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

Abstract

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

9 pages, 2 figures. Accepted for publication in MNRAS

References in corpus (15)

• A bright millisecond radio burst of extragalactic origin
• Fast Radio Bursts
• Fast radio bursts as synchrotron maser emission from decelerating relativistic blast waves
• INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154
• The Physical Mechanisms of Fast Radio Bursts
• HXMT Identification of a non-thermal X-ray burst from SGR J1935+2154 and with FRB 200428
• Implications of a "Fast Radio Burst" from a Galactic Magnetar
• FRB Coherent Emission from Decay of Alfven Waves
• Fast radio bursts and their high-energy counterpart from magnetar magnetospheres
• Coherent inverse Compton scattering by bunches in fast radio bursts
• Magnetospheric curvature radiation by bunches as emission mechanism for repeating fast radio bursts
• Pair separation in parallel electric field in magnetar magnetosphere and narrow spectra of fast radio bursts
• STARE2: Detecting Fast Radio Bursts in the Milky Way
• Transparency of Fast Radio Burst Waves in Magnetar Magnetospheres
• Coherent curvature radiation: maximum luminosity and high-energy emission

Cited by in corpus (4)

• The Physics of Fast Radio Bursts
• Polarization of Fast Radio Bursts: radiation mechanisms and propagation effects
• Coherent Curvature Radiation Spectrum by Dynamically Fluctuating Bunches in Magnetospheres
• FRB$-$SRB$-$XRB: Geometric and Relativistic Beaming Constraints of Fast Radio Bursts from the Galactic Magnetar SGR J1935+2154