed inside supernova remnants and that obtained from Galactic cosmic-ray propagation studies.