http://arxiv.org/abs/2304.03001
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 the first electromagnetic relativistic particle-in-cell (PIC) simulations of the electron-positron cyclotron maser for cyclotron frequency smaller than the plasma frequency. In four distinct simulation cycles, we focused on the effects of varying plasma parameters on the instability growth rate and saturation energy. In contrast to the results obtained from electron-proton plasma simulations, we found that the pulsar electron-positron maser instability does not generate distinguishable X and Z modes. On the contrary, a singular electromagnetic XZ mode is generated close to or above the plasma frequency. 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 $v_\mathrm{th}=$ 0.2 – 0.3$c$. For low density ratios, the highest peak of the XZ mode is at the double 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 $\sim$ 30 mJy from an area of 100 km$^2$ for an observer at 1 kpc distance without the inclusion of relativistic beaming effects, which may account for multiple orders of magnitude.
M. Labaj, J. Benáček and M. Karlický
Fri, 7 Apr 23
31/50
Comments: 12 pages, 9 figures, 1 table, submitted to A&A