0 Assigned ID: 5643 ----- Attempting Submission 1 (Tue Mar 26 20:57:09 GMT 2024) ----- Changed the flash levels appropriately to account for CTE issues. -1387783063 ----- Attempting Submission 1 (Fri Aug 16 15:10:41 GMT 2024) ----- HST Phase II Proposal 17748 successfully submitted. Receipt: # 17748-1 ----- Attempting Submission 2 (Mon Oct 21 22:35:17 GMT 2024) ----- ----- Attempting Submission 3 (Mon Nov 11 19:13:10 GMT 2024) ----- AT 2021lwx (aka "Scary Barbie") is an ultraluminous, long-duration (500 days in rest frame), energetic transient of unclear origin at a redshift of 0.9945. With an estimated pseudo-bolometric peak luminosity of log (L/[erg/s]) = 45.7 and a radiative energy of over 10^53 erg, AT 2021lwx represents one of the most energetic and luminous transients ever observed, and, impressively, is still evolving. Modeling of AT 2021lwx suggests that it is associated with the tidal disruption of a 14-15 solar mass star by a supermassive black hole (SMBH) of order 10^8 solar masses, or accretion of a giant molecular cloud (GMC) onto a dormant 10^8 to 10^9 solar mass SMBH. AT 2021lwx is an excellent laboratory to understand extreme accretion scenarios associated with SMBHs, yet intriguingly no host galaxy has been detected. We request two orbits of HST/WFC3 observations and one orbit of NUV spectroscopy with STIS, to image AT 2021lwx, search for its host galaxy, and map signatures of outflows. These observations will resolve any extended galaxy structure surrounding the transient, further enabling characterization of its properties. Pinpointing the location of AT 2021lwx relative to its host galaxy is a fundamental test of current interpretations. Our time-sensitive observations are necessary during Cycle 32 because the transient is fading consistently. The NUV spectroscopy will provide much needed diagnostics of outflowing material from accretion processes. Extending coverage to rest-frame Ly alpha is especially important, since the total power emitted at this line can significantly constrain radiative transfer models. WFC3/UVIS Imaging (2 Orbits): Using two dithered exposures in UVIS/F275W and UVIS/F775W and three dithered exposuresin UVIS/F390W and UVIS/F850LP filters, we will measure UV-optical emission to constrain the SED model of AT 2021lwx as well as determine the existence of any underlying host galaxy of the transinet using the high spatial resolving power of HST observations. These exposures fit within 2 orbits, including overheads. NUV Spectroscopy with STIS (1 Orbit): STIS/G230L spectra will cover 1570-3180 angstrom, targeting redshifted Lyman alpha, NV, Si IV, and C IV emissions from AT 2021lwx. An exposure for target acquisition with STIS CCD is included. Bhagya Subrayan is a PhD candidate at Purdue University. She is the lead author of the multi- wavelength study and analysis of AT 2021lwx aka "Scary Barbie" (Subrayan+ 2023). She is a stellar evolution theorist who models atmospheres of supernova progenitor star systems. She is also an expert in applications of statistical methods and machine learning in time-domain astronomy. Data from this proposal will contribute to her dissertation. Prof. Dan Milisavljevic is an expert in multi wavelength observations and interpretations of supernovae and supernova remnants, old supernovae, exotic supernovae, other exotic transients, and their progenitors. He has published on the 3D kinematic and chemical propoerties of Cassiopeia A aand the Crab Nebula. He is the PI of JWST Cycle 1 proposal on Cassiopeia A. Prof. Raffaella Margutti is an expert in multimessenger observations and interpretations of gamma-ray bursts, supernovae, exotic supernovae, other exotic transients, their mass loss, and their progenitors. She specializes in understanding the physical processes that drive these high energy phenomenon utilizing observations ranging from radio to gamma-rays. Prof. Ryan Chornock is an expert in the discovery, followup, and spectral interpretation of supernovae and unusual optical transients. He has led and contributed to multiple publications on supernovae, tidal disruption events and gamma-ray bursts. Prof. Luc Dessart is an expert in radiative transfer hydrodynamical modelling of supernova explosions using CMFGEN And HERACLES code. He has significance expertise and expertise in modelling various high energy astrophysical phenomaenon including mass loss mechanisms in core-collapse supernovae, superluminous supernovae and binary systems. Dr. Kyoung-Soo Lee specializes in evolution of galaxy and galaxy clusters in cosmic time. She is an expert in pathways of galaxy formation at high redshifts and utilizes narrowband imaging and spectroscopic observaations to search for protoclusters at different redshifts. Dr. Dimitrios Giannios is a specialist in theoretical astrophysics with focus on high-energy astrophysical phenomenon, active galactic nuclei, black holes, neutron stars and gravitational physics. Dr. Paul Duffell is an expert in numerical gas dynamics and magnetohydrodynamics (MHD). He has developed powerful numerical codes for solving MHD equations for evolving astrophysical flows. He has experience supernovae, gamma ray bursts, hydrodynamic instabilities and turbulence, binary black hole and neutron star mergers, active galactic nuclei. Dr. Peter Maksym is an expert on acctive galactic nuclei (AGN) and their interactions with host galaxies. He extensively works on multiwavelength observations of extragalactic tidal disruptions of stars by supermassive black holes. Vandana Ramakrishnan is a graduate student who specializes in high redshift galaxy formation, evolution and galaxy clusters. She specializes in using stellar population models to infer properties of galaxies including stellar mass, metallicities and star formation histories. Braden Garretson is an expert in the application of machine learning to supernovae from all-sky surveys and has experience in X-ray spectral analysis of magnetars and supernova remnants. Danielle Dickinson specializes in interacting supernovae and extensively studies mass-loss mechanisms and progenitor systems of core-collapse supernovae using supernova remnants. Supermassive Black Holes and Active Galaxies Galaxies 6 false true true false false false false false SUPPORTED UNIDENTIFIED ACCRETION DISK OPTICAL EMITTER TIDAL TAIL ULTRAVIOLET EMITTER ZTF20ABRBEIE SCARYBARBIE J2000 J2000 STAR OF NO J2000 WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F390W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F625W WFC3/UVIS Imaging No No F775W STIS/NUV-MAMA Spectroscopic No No G230L 2376 POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 1 false POS-TARG DITHER 0.3 LINE false false 3 90.0 STIS-ALONG-SLIT 2 false POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 3 false 1731351827521 The scheduling data was generated by CASM 32.1.3. CASM was run in Phase II mode. 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