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Whether QPEs truly disappeared in October 2023 or continued at undetectable faintness

Ascertain whether quasi-periodic eruptions in eRO-QPE1 ceased entirely during October 2023 or continued at amplitudes below NICER’s detectability threshold by establishing the presence or absence of faint QPEs during that period with sufficiently sensitive observations.

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Background

The authors observed a non-detection of QPEs by NICER in October 2023, followed by a single peak in November 2023 and a faint QPE detected by XMM-Newton in January 2024. These observations raise the question of whether QPEs actually disappeared or persisted at lower luminosities.

Resolving this uncertainty is important for understanding the secular evolution of QPE activity and its relationship to the quiescent accretion state.

References

We cannot say definitively whether QPEs disappeared altogether in Oct 2023 (as NICER\ is not sensitive enough to detect the quiescence), and indeed the presence of one peak in the Nov 2023 observations suggests they may have been ongoing at an undetectable faintness all along.

— Testing EMRI models for Quasi-Periodic Eruptions with 3.5 years of monitoring eRO-QPE1 (2402.08722 - Chakraborty et al., 13 Feb 2024) in Conclusions, Section 5