|Annu. Rev. Astron. Astrophys. 1988. 36:
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We mention above that a synchrotron "thermal" instability excites compressional modes with a wave vector transverse to the local magnetic field, leading to filamentary structures parallel to the field. These structures are nonstationary and evolve rapidly at the time scale of synchrotron emission. Numerical results by Bodo et al (1992) have shown that the nonlinear development of the instability makes the filaments brighter than the background if a continuous supply of (reaccelerated) relativistic electrons is guaranteed. In terms of time scales of particle diffusion, the origin of these fresh particles could be the hot spots themselves, when present, or weak shocks in a turbulent medium.