Pat Kelly

Supernovae, Strong Lensing, and Cosmology

In 1964, Sjur Refsdal hypothesized that a supernova (SN) whose light traveled in multiple paths around a strong gravitational lens could be used as an exquisitely sensitive probe. I will talk about the first such multiply imaged SN, which exploded behind the MACS J1149.6+2223 cluster at redshift z=0.544. We have obtained 30 orbits of HST near-infrared grism spectra of SN Refsdal and are building light curves of the four images of the SN which form an Einstein Cross. An additional image of Refsdal is predicted to appear at a different position in the cluster field as early as this fall, and our HST monitoring campaign has begun to rule out model predictions for the timing of the reappearance. In a second half of the talk, I will also discuss a population of SN Ia erupting in strongly star-forming host-galaxy environments. It appears to be possible to calibrate the luminosities of these SN Ia with almost twice the precision of the overall population, and their uniform behavior may provide an important clue about SN Ia progenitor systems.