Search for Cosmic-Ray Electron and Positron Anisotropies with Seven Years of Fermi Large Area Telescope Data

High-Statistics Measurement of the Cosmic-Ray Electron Spectrum with H.E.S.S

Owing to their rapid cooling rate and hence loss-limited propagation distance, cosmic-ray electrons and positrons (CRe) at very high energies probe local cosmic-ray accelerators and provide constraints on exotic production mechanisms such as annihilation of dark matter particles. We present a high-statistics measurement of the spectrum of CRe candidate events from 0.3 to 40 TeV with the High Energy Stereoscopic System, covering 2 orders of magnitude in energy and reaching a proton rejection power of better than 10^{4}. The measured spectrum is well described by a broken power law, with a break around 1 TeV, where the spectral index increases from Γ_{1}=3.25±0.02(stat)±0.2(sys) to Γ_{2}=4.49±0.04(stat)±0.2(sys). Apart from the break, the spectrum is featureless. The absence of distinct signatures at multi-TeV energies imposes constraints on the presence of nearby CRe accelerators and the local CRe propagation mechanisms.

Undiscovered Pulsar in the Local Bubble as an Explanation of the Local High Energy Cosmic Ray All-Electron Spectrum

Cosmic ray electrons and positrons are tracers of particle propagation in the interstellar medium (ISM). A recent measurement performed using the High Energy Stereoscopic System extends the all-electron (electron+positron) spectrum up to 20 TeV, probing very local sources and transport due to the ∼10 kyr cooling time of these particles. An additional key local measurement was the recent estimation of the ISM diffusion coefficient around Geminga performed using the High-Altitude Water Cherenkov Observatory. The inferred diffusion coefficient is much lower than typically assumed values. It has been argued that if this diffusion coefficient is representative of the local ISM, pulsars would not be able to account for the all-electron spectrum measured at Earth. Here we show that a low diffusion coefficient in the local ISM is compatible with a pulsar wind nebula origin of the highest energy electrons, if a so-far-undiscovered pulsar with spin-down power ∼10^{33-34}  erg/s exists within 30-80 pc of Earth. The existence of such a pulsar is broadly consistent with the known population and may be detected in near future survey observations.

Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments, and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements, although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the Dark Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The largest part of the spectrum can be well fitted by a 'smoothly broken power-law' model rather than a single power-law model. The direct detection of a spectral break at about 0.9 teraelectronvolts confirms the evidence found by previous indirect measurements, clarifies the behaviour of the CRE spectrum at energies above 1 teraelectronvolt and sheds light on the physical origin of the sub-teraelectronvolt CREs.