Neutron stars and stellar-mass black holes are the remnants of massive star explosions. Most massive stars reside in close binary systems, but signatures for binarity or evidence for the formation of a compact object during a supernova explosion are still lacking. In this talk, I report the discovery of a stripped-envelope supernova, SN2022jli, which shows 12.4-day periodic undulations during the declining light curve. Narrow Hαemission is detected in late-time spectra with concordant periodic velocity shifts, likely arising from hydrogen gas stripped from a companion and accreted onto the compact remnant. A new Fermi-LAT gamma- ray source is temporally and positionally consistent with SN2022jli. The arrival times of the gamma-ray photons also show evidence of the 12.4-day period, strengthening the association of the gamma-ray source with SN2022jli. The observed properties of SN2022jli, including periodic undulations in the optical light curve, coherent Hαemission shifting, and evidence for a gamma- ray source, point to the explosion of a massive star in a binary system leaving behind a bound compact remnant. Mass accretion from the companion star onto the compact object powers the light curve of the supernova and generates the gamma-ray emission. The discovery of SN 2022jli open a new window to directly probe the final evolution of massive compact binaries, including accretion-powered systems and, eventually, the progenitors of gravitational wave sources.
