For a discussion of Io-D events see also my page:
Dynamic spectra of Io-D arcs, from STEREO WAVES daily summaries:
http://herrero.freei.me/Io-D/index.html
Hercules A
Radio-Optical View of the Galaxy Hercules A - Many thanks to: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)