Universität zu Köln

Subroweit, Matthias ORCID: 0000-0001-6165-8525 (2021). Study of Radiation Outbursts in the Vicinity of a Supermassive Black Hole - Flare Statistics of Sgr A*. PhD thesis, Universität zu Köln.

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Abstract

The center of the Milky Way harbors a bright radio source, Sagittarius A* (Sgr A*). Nowadays there is strong evidence that Sgr A* is the radiative counterpart of a Supermassive Black Hole (SMBH) with a mass of approximately four million solar masses at a distance of about 25000 light years from the sun. Due to its proximity, Sgr A* provides us with an unique opportunity to study an SMBH with the highest obtainable resolution. Sgr A* shows radiation outbursts, also referred to as flares, across the entire frequency regime. Light time travel arguments suggest that these flares must have their origin in the innermost accretion flow onto Sgr A*. Therefore, their investigation and understanding might be crucial to shed light on the physical conditions in the direct vicinity of a SMBH. The concrete physical mechanisms in the accretion flow onto Sgr A* giving rise to the flares are not yet fully understood. Although most models include some form of synchrotron emission to explain the occurring flares from the radio to the near-infrared (NIR) regime, the mechanisms behind X-ray flares are highly disputed. Mainly two concurrent models are currently debated: high energy synchrotron, or synchrotron self-Compton (SSC) emission. Both possible explanations differ significantly in terms of the predicted electron energies and plasma densities. In this thesis I present three papers which statistically elaborate on the putative emission mechanism. For my investigations I used submillimeter (submm) data obtained with the LArge BOlometer CAmera (LABOCA), which was mounted at the Atacama Pathfinder EXperiment (APEX) telescope, radio data from the Australia Telescope Compact Array (ATCA) and X-ray data from the Chandra X-ray Observatory (CXO) obtained during the X-ray Visionary Project (XVP) campaign. I analyze the flux density distribution of this data and find that the distributions can be described by power-laws. I also present a count rate distribution fitting routine for the X-ray data based on Approximate Bayesian Computation (ABC). My statistical analyses reveal, that the observed lightcurves of Sgr A* at different wavebands can be explained by a combined model of adiabatically expanding synchrotron blobs and SSC scattering.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Subroweit, Matthias subroweit@ph1.uni-koeln.de orcid.org/0000-0001-6165-8525 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-640533
Date:	2021
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language Astronomy English Galactic Center English Black Hole English
Date of oral exam:	11 February 2022
Referee:	Name Academic Title Eckart, Andreas Prof. Dr. Schilke, Peter Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/64053