Kavli Affiliate: Kaisey Mandel
| First 5 Authors: Patrick L. Kelly, Steven Rodney, Tommaso Treu, Simon Birrer, Vivien Bonvin
| Summary:
In late 2014, four images of Supernova (SN) "Refsdal," the first known
example of a strongly lensed SN with multiple resolved images, were detected in
the MACS J1149 galaxy-cluster field. Following the images’ discovery, the SN
was predicted to reappear within hundreds of days at a new position ~8
arcseconds away in the field. The observed reappearance in late 2015 makes it
possible to carry out Refsdal’s (1964) original proposal to use a multiply
imaged SN to measure the Hubble constant H0, since the time delay between
appearances should vary inversely with H0. Moreover, the position, brightness,
and timing of the reappearance enable a novel test of the blind predictions of
galaxy-cluster models, which are typically constrained only by the positions of
multiply imaged galaxies. We have developed a new photometry pipeline that uses
DOLPHOT to measure the fluxes of the five images of SN Refsdal from difference
images. We apply four separate techniques to perform a blind measurement of the
relative time delays and magnification ratios (mu_i/mu_1) between the last
image SX and the earlier images S1-S4. We measure the relative time delay of
SX-S1 to be 376.0+5.6-5.5 days and the relative magnification to be
0.30+0.05-0.03. This corresponds to a 1.5% precision on the time delay and 17%
precision for the magnification ratios, and includes uncertainties due to
millilensing and microlensing. In an accompanying paper, we place initial and
blind constraints on the value of the Hubble constant.
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