17894( 5) - 19-Dec-2024 17:51:41 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17894 Version: 5 Check-in Time: 19-Dec-2024 17:51:41 STScI Edit Number: 0 Title HST imaging and spectroscopy of the first off-nuclear tidal disruption event candidate ------------------------------------------------------------------------------------ Type Cycle GO/DD 32 ------------------------------------------------------------------------------------ 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: Mr. Itai Sfaradi University of California - Berkeley N CoI: Dr. Kate Denham Alexander University of Arizona N CoI: Dr. Wenbin Lu University of California - Berkeley N CoI: Luke Kelley University of California - Berkeley N ------------------------------------------------------------------------------------ Abstract The hierarchical assembly of galaxies through mergers naturally predicts the presence of off-nuclear massive black holes (MBHs). While tidal disruption events (TDEs) offer a unique avenue to probe this elusive population of wandering MBHs, no offset TDE has been observationally identified. Here we propose HST imaging and UV spectroscopy of AT2024tvd, a newly discovered TDE exhibiting a significant offset from its host galaxy's nucleus. AT2024tvd is the most compelling off-nuclear TDE candidate to date, showing all hallmark properties of nuclear TDEs --- luminous variable soft X-rays, a long-lived hot UV/optical component, and broad hydrogen and helium emission lines in its optical spectrum --- while astrometry from ZTF (optical) and Chandra (X-ray) suggests a spatial offset of ~1 arcsec. HST imaging will (1) unambiguously confirm the off-nuclear nature of AT2024tvd, (2) refine its position to precisely measure the offset, and (3) search for faint merger-related features in the host galaxy. Additionally, UV spectroscopy will allow us to extend our spectroscopic comparisons with nuclear TDEs to the peak of the spectral energy distribution and test the reprocessing scenario for TDE's UV/optical emission. This program will pioneer the intersection of time-domain astronomy and galaxy evolution, using TDEs to uncover the origins and demographics of off-nuclear massive black holes. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will observe AT2024tvd for four orbits. First, we will use WFC3/UVIS to image the field for one orbit. We will use two filters: F225W and F625W. Next, we will use STIS-MAMA to do spectroscopy for three orbits, including two orbits in FUV with the G140L grating and one orbit in NUV with the G230L grating. ------------------------------------------------------------------------------------ 17894( 5) - 19-Dec-2024 17:51:41 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AT2024TVD UNIDENTIFIED, ACCRETION RA=17H10M42.5738S +/- 0.1", J2000 Z = V = 19.0 +/- 0.3 FUV and NUV fluxes are DISK, OPTICAL EMITTER, DEC=+28D50'15.11" +/- 0.1" 0.04494 estimated to be 18.9 +/- 0.3 mag (AB ULTRAVIOLET EMITTER, system) X-RAY EMITTER Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0 ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2024TVD-OF STAR, UNDESIGNATED RA=17H10M42.9677S +/- 0.035", J2000 V = 17.1 +/- 0.3 FSET DEC=+28D49'40.93" +/- 0.044" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016 -2.009730927846606E-4 -0.004187000000000001 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17894( 5) - 19-Dec-2024 17:51:41 - [ 3] 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 ------------------------------------------------------------------------------------------------------------------------------------ 17894( 5) - 19-Dec-2024 17:51:41 - [ 4] Visit: 01 Visit Requirements: BETWEEN 10-JAN-2025:12:00:00 AND 25-JAN-2025:12:00:00; TOO RESPONSE TIME 35.0D 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 AT2024TVD WFC3/UVI ACCUM UVIS2-C1K F225W FLASH=21 1 130 S (390 PATTERN 1 1 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2024TVD WFC3/UVI ACCUM UVIS2-C1K F625W FLASH=5 1 589 S PATTERN 1 2 S 1C-SUB (1767 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2024TVD 1 WFC3/UVI ACCUM UVIS2-C1 F225W 1 none none none 1 N/A S K1C-SUB AT2024TVD 1 WFC3/UVI ACCUM UVIS2-C1 F225W 2 none none none 1 N/A S K1C-SUB AT2024TVD 1 WFC3/UVI ACCUM UVIS2-C1 F225W 3 none none none 1 N/A S K1C-SUB AT2024TVD 2 WFC3/UVI ACCUM UVIS2-C1 F625W 1 none none none 1 N/A S K1C-SUB AT2024TVD 2 WFC3/UVI ACCUM UVIS2-C1 F625W 2 none none none 1 N/A S K1C-SUB AT2024TVD 2 WFC3/UVI ACCUM UVIS2-C1 F625W 3 none none none 1 N/A S K1C-SUB 17894( 5) - 19-Dec-2024 17:51:41 - [ 5] Visit: 02 Visit Requirements: BETWEEN 10-JAN-2025:12:00:00 AND 25-JAN-2025:12:00:00; TOO RESPONSE TIME 35.0D 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 AT2024TVD-O STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 30 S (30 FFSET S) Comments: This is an offset star. ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2024TVD STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=520 1 2005 S -MAMA G (2005 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 AT2024TVD STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=657 1 2624 S -MAMA G (2624 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 AT2024TVD STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=657 1 2624 S -MAMA G (2624 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2024TVD-OFFSET 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A AT2024TVD 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 1 N/A -MAMA G AT2024TVD 3 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 2 N/A -MAMA G AT2024TVD 4 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 3 N/A -MAMA G 17894( 5) - 19-Dec-2024 17:51:41 - [ 6] Summary Form for Proposal 17894 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=520, BUFFER-TIME=657, FLASH=21, FLASH=5 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 10-JAN-2025:12:00:00 AND 25-JAN-2025:12:00:00, PATTERN 1 1, PATTERN 1 2, TOO RESPONSE TIME 35.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F225W, F625W, G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2024TVD, AT2024TVD-OFFSET ------------------------------------------------------------------------------------------------------------------------------------