Spatio-temporal Characteristics of Very Long-periodic Pulsations in Solar Metrewave Bursts: Implications for their Origins

TL;DR

This study investigates the origin and characteristics of very long-periodic pulsations in solar radio bursts, linking them to sunspot activity and coronal loop dynamics, with implications for understanding solar magnetic phenomena.

Contribution

It provides new observational evidence connecting VLPs in type-I bursts to sunspot and coronal loop oscillations, supporting plasma emission as their primary mechanism.

Findings

Detected a quasi-period of about 160-170 seconds in radio and solar structures.

Established a correlation between burst chains, magnetic flux emergence, and sunspot activity.

Supported plasma emission and slow magnetoacoustic waves as the origin of VLPs.

Abstract

We traced the origin of very long-periodic pulsations (VLPs) in type-I burst chains on 2024 February 14. Seven successive and repetitive pulsation structures appeared in radio dynamic spectra in the metric waveband, which were simultaneously measured by CBSm, DART, and MUSER-L. A quasi-period at about 160$^{+11}_{-6}$ s, determined by the fast Fourier transform, was detected in the frequency range of about 210-280 MHz. Imaging observations from DART and SDO reveal that the type-I burst chains occur above two groups of sunspot umbrae connected by coronal loops. A quasi-period of approximately 170 s was also identified in the sunspot umbrae and coronal loops. The burst chains exhibit strong circular polarization and high brightness temperature, and they show spatiotemporal correlation with emerging magnetic flux. The number densities at the loop top and double footpoints can produce radio emission and generate type-I burst chains in the frequency range of 210-280 MHz. Our observations support the scenario that plasma emission serves as the primary generation mechanism of type-I bursts, with VLPs most likely being modulated by the slow magnetoacoustic waves originating from sunspot umbrae. The observed frequency drift of burst chains may reflect the density attenuation along coronal loops.