Phase-resolved oscillations

Quasi-periodic oscillations are the “heart-beat” of black holes and neutron stars: oscillations with changing phase and frequency, probably due to the complicated motion of matter around these objects. Besides characterizing how these frequencies evolve in time (accelerate, decelerate, for example, when the luminosity increases), it is important to understand their exact physical meaning. A few examples in the literature use different approaches to the problem, and calculate the different spectrum of the light emitted at different phases of these oscillations. This is highly non-trivial: one cannot follow easily the single “heartbeat”, but needs to apply a strong de-noising to the signal first, and then calculate the average spectrum during the oscillation.