Interpretations for Low‐ and High‐Frequency QPO Correlations of X‐Ray Sources among White Dwarfs, Neutron Stars, and Black Holes

Abstract

ABSTRACTAn empirical linear relation is found to exist between the high and low frequencies (νhigh, νlow) of quasi‐periodic oscillations (QPOs) for black hole candidates (BHCs), neutron stars (NSs), and white dwarfs (WDs) in binary systems, spanning 5 orders of magnitude in frequency. For the NS Z (atoll) sources, νhigh and νlow are identified as the lower kHz QPO frequency and horizontal‐branch oscillation (HBO) frequency νHBO (broad noise components); for the BHCs and low‐luminosity NSs, they are the QPOs and broad noise components at frequencies between 1 and 10 Hz; for WDs, they are the “dwarf nova oscillations” (DNOs) and QPOs of cataclysmic variables (CVs). To interpret this relation, our model ascribes νhigh to the Alfvén wave oscillation frequency at a preferred radius, and νlow to the same mechanism at another radius. We can then obtain νlow = 0.08νhigh and the relation between the upper kHz QPO frequency ν2 and the HBO frequency, νHBO≃(56 Hz)(ν2/kHz)2, which are in accordance with the observed empirical relations. Furthermore, some implications of the model are discussed, including why QPO frequencies of WDs and NSs span 5 orders of magnitude.