A new model for the continuum spectra of AM CVn binaries and multi-messenger inference with normalizing flows
arXiv:2607.12971
The paper presents a forward model that connects the physical parameters of AM CVn ultra‑compact binaries to their X‑ray, optical, and ultraviolet continuum emission, and estimates the likelihood of joint detections with LISA and upcoming telescopes. It also introduces a convolutional neural network combined with normalizing flows to infer binary parameters from simulated multi‑messenger data.
Abstract
Future electromagnetic telescopes, such as , , and an -like mission, along with milli-Hz gravitational-wave (GW) detectors such as , are expected to unearth the population of Galactic ultra-compact binaries (UCBs). Joint multi-messenger detections will probe the uncertain formation, evolution, and observables of mass-transferring UCBs such as AM CVns, but theoretical tools need to be advanced to anticipate future data challenges. Motivated by this, we present a new forward model for the continuum emission of AM CVn binaries that connects source binary parameters to X-ray, optical, and ultraviolet observables. The model assumes GW-driven mass transfer with physically motivated prescriptions for accretion energetics, emission geometry, absorption, and instrumental response. Combining this with observations and the output of binary population synthesis enables exploration of the multi-messenger properties of AM CVns. Although uncertain, our model predicts that approximately one per AM CVn binaries will permit a joint multi-messenger detection with , , and . We also develop a framework for inferring binary parameters from the inverse model with a convolutional neural net and normalizing flows. Testing the trained flow with our synthetic AM CVn population, we find mean absolute fractional error on the inferred accretor mass of M, donor mass of M, orbital period of s, and distance of pc, while Spearman's rank shows strongly correlated true and predicted distributions except for the donor mass. These efforts lay a foundation for follow-up studies that will explore detailed binary astrophysics and observational requirements for effective multi-messenger scientific discovery in the coming decade.