The investigation of thermal emission parameters at radio wavelengths as a probe for gamma-ray energies in classical novae

• Autor(a) principal: Coimbra, Teresa Flores
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33724
• topic: Classical novae; Radio continuum; Gamma-rays continuum

The study of Classical Novae over the last two decades has fastly changed due to the upgrade of radio telescopes, such as the Karl Jansky Very Large Array, and the advent of space-based γ-ray telescopes, such as Fermi. Multi-frequency studies of these objects are able to provide us detailed information about the physical conditions after eruptions enabling us to study the contributions of novae to their interstellar medium. Some, if not all, classical novae are predicted to release GeV γ-rays, although the origin of these emissions is yet to be fully understood. However, there are significant indications that it is connected to internal shocks within the ejected material, which also causes the non-thermal emission and dust production. The radio light curves of 7 classical novae (V959 Mon, V1324 Sco, V5668 Sgr, V357 Mus, V906 Car, V5589 Sgr, and V1723 Aql) were fitted with a spherically symmetric thermal emission model in this study, of which 2 are from previously unpublished data (V5668 Sgr and V357 Mus). The model is based on the “Hubble Flow Model” and is coupled with the Markov Chain Monte Carlo (MCMC) code, emcee. This is the first time the emcee code was coupled to fit radio light curves of novae. Non-thermal emission was clearly evident in the results of the fit, as expected from previous studies of these novae. In 6 out of the 7 novae the model was capable to decouple the two components of the emission. Of the 7 novae, only 5 were detected with γ-ray emission. This dissertation aims to identify connections between the thermal emission input parameters (distance, filling factor, maximum expansion velocity, and mass of ejecta) and the γ-ray brightness or the limit of nondetection. To date, attempts to find correlations between parameters at different wavelengths and γ-ray emission, or lack of, were met with various successes. We find an inverse correlation between the ejecta mass and the γ-ray luminosity. This inverse correlation is reminiscent of the attenuation of γ-ray photons by an absorbing screen (most likely the ejecta itself). The inverse correlation found between the γ-ray emission and ejected mass may also help explain the origin of the 102 factor observed in the values of detected γ-ray luminosit.