Science Seminars

3/31/2016- Lynn Wilson; Relativistic electrons produced by foreshock disturbances

Speaker: Lynn Wilson (NASA GSFC)
Date: Tuesday, Mar 31, 2020
Time: 4:00 PM
Location: SPSC W120

Seminar Abstract:

Charged particles reflected and accelerated to suprathermal or even ultra relativistic energies by strong (i.e., high Mach number) astrophysical collisionless shock waves can stream away forming a foreshock region in communication with the shock.  Foreshocks — observed since the 1960s — are primarily populated by suprathermal ions (some contain relativistic particles) energized at or near the shock.  The drift between foreshock ions and incident upstream flow generates electromagnetic waves and large-scale, transient structures — called foreshock disturbances or FDs –, which have also been recently shown to energize ions, causing most work to focus on ion acceleration.  Relativistic electrons were found at the high Mach number Kronian bow shock but no research has ever proposed Earth’s lower Mach number bow shock, let alone the FDs, as a relativistic electron source.  We present THEMIS satellite observations of relativistic electrons (>200 kiloelectronvolts) locally produced by terrestrial FDs.  Previous work attributed such electrons to escaping magnetospheric particles or a solar source.  However, the enhancements do not coincide with any solar activity and are localized to FDs, supporting the conclusion that they are locally energized.  The discovery of relativistic electrons generated by FDs could fundamentally change our understanding of shock acceleration, given the ubiquity of foreshocks in collisionless plasmas.