18131( 4) - 14-Nov-2025 12:55:20 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18131 Version: 4 Check-in Time: 14-Nov-2025 12:55:20 STScI Edit Number: 0 Title Unveiling Wandering Black Holes: HST Imaging and UV Spectroscopy of Off-nuclear Tidal Disruption Events ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Yuhan Yao University of California - Berkeley Y CoI: Prof. Ryan Chornock University of California - Berkeley N CoI: Dr. Charlotte Ward Princeton University N CoI: Dr. Raffaella Margutti University of California - Berkeley N CoI: Dr. Wenbin Lu University of California - Berkeley N ------------------------------------------------------------------------------------ Abstract The hierarchical assembly of galaxies and dynamical interactions in galactic nuclei naturally predict a population of off-nuclear massive black holes (MBHs), yet direct observational evidence remains limited. Off-nuclear tidal disruption events (TDEs) provide a unique avenue to probe these elusive wandering MBHs. We propose HST ToO observations of two offset TDE candidates selected with optical time-domain surveys. For each candidate, we request 1 orbit of WFC3 imaging and 4 orbits of SITS UV spectroscopy. The imaging will confirm the off-nuclear nature of the transient, precisely measure its offset from the host galaxy nucleus, and search for morphological signatures of recent mergers. The spectroscopic observations will constrain kick velocities and provide key diagnostics for this rare class of events. This program will increase the number of optically selected off-nuclear TDEs from one to three, enabling the first steps toward characterizing the demographics and physical origins of offset MBHs powering TDEs. ------------------------------------------------------------------------------------ Observations Description ------------------------ This proposal consists of non-disruptive ToO observations (up to 25 days response time) of 2 off-nuclear tidal disruption events (TDEs), each for 5 orbits with HST. Each TDE trigger will be for an off-nculear TDE candidate that has (1) a peak g-band magnitude of <19.5, (2) a significant offset (>3-sigma) from the nearest galaxy nucleus determined via forward modeling of science images, and (3) an optical spectrum that is consistent with one of the established TDE classes: TDE+H, TDE+H+He, TDE+He, TDE-featureless. The 1 orbit of WFC3 imaging observation will be triggered if these three criteria are met. The 4 orbits of STIS spectroscopic observations will be triggered if the expected g-band magnitude is <20 mag. Due to the fact that the spectroscopic component will only be triggered if the predicted g<20, we have broken up each TDE trigger into 3 visits: first visit: 1 orbit with WFC3 imaging second visit: 2 orbits with STIS/FUV-MAMA using G140L with the 52x0.2 aperture third visit: 2 orbits with STIS/NUV-MAMA using G230L with the 52x0.2 aperture 18131( 4) - 14-Nov-2025 12:55:20 - [ 2] Each spectroscopic visit requires an ACQ in the first orbit. As these are triggered observations, we do not yet know the exact brightness of the TDE. We expect that the TDE will be a UV-bright point source that is offset from a (much redder) galaxy nucleus. Since the TDE is offset from the host, we have chosen nearby stars for aquisition observations, from which offsets will be applied to observe the TDEs. The exposure times may be adjusted depending on the actual properties of the target, so we have not provided ETC output until the actual fluxes are known. A ToO activation on TDE1 should trigger Visit 01, and also Visits 02 and 03 if the predicted g < 20. A ToO activation on TDE2 should trigger Visit 04, and also Visits 05 and 06 if the predicted g < 20. ------------------------------------------------------------------------------------ 18131( 4) - 14-Nov-2025 12:55:20 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 5 TDE2025ABCR UNIDENTIFIED, RA=01H46M55.3877S +/- 0.1", J2000 V = 19.5 +/- 0.3 ULTRAVIOLET EMITTER DEC=-15D22'15.75" +/- 0.1" Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 6 GAIA24527995 EXT-STAR, M III-I RA=01H46M54.2745S +/- 0.0034 ", J2000 V = 16.6 +/- 0.1 45790172672 DEC=-15D22'14.50" +/- 0.0024" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016 1.8888970964772424E-4 -0.075069 0.0033337 ------------------------------------------------------------------------------------------------------------------------------------ 18131( 4) - 14-Nov-2025 12:55:20 - [ 4] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 1 TDE1 UNIDENTIFIED, NUCLEUS, (1) SPECTROSCOPIC TDE (2) >3-SIGMA V = 18 +/- 2 ULTRAVIOLET EMITTER OFFSET FROM HOST GALAXY CENTER (3) G<19.5 ------------------------------------------------------------------------------------------------------------------------------------ 2 TDE2 UNIDENTIFIED, NUCLEUS, (1) SPECTROSCOPIC TDE (2) >3-SIGMA V = 18 +/- 2 ULTRAVIOLET EMITTER OFFSET FROM HOST GALAXY CENTER (3) G<19.5 ------------------------------------------------------------------------------------------------------------------------------------ 3 TDE1-OFFSET STAR, UNDESIGNATED A STAR THAT IS NEARBY TDE1 FOR V = 15 +/- 2 ACQUISITION ------------------------------------------------------------------------------------------------------------------------------------ 4 TDE2-OFFSET STAR, UNDESIGNATED A STAR THAT IS NEARBY TDE2 FOR V = 15 +/- 2 ACQUISITION ------------------------------------------------------------------------------------------------------------------------------------ 18131( 4) - 14-Nov-2025 12:55:20 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.135 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18131( 4) - 14-Nov-2025 12:55:20 - [ 6] Visit: 01 Visit Requirements: TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: 