Observational analysis of a circular ribbon flare with a rotating jet

¹ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, PR China
² Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, PR China
³ Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences (CAS), Nanjing 210023, PR China

^⋆ Corresponding author: guoyang@nju.edu.cn

Received: 13 September 2024
Accepted: 21 August 2025

Abstract

Context. Circular ribbon flares, a typical kind of multi-ribbon flare, have been the focus of many studies. Along with the flares themselves, many other related phenomena also merit investigation, such as jets, chromosphere condensation, and magnetohydrodynamic (MHD) waves.

Aims. We analyzed a circular ribbon flare accompanied by a rotating jet that occurred on 2023 May 25, and we find observational evidence of chromosphere condensation in the flare ribbon and an Alfvén wave along the jet.

Methods. We derived the plane-of-sky velocity of the cool component of the jet using the Fourier local correlation tracking method, and we obtained the Doppler velocity of the flare and the cool component of jet by analyzing the spectrum observed by the Chinese Hα Solar Explorer (CHASE). To obtain the magnetic topology of the circular ribbon flare, we performed a nonlinear force-free field extrapolation using the photosphere vector magnetogram observed by the Helioseismic and Magnetic Imager (HMI). We additionally fit the hard X-Ray (HXR) energy spectrum obtained by the Hard X-ray Imager (HXI) aboard the Advanced Space-based Solar Observatory (ASO-S), and made a comparison between the Doppler velocity and the HXR sources.

Results. We derive the velocity field of the cool component of jet, illustrate the spine-fan magnetic structure of the circular ribbon flare, and by comparing the vector magnetic field and the vector velocity field, we find a strong correlation between their inclination and azimuth angles, indicating that the jet mostly moves along the magnetic field. Through the Doppler velocity of the flare ribbon derived by CHASE observations, the redshift in the Hα waveband indicates the existence of chromosphere condensation. The HXI HXR spectra and images demonstrate that nonthermal electrons are the primary source of the chromosphere condensation.