Speaker
Description
Pulsating Ultraluminous X-ray Sources (PULXs) are extragalactic off-nuclear, point-like objects with extremely high X-ray luminosities that show coherent pulsations typical for neutron stars. Only three such candidates have been reported to show quasi-periodic oscillations (QPOs) in the mHz range to date. We review two of the leading models that describe the QPOs from these sources. In the case of strong-gravity frame-dragging models, we demonstrate that they are unlikely to explain the QPOs in most scenarios. Alternatively, applying Dong Lai’s magnetic precession model, we derive a simple formula that links the QPO and pulsation frequencies of their system. Notably, both the magnetic field and the accretion rate are eliminated from the formula, making it broadly applicable across sources. Our model accurately reproduces the trend between QPO frequency and pulsation frequency to within a factor of order unity that depends on the accretion geometry.