Work

Type III radio bursts associated with jets in two solar flares

Year: 2026

Type: article

Abstract: Context . A challenging issue is the significant velocity discrepancy between jets and energetic electrons accelerated by magnetic reconnection in solar flares. Aims . We investigated the velocities of jets derived from extreme-ultraviolet (EUV) observations and those of energetic electrons inferred from type III radio bursts in two solar flares on 26 March 2024. Methods . The jet velocities were measured from the time-distance maps of the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), while the energetic electron velocities were inferred from the type III radio burst spectra using the Aschwanden density model. Results . These two flares are homologous events occurring in the same active region of NOAA 13615. They produce jets and type III radio bursts detected by SDO/AIA, Daocheng Radio Telescope (DART), Chashan Broadband Solar Radio Spectrometer at meter wavelengths (CBSm), and Radio and Plasma Waves (RPW). Linear fits to the jet trajectories in the plane-of-sky yield jet velocities of 436 km s −1 and 456 km s −1 for the first and second flares, respectively. The corresponding type III electron beam velocities, inferred from the Aschwanden model fitting the CBSm data, are 32.3 Mm s −1 (or 0.1 c) and 22.0 Mm s −1 (or 0.07 c), respectively. These velocities correspond to the kinetic energies of 3.0 keV and 1.4 keV, which are much lower than the cutoff energies (i.e., 18 keV) detected by the Spectrometer/Telescope for Imaging X-rays (STIX). Moreover, our DART observations show type III burst sources as funnel-like structures varying in either frequency or height in both flares. Their sizes increase rapidly with decreasing frequency, such as a ninefold expansion from 477 MHz to 164 MHz, indicating the magnetic field decreases by a factor of nine from 0.04 R ⊙ (447 MHz) to 0.10 R ⊙ (164 MHz). Conclusions . Jets are accelerated by magnetic pressure gradients, with inferred magnetic field strengths of about 60 G at the boundaries of the reconnection regions in both events. Type III electron beams are accelerated by electric fields, with strengths of 4.3–15 ×10 −4 V m −1 and 1.0–3.7×10 −4 V m −1 estimated in the current sheet for the first and second flares, respectively.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202660823