0 Assigned ID: 7060 ----- Attempting Submission 1 (Tue Apr 14 13:07:55 GMT 2026) ----- HST Phase I Proposal 7060 successfully submitted. Receipt: # 7060-1 ----- Attempting Submission 2 (Tue Apr 14 22:03:54 GMT 2026) ----- HST Phase I Proposal 7060 successfully submitted. Receipt: # 7060-2 ----- Attempting Submission 3 (Wed Apr 15 22:14:52 GMT 2026) ----- HST Phase I Proposal 7060 successfully submitted. Receipt: # 7060-3 ----- Attempting Submission 4 (Thu Apr 16 21:39:26 GMT 2026) ----- Second submission of Phase2, with some modifications to the exposure and subarray strategy. We may wish to update some details pending feedback from the support science team. -1727179826 ----- Attempting Submission 1 (Mon Aug 17 21:11:13 GMT 2026) ----- HST Phase II Proposal 18388 successfully submitted. Receipt: # 18388-1 ----- Attempting Submission 2 (Tue Aug 18 16:14:36 GMT 2026) ----- Resolving the Connection between LFBOTs and Star Formation Luminous Fast Blue Optical Transients (LFBOTs) are a class of rare, exotic transients likely produced by the rapid accretion of material onto a black hole. Their properties indicate that the mass scale of the accreted object, the black hole, or both are quite different to what is known from other populations: they may result from the formation of very massive (>50 solar mass) stellar black holes following core-collapse or the disruption of stars by intermediate-mass (10^4 solar mass) black holes. The uncertainty in their progenitors arises in large part because their hosts are too distant to usefully resolve from the ground. HST observations have played essential roles in establishing the age and mass of various transient populations, by identifying (or ruling out) associations with young star-forming regions and statistically associating the locations of the transients with the distribution of UV light across the host more broadly. The sample of LFBOTs is now sufficiently large to deploy these methods on this population. We propose to use HST to study the local environments of the full sample of confirmed LFBOTs to test different models of their origins and constrain the mass scales of the progenitor star and black hole. By testing a potential production channel for large black holes - or alternatively, unveiling a population of previously hidden intermediate mass black holes - the results will have important implications for our understanding of the properties and evolution of black holes in the universe more generally. The goal of the program is to obtain resolved imaging (in the rest-frame near-UV where possible) of a set of LFBOT host galaxies to ascertain whether the transients hosted within these galaxies lie in or near star-forming regions. The galaxies are distant and span a wide range of surface brightnesses, and range between redshift 0.03 to 0.34. Where possible, our goal is to map the position of the transient (available from ground-based optical imaging and/or radio interferometry) onto the host to approximately 0.1 arcsec relative astrometric accuracy. For brighter galaxies (visits 1, 2, 4, 5, 8) we use a single orbit with a standard UVIS 3-point line dither in either F336W or F390W with the detector subarrayed (C1K1C-SUB) to avoid a buffer delay. This is followed by a shorter observation using 2-point line dither in F350LP (with no subarray using the C1K1C-CTE aperture), primarily for astrometric purposes (but also to characterize the optical light distribution of the host). For somewhat fainter galaxies (visits 3, 6, 7, 9, 10), we observe for 2 orbits (or in one case 3 orbits) using F336W or F390W and use a 2-point line dither within each orbit, with additional small offsets applied between orbits. The last orbit includes 2-point line dither in F350LP, with the F336W/F390W observations during that orbit shortened accordingly. As with the brighter galaxies, the F336W/F390W observations are subarrayed but the F350LP observations are not. For the faintest galaxies (visits 11, 12, 13), we observe only in long-pass filters, using a 4-point dither spanning two orbits (F200LP), plus one additional orbit using a 4-point dither in F350LP. We use the flash option as needed to ensure at least 20 e-/pix as recommended by the APT. Daniel Perley (PI), an associate professor at Liverpool John Moores University, has over 15 years of experience in the studies of host galaxies of rare extragalactic transients, and has authored several papers on the host populations of GRBs and of superluminous supernovae, as well as on the discovery and characterization of LFBOTs. Anna Ho, an assistant professor at Cornell University, has years of experience discovering LFBOTs (as well as other energetic extragalactic transients) and characterizing their multiwavelength emission. She has authored a variety of papers related to the object types relevant to this proposal (LFBOTs, LGRBs, energetic SNe). Lin Yan has extensive experience in observational galaxies at high redshift, and is also an expert in UV spectroscopy of superluminous supernovae. Andrew Levan is a professor at Radboud University and the department chair of astrophysical transients. He is an expert on a wide variety of energetic transients, including LGRBs and LFBOTs. He is also an expert on HST observations. Steve Schulze is a Research Associate at the Weizmann Institute of Science. He has led and conducted a wide variety of studies on the properties and environments of exotic transients. Ragnhild Lunnan is an assistant professor at Stockholm University and previously did her PhD thesis work on astrometric studies of SLSN host galaxies using HST. She continues to work actively in studies of superluminous supernova and other energetic transients. Cassie Sevilla is a Ph.D. student at Cornell University working with Professor Anna Ho. LFBOTs will be a major part of her Ph.D. thesis, and she recently submitted a paper on the multiwavelength characterization of the LFBOT sample whose host galaxies are proposed here. Gokul Srinivasaragavan recently completed his Ph.D. at the University of Maryland and will begin a postdoctoral fellowship later in 2026. He is an expert on engine-driven transients. Jacob Wise and Zoe McGrath are Ph.D. students at LJMU working with Daniel Perley. Jacob Wise's PhD thesis topic is on extremely energetic transients (including LFBOTs); Zoe McGrath's PhD topic is on accretion-powered transients (including LFBOTs). 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "01" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:53:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 630976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "01" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2671 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2977 :pcs-gap 0 ) true 1 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v02.