Explanation of the knee-like feature in the DAMPE cosmic $e^-+e^+$ energy spectrum

TL;DR

This paper explains the knee-like feature in DAMPE's cosmic electron spectrum as resulting from electron acceleration and cooling in supernova remnants, or influence from a nearby old SNR, with implications for anisotropy detection.

Contribution

It proposes a novel explanation for the spectral break in cosmic electrons based on SNR acceleration and cooling, linking it to observed features and potential anisotropy signals.

Findings

Spectral break at ~0.9 TeV explained by SNR electron cooling.

Nearby old SNR could cause the spectral feature and anisotropy.

Electrons from young SNRs contribute to >TeV energies.

Abstract

The DArk Matter Particle Explorer (DAMPE), a space-based high precision cosmic ray detector, has just reported the new measurement of the total electron plus positron energy spectrum up to 4.6 TeV. A notable feature in the spectrum is the spectral break at $\sim 0.9$ TeV, with the spectral index softening from $-3.1$ to $-3.9$. Such a feature is very similar to the knee at the cosmic nuclei energy spectrum. In this work we propose that the knee-like feature can be explained naturally by assuming that the electrons are accelerated at the supernova remnants (SNRs) and released when the SNRs die out with lifetime around $10^5$ years. The cut-off energy of those electrons have already decreased to several TeV due to radiative cooling, which may induce the observed TeV spectral break. Another possibility is that the break is induced by a single nearby old SNR. Such a scenario may bring a large electron flux anisotropy that is observable by the future detectors. We also show that a minor part of electrons escaping during the acceleration in young and nearby SNRs are able to contribute to several TeV or higher energy region of the spectrum.