  Recent observations with the MeerKAT radio telescope reveal a unique
population of faint non-thermal filaments pervading the central molecular zone
(CMZ). Some of those filaments are organized into groups of almost parallel
filaments, seemingly sorted by their length, so that their morphology resembles
a harp with radio emitting "strings". We argue that the synchrotron emitting
GeV electrons of these radio harps have been consecutively injected by the same
source (a massive star or pulsar) into spatially intermittent magnetic fiber
bundles within a magnetic flux tube or via time-dependent injection events.
After escaping from this source, the propagation of cosmic ray (CR) electrons
inside a flux tube is governed by the theory of CR transport. We propose to use
observations of radio harp filaments to gain insight into the specifics of CR
propagation along magnetic fields of which there are two principle modes: CRs
could either stream with self-excited magneto-hydrodynamical waves or diffuse
along the magnetic field. To disentangle these possibilities, we conduct
hydrodynamical simulations of either purely diffusing or streaming CR electrons
and compare the resulting brightness distributions to the observed synchrotron
profiles of the radio harps. We find compelling evidence that CR streaming is
the dominant propagation mode for GeV CRs in one of the radio harps.
Observations at higher angular resolution should detect more radio harps and
may help to disentangle projection effects of the possibly three-dimensional
flux-tube structure of the other radio harps.

High Energy Astrophysical Phenomena;Astrophysics of Galaxies