Abstract We present O − C (“observed minus calculated”) timing analysis of the quasiperiodic eruption (QPE) source eRO-QPE2 with a multimission X-ray campaign including 32 observed eruptions spanning a month (i.e., 325 cycles). For disk instability models, the O − C is consistent with a damped random walk of the recurrence, albeit with highly uncertain parameters. For models with an underlying orbital clock, we infer a period of P ∼ 2.24 hr and two hierarchical superperiodic modulations with periods of ∼4.4 days (∼47 P ) and ≈95 days (≈1000 P ). We found no negative period derivative, with ∣ P ̇ ∣ ≲ 2 × 1 0 − 6 s s −1 at 3 σ . This limits gravitational-wave decay disfavoring high-eccentricity white dwarfs and high-mass/eccentricity intermediate-mass black holes. For disk-collision models, where the P ̇ from gas drag and the QPE integrated energy bound the local disk density, a main-sequence star is disfavored as extreme mass-ratio inspiral (EMRI) secondary unless debris streams are present. The correlated odd/even O − C disfavors both disk crossings per orbit being observed. Interpreting the data with one observed event per orbit, the short modulation is consistent with apsidal precession for a ∼ 140 R g , e ≈ 0.1, and M BH ≈ 1.5 × 10 5 M ⊙ . The longer modulation (much less constrained) is inconsistent with EMRI nodal precession, and disk precession is allowed in a limited parameter volume, while a hierarchical triple with an outer black hole at ∼0.4 mpc and mass ∼(0.1–1) × M BH is viable. However, more robust EMRI trajectory models yield no reliable solution, possibly due to narrow likelihood peaks in a high-dimensional space with sparse data.
Arcodia et al. (Thu,) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: