Abstract
Abstract
The multiply imaged SN 2022riv was discovered through a search of galaxy cluster fields as part of a Hubble Space Telescope (HST) SNAP program to find highly magnified stars. The supernova (SN) was detected in the image corresponding to the longest time delay of a galaxy at redshift
z
= 1.522, strongly lensed by the foreground galaxy cluster RX J2129.7+0005. Follow up James Webb Space Telescope (JWST) NIRSpec G140M and PRISM spectroscopy yields an SN Ia classification. Using the SALT3-NIR light-curve fitter, we obtain a cosmology-independent measurement of the magnification of 5.35 ± 1.01 for the last-to-arrive image of the SN, with multiple SALT SN spectral time-series models yielding consistent constraints. The last-to-arrive image of SN 2022riv we detect appeared adjacent to the brightest cluster galaxy (BCG) at a location with an exceptionally high stellar mass density (∼1–2 dex higher than that of SN Refsdal), where microlensing is expected to introduce a 20%–50% modulation of the magnification. Analyzing six independent lens models of the cluster, we find that four predict the magnification with much greater precision (
p
σ
) prior to accounting for microlensing, whereas
HoliGRALE
favors a significantly higher value of 15.39 ± 0.85. After incorporating nominal microlensing, the
HoliGRALE
prediction is within 1
σ
tension with our measurement. A companion paper will present constraints on the relative time delay of the image that arrived earlier.