Herringbone Structures during an X-class Eruptive Flare

Abstract In this paper, we report quasiperiodic 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 nonradially in the southeast direction with an inclination angle of ∼35 . ° 4. The fast coronal mass ejection (CME) at a speed of ∼2852 km s −1 drives a shock wave and a coronal extreme-ultraviolet wave. The herringbone structures lasting for ∼4 minutes take place at the initial stage of a group of type II radio bursts. The herringbones in the frequency range 20−70 MHz are characterized by simultaneous forward-drift and reverse-drift bursts with average durations of ∼2.5 and ∼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 ∼3.6 and ∼4.1 MHz s −1 , respectively. The speeds of electron beams producing the herringbones are estimated to be 0.04 c −0.41 c , with average values of ∼0.23 c and ∼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 ⊙ above the photosphere, which are consistent with the height of the CME front (∼0.75 R ⊙ ) when the shock forms. Quasiperiodic 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.