Investigation of frequency drift in a solar radio type I burst chain

Abstract

In this paper, we study a type I burst chain exhibiting a negative frequency drift. This event was observed simultaneously on 6 August 2023 by the Daocheng Radio Telescope (DART) and Chashan broadband solar radio spectrometer at meter wavelengths (CBSm). It lasted for 174 s, with an average drift rate of −0.48 MHz s⁻¹ from 241 to 157 MHz. Based on the fundamental and harmonic emissions of plasma mechanism, this type I burst chain displays its source motion upward with a velocity from 120 km s⁻¹ to 540 km s⁻¹ after fitting its dynamic spectra with both Newkirk and Aschwanden electron density models. During its lifetime, the source's total displacement of 21–;94 Mm is below the DART spatial resolution, resulting into no motion seen on DART images. It is interesting that a mini-jet is observed simultaneously by SDO/AIA in the radio emission region with a speed of 296 km s⁻¹, which is consistent with the radio source upward motion velocities detected here, indicating that the type I burst chain could possibly originate from the nonthermal electrons accelerated by a moving magnetic reconnection following this mini-jet. These findings would help us to improve the understanding of the characteristics and origin of type I bursts.