Fossil AGN as cosmic particle accelerators
Remnants of active galactic nucleus (AGN) jets and their surrounding cocoons leave colossal magnetohydrodynamic (MHD) fossil structures storing total energies ∼1060 erg. The original active galacic nucleus (AGN) may be dead but the fossil will retain its stable magnetic configuration resembling the reversed-field pinch (RFP) encountered in laboratory MHD experiments. Slow decay of the large-scale RFP field induces electric fields which can accelerate cosmic rays with an E-2 power-law up to ultra-high energies. A similar mechanism, operting for fossil micro- quasars could contribute to Galactic cosmic rays and be responsible for some unidentified GeV and TeV gamma-ray sources.