Determine whether ALS 2025 will evolve into a deep low state

Determine whether the ongoing anomalous low state ALS 2025 in Her X-1 will evolve from the observed transition state into a deep low state involving complete occultation of the direct X-ray-emitting region.

Background

The study identifies ALS 2025 as an ongoing anomalous low-state candidate lasting more than four superorbital cycles. Unlike ALS 1999 and ALS 2003, for which a deep low state was detected, the available Swift BAT observations do not yet show a distinct second gap or complete disappearance of the main high state in the hard-X-ray band.

The authors interpret a future secondary flux decrease as a possible signature that the primary high-flux compact emission region has become completely occulted. Establishing whether ALS 2025 reaches this regime would test the proposed two-component geometric screening model and determine whether a deep low state can emerge in the hard-X-ray band.

References

Finally, the recently discovered and still ongoing ALS 2025~\citep{mih26} was also identified in this study (see the bottom panel of Figure~\ref{rank_select_mh}), although we are currently unable to determine whether it will reach the deep low state.

— Superorbital Phase Evolution and Identification of New Anomalous Low State Candidates for Her X-1  (2610.01123 - Chou et al., 1 Oct 2026) in Section 4.1, subsection “The Two-Component Geometric Screening Model” (discussion of ALS 2025); Section 2.2, subsection “Identification of New Anomalous Low State Candidates”