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| Hauptseite > Publikationsdatenbank > From hard to soft: Following the evolution of QPOs |
| Hauptseite > Publikationsdatenbank > From hard to soft: Following the evolution of QPOs |
| Poster (After Call) | FZJ-2024-00092 |
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2023
Abstract: In 2021, the Neutron star Interior Composition Explorer (NICER) onboard the International Space Station closely monitored an outburst of GX 339-4, the prime example of a low-mass black hole X-ray binary. The dense coverage of this outburst and the increased sensitivity of NICER compared to previous missions allowed us to study in detail the evolution of quasi-periodic oscillations (QPOs) and noise components in the intermediate states as the source transitions from the hard to the soft state. The evolution between these states is a somewhat erratic process with multiple transitions. In our study, we were able to follow the emergence and disappearance of the different types of QPOs in more detail and gain further insight into their evolution. In addition to the power-density spectra, we also investigated the evolution of spectral parameters, but found only a strong correlation between the hardness ratio and the type of QPO observed. We present the results of our study and discuss implications of our findings for the occurrence and coherence of type-B QPOs and their relation to changes in the accretion geometry of the system. We will also consider them in light of the Comptonisation models for type-C and type-B QPOs.
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