0 Assigned ID: 6500 ----- Attempting Submission 1 (Thu Apr 10 16:00:14 GMT 2025) ----- HST Phase I Proposal 6500 successfully submitted. Receipt: # 6500-1 ----- Attempting Submission 2 (Thu Apr 10 20:25:10 GMT 2025) ----- Increased IR dithering to reduce pixel self-persistence as suggested. Multiplied previous values by 3: Point spacing 0.572 -> 1.716, line spacing 0.365 -> 1.095 -483474895 ----- Attempting Submission 1 (Thu Aug 14 14:16:35 GMT 2025) ----- HST Phase II Proposal 18012 successfully submitted. Receipt: # 18012-1 ----- Attempting Submission 2 (Fri Oct 03 14:36:51 GMT 2025) ----- Cosmology with the first gravitationally-lensed supernovae discovered by LSST within Euclid galaxy-galaxy lenses Local and early Universe measurements of the cosmic expansion rate disagree by 8% if the concordance cosmological model is correct. Before we claim new physics, additional high precision measurements of the expansion rate (H0) are desperately needed to rule out systematic errors. Strong gravitationally lensed supernovae (SNe) are perfect for such a measurement, but rates have historically been too low to build a cosmologically useful sample. With the advent of the Rubin Observatory's Legacy Survey of Space and Time we can now discover enough lensed SNe to make a precise constraint on H0, leveraging the standardisable nature of Type-Ia SNe to ensure that systematics are well controlled. The most exciting lensed SNe will occur in already known galaxy-galaxy lenses since they guarantee long time delays, large image separations and a multiply imaged host -- all of which are critical for precision cosmology. With the rapidly growing galaxy-galaxy lens sample of Euclid we can expect two doubly imaged SN-Ia to occur in a Euclid-discovered galaxy-galaxy lens during Cycle 33. We propose to use HST to 1) obtain astrometry of these SN images to milliarcsecond precision, and 2) obtain high resolution imaging of the lensed host galaxy after the SN has faded. This data will immediately allow us to measure the Hubble constant with 6% precision and build the foundation for a 2% measurement within 5 years. Our program consists of two epochs per gravitationally-lensed supernova (glSN) system: the first will occur immediately on discovery of the glSN, and will catch the multiple images of the glSN in F814W where they are brightest, providing milliarcsecond precision astrometry on the source positions. We also observe in F160W during this first epoch to constrain dust extinction when combined with ground optical colours. The second epoch is an observation taken much later when the glSN images have completely faded, which will provide accurate measurements of the lens galaxy's and lensed host galaxy's light profiles without contamination from the glSN. For this we observe again with F814W to ensure consistency with the first epoch, and this time with F475W as this provides excellent angular resolution in a wavelength where the lensed host is likely to be both bright and highly clumpy, which are the optimal conditions for precise lens modelling. Our team is fully funded on tenured academic research posts, postdoctoral fellowships, and PhD stipends. We have sufficient computing resources available to complete this project. The team consists of experts in transient astronomy who will oversee the initial discovery of the gravitationally-lensed supernovae that are the main focus of this proposal (D. Ryczanowski, A. Sainz de Mureita, A. Goobar, P. Nugent, F. Poidevin, G. Smith). Additionally, many of the team are directly involved with previous searches for lensed supernovae, including the few lensed SNe discovered to date, and cosmological applications of lensed supernovae (D. Ryczanowski, A. Sainz de Mureita, T. Collett, A. Goobar, P. Nugent, S. Dhawan, S. Suyu, J. Diego). Team members have time on Keck for spectroscopy to type and measure redshifts for lensed SN candidates, and time on the MPG2.2m telescope and Liverpool Telescope for cadenced monitoring of lensed SN lightcurves which is critical for measuring time delays. Members of our team (N. Lines, T. Li, M. Walmsley, T. Collett, S. Serjeant, C. Krawczyk, W. Enzi, L. Weisenbach, D. Sluse, G. Mahler) are leading the Euclid lens search, and are actively using machine learning to discover galaxy-galaxy lenses -- the key to our proposal -- as soon as data are off the telescope. The first 500 lenses in the now public 64 deg$^2$ Q1 area are published. N. Lines has already found several thousands more in the unpublished dataset. This trend will continue throughout Euclid's observing campaign. Our team also has experts in cosmology-grade lens modelling, including the use of the state-of-the-art Herculens code (T. Collett, C. Krawczyk, W. Enzi, T. Li, G. Granata, C. Grillo, G. Mahler), who will lead the construction of detailed lens models of the observed system and convert these into cosmological constraints. In addition, our team has experts in gravitational microlensing of supernovae (L. Weisenbach, S. Suyu), and will provide models to quantify and minimise the impact of microlensing on our cosmological inference. Galaxies 6 false false false false false false SUPPORTED EXT-STAR SUPERNOVA SN lensed by a Euclid-discovered galaxy-galaxy lens Point source magnitudes (SN) between 26.5 and 21.5 magnitudes in F814W. Extended source magnitudes (lens galaxies) 22.5 mag or brighter (F814W). GALAXY EINSTEIN RING ELLIPTICAL GRAVITATIONAL LENS Observations of the lens system after the supernova has completely faded Extended source magnitudes (lens galaxies) 22.5 mag or brighter (F814W). WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F475W POS-TARG DITHER 0.145 Dither pattern for all exposures LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER 1.716 LINE 1.095 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 2 false /private/var/folders/d2/2srxjw1153xg98d5dknc0hsr0000gn/T/OPVisit11989075158737739757.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. This is the visit that will observe the multiple images of the lensed supernova. These observations will be in F814W and F160W. (Tic-Visit :proposal-id 18012 :visit-id "01" :proposal-version -1 :trans-version "20250624" :date "03-Oct-2025 15:36:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1781712 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18012 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18012 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2589 :al-overhead-at-end 116 :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 18012 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2594 :al-overhead-at-end 0 :internal-dur-at-end 538 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 Target of opportunity /Users/dan/Documents/PhD/proposals/HST_cycle_33/OP-cache/glSN_phase2-v02.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. This is the visit that will observe the lens system after the SN has completely faded, a few months after the first visit. These observations will be in F814W and F475W. (Tic-Visit :proposal-id 18012 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "14-Aug-2025 15:05:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 2310000 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18012 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18012 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 123 :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 18012 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 123 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 On hold until the SN (previous target of opportunity observation) has faded.