Herringbone structures during an X-class eruptive flare

Abstract: In this paper, we report quasi-periodic herringbone structures during the impulsive phase of an X-class flare, coinciding with the distinct acceleration phase of eruptive prominence ejection on 2023 December 31. The prominence propagates non-radially in the southeast direction with an inclination angle of $\sim$35$\fdg$4. The fast coronal mass ejection (CME) at a speed of $\sim$2852 km s$^{-1}$ drives a shock wave and a coronal EUV wave. The herringbone structures lasting for $\sim$4 minutes take place at the initial stage of a group of type II radio burst. The herringbones in the frequency range 20$-$70 MHz are characterized by simultaneous forward-drift and reverse-drift bursts with average durations of $\sim$2.5 s and $\sim$3.1 s. The frequency drift rates of these bursts fall in a range of 1.3$-$9.4 MHz s$^{-1}$ with average values of $\sim$3.6 and $\sim$4.1 MHz s$^{-1}$, respectively. The speeds of electron beams producing the herringbones are estimated to be 0.04$-$0.41 $c$, with average values of $\sim$0.23 $c$ and $\sim$0.11 $c$ for forward-drifting and reverse-drift bursts, respectively. The heights of particle acceleration regions are estimated to be 0.64$-$0.78 $R_{\sun}$ above the photosphere, which are consistent with the height of CME front ($\sim$0.75 $R_{\sun}$) when the shock forms. Quasi-periodic pulsations with periods of 17.5$-$21.3 s are found in the radio fluxes of herringbones, suggesting that electrons are accelerated by the CME-driven shock intermittently.