Flip-flop QPO changes during state transitions: a case study of GX339-4 and theoretical discussion

• DOI: 10.48550/arxiv.2502.08718
• Publication Date: 2025-02-12
• Authors: D. J. K. Buisson; G. Marcel; Vanessa López-Bar...; S. E. Motta; Sarah Turner; F. Vincentelli
• Keywords: Flip-flop

We analyse the 2021 outburst from black hole X-ray binary GX339-4 observed by NICER around hard to soft transition, when system exhibits flip-flops between two distinct luminosity states: a bright state with 5-6 Hz quasi-periodic oscillation (QPO) and dim showing only strong broadband noise. Despite marked differences in variability patterns these states, spectral energy distributions remain strikingly similar, minor changes body component range. find that QPO frequency correlates count rates hardness, suggesting tight coupling mechanism accretion disc's properties. Additionally, we demonstrate can occur on very short timescales, almost 50 within ~1200 s, while both states also stable over longer periods (at least 1000 s). explore various models explain observations, including possibility corona's speed is near sound speed, affecting presence of QPOs. However, exact driving QPOs remains unclear. Our findings emphasize complexity phenomena necessity for further theoretical observational studies unravel intricacies flip-flop behaviours binaries.