Encounters
Z Source ○꠹｜encounter｜ENC｜20260911232503-00-•
Another avenue for QPO investigations is the study of phase lags and coherence functions that compare two different energy bands, e.g., 2–6 versus 13–30 keV. Such analyses have been conducted for the QPOs in XTE J1550-564. Unexpectedly, the phase lag measurements showed groups distinguished by positive, negative, and ∼zero lags defining, respectively, LFQPO types A, B, and C (Wijnands et al. 1999; Cui et al. 2000b; Remillard et al. 2002b; Casella et al. 2004). These details are surely complicated, but the ramifications are very significant. The A and B types are associated with the SPL state and the presence of high-frequency QPOs. On the other hand, C-type LFQPOs mostly occur in the intermediate and hard states, and they are responsible for the frequency versus disk flux correlation shown in Figure 10. There are also similarites between these BH LFQPO subtypes and the three QPOs of Z-type neutron-star systems (Casella, Belloni, & Stella 2005).
Source: Remillard & McClintock 2006 ┃ X-Ray Properties… ⚬𓂃
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