Multiwavelength observations of flaring activity on the Sun and M dwarf stars

Abstract

The Sun’s magnetic dynamo drives a wide range of activity observed across the electromagnetic spectrum, including flares and coronal mass ejections (CMEs). Low frequency radio emission from these events is important for probing the conditions in the solar corona, offering insights into outstanding questions relating to electron acceleration and magnetic variability. In particular, Type II and Type IV radio bursts provide signatures of shocks propagating in the corona. Understanding the kinematics of these shocks is crucial for predicting and mitigating the potential effects of space weather on Earth.

M dwarfs, the most common type of star in the galaxy, can exhibit magnetic activity that is several orders of magnitude more intense than that observed on the Sun. With the detection of planets around M dwarfs, their activity has drawn renewed focus in the context of exoplanet habitability. Emission from flares on M dwarfs spans the electromagnetic spectrum, with particularly notable rapid increases in photometric luminosity. However, a definitive detection of a shock wave propagating through a stellar corona remains elusive. One of the most promising methods for identifying these shock signatures is through low frequency radio observations, which aim to detect radio bursts similar to those produced by solar shocks. Recent radio surveys at low frequencies have led to the detection of various forms of radio emission, providing new insights into the complex magnetic environments of M dwarfs.

Multiwavelength observations of solar activity can help to constrain the kinematics of these complex events. The first goal of this research was to investigate a shock event in the solar corona to probe the coronal conditions. A solar shock associated with a powerful flare was captured with multiple instruments at Extreme Ultraviolet (EUV) and radio wavelengths. EUV observations revealed an EUV wave travelling away from the shock origin. Combined with radio imaging and dynamic spectrum observations, the expansion of the shock could be mapped at multiple heights in the solar corona. These observations revealed that the shock was influenced by magnetic and plasma density conditions in the low corona, altering the expansion, possibly revealing a coronal channel.

The remaining two research goals focused on the search for multiwavelength detections of activity on low mass stars. The aim was to perform a similar analysis to solar activity, using multiple signatures to constrain the emission mechanism and better understand the stellar magnetic environment. Simultaneous optical and radio wavelength observations with the Transiting Exoplanet Survey Satellite (TESS) and the Australian Square Kilometre Array Pathfinder (ASKAP) telescope detected four M dwarfs. While none of these stars flared during the observations, their signatures at radio wavelengths provided valuable insights into the quiescent emission mechanisms of these stars. The final research project once again utilised multiwavelength observations with TESS and the LOw Frequency ARray (LOFAR), with the radio observations occurring at lower frequencies. This search yielded a number of candidate stars which require follow up observations. The detections add to the growing number of radio-emitting M dwarfs, and place constraints on the detection density of M dwarfs in wide-field observations.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Dublin Institute for Advanced Studies & Armagh Observatory and Planetarium
Supervisor	John Doyle (Supervisor) & Gavin Ramsay (Supervisor)