Speaker
Description
We examine limits to the energy to which cosmic rays can be accelerated by the
termination shocks in the southern jet of radiogalaxy 3C 445. At high radio frequencies, the southern hotspot shows two sub structures named SE and SW.
By using the observed flux density at 22 GHz in SE and SW, we find that a
hotspot magnetic field of about 500 micro Gauss is required to explain the synchrotron emission. The upper-energy cut-off in the hotspot synchrotron spectrum is at a frequency < 5x10^15 Hz, indicating that the maximum energy of non-thermal electrons accelerated at the jet reverse shock is ~ 1 TeV in a magnetic field of 500 micro Gauss.
Based on the condition that the magnetic-turbulence scalelength has to be larger than the plasma skin depth, and that the energy density in non-thermal particles cannot violate the limit imposed by the jet kinetic luminosity, we show that the electrons maximum energy cannot be constrained by synchrotron losses as traditionally assumed. In addition to that, and assuming that the shock is quasi-perpendicular, we show that non-resonant hybrid instabilities generated by the streaming of cosmic rays with energy
~ 1 TeV can grow fast enough to amplify the jet magnetic field up to 500 micro Gauss and accelerate particles up to the maximum energy observed in 3C445 SE and SW.
This result has important implications for the acceleration of ultra high energy cosmic rays.