Pat Kelly
(UCB)
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.