Program: GS-2024A-FT-105

We have identified a new ultra-compact binary based on its SkyMapper colors and Gaia astrometry. We find a strong periodic signal at P=13.8 min in archival photometry from the Transiting Exoplanet Survey Satellite (TESS). Our follow-up optical spectroscopy shows radial velocity variations at orbital period P=27.7 min with an exceptionally large velocity semi-amplitude K=700 km/s, confirming a binary origin for the photometric variability seen in TESS. Given the large velocity semi-amplitude and short Gaia distance (550 pc), this binary may be one of the loudest gravitational wave sources identified and a Type Ia supernova progenitor. Here we propose to obtain 1-hour of high-speed multi-band photometry of this new ultra-compact binary to enable precise binary characterization through detailed light curve modeling. Our observations will additionally probe short timescale photometric variability and provide a precise timing measurement for long-term orbital decay monitoring in preparation for the launch of LISA.