A new model for the continuum spectra of AM CVn binaries and multi-messenger inference with normalizing flows
Abstract
Future electromagnetic telescopes, such as NewAthena, CASTOR, and an AXIS-like mission, along with milli-Hz gravitational-wave (GW) detectors such as LISA, 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 LISA 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 $7000$ AM CVn binaries will permit a joint multi-messenger detection with LISA, CASTOR, and AXIS. 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 $0.05$, donor mass of $0.26$, orbital period of $0.1$, and distance of $0.2$, 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.
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BibTeX
@misc{steinle2026model,
title = {{A new model for the continuum spectra of AM CVn binaries and multi-messenger inference with normalizing flows}},
author = {Nathan Steinle and Samar Safi-Harb and Austin MacMaster and Liliana Rivera Sandoval and Katelyn Breivik and Tyrone E. Woods and Tom Maccarone and Tom Wagg},
howpublished = {arXiv},
year = {2026},
month = jul,
doi = {10.48550/arxiv.2607.12971},
eprint = {2607.12971},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.12971},
}
RIS
TY - UNPB
TI - A new model for the continuum spectra of AM CVn binaries and multi-messenger inference with normalizing flows
AU - Nathan Steinle
AU - Samar Safi-Harb
AU - Austin MacMaster
AU - Liliana Rivera Sandoval
AU - Katelyn Breivik
AU - Tyrone E. Woods
AU - Tom Maccarone
AU - Tom Wagg
PY - 2026
DA - 2026/07/14
PB - arXiv
DO - 10.48550/arxiv.2607.12971
UR - https://arxiv.org/abs/2607.12971
AB - Future electromagnetic telescopes, such as NewAthena, CASTOR, and an AXIS-like mission, along with milli-Hz gravitational-wave (GW) detectors such as LISA, 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 LISA 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 $7000$ AM CVn binaries will permit a joint multi-messenger detection with LISA, CASTOR, and AXIS. 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 $0.05$, donor mass of $0.26$, orbital period of $0.1$, and distance of $0.2$, 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.
ER -