Physikalisches Kolloquium: Dr. Ekaterina Sokolova-Lapa – Magnetic fields shaping X-ray emission from accreting neutron stars: from vacuum polarisation to field geometry (Habilitationsvortrag)

Titel: Magnetic fields shaping X-ray emission from accreting neutron stars: from vacuum polarisation to field geometry (Habilitationsvortrag)

Abstract:
Neutron stars are remnants of stellar evolution that contain some of the densest stable matter and possess some of the strongest magnetic fields in the Universe. In binary systems where a neutron star accretes matter from a massive stellar companion, its magnetic field shapes the accretion process, the deceleration of matter and the emission mechanisms that produce X-rays. Near the surface, competition between gas, radiation and magnetic pressure creates complex flow dynamics, with emission emerging from a compact hot spot or an extended accretion column. At typical surface field strengths of hundreds of millions of Tesla, the polarised quantum-electrodynamic (QED) vacuum can further modify matter-radiation interactions, affecting X-ray formation and even plasma dynamics.

The origin of the X-rays remains debated: they may form mainly through thermal Comptonization in a decelerated region or be reprocessed by bulk Comptonization in the accretion flow, a mechanism that also has implications for how the matter slows down. In this talk, I will present a new approach to testing these scenarios through radiation beaming and cyclotron lines -- the absorption features seen in X-ray spectra. I will show how magnetised plasma and the QED vacuum shape these angle-dependent signatures and the polarisation of the radiation. Combined with gravitational light bending and neutron star rotation, the signatures offer a way to infer the large-scale magnetic field and spin orientation, which can constrain the history of mass transfer and binary evolution. Polarisation offers a further test: vacuum-plasma interplay can help explain the unexpectedly low linear polarisation and its complex variation with energy and rotational phase found in recent observations. Future X-ray missions promise higher-resolution spectra and more sensitive polarimetry. Developing the physical models needed to interpret these observations will enable stringent tests of emission physics in extreme environments.

Sprecher / Speaker: Dr. Ekaterina Sokolova-Lapa, ECAP, FAU

Kontakt / Contact: Department Physik