Cake Talk by Gabriel Brammer
Gravitational lensing by the galaxy cluster MACS J0138.0-2155 provides multiple dramatically magnified views of a distant massive quiescent galaxy, MRG-0138, at z=1.95 and a rich opportunity for studying massive galaxy evolution in the early universe. I will present our recent serendipitous discovery of a transient source associated with MRG-0138, dubbed "SN Requiem". Three multiple images of the transient are visible in archival Hubble observations from 2016, making it the most distant multiply-imaged transient yet discovered, and its colors and brightnesses are most consistent with a Type 1a supernova explosion fortuitously caught near peak brightness. The lensing model of the cluster potential indicates relative time delays of the three observed images of order 100 days and predicts a fourth image to arrive in the year 2037±2. If observed at that time, SN Requiem will yield a time delay with an unprecedented precision < 1%, which, along with other time delay measurements expected from upcoming surveys like Rubin and Euclid, can provide unique probes of the cosmic expansion rate and dark energy models.