Title : Illuminating a Dark Lens : A Type Ia Supernova Magnified by Galaxy Cluster Abell 2744

Abstract :

SN HFF14Tom is a Type Ia Supernova (SNIa) discovered at z = 1.33 behind the galaxy cluster Abell 2744 (z = 0.308). This SN has a projected separation from the cluster core of ∼40′′, closer than any other cluster-lensed SN Ia. As such, it provides the first opportunity to confront gravitational lens models of galaxy clusters with the direct measurement of an absolute magnification at the edge of the strong-lensing region. We derive a tightly constrained measure of the peak apparent magnitude, corrected for light curve shape and exinction. In a cosmology-independent analysis, we find that HFF14Tom is 0.71 ± 0.12 magnitudes brighter than unlensed SNe Ia at similar redshift, implying a lensing magnification of μobs = 1.9 ± 0.2. Predicted magnifications from 7 independent groups are systematically biased to higher values, with a mean of μmod = 2.4 ± 0.3 and some models disagreeing by > 6σ.

Status : First draft complete through the end of Section 4.