17748( 5) - 11-Dec-2024 17:07:40 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17748 Version: 5 Check-in Time: 11-Dec-2024 17:07:40 STScI Edit Number: 1 Title HST Observations of the Most Energetic and Luminous Optical Transient AT 2021lwx aka Scary Barbie ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Bhagya Subrayan University of Arizona Y CoI: Dr. Dan Milisavljevic Purdue University N CoI: Prof. Ryan Chornock University of California - Berkeley N CoI: Dr. Raffaella Margutti University of California - Berkeley N CoI: Dr. Luc Dessart CNRS, Institut d'Astrophysique de Paris N CoI: Dr. Kyoung-Soo Lee Purdue University N CoI: Dr. D Giannios Purdue University N CoI: Dr. Walter Peter Maksym III NASA Marshall Space Flight Center N CoI: Ms. Vandana Ramakrishnan Purdue University N CoI: Prof. Paul Duffell Purdue University N CoI: Ms. Danielle Dickinson Purdue University N CoI: Mr. Braden - Garretson Purdue University N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 17748( 5) - 11-Dec-2024 17:07:40 - [ 2] 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. ------------------------------------------------------------------------------------ 17748( 5) - 11-Dec-2024 17:07:40 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AT2021LWX UNIDENTIFIED, ACCRETION RA=21H13M48.4080S +/- 0.05", J2000 Z = V = 22.00 +/- 0.05 DISK, OPTICAL EMITTER, DEC=+27D25'50.48" +/- 0.1" 0.9945 TIDAL TAIL, ULTRAVIOLET EMITTER 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 ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-OFFSET STAR, OF RA=21H13M49.3858S +/- 0.0221", J2000 V = 13 +/- 0.5 DEC=+27D25'41.11" +/- 0.0296" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -1.714868197684634E-4 -0.007061812 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17748( 5) - 11-Dec-2024 17:07:40 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.145 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.3 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 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 ------------------------------------------------------------------------------------------------------------------------------------ 17748( 5) - 11-Dec-2024 17:07:40 - [ 5] Visit: 01 Visit Requirements: BETWEEN 2025.128 AND 2025.154 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 AT2021LWX WFC3/UVI ACCUM UVIS2 F275W FLASH=22 1 390 S (780 PATTERN 1 1-2 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2021LWX WFC3/UVI ACCUM UVIS2 F775W FLASH=17 1 390 S (780 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 AT2021LWX WFC3/UVI ACCUM UVIS2 F390W FLASH=20 1 390 S PATTERN 3 3-4 S (1170 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 AT2021LWX WFC3/UVI ACCUM UVIS2 F850LP FLASH=20 1 390 S S (1170 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2021LWX 1 WFC3/UVI ACCUM UVIS2 F275W 1 none none none 1 N/A S AT2021LWX 1 WFC3/UVI ACCUM UVIS2 F275W 2 none none none 1 N/A S AT2021LWX 2 WFC3/UVI ACCUM UVIS2 F775W 1 none none none 1 N/A S AT2021LWX 2 WFC3/UVI ACCUM UVIS2 F775W 2 none none none 1 N/A S AT2021LWX 3 WFC3/UVI ACCUM UVIS2 F390W 1 none none none 1 N/A S AT2021LWX 3 WFC3/UVI ACCUM UVIS2 F390W 2 none none none 2 N/A S AT2021LWX 3 WFC3/UVI ACCUM UVIS2 F390W 3 none none none 2 N/A S AT2021LWX 4 WFC3/UVI ACCUM UVIS2 F850LP 1 none none none 2 N/A S AT2021LWX 4 WFC3/UVI ACCUM UVIS2 F850LP 2 none none none 2 N/A S AT2021LWX 4 WFC3/UVI ACCUM UVIS2 F850LP 3 none none none 2 N/A S 17748( 5) - 11-Dec-2024 17:07:40 - [ 6] Visit: 02 Visit Requirements: BETWEEN 2025.128 AND 2025.154 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 STAR-OFFSET STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S (0.5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2021LWX STIS/NUV ACCUM 52X0.5 G230L 2376 1 644 S PATTERN 2 2 -MAMA (1932 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 | ------------------------------------------------------------------------------------------------------------------------------------ STAR-OFFSET 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A AT2021LWX 2 STIS/NUV ACCUM 52X0.5 G230L 2376 1 none none none 1 N/A -MAMA AT2021LWX 2 STIS/NUV ACCUM 52X0.5 G230L 2376 2 none none none 1 N/A -MAMA AT2021LWX 2 STIS/NUV ACCUM 52X0.5 G230L 2376 3 none none none 1 N/A -MAMA 17748( 5) - 11-Dec-2024 17:07:40 - [ 7] Summary Form for Proposal 17748 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.5, F28X50LP, UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/NUV-MAMA, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=17, FLASH=20, FLASH=22 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 2025.128 AND 2025.154, PATTERN 1 1-2, PATTERN 2 2, PATTERN 3 3-4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F275W, F390W, F775W, F850LP, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2021LWX, STAR-OFFSET ------------------------------------------------------------------------------------------------------------------------------------