Abstract
In Hubble Space Telescope (HST) imaging taken on 10 November 2014, four
images of supernova (SN) 'Refsdal' (z = 1.49) appeared in an
Einstein-cross--like configuration (images S1-S4) around an early-type galaxy
in the cluster MACS J1149.5+2223 (z = 0.54). The gravitational potential of the
cluster creates three full images of the star-forming host galaxy of the SN.
Almost all lens models of the cluster have predicted that the SN should
reappear within approximately one year in a second host-galaxy image, offset by
~8" from the previous images. In HST observations taken on 11 December 2015, we
find a new source that we interpret as a new image of SN Refsdal. This marks
the first time the appearance of a SN at a particular time and location in the
sky was successfully predicted in advance! We use these data and the light
curve from the first four observed images of SN Refsdal to place constraints on
the relative time delay and magnification of the new image (SX), compared to
images S1-S4. This enables us, for the first time, to test lens model
predictions of both magnifications and time delays for a lensed SN. We find
that the timing and brightness of the new image are consistent with the blind
predictions of a fraction of the models. The reappearance illustrates the
discriminatory power of this blind test and its utility to uncover sources of
systematic uncertainty in the lens models. From planned HST photometry, we
expect to reach a precision of 1-2% on the relative time delay between S1-S4
and SX.
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