Stratos Boutloukos

They key ingedients into resolving the nature of accretion-powered QPOs in LMXBs

A solid understanding of the nature of high-frequency QPOS is needed as it can provide additional constraints to NS properties like the spin. Despite the wealth of kHz QPO detections, however, their nature is still debated. Part of the problem is the low significance leading to variable analysis techniques, resulting among others to false alarms, like e.g. the highest frequency QPO in 4U 0614+09. Theory has however also not caught up as rapidly as observational trends, like the dependence of QPO frequency separation with spin. I discuss here some other observational aspects that have often been neglected in modelling, like the amplitude and coherence of oscillations. Additional help may come from the relation to the low-frequency QPOs, through their larger statistics and the difficulties in explaining those as e.g. a LT-precession. Ultimately, the solution will come through a next generation X-ray instrument like LOFT.