This is a (non-disruptive) DDT proposal on the off-nculear tidal disruption event AT2024tvd. 626573659 Assigned ID: 6024 ----- Attempting Submission 1 (Mon Nov 25 23:39:40 GMT 2024) ----- Resubmit after slight setup change in spectroscopy. 556351594 ----- Attempting Submission 1 (Wed Dec 18 17:20:18 GMT 2024) ----- ----- Attempting Submission 2 (Wed Dec 18 18:40:10 GMT 2024) ----- ----- Attempting Submission 4 (Thu Dec 19 17:48:15 GMT 2024) ----- HST imaging and spectroscopy of the first off-nuclear tidal disruption event candidate 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. 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. Dr. Yuhan Yao is a Miller postdoctoral fellow at UC Berkeley, specialized in using time domain surveys such as the Zwicky Transient Facility to select TDEs and multi-wavelength characterization of transients. The Chandra observation included in this proposal was obtained as part of her DDT program. Prof. Ryan Chornock is an expert on optical/UV observations of TDEs and other optical transients. He is the co-chair of the ZTF Massive Black Hole Science Working Group. Dr. Charlotte Ward is a postdoctoral research associate at Princeton University. She has experienced in finding off-nuclear AGN-powered transients and have developed forward modeling techniques for multi-epoch imaging of transient-host systems. Dr. Raffaella Margutti is an associate professor at UC Berkeley. She is an expert of high-energy observations of transients. Dr. Wenbin Lu is an assistant professor at UC Berkeley. He is an expert in modeling the hydrodynamics of and radiation from TDEs. Dr. Kate Alexandar is an assistant professor at the University of Arizona. She is an expert in radio obseravtions of transients such as TDEs. The VLA observation included in this proposal was obtained as part of her program. Dr. Itai Sfaradi is a postdoctoral at UC Berkeley, specialized in transient radio observations. The VLA observation included in this proposal was reduced by him. Dr. Luke Kelley is an assistant adjunct professor at UC Berkeley. He is an expert on cosmological simulations of massive black hole binaries. Supermassive Black Holes and Active Galaxies Galaxies 3 false SUPPORTED UNIDENTIFIED ACCRETION DISK OPTICAL EMITTER ULTRAVIOLET EMITTER X-RAY EMITTER NO J2000 J2000 FUV and NUV fluxes are estimated to be 18.9 +/- 0.3 mag (AB system) STAR UNDESIGNATED NO J2000 WFC3/UVIS Imaging No No F225W WFC3/UVIS Imaging No No F625W STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/NUV-MAMA Spectroscopic No No G230L 2376 POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false The scheduling data was generated by CASM 32.1.3. CASM was run in Phase II mode. 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CASM was run in Phase II mode. /private/var/folders/51/8dbdmtw12rn86njf20zwrsc80000gn/T/OPVisit11184523546426574784.xml (Tic-Visit :proposal-id 17894 :visit-id "02" :proposal-version -1 :trans-version "20240604" :date "19-Dec-2024 09:46:53.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 904960 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17894 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17894 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2652 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3032 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17894 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2652 :al-overhead-at-end 0 :internal-dur-at-end 2278 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3032 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17894 :visit-id "02" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2652 :al-overhead-at-end 0 :internal-dur-at-end 582 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3032 :pcs-gap 0 ) true 3 0 This is an offset star.