Requiem's Return: Precision cosmology from a decade-delayed, strongly-lensed supernova and its new sibling

Fifth submission. -1758272167 Assigned ID: 6309 ----- Attempting Submission 1 (Wed Apr 09 23:02:55 GMT 2025) ----- HST Phase I Proposal 6309 successfully submitted. Receipt: # 6309-1 ----- Attempting Submission 2 (Thu Apr 10 18:05:19 GMT 2025) ----- HST Phase I Proposal 6309 successfully submitted. Receipt: # 6309-2 ----- Attempting Submission 3 (Thu Apr 10 18:25:34 GMT 2025) ----- HST Phase I Proposal 6309 successfully submitted. Receipt: # 6309-3 ----- Attempting Submission 4 (Thu Apr 10 22:13:49 GMT 2025) ----- HST Phase I Proposal 6309 successfully submitted. Receipt: # 6309-4 ----- Attempting Submission 5 (Thu Apr 10 22:37:20 GMT 2025) ----- Moved missed visit to November. -1145560892 Your proposal could not be saved. Submission aborted. ----- Attempting Submission 1 (Mon Jul 21 14:32:09 GMT 2025) ----- HST Phase II Proposal 18069 successfully submitted. Receipt: # 18069-1 ----- Attempting Submission 2 (Mon Jul 21 19:16:14 GMT 2025) ----- ----- Attempting Submission 3 (Wed May 06 22:57:12 GMT 2026) ----- Requiem's Return: Precision cosmology from a decade-delayed, strongly-lensed supernova and its new sibling This program will capture the reappearance of a strongly lensed Type Ia supernova (SN Ia), SN Requiem, a decade after its initial discovery. Lensed by the galaxy cluster MACS J0138-2155, the first three images of SN Requiem at z=1.95 were seen in a 2016 HST visit; the fourth is predicted to appear a decade later. In 2023, this system became even more remarkable with JWST's discovery of a second lensed SN Ia in the same host galaxy, named SN Encore. Detecting SN Requiem's fourth image enables the first joint Hubble constant (H0) measurement from two lensed SNe in one system. Using archival JWST, HST, and MUSE data, we built seven lens mass models of the cluster, incorporating both statistical and systematic uncertainties, to predict SN Requiem's reappearance. If H0 = 73 km/s/Mpc, the fourth image is expected in June-Nov 2026; if H0 = 67.4 km/s/Mpc, then Apr-Sept 2027. We propose two HST cycles to monitor the cluster and catch the reappearance, triggering JWST ToO imaging and spectroscopy upon detection to measure the longest-ever lensing time delay (~10 years). This allows a Requiem+Encore H0 measurement with <3% uncertainty -- the most precise from lensed SNe to date -- and directly addresses the Hubble tension between early- and late-Universe values. Our program leverages HST WFC3/IR as the most efficient tool to monitor the system and detect SN Requiem, and JWST to capture the full UV-NIR photometric and spectroscopic evolution of this rare event. We have used the existing HST detections of SN Requiem, in conjunction with our mass models and microlensing simulations, to predict the SN-R4 reappearance brightness range in HST F110W/F160W filters. These filters are the optimal choice as they are the most efficient means of sampling the rest-frame UV+optical SED of a z = 2 SN with HST, providing roughly rest-frame u + B and V band, respectively. These filters were used to detect SN Requiem in 2016, enabling immediate difference imaging at SN-R4 and a direct comparison to SN-R1,2,3. We choose 3sigma limiting magnitudes for both filters that enable a 2-filter detection for ~90% of the detection range. Reaching these depths requires 2 orbits (1.5 F160W, 0.5 F110W) per visit. If the SN is only detected in F160W, we will require detections in all (6) exposures across both orbits. We will monitor with ~monthly cadence during the HST visibility windows, corresponding to a ~10 rest-frame day cadence. This is designed such that during the monitoring windows we guarantee a pre-peak detection and near-peak JWST follow-up, as the rise time for SNe Ia is generally 15-20 rest-frame days. We require 7 visits in Cycle 33 and 6 in Cycle 34 considering a ~5 month gap when SN Requiem is behind the sun. The total HST request is therefore 2x7 + 2x6 = 26 orbits. Only one observing gap is filled with a JWST visit. The LensWatch team brings together researchers with deep experience using HST for SN science and those with expertise in gravitational lensing studies. We are engaged in complementary programs that have led to the most precise measurements of the Hubble constant to date, both through the Cepheid+SNIa distance ladder (Riess et al. 2019), and using strongly-lensed quasar time delays (see, e.g., Suyu et al. 2017). From >25 previous HST programs, our team members have published over 300 journal articles on these topics. PI Pierel is PI of the LensWatch collaboration, which has executed HST observations for 2 previous lensed SNe, including SN Encore. He has also led or contributed to time-delay measurements for 5 lensed SNe, including each of those used for cosmology. Pierel has extensive experience planning HST and JWST programs, measuring HST photometry, and fitting SN light curve models. He extended most of the existing light curve models to the infrared for use with JWST, and created the SNTD software package used for time-delay measurements. Co-PI Suyu is an expert in strong lensing and time-delay cosmography, particularly with lensed quasars and lensed supernovae. Co-I Larison is an expert in SNIa cosmology and has contributed to the analyses of lensed SNe observed by LensWatch. Co-I Diego is an expert in Gravitational lensing modelling, including microlensing simulations of lensed SNe. Co-I Koekemoer has scientific expertise in high-z galaxies, AGN, transients, and is the primary architect of the science data products and mosaics for many large HST and JWST surveys. Co-I Schuldt is an expert in strong lens mass modeling on galaxy and cluster scale, on time delay cosmography, and deep learning applications. Co-Is Newman and Gu led the discovery program for SN Encore. Co-I Oguri is an expert in gravitational lens mass modeling and time delay cosmographic analyses. Co-I Zitrin is an expert in gravitational lensing modelling, and has been involved in analyzing some of the previously multiply imaged SNe. Co-I Kamieneski has expertise in gravitational lens modeling and has participated in the time-delay analysis of SN H0pe and SN Encore. Co-I Millon has expertise in time-delay cosmography, including time-delay measurements and high-precision photometry from both ground-based and space-based imaging. Co-I Mamuzic has expertise in chromatic microlensing simulations of SNIa. Co-I Acebron has experience in lens cluster modelling, using different software and methodologies, and time-delay cosmography Co-I Rosati's expertise lies in X-ray, Optical and Spectroscopic studies of galaxy clusters and in the field of gravitational lensing. Co-I Bergamini is an expert in the strong lens modelling of galaxy clusters, MUSE data exploitation to measure the velocity dispersions of cluster members and its implementation in strong lensing models. Co-I Taubenberger is an expert in observations and data analysis of SNe. Co-I Pascale has experience in cluster strong-lens modeling and time-delay cosmography. Co-I Jee is an expert in both strong and weak lensing studies of galaxy clusters. Co-I Cha is an expert in detailed mass reconstruction of galaxy clusters based on free-form algorithms. He developed the MARS algorithm. Co-I Shajib has expertise in lens modeling and time-delay cosmography. Co-I Canameras is an expert in strong lensing and galaxy evolution through multiwavelength observations. Co-I Grillo is an expert on strong lensing, particularly on time delay cosmography with strongly lensed supernovae. Co-I Perez-Fournon is an expert in SN discovery and classification (e.g. with GTC, NOT, and LT), photometric and spectroscopic follow-up, and in detailed studies of superluminous supernovae Co-I Jha has expertise in HST and JWST observations and analysis of supernovae. Co-I Huang has expertise in HST observations, analysis of supernovae, and strong lens modeling. Co-I Granata has expertise in strong lensing modeling of galaxy clusters and stellar kinematics of cluster galaxies. Co-I Frye has expertise in cluster-scale strong lens modeling and time-delay cosmography. Co-I Agrawal has expertise in analyzing lenses supernovae with SALT-3 and BayeSN. The proposers have written the entire proposal on their own without the use of GAI. They only used ChatGPT in the final stage to proofread and make minor edits. Stellar Physics and Stellar Types Galaxies 6 false false false false false false false true PRIMARY 25.8 true SUPPORTED EXT-STAR SUPERNOVA TYPE IA J2000 J2000 WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.605 LINE false false 3 41.788 WFC3-IR-DITHER-LINE-3PT 1

