2025A&A...697A.146B

Context. Through gravitational lensing, galaxy clusters can magnify supernovae (SNe) and thereby create multiple images of the same SN. This enables measurements of cosmological parameters (primarily the Hubble constant), which will be increasingly important in the context of upcoming surveys from the Nancy Grace Roman Space Telescope (Roman) and Vera C. Rubin Observatory.
Aims. We study the prospects of detecting strongly lensed supernovae in cluster fiels with Roman's High Latitude Time Domain Survey (HLTDS) and the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST).
Methods. We employed two approaches: one focusing on known multiply imaged galaxies (arcs) behind cluster fields, along with the SN rates specific to those galaxies (arc-specific), while the second is based on the expected number of lensed SNe exploding in a given volume behind a galaxy cluster (volumetric). We collected all the clusters in the literature that feature a) a well-constrained lens model and b) multiply imaged galaxies behind clusters with high-quality data for the multiply imaged galaxies behind clusters. This allowed us to determine the supernova rate for each galaxy. We provide predictions for 46 clusters visible to the Vera C. Rubin Observatory, as well as for 9 observable by Roman's HLTDS, depending on whether the clusters fall within the survey's observing field.
Results. We predict that the number of multiply imaged SNe discovered by LSST in its first three years is 3.95 ± 0.89 from the first approach or 4.94 ± 1.02 from the second. Based on the current proposed observing strategy for the HLTDS, which specifies the requirements on galactic and ecliptic latitudes, the expected number of multiply imaged supernovae ranges from 0.38 ± 0.15 to 5.2 ± 2.2, depending on the specific cluster observed. However, the exact fields to be targeted remain a matter of discussion.
Conclusions. We conclude that LSST offers great prospects for detecting multiply imaged SNe. If adequate follow-up campaigns are conducted, these capabilities will enable measurements of cosmological parameters independent of conventional probes. These predictions are effectively lower limits, as we only considered the most massive and well-studied clusters in the present work. Here, we provide a recommendation for HLTDS observing field selection, namely: either MACS J0553.4-3342 or Abell 1758a should be observed by the survey to maximize the number of potential multiply imaged SN discoveries.