Promotionsvortrag Physik: „X-ray observations of accreting compact objects “

Ankündigung des Promotionsvortrags von: Herrn Ole König

In my dissertation, I study the physics of accreting compact objects. Accretion of matter from a stellar companion leads to the formation of a disk around the compact object, which efficiently converts gravitational potential energy into radiation. In black hole binaries, strongly variable X-rays are detected with space-based telescopes. Already shortly after the discovery of the first black hole, Cygnus X-1, it was realized that this hard X-ray variability can be used to probe the innermost region of the system. How the variability of the accretion disk impacts the behavior of Cygnus X-1, however, can only be reliably studied in the soft X-ray regime. In recent years, these studies have become possible with a new X-ray mission. I will show that the phenomenology in the soft X-rays provides new constraints on the flow of matter in the direct vicinity of accreting black hole binaries.

In the second part, I study the nova phenomenon of accreting white dwarfs. In a binary system with a donor star, hydrogen-rich material accumulates in an envelope on the surface of the white dwarf. Once the envelope has reached critical mass, the system undergoes runaway thermonu-clear burning, which results in the envelope to expand rapidly. For more than 30 years, nova theo-ry has predicted the existence of a fireball phase following directly on from the runaway fusion, which should be observable as a short, bright, and soft X-ray flash before the nova becomes visi-ble in the optical. Here, I present the discovery of this X-ray flash in the Galactic nova YZ Reticuli with the eROSITA telescope. The flash occurred half a day before the source brightened in the optical, confirming the proposed theory. Using a simulation-based analysis approach, I could con-strain the temperature and radius of the expanding photosphere.

(Vortrag auf Englisch)

Dem Vortrag schließt sich eine Diskussion von 15 Minuten an. Vortrag und Diskussion sind öffentlich. Diesen Verfahrensteilen folgt ein nicht öffentliches Rigorosum von 45 Minuten.