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 TDE2025ABCR WFC3/UVI ACCUM UVIS2-C1K F625W FLASH=1 1 802 S PATTERN 1 1 S 1C-SUB (2406 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 | ------------------------------------------------------------------------------------------------------------------------------------ TDE2025ABCR 1 WFC3/UVI ACCUM UVIS2-C1 F625W 1 none none none 1 N/A S K1C-SUB TDE2025ABCR 1 WFC3/UVI ACCUM UVIS2-C1 F625W 2 none none none 1 N/A S K1C-SUB TDE2025ABCR 1 WFC3/UVI ACCUM UVIS2-C1 F625W 3 none none none 1 N/A S K1C-SUB 18131( 4) - 14-Nov-2025 12:55:20 - [ 7] Visit: 02 Visit Requirements: TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: 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 GAIA2452799 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 20 S (20 54579017267 S) 2 ------------------------------------------------------------------------------------------------------------------------------------ 2 TDE2025ABCR STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=7622 1 1989 S -MAMA G (1989 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TDE2025ABCR STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=7622 1 2568 S -MAMA G (2568 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 | ------------------------------------------------------------------------------------------------------------------------------------ GAIA245279954579017 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2672 TDE2025ABCR 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 1 N/A -MAMA G TDE2025ABCR 3 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 2 N/A -MAMA G 18131( 4) - 14-Nov-2025 12:55:20 - [ 8] Visit: 03 Visit Requirements: TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: 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 GAIA2452799 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 20 S (20 54579017267 S) 2 ------------------------------------------------------------------------------------------------------------------------------------ 2 TDE2025ABCR STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1558 1 1989 S -MAMA G (1989 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TDE2025ABCR STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1558 1 2568 S -MAMA G (2568 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 | ------------------------------------------------------------------------------------------------------------------------------------ GAIA245279954579017 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 2672 TDE2025ABCR 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 N/A -MAMA G TDE2025ABCR 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 2 N/A -MAMA G 18131( 4) - 14-Nov-2025 12:55:20 - [ 9] Visit: 04 Visit Requirements: TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: 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 TDE2 WFC3/UVI ACCUM UVIS2-C1K F625W FLASH=3 1 750 S PATTERN 1 1 S 1C-SUB (2250 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 | ------------------------------------------------------------------------------------------------------------------------------------ TDE2 1 WFC3/UVI ACCUM UVIS2-C1 F625W 1 none none none 1 N/A S K1C-SUB TDE2 1 WFC3/UVI ACCUM UVIS2-C1 F625W 2 none none none 1 N/A S K1C-SUB TDE2 1 WFC3/UVI ACCUM UVIS2-C1 F625W 3 none none none 1 N/A S K1C-SUB 18131( 4) - 14-Nov-2025 12:55:20 - [ 10] Visit: 05 Visit Requirements: TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: 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 TDE2-OFFSET STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 30 S (30 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 TDE2 STIS/FUV ACCUM 52X0.2 G140L 1425 1 1800 S -MAMA (1800 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TDE2 STIS/FUV ACCUM 52X0.2 G140L 1425 1 2200 S -MAMA (2200 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 | ------------------------------------------------------------------------------------------------------------------------------------ TDE2-OFFSET 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A TDE2 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 N/A -MAMA TDE2 3 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 2 N/A -MAMA 18131( 4) - 14-Nov-2025 12:55:20 - [ 11] Visit: 06 Visit Requirements: TOO RESPONSE TIME 25.0D On Hold Comments: Additional Comments: 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 TDE2-OFFSET STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 30 S (30 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 TDE2 STIS/NUV ACCUM 52X0.2 G230L 2376 1 1800 S -MAMA (1800 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TDE2 STIS/NUV ACCUM 52X0.2 G230L 2376 1 2200 S -MAMA (2200 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 | ------------------------------------------------------------------------------------------------------------------------------------ TDE2-OFFSET 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A TDE2 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 1 N/A -MAMA TDE2 3 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 N/A -MAMA 18131( 4) - 14-Nov-2025 12:55:20 - [ 12] Summary Form for Proposal 18131 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP, UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=1558, BUFFER-TIME=7622, FLASH=1, FLASH=3 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, TOO RESPONSE TIME 25.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F625W, G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names GAIA2452799545790172672, TDE2, TDE2-OFFSET, TDE2025ABCR ------------------------------------------------------------------------------------------------------------------------------------