Test whether ALS 2025 produces a secondary hard-X-ray flux decrease

Determine whether continued hard-X-ray monitoring of ALS 2025 reveals a secondary flux decrease corresponding to complete occultation of Her X-1’s direct X-ray-emitting region.

Background

The rank-searching method detects a primary gap between the normal and transition states but has not identified a secondary gap marking the transition into a deep low state in the Swift BAT data. The authors attribute this absence to the limited duration and evolutionary coverage of the observed hard-X-ray events rather than treating it as evidence that the regime does not exist.

ALS 2025 offers an opportunity to test the model because it was still ongoing at the end of the adopted observational baseline. A sufficiently prolonged continuation could reveal the predicted secondary gap and provide direct observational evidence for complete geometric occultation of the compact direct-emission region.

References

Whether such an evolution will occur cannot yet be determined within the observational baseline adopted in this study. Future hard-X-ray monitoring may reveal a secondary flux decrease (the second gap) associated with the complete occultation of the direct X-ray-emitting region, thereby providing a direct observational test of our two-component geometric model in the hard-X-ray regime.

— 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”