Speaker
Description
GX 339–4 is a low-mass X-ray binary often used as an archetype, showing typical outburst behaviour. The source undergoes a full outburst every 2–3 years, passing through all known accretion states. We used NICER data to study the spectral-timing properties of the 2024 outburst of GX 339–4 and to compare them with the 2021 outburst. In particular we focused on rapid “flip-flop” transitions, i.e. step-like changes in X-ray flux that often come with changes in the timing properties. Through Monte Carlo simulations we assessed the statistical significance of candidate QPO peaks in the power spectra, testing for the short-timescale appearance and disappearance of Type-B QPO signatures. We used this statistically defined classification to compare variability across flip-flop levels, to extract energy spectra for intervals with and without QPO signatures, and to study relations between QPO peak frequency and other variability properties. This analysis highlights the importance of high-throughput, high-time-resolution observations to capture rapid accretion regime changes and transient variability components. We will discuss how NewAthena, with its large effective area and spectral capabilities, will enable deeper investigation of the physical mechanisms driving rapid state switching and QPO phenomenology in black hole X-ray binaries.
