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Title: Modelling variable radio emission from young stellar flares
Author: Waterfall, Charlotte
ISNI:       0000 0005 0290 4094
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2020
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Variable X-ray and radio emission is frequently observed from flares on the Sun as well as low mass, young stellar objects known as T-Tauri stars. These T-Tauri flares are several times more luminous than their solar analogues; a result of their more active magnetospheres. The temporal relationship between the thermal X-ray and nonthermal radio emission seen in flares is described by the Neupert effect, where the thermal X-rays are produced following the plasma heating by the non-thermal particles. The Gudel-Benz relation also correlates the peak of the thermal X-ray and ¨ non-thermal radio emission from flares. This relation has long been applied to solar flares as well as extended to flares on other main sequence stars. However, combining observations of T-Tauri flares from multiple sources suggests that the radio emission produced in the magnetospheres of T-Tauri stars is far greater than expected. Modelling of T-Tauri flares is carried out, using fast gyrosynchrotron codes to calculate the gyrosynchrotron emission produced from flux tubes that connect the star with its accretion disk. Initially, the effect of varying peak flaring parameters on the radio and X-ray emission is investigated. The resulting peak X-ray and radio luminosities of logLX [erg s -1 ] = 30.5, logLR [erg s-1 Hz -1 ] = 16.3 agree well with observations and also fall below the Gudel-Benz relation. A secondary model, that incorporates time dependent ¨ effects of the radio emission using 3D MHD data, also produces large radio luminosities that agree with observations. This model also provides the first multi-frequency (1-1000 GHz) intensity and circular polarisation predictions for a flaring T-Tauri star over time. In both models, the peak flux occurs around 30 GHz. The peak flux at each increasing time step is also found to decrease and move to lower frequencies. These models provide important constraints on the physical properties of the flaring star-disk environment, as well as predictions for the observable fluxes from different viewing angles.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available