A Gravitationally Lensed Supernova with an Observable Two-Decade Time Delay

Abstract: When the light from a distant object passes very near to a foreground galaxy or cluster, gravitational lensing can cause it to appear as multiple images on the sky. If the source is variable, it can be used to constrain the cosmic expansion rate and dark energy models. Achieving these cosmological goals requires many lensed transients with precise time delay measurements. Lensed supernovae (SN) are attractive for this purpose because they have relatively simple photometric behavior, with well-understood light curve shapes and colours $-$ in contrast to the stochastic variation of quasars. Here we report the discovery of a multiply-imaged supernova, AT2016jka ("SN Requiem"). It appeared in an evolved galaxy at $z=1.95$, gravitationally lensed by a foreground galaxy cluster. It is likely a Type Ia supernova $-$ the explosion of a low-mass stellar remnant, whose light curve can be used to measure cosmic distances. In archival Hubble Space Telescope imaging, three lensed images of the supernova are detected with relative time delays of $<$200 days. We predict a fourth image will appear close to the cluster core in the year 2037$\pm$2. Observation of the fourth image could provide a time delay precision of $\approx$7 days, $<1\%$ of the extraordinary 20 year baseline. The SN classification and the predicted reappearance time could be improved with further lens modelling and a comprehensive analysis of systematic uncertainties.

Analysis of Gravitationally Lensed Supernova "SN Requiem" and Its Implications for Cosmology

The paper by Rodney et al. focuses on the discovery and analysis of a gravitationally lensed supernova (SN) known as "SN Requiem." This supernova, identified in archival Hubble Space Telescope (HST) data, is notably positioned in an evolved galaxy, gravitationally lensed by a foreground galaxy cluster at redshift ( z=1.95 ). This discovery is significant due to the exceptional time-delay anticipated for one of its images—an unprecedented duration of approximately two decades.

Scientific Insights

1. Lensing and Cosmological Implications: The phenomenon of gravitational lensing can produce multiple images of a distant source. Such lensed sources, especially variable ones like supernovae, are important tools for measuring the cosmic expansion rate and evaluating dark energy models. The detailed study of SN Requiem highlights its potential contribution to these cosmological goals, given its relatively simplified photometric behavior compared to quasars.

2. Observational Details: Utilizing HST imaging, three distinct images of SN Requiem were detected, showing relative time delays of (<200) days. A fourth image is predicted to appear near the cluster core approximately in 2037(\pm)2, offering a time delay measurement with extraordinary precision (around 7 days). This time delay precision is less than 1% of the total baseline, thereby providing an opportunity for precise cosmological measurements.

3. SN Classification: Through detailed analysis, SN Requiem is believed to be a Type Ia supernova—an explosion of a low-mass stellar remnant. Type Ia supernovae are valuable as cosmological markers due to their well-understood light curve shapes and colors, enabling measurements of cosmic distances.

Implications and Future Developments

• Contribution to Cosmological Measurements: SN Requiem, and similar lensed SNe, are anticipated to enhance the precision of cosmological measurements, particularly the Hubble constant (( H_0 )). Lensed quasars have been pivotal in this regard, already contributing notable independent data for resolving discrepancies in ( H_0 ) estimations. As the catalog of lensed SNe expands, they will become increasingly significant for similar cosmological analyses.

• Understanding Dark Energy: Theoretical refinements and observational enhancements could push the catalog to comprise around 100 or more well-measured lensing time delays. Such improvements will bolster efforts to determine the nature and development of dark energy over cosmic time scales.

• Synergy with Future Surveys: Future space telescopes, like the Roman Space Telescope and ground-based instruments such as the Rubin Observatory, will observe significant numbers of lensed SNe across galaxy and cluster lenses. Their observations will complement existing catalogs, including SN Requiem, further reinforcing cosmological investigations.

• Potential for Investigation of Cluster-Scale Lenses: The lengthy time delays associated with cluster-lensed SNe, exemplified by SN Requiem, offer non-limited cosmological precision that becomes advantageous relative to time delay measurement uncertainty. Simplified observational strategies enable these phenomena to serve as reliable cosmological probes.

Conclusion

Rodney et al.'s research on SN Requiem significantly contributes to the understanding of gravitationally lensed supernovae and their implications for cosmology. With a scientifically grounded and methodically detailed approach, this paper sets the stage for future discoveries and analyses that will integrate lensed SNe into the broader context of cosmic system investigations. As continuing observations and modeling evolve, SN Requiem and subsequent similar events will prove instrumental in refining our understanding of the universe's expansion dynamics and the properties of dark energy. Their systematic study and time-resolved high precision data, as anticipated with SN Requiem's reappearance, presents promising advancements in observational cosmology.