false

1778108117509 The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /private/var/folders/9x/wtzrcm85559bwf_5h58_8ml40002rz/T/OPVisit14522895671769437669.xml 1762785825000 15.0 (Tic-Visit :proposal-id 18069 :visit-id "01" :proposal-version -1 :trans-version "20250929" :date "06-May-2026 18:55:17.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1932384 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18069 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18069 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18069 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 1778108118975 The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /private/var/folders/9x/wtzrcm85559bwf_5h58_8ml40002rz/T/OPVisit6780300829506196493.xml (Tic-Visit :proposal-id 18069 :visit-id "08" :proposal-version -1 :trans-version "20250929" :date "06-May-2026 18:55:18.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1932384 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18069 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18069 :visit-id "08" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18069 :visit-id "08" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 1778108120025 Timing link suitability includes constraints ([04 After 03 by 27.0 to 33.0 days]) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /private/var/folders/9x/wtzrcm85559bwf_5h58_8ml40002rz/T/OPVisit1958527907615750715.xml (Tic-Visit :proposal-id 18069 :visit-id "03" :proposal-version -1 :trans-version "20250929" :date "06-May-2026 18:55:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1932384 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18069 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18069 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18069 :visit-id "03" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 1778108121042 Timing link suitability includes constraints ([04 After 03 by 27.0 to 33.0 days] [05 After 04 by 27.0 to 33.0 days]) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /private/var/folders/9x/wtzrcm85559bwf_5h58_8ml40002rz/T/OPVisit6902429490770838799.xml (Tic-Visit :proposal-id 18069 :visit-id "04" :proposal-version -1 :trans-version "20250929" :date "06-May-2026 18:55:20.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1932384 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18069 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18069 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18069 :visit-id "04" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 1778108122322 Timing link suitability includes constraints ([05 After 04 by 27.0 to 33.0 days]) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /private/var/folders/9x/wtzrcm85559bwf_5h58_8ml40002rz/T/OPVisit15871355947312950942.xml (Tic-Visit :proposal-id 18069 :visit-id "05" :proposal-version -1 :trans-version "20250929" :date "06-May-2026 18:55:22.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1932384 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18069 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18069 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18069 :visit-id "05" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 1778108123349 The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /private/var/folders/9x/wtzrcm85559bwf_5h58_8ml40002rz/T/OPVisit14197322680793272351.xml (Tic-Visit :proposal-id 18069 :visit-id "06" :proposal-version -1 :trans-version "20250929" :date "06-May-2026 18:55:23.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1932384 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18069 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18069 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18069 :visit-id "06" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 1778108124713 The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /private/var/folders/9x/wtzrcm85559bwf_5h58_8ml40002rz/T/OPVisit1954255095959829410.xml (Tic-Visit :proposal-id 18069 :visit-id "07" :proposal-version -1 :trans-version "20250929" :date "06-May-2026 18:55:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1932384 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18069 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18069 :visit-id "07" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18069 :visit-id "07" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0