Herringbone structures during an X-class eruptive flare

TL;DR

An analysis of quasi-periodic herringbone radio bursts during the impulsive phase of a powerful solar eruptive event is presented. The study uses multi-instrument observations to identify forward- and reverse-drift herringbones in the 20–70 MHz range, estimate electron-beam velocities and acceleration-region heights from coronal density models, and detect quasi-periodic pulsations in the radio flux. Key findings include herringbones lasting about 4 minutes with drift rates of 1.3–9.4 MHz per second, electron-beam speeds from 0.04c to 0.41c, acceleration-region heights of 0.64–0.78 solar radii, and QPP periods of 17.5–21.3 s. The results link CME-driven shocks to fine-structure radio emissions, constraining particle acceleration geometry and coronal density profiles and motivating further statistical and numerical studies.

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.

Figures (12)

• Figure 1: Top and middle panels: snapshots of AIA 304 and 171 Å images showing the non-radial prominence eruption and X5.0 flare. In panel (a4), a straight slice (S1) is used to investigate the evolution of prominence (EP). Bottom panels: snapshots of AIA 211 Å images showing the EUV wave propagating southward. In panel (c4), a curved slice (S2) is used to investigate the evolution of EUV wave.
• Figure 2: GOES-16/SUVI base-difference images in 304 Å (top panels) and 195 Å (bottom panels). The EP, flare, and EUV wave are labeled. In panel (b2), the cyan plus symbols denote the CME leading edge.
• Figure 3: (a)-(b) Time-distance diagrams of S1 in AIA 171 and 304 Å. The cyan pluses signify the trajectory of the prominence along S1. (c) Time-distance diagram of S2 in AIA 211 Å. The coronal dimming and speed of EUV wave ($\sim$600 km s$^{-1}$) along S2 are labeled.
• Figure 4: WL images of the halo CME and shock observed by LASCO-C2 (a1)-(a3), LASCO-C3 (a4), and STA/COR2 (b1)-(b4) during 21:53$-$22:53 UT.
• Figure 5: (a) Trajectory of the EP along S1 in the FOV of AIA (yellow circles) and SUVI (orange circles). A curve fitting (grey line) using a quadratic function results in an acceleration of $\sim$2.2 km s$^{-2}$. (b) SXR light curves of the flare in 1$-$8 Å (maroon line) and 0.5$-$4 Å (green line). Two vertical dashed lines signify the time range of panel (a). Heights of the CME leading edge in the FOVs of SOHO/LASCO and STA/COR2 are drawn with purple and magenta circles. A linear fitting (dark blue line) results in an apparent speed of $\sim$2839 km s$^{-1}$. (c) Radio fluxes of the herringbones at 30.3, 45.3, and 47.4 MHz.