Anomalous Cosmic Ray Hydrogen
Cosmic rays can be accelerated in different ways. Some cosmic rays (called anomalous
cosmic rays or ACR) are accelerated in the Solar System, at the shock where the
solar wind meets interstellar space. Others are accelerated outside the
solar system, by various processes in the Milky Way Galaxy and are called GCRs.
Eric's PhD thesis research involved separating these two components for
cosmic ray hydrogen, and identifying which part of the observed hydrogen
cosmic rays were ACRs.
The key idea was that ACRs and GCRs, because they are accelerated by
different processes, have different energies. GCRs have higher
energies than ACRs. Therefore, you should be able (theoretically) to
identify the two components by looking at their spectra.
This can be seen in the proton (hydrogen nuclei) energy spectra below, which
show two separate humps. Comparing the hydrogen spectra with those from
other elemental cosmic rays, Eric speculated that the lower energy hump was
from the population of ACRs and the higher energy hump is from GCRs.
The data he used in this work were from the Voyager 1 and 2 spacecraft,
which approached the solar wind termination shock in the late 1980s.
Spectra for Voyager 1 (left column)
and Voyager 2 (right column) for the time periods 1994
days 157-261 (a and b), 1994 days 1 - 105 (c and d) and 1993 days 53 - 157
(e and f). The flux is measured in particles/(M2 sr sec MeV).