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "02" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:53:18.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 630976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "02" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2672 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v03.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "03" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:53:22.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 684448 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2619 :al-overhead-at-end 59 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18388 :visit-id "03" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2619 :al-overhead-at-end 59 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18388 :visit-id "03" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2608 :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 3001 :pcs-gap 0 ) true 3 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v04.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "04" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:53:28.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 630976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "04" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2672 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2977 :pcs-gap 0 ) true 1 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v05.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "05" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:53:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 630976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "05" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2682 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v06.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "06" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:53:58.0" :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 648800 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2639 :al-overhead-at-end 59 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3026 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18388 :visit-id "06" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2627 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3026 :pcs-gap 0 ) true 2 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v07.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "07" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:54:07.0" :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 648800 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "07" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 82 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2977 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18388 :visit-id "07" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2597 :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 2977 :pcs-gap 0 ) true 2 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v08.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "08" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:54:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 630976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "08" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2663 :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 2974 :pcs-gap 0 ) true 1 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v09.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "09" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:54:17.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 630976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "09" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2682 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v10.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "10" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:54:22.0" :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 648800 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "10" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2595 :al-overhead-at-end 79 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18388 :visit-id "10" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2588 :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 2976 :pcs-gap 0 ) true 2 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v11.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "11" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:54:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 2309984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "11" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 96 :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 18388 :visit-id "11" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 96 :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 18388 :visit-id "11" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 116 :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 3 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v12.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "12" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:54:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 2309984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "12" :obset-id "12" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "12" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 96 :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 18388 :visit-id "12" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 96 :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 18388 :visit-id "12" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 116 :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 3 0 /Users/dperley/research/Observing/HST34/OP-cache/HST18388-e-v13.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18388 :visit-id "13" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 16:54:43.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 2309984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18388 :visit-id "13" :obset-id "13" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18388 :visit-id "13" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 96 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18388 :visit-id "13" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 96 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18388 :visit-id "13" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 116 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 3 0