We present the discoveries of two of AM CVn systems, Gaia14aae and SDSS~J080449.49+161624.8, which show X-ray pulsations at their orbital periods, indicative of magnetically collimated accretion. Both also show indications of higher rates of mass transfer relative to the expectations from binary evolution driven purely by gravitational radiation, based on existing optical data for Gaia14aae, which show a hotter white dwarf temperature than expected from standard evolutionary models, and X-ray data for SDSS~J080449.49+161624.8 which show a luminosity 10-100 times higher than those for other AM~CVn at similar orbital periods. The higher mass transfer rates could be driven by magnetic braking from the disk wind interacting with the magnetosphere of the tidally locked accretor. We discuss implications of this additional angular momentum transport mechanism for evolution and gravitational wave detectability of AM CVn objects.
@article{arxiv.2302.12318,
title = {Strongly magnetized accretion in two ultracompact binary systems},
author = {Thomas J. Maccarone and Thomas Kupfer and Edgar Najera Casarrubias and Liliana Rivera Sandoval and Aarran Shaw and Chris Britt and Jan van Roestel and Dave Zurek},
journal= {arXiv preprint arXiv:2302.12318},
year = {2023}
}