Testing the Shock-cooling Emission Model from Star–Disk Collisions for Quasiperiodic Eruptions

Abstract Quasiperiodic eruptions (QPEs), the repeated outbursts observed in soft X-ray bands, have attracted broad interest, but their physical origin is under debate. One of the popular models, the star–disk collision model, suggests that QPEs can be produced through periodic collisions of an orbiting star with the accretion disk of a central black hole (BH). However, previous tests of the star–disk collision model mainly focus on the timing analysis. Other observed properties, such as peak luminosities L p , durations t e , and radiation temperatures T p of the eruptions, are not systematically investigated. For a sample of six QPE sources and two QPE-like sources, we test the shock-cooling emission model from star–disk collisions by using these observables to derive the constraints on the stellar radius R ⋆ . We find that, except for two sources (eRO-QPE3 and eRO-QPE4), the rest of the sample either has no allowed R ⋆ to simultaneously reproduce the observed L p and t e or the required R ⋆ is too large to avoid being disrupted by the central BH. For the two exceptions, a stellar radius of the order of 1 R ⊙ is necessary to satisfy all the constraints. Another issue with the simplest version of this model is that it predicts kT p ∼ 10 eV, one order of magnitude lower than the observed value.