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One widely discussed mechanism to produce highly coherent radio emission offast radio bursts (FRBs) is coherent emission by bunches, either via curvatureradiation or inverse Compton scattering (ICS). It has been suggested that theplasma oscillation effect can significantly suppress coherent emission power bybunches. We examine this criticism in this paper. The suppression factorformalism was derived within the context of radio pulsars in which radio wavesare in the low-amplitude, linear regime and cannot directly be applied to thelarge-amplitude, non-linear regime relevant for FRBs. Even if one applies thislinear treatment, plasma suppression is not important for two physical reasons.First, for an efficient radiation mechanism such as ICS, the required plasmadensity is not high so that a high-density plasma may not exist. Second, bothbunched coherent mechanisms demand that a large global parallel electric field($E_\parallel$) must exist in the emission region in order to continuouslyinject energy to the bunches to power an FRB. In order to produce typical FRBduration via coherent curvature or ICS radiation, a parallel electric fieldmust be present to balance the acceleration and radiation back-reaction. Theplasma suppression factor should be modified with the existence of$E_\parallel$. We show that the correction factor for curvature radiation,$f_{\rm cur}$, increases with $E_\parallel$ and becomes 1 when $E_\parallel$reaches the radiation-reaction-limited regime. We conclude that the plasmasuppression effect can be ignored for realistic FRB emission models invokingbunched coherent radio emission.

The plasma suppression effect can be ignored in realistic FRB models invoking bunched coherent radio emission