Uncovering the connection between accretion geometry and the QPO phenomenon in GRS 1716-249

Quasi-periodic oscillations (QPOs) are commonly observed in the X-ray power spectra of black hole X-ray binaries. Several different types of these quasi-periodic signals have been identified but the origin behind them remains uncertain, with several theories being considered. In particular, the type C QPOs are thought to be possibly associated with the precession of either the inner accretion disk or jet base, i.e. they are thought have a geometric origin in the sense that the geometry we see changes. These geometric changes will then lead to the observed modulation of the X-ray flux, but they should also lead to changes of the observed X-ray spectrum. In this work, we study the question whether these geometric changes can be seen in the X-ray reflection spectrum? To answer this question, we perform a QPO-phase resolved spectral analysis of the NuSTAR observations of the black hole X-ray binary GRS 1716-249 during its 2016/2017 outburst. We are able to detect statistically significant differences in the reflection parameters dependent on the QPO phase and the stage of the outburst. However, understanding the connection of these observed changes of the reflection parameters throughout the outburst to observed changes of the QPO remains challenging. This could be indicative of a more complex geometrical picture than most simple QPO models assume.