New Insights into Type-I Solar Noise Storms from High Angular Resolution Spectroscopic Imaging with the Upgraded Giant Metrewave Radio Telescope

TL;DR

This study uses high-resolution radio imaging to reveal small-scale structures in solar noise storms, challenging previous assumptions about their morphology and linking burst behavior to coronal disturbances.

Contribution

It demonstrates the capability of the upgraded GMRT to resolve structures as small as 9 arcseconds in solar noise storms, revealing new insights into their morphology and underlying physical processes.

Findings

Detected structures as small as 9 arcseconds, smaller than previously reported.

Type-I bursts are narrowband but likely caused by traveling disturbances inducing magnetic reconnections.

Observed correlated morphological changes across a wide frequency range.

Abstract

Type-I solar noise storms are perhaps the most commonly observed active radio emissions from the Sun at meter-wavelengths. Noise storms have a long-lived and wideband continuum background with superposed islands of much brighter narrowband and short-lived emissions, known as type-I bursts. There is a serious paucity of studies focusing on the morphology of these two types of emissions, primarily because of the belief that coronal scattering will always wash out any features at small angular scales. However, it is important to investigate their spatial structures in detail to make a spatio-temporal connection with observations at extreme-ultraviolet/ X-ray bands to understand the detailed nature of these emissions. In this work, we use high angular resolution observations from the upgraded Giant Metrewave Radio Telescope to demonstrate that it is possible to detect structures with angular scales as small as $\sim 9\arcsec$, about three times smaller than the smallest structure reported to date from noise storms. Our observations also suggest while the individual type-I bursts are narrowband in nature, the bursts are probably caused by traveling disturbance(s) inducing magnetic reconnections at different coronal heights, and thus leading to correlated change in the morphology of the type-I bursts observed at a wide range of frequencies.