Nearby sources may contribute to cosmic-ray electron ( CRE ) structures at high energies .
Recently , the first DAMPE results on the CRE flux hinted at a narrow excess at energy \sim 1.4 TeV .
We show that in general a spectral structure with a narrow width appears in two scenarios : I ) “ Spectrum broadening ” for the continuous sources with a \delta -function-like injection spectrum .
In this scenario , a finite width can develop after propagation through the Galaxy , which can reveal the distance of the source .
Well-motivated sources include mini-spikes and subhalos formed by dark matter ( DM ) particles \chi _ { s } which annihilate directly into e ^ { + } e ^ { - } pairs .
II ) “ Phase-space shrinking ” for burst-like sources with a power-law-like injection spectrum .
The spectrum after propagation can shrink at a cooling-related cutoff energy and form a sharp spectral peak .
The peak can be more prominent due to the energy-dependent diffusion .
In this scenario , the width of the excess constrains both the power index and the distance of the source .
Possible such sources are pulsar wind nebulae ( PWNe ) and supernova remnants ( SNRs ) .
We analysis the DAMPE excess and find that the continuous DM sources should be fairly close within \sim 0.3 kpc , and the annihilation cross sections are close to the thermal value .
For the burst-like source , the narrow width of the excess suggests that the injection spectrum must be hard with power index significantly less than two , the distance is within \sim ( 3 - 4 ) kpc , and the age of the source is \sim 0.16 Myr .
In both scenarios , large anisotropies in the CRE flux are predicted .
We identify possible candidates of mini-spike and PWN sources in the current Fermi-LAT 3FGL and ATNF catalog , respectively .
The diffuse \gamma -rays from these sources can be well below the Galactic diffuse \gamma -ray backgrounds and less constrained by the Ferm-LAT data , if they are located at the low Galactic latitude regions .