MG15 - Talk detail

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Observational efforts are underway to accurately measure the key properties of supermassive black holes such as Sagittarius A*, and the Event Horizon Telescope (EHT) aims to image the black hole's accretion flow at the scale of the event horizon. To enhance theoretical understanding of the link between a black hole's key properties and its observed source geometry, we investigate the relation between a black hole's spin parameter and the appearance of its surrounding accretion disk to a distant observer. We use radiative-transfer calculations in the context of both a jet-dominated and a disk-dominated radiative model. We find that, at observer inclinations greater than 30 degrees, i.e., the majority of cases, the disk-dominated model is moderately skewed, while the jet-dominated model is approximately symmetric. Additionally, we create a number of VR animations, which simulate the appearance of the accretion flow to an observer who is traveling through the accretion disk itself. This is achieved using a full-sky camera. Besides being of scientific interest, we find that such animations are an effective tool for scientific outreach purposes.

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The Event Horizon Telescope aims to image the shadow of the supermassive black hole Sagittarius A* for the very first time. In order for us to interpret its observations, we need a realistic model that connects the microphysics of the plasma processes to observable source characteristics, such as source size and spectral energy distribution (SED). Recent models of SgrA* are based on GRMHD simulations that describe the dynamics of the flow combined with ray tracing simulations that calculate the SED. One of the free parameters of these models is the distribution function of the radiatively important electron population, which can heavily influence the shape of the SED. In the past, it was often assumed that the source of the emission is a thermal electron population. We recently extended these models to include an accelerated electron population by using a kappa-distribution function. We showed that our new model is capable of recovering the observable source characteristics of SgrA*. We concluded that for the quiescent state of SgrA* accelerated electrons are not of vital importance, but in the case of NIR flare emission the presence of accelerated particles is necessary. Our model can recover the observed spectral shape at NIR frequencies when five percent of the electrons is accelerated inside the highly magnetized jet region.

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