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PIC simulations of electron-positron cyclotron maser forming pulsar radio zebras

Presentation #107.49 in the session Stellar/Compact Objects - Poster Session.

Published onMay 03, 2024
PIC simulations of electron-positron cyclotron maser forming pulsar radio zebras

The microwave radio dynamic spectra of the Crab pulsar interpulse contain fine structures represented via narrow-band quasiharmonic stripes. This pattern significantly constrains any potential emission mechanism. Similarly to the zebra patterns observed in, for example, type IV solar radio bursts or decameter and kilometer Jupiter radio emission, the double plasma resonance (DPR) effect of the cyclotron maser instability may interpret observations. We present electromagnetic relativistic particle-in-cell (PIC) simulations of the electron-positron cyclotron maser for cyclotron frequency smaller than the plasma frequency. We focused on the effects of varying plasma parameters on the instability growth rate and saturation energy. The physical parameters were the ratio between the plasma and cyclotron frequency, the density ratio of the ‘hot’ loss-cone velocity distribution to the ‘cold’ background plasma, and the loss-cone characteristic velocity. In contrast to the results obtained from electron-proton plasma simulations (for example, in solar system plasmas), we find that the pulsar electron-positron maser instability does not generate distinguishable X and Z modes. On the contrary, a singular electromagnetic XZ mode was generated in all studied configurations close to or above the plasma frequency. The highest instability growth rates were obtained for the simulations with integer plasma-to-cyclotron frequency ratios. The instability is most efficient for plasma with characteristic loss-cone velocity in the range vth = 0.2 - 0.3c. For low density ratios, the highest peak of the XZ mode is at double the frequency of the highest peak of the Bernstein modes, indicating that the radio emission is produced by a coalescence of two Bernstein modes with the same frequency and opposite wave numbers. Our estimate of the radiative flux generated from the simulation is up to 30 mJy from an area of 100 km2 for an observer at 1 kpc distance without the inclusion of relativistic beaming effects, which may account for multiple orders of magnitude.

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