Unveiling the Role of Magnetic Field in Generating Quasi-Periodic Oscillations

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• Martina Veresvarska / Durham University
• Wednesday 30 October 2024, 13:40-14:05
• The Hoyle Lecture Theatre + Zoom .

If you have a question about this talk, please contact Xander Byrne.

Almost all accreting black hole and neutron star X-ray binary systems (XRBs) exhibit prominent brightness variations on a few characteristic time-scales and their harmonics. These quasi-periodic oscillations (QPOs) are thought to be associated with the precession of a warped accretion disc, but the physical mechanism that generates the precessing warp remains uncertain. Relativistic frame dragging (Lense-Thirring precession) is one promising candidate, but a misaligned magnetic field is an alternative, especially for neutron star XRBs. Here, we report the discovery of 5 accreting white dwarf systems (AWDs) that display strong optical QPOs with characteristic frequencies and harmonic structures that suggest they are the counterpart of the QPOs seen in XRBs. Since AWDs are firmly in the classical (non-relativistic) regime, Lense-Thirring precession cannot account for these QPOs. By contrast, a weak magnetic field associated with the white dwarf can drive disc warping and precession in these systems, similar to what has been proposed for neutron star XRBs. Our observations confirm that magnetically-driven warping is a viable mechanism for generating QPOs in disc-accreting astrophysical systems, certainly in AWDs. And furthermore, I will discuss the possible new application of the model to explain mHz QPOs in Ultraluminous X-ray Sources (ULXs). Additionally, they establish a new way to estimate magnetic field strengths, even in relatively weak-field systems where other methods are not available.

This talk is part of the Institute of Astronomy Seminars series.

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