How intense can the electrons get at Mars? Frahm et al.  sorted through 24 million observed spectra from the 13 years of Mars Express electron data and identified the top ten largest energy flux intervals. Most of them were of solar origin, observed in the sheath region around the planet, while a few are perhaps created within near-Mars space, including a couple from the nightside ionosphere concurrent with Mars auroral observations. The distribution of these precipitating electrons is very similar to those on the dayside. This leads them to conclude that no special or exotic energization process is needed to get aurora at Mars, just the right magnetic configuration to allow for electrons to make it down the field lines and into the upper atmosphere.
They also compared the Mars spectra against those from Earth and Venus, noting that the most intense spectra from Venus and Mars have roughly the same properties but that Earth spectra are usually different. Earth has a strong intrinsic dipole magnetic field while the other two do not, indicating electron energization processes are highly dependent on the planetary magnetic environment.
Citation: Frahm, R. A., Winningham, J. D., Coates, A. J., Gérard, J.‐C., Holmström, M., & Barabash, S. . The largest electron differential energy flux observed at Mars by the Mars Express spacecraft, 2004–2016. Journal of Geophysical Research: Space Physics, 123. https://doi.org/10.1029/2018JA025311
—Mike Liemohn, Editor-in-Chief, JGR: Space Physics