Magnetic pumping model for energizing superthermal particles applied to observations of the Earth's bow shock

Abstract:

Energetic particle generation is an important component of a variety of astrophysical systems,

from seed particle generation in shocks to the heating of the solar wind. It has been

shown that magnetic pumping is an efficient mechanism for heating thermal particles, using

the largest-scale magnetic fluctuations. Here we show that when magnetic pumping is

extended to a spatially-varying magnetic flux tube, magnetic trapping of superthermal particles

renders pumping an effective energization method for particles moving faster than the

speed of the waves and naturally generates power-law distributions. We validated the theory

by spacecraft observations of the strong, compressional magnetic fluctuations near the

Earth’s bow shock from the Magnetospheric Multiscale mission [1]. Given the ubiquity of

magnetic fluctuations in different astrophysical systems, this mechanism has the potential to

be transformative to our understanding of how the most energetic particles in the universe

are generated.

[1] E. Lichko and J. Egedal, Nature Com. 11, 2942, 2020

The work is supported by by NASA Grant No. NNX15AJ73G.