18012( 3) - 07-Oct-2025 06:03:05 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18012 Version: 3 Check-in Time: 07-Oct-2025 06:03:05 STScI Edit Number: 0 Title Cosmology with the first gravitationally-lensed supernovae discovered by LSST within Euclid galaxy-galaxy lenses ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Daniel Ryczanowski University of Portsmouth Y CoI: Dr. Thomas E. Collett University of Portsmouth Y CoI: Ana Sainz de Murieta University of Portsmouth Y CoI: Mr. Tian Li Portsmouth University/ICG N CoI: Natalie Lines University of Portsmouth N CoI: Prof. Ariel Goobar Stockholm University N CoI: Dr. Jose M. Diego Instituto de Fisica de Cantabria N CoI: Dr. Suhail Dhawan University of Cambridge N CoI: Prof. Stephen Serjeant Open University N CoI: Prof. Graham Smith University of Birmingham N CoI: Prof. Sherry H. Suyu Technical University of Munich N CoI: Dr. Guillaume Mahler Universite de Liege N CoI: Giovanni Granata Portsmouth University/ICG N CoI: Prof. Claudio Grillo Universita di Milano N CoI: Dr. Frederick Poidevin Instituto de Astrofisica de Canarias N CoI: Dr. Peter E. Nugent Lawrence Berkeley National Laboratory N CoI: Luke Weisenbach University of Portsmouth N CoI: Dr. Coleman Krawczyk Portsmouth University/ICG N CoI: Dr. Wolfgang Johannes Rudolf Enzi University of Portsmouth N CoI: Dr. Leonidas A Moustakas Jet Propulsion Laboratory N CoI: Mr. Christopher Storfer University of Hawaii N CoI: Dr. Dominique Sluse Universite de Liege N CoI: Mr. Philip Holloway University of Oxford N CoI: Dr. Mike Walmsley University of Toronto N CoI: Ana Acebron Instituto de Fisica de Cantabria N CoI: Dr. Alejandra Melo Max Planck Institute for Astrophysics N CoI: Dr. Stefan Schuldt Universita di Milano N ------------------------------------------------------------------------------------ Abstract 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 18012( 3) - 07-Oct-2025 06:03:05 - [ 2] 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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. ------------------------------------------------------------------------------------ 18012( 3) - 07-Oct-2025 06:03:05 - [ 3] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 1 GRAVITATIONA EXT-STAR, SUPERNOVA SN LENSED BY A EUCLID-DISCOVERED Point source magnitudes (SN) between 26.5 and 21.5 LLY-LENSED-S GALAXY-GALAXY LENS magnitudes in F814W. Extended source magnitudes (lens N galaxies) 22.5 mag or brighter (F814W). ------------------------------------------------------------------------------------------------------------------------------------ 2 LENS-AFTER-S GALAXY, EINSTEIN RING, OBSERVATIONS OF THE LENS SYSTEM Extended source magnitudes (lens galaxies) 22.5 mag or N-FADED ELLIPTICAL, AFTER THE SUPERNOVA HAS COMPLETELY brighter (F814W). GRAVITATIONAL LENS FADED ------------------------------------------------------------------------------------------------------------------------------------ 18012( 3) - 07-Oct-2025 06:03:05 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.145 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO Pattern_Comments: Dither pattern for all exposures ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 1.716 Line_Spacing 1.095 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18012( 3) - 07-Oct-2025 06:03:05 - [ 5] Visit: 01 (Supernova-visit) Visit Requirements: ON HOLD ; TOO RESPONSE TIME 21.0D On Hold Comments: Target of opportunity Additional Comments: This is the visit that will observe the multiple images of the lensed supernova. These observations will be in F814W and F160W. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GRAVITATION WFC3/UVI ACCUM UVIS F814W 1 775 S PATTERN 1 1 ALLY-LENSED S (3100 S) -SN ------------------------------------------------------------------------------------------------------------------------------------ 2 GRAVITATION WFC3/IR MULTIAC IR F160W NSAMP=8, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 2 ALLY-LENSED CUM (1411.742 -SN S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GRAVITATIONALLY-LEN 1 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A SED-SN S GRAVITATIONALLY-LEN 1 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 N/A SED-SN S GRAVITATIONALLY-LEN 1 WFC3/UVI ACCUM UVIS F814W 3 none none none 1 N/A SED-SN S GRAVITATIONALLY-LEN 1 WFC3/UVI ACCUM UVIS F814W 4 none none none 2 N/A SED-SN S GRAVITATIONALLY-LEN 2 WFC3/IR MULTIAC IR F160W 1 none none none 2 N/A SED-SN CUM GRAVITATIONALLY-LEN 2 WFC3/IR MULTIAC IR F160W 2 none none none 2 N/A SED-SN CUM GRAVITATIONALLY-LEN 2 WFC3/IR MULTIAC IR F160W 3 none none none 2 N/A SED-SN CUM GRAVITATIONALLY-LEN 2 WFC3/IR MULTIAC IR F160W 4 none none none 2 N/A SED-SN CUM 18012( 3) - 07-Oct-2025 06:03:05 - [ 6] Visit: 02 (Lens-visit) Visit Requirements: SAME ORIENT AS 01; ON HOLD ; TOO RESPONSE TIME 21.0D On Hold Comments: On hold until the SN (previous target of opportunity observation) has faded. Additional Comments: 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. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LENS-AFTER- WFC3/UVI ACCUM UVIS F814W FLASH=9 1 500 S PATTERN 1 1-2 SN-FADED S see below (2106 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 LENS-AFTER- WFC3/UVI ACCUM UVIS F475W FLASH=10 1 500 S SN-FADED S see below (2106 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LENS-AFTER-SN-FADED 1 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 529.0 S S LENS-AFTER-SN-FADED 1 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 529.0 S S LENS-AFTER-SN-FADED 1 WFC3/UVI ACCUM UVIS F814W 3 none none none 2 524.0 S S LENS-AFTER-SN-FADED 1 WFC3/UVI ACCUM UVIS F814W 4 none none none 2 524.0 S S LENS-AFTER-SN-FADED 2 WFC3/UVI ACCUM UVIS F475W 1 none none none 1 529.0 S S LENS-AFTER-SN-FADED 2 WFC3/UVI ACCUM UVIS F475W 2 none none none 1 529.0 S S LENS-AFTER-SN-FADED 2 WFC3/UVI ACCUM UVIS F475W 3 none none none 2 524.0 S S LENS-AFTER-SN-FADED 2 WFC3/UVI ACCUM UVIS F475W 4 none none none 2 524.0 S S 18012( 3) - 07-Oct-2025 06:03:05 - [ 7] Summary Form for Proposal 18012 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=10, FLASH=9, NSAMP=8, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ON HOLD , PATTERN 1 1, PATTERN 1 1-2, PATTERN 2 2, SAME ORIENT AS 01, TOO RESPONSE TIME 21.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W, F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names GRAVITATIONALLY-LENSED-SN, LENS-AFTER-SN-FADED ------------------------------------------------------------------------------------------------------------------------------------