17854( 3) - 14-Sep-2024 03:07:52 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17854 Version: 3 Check-in Time: 14-Sep-2024 03:07:52 STScI Edit Number: 0 Title Late time constraints on a luminous LFBOT-TDE intermediate ------------------------------------------------------------------------------------ Type Cycle GO/DD 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Jean Somalwar California Institute of Technology Y CoI: Dr. Vikram Ravi California Institute of Technology Y CoI: Dr. Raffaella Margutti University of California - Berkeley N CoI: Erica Hammerstein University of Maryland Y CoI: Dr. Yuhan Yao University of California - Berkeley N CoI: Prof. Ryan Chornock University of California - Berkeley N CoI: Dr. Edward Nathan California Institute of Technology N ------------------------------------------------------------------------------------ Abstract We request two orbits of Hubble Space Telescope/WFC3 imaging to measure the position and spectral energy distribution of an unprecedented optical transient. This event, AT 2024puz is one of the rare times where we are presented with something truly new: it is remarkably luminous in the optical (~1e45 erg/s) and X-rays (~1e44 erg/s) while being very fast (~20 days above half-peak) and persistently blue. It is located within a dwarf galaxy: from current constraints, it appears offset from the host center of light, although the sensitivty and resolution are not enough to be certain. AT 2024puz resembles either the slowest, most luminous fast blue optical transient (LFBOT), or a fast but luminous tidal disruption event (TDE). LFBOTs are a new, mysterious class of