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We develop a model of the generation of coherent radio emission in the Crabpulsar, magnetars and Fast Radio Bursts (FRBs). Emission is produced by areconnection-generated beam of particles via a variant of Free Electron Laser(FEL) mechanism, operating in a weakly-turbulent, guide-field dominated plasma.We first consider nonlinear Thomson scattering in a guide-field dominatedregime, and apply to model to explain emission bands observed in Crab pulsarand in Fast Radio Bursts. We consider particle motion in a combined fields ofthe electromagnetic wave and thee lectromagnetic (Alfvenic) wiggler. Chargebunches, created via a ponderomotive force, Compton/Raman scatter the wigglerfield coherently. The model is both robust to the underlying plasma parametersand succeeds in reproducing a number of subtle observed features: (i) emissionfrequencies depend mostly on the length $\lambda_t$ of turbulence and theLorentz factor of the reconnection generated beam, $\omega \sim \gamma_b^2 (c/\lambda_t) $ - it is independent of the absolute value of the underlyingmagnetic field. (ii) The model explains both broadband emission and thepresence of emission stripes, including multiple stripes observed in the HighFrequency Interpulse of the Crab pulsar. (iii) The model reproduces correlatedpolarization properties: presence of narrow emission bands in the spectrumfavors linear polarization, while broadband emission can have arbitrarypolarization. (iv) The mechanism is robust to the momentum spread of theparticle in the beam. We also discuss a model of wigglers as non-linearforce-free Alfven solitons (light darts).

Coherent emission in pulsars, magnetars and Fast Radio Bursts: reconnection-driven free electron laser