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- 19.09.. Vittoria Vecchiotti (IFY, NTNU): The high-energy Galactic gamma-ray emission: the diffuse component and the role of unresolved pulsar wind nebulae
Abstract: The study of the Galactic gamma-ray and neutrino diffuse emission represents an indirect way to investigate cosmic-ray propagation in the Galaxy. However, the signal produced by unresolved sources contaminates diffuse emission measurements, making their interpretation challenging. In order to quantify the relevance of the unresolved source component, we performed a population study of the H.E.S.S. Galactic Plane Survey under the assumption of sources powered by pulsar activity. We estimate the total TeV flux produced by all the sources in our Galaxy. In particular, our results show that a non-negligible fraction of this flux is produced by faint sources below the H.E.S.S. detection threshold. In the GeV energy range, a significant fraction of the TeV source population cannot be resolved by Fermi-LAT providing a relevant contribution to the large-scale diffuse emission, ranging within $\sim 4\%-40\%$ of the total diffuse $\gamma$-ray emission in the inner Galaxy. Hence, this unresolved component may account for a large part of the spectral index variation observed by Fermi-LAT as a function of the Galactocentric distance. Lastly, we calculate the hadronic diffuse emission in the sub-PeV energy range under different model assumptions and compare it to the large-scale diffuse emission observed by Tibet AS$\gamma$. We show that a pure hadronic emission underpredicts the measurements requiring the presence of an unresolved source component.
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- 10.10. Lluis Mas-Ribas (IFY, AI NTNU): Oes
Abstract: Cle From Galaxy Cores to Cosmology with Ultraviolet Quasar Spectra
Abstract: The spectra of distant quasars typically present absorption signatures imprinted by the media encountered by the quasar light on its journey to our detectors. The sources of these features range from the hot gas in the immediate vicinity of supermassive black holes to the diffuse intergalactic medium tracing the underlying dark matter structure, altogether spanning about nine orders of magnitude in spatial scales. In this talk I will give an overview of the research that is being done in these fronts by making use of the ultraviolet spectra of high-redshift quasars. In particular, I will discuss in a non-technical manner measurements of the distribution of matter in the intergalactic medium, the clustering and chemical enrichment of galaxies and quasars, and the acceleration mechanisms behind black hole winds.
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- 17.10. Roger Blandford (U Stanford): On the Acceleration of Atomic Nuclei to a Hundred Joules
Abstract: Cosmic rays are observed to have energies measured to be as high as 200 EeV. A major puzzle is to explain how they are accelerated. In this lecture, I will summarize what we have learned about the composition, spectrum and isotropy from non-relativistic to these “Ultra High" energies. I will then briefly outline the most promising of the mechanisms that have been proposed. Finally I will sketch a scheme in which the entire spectrum is produced, hierarchically, by a “bootstrap” process operating at astrophysical shock fronts of successively larger scale.
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