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SUMMARY:Unveiling the Role of Magnetic Field in Generating Quasi-Periodic 
 Oscillations - Martina Veresvarska / Durham University
DTSTART:20241030T134000Z
DTEND:20241030T140500Z
UID:TALK223984@talks.cam.ac.uk
CONTACT:Xander Byrne
DESCRIPTION:Almost all accreting black hole and neutron star X-ray binary 
 systems (XRBs) exhibit prominent brightness variations on a few characteri
 stic time-scales and their harmonics. These quasi-periodic oscillations (Q
 POs) are thought to be associated with the precession of a warped accretio
 n disc\, but the physical mechanism that generates the precessing warp rem
 ains uncertain. Relativistic frame dragging (Lense-Thirring precession) is
  one promising candidate\, but a misaligned magnetic field is an alternati
 ve\, especially for neutron star XRBs. Here\, we report the discovery of 5
  accreting white dwarf systems (AWDs) that display strong optical QPOs wit
 h characteristic frequencies and harmonic structures that suggest they are
  the counterpart of the QPOs seen in XRBs. Since AWDs are firmly in the cl
 assical (non-relativistic) regime\, Lense-Thirring precession cannot accou
 nt for these QPOs. By contrast\, a weak magnetic field associated with the
  white dwarf can drive disc warping and precession in these systems\, simi
 lar to what has been proposed for neutron star XRBs. Our observations conf
 irm that magnetically-driven warping is a viable mechanism for generating 
 QPOs in disc-accreting astrophysical systems\, certainly in AWDs. And furt
 hermore\, I will discuss the possible new application of the model to expl
 ain mHz QPOs in Ultraluminous X-ray Sources (ULXs). Additionally\, they es
 tablish a new way to estimate magnetic field strengths\, even in relativel
 y weak-field systems where other methods are not available.\n
LOCATION:The Hoyle Lecture Theatre + Zoom 
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