Master's Thesis Defense by Panos Charalampopoulos

Supervisor: Katie Auchettl
External Examiner: Hans Kjeldsen

Title: Probing the multi-wavelength light-curve evolution of Tidal Disruption Events

Abstract: The strong tidal forces of supermassive black holes (SMBH) residing in the nuclei of galaxies, can rip apart stars that pass within their tidal radius. A tidal disruption event (TDE) is the flare of electromagnetic radiation produced by the subsequent accretion of the stellar debris and it is observable from the X-rays to the UV-optical wavelengths. In this thesis, we undertake a systematic and comprehensive study of their optical/UV light curves to better understand the properties of these events as a class and used them as a way to probe the accretion properties of SMBHs. The light curves of TDEs is expected to decay following a t^-5/3 power-law indicating fallback accretion. We find that the decay of their monochromatic light-curves deviates from this canonical picture, especially at late-times, and is more consistent with shallower power-law indices indicating emission from an accretion disk. We looked for correlations between our derived power-law indices and the black hole masses of the TDEs in our sample but we report there is no apparent trend in our results. By studying the evolution of the light-curves and the energies released, we find that the UV bands evolve quite differently than the optical ones indicating that they potentially probe different parts of the accretion. Finally, by calculating the isotropic luminosities (L_90) and the times over which these luminosities are radiated (T_90), we find that optical-UV TDEs must undergo significant reprocessing and they naturally populate a “valley” between non-thermal, jetted and thermal, non-jetted X-ray TDEs.