@ARTICLE{2018SSRv..214...82O,
       author = {Oka, M. and Birn, J. and Battaglia, M. and Chaston, C.C. and Hatch, S.M. and Livadiotis, G. and Imada, S. and Miyoshi, Y. and Kuhar, M. and Effenberger, F. and Eriksson, E. and Khotyaintsev, Y.V. and Retinò, A.},
        title = "{Electron Power-Law Spectra in Solar and Space Plasmas}",
      journal = {Space Science Reviews},
     keywords = {Particle acceleration, Magnetic reconnection, Shocks, Solar flares, Magnetotail, Solar wind, Astrophysics - Solar and Stellar Astrophysics, Physics - Space Physics},
         year = "2018",
        month = "Aug",
       volume = {214},
       number = {5},
          eid = {82},
        pages = {82},
     abstract = "{Particles are accelerated to very high, non-thermal energies in solar
        and space plasma environments. While energy spectra of
        accelerated electrons often exhibit a power law, it remains
        unclear how electrons are accelerated to high energies and what
        processes determine the power-law index {ensuremath{delta}} .
        Here, we review previous observations of the power-law index
        {ensuremath{delta}} in a variety of different plasma
        environments with a particular focus on sub-relativistic
        electrons. It appears that in regions more closely related to
        magnetic reconnection (such as the `above-the-looptop' solar
        hard X-ray source and the plasma sheet in Earth's magnetotail),
        the spectra are typically soft ({ensuremath{delta}}
        {ensuremath{gtrsim}}4). This is in contrast to the typically
        hard spectra ({ensuremath{delta}} {ensuremath{lesssim}}4)
        that are observed in coincidence with shocks. The difference
        implies that shocks are more efficient in producing a larger
        non-thermal fraction of electron energies when compared to
        magnetic reconnection. A caveat is that during active times in
        Earth's magnetotail, {ensuremath{delta}} values seem spatially
        uniform in the plasma sheet, while power-law distributions still
        exist even in quiet times. The role of magnetotail reconnection
        in the electron power-law formation could therefore be
        confounded with these background conditions. Because different
        regions have been studied with different instrumentations and
        methodologies, we point out a need for more systematic and
        coordinated studies of power-law distributions for a better
        understanding of possible scaling laws in particle acceleration
        as well as their universality.}",
          doi = {10.1007/s11214-018-0515-4},
archivePrefix = {arXiv},
       eprint = {1805.09278},
 primaryClass = {astro-ph.SR},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2018SSRv..214...82O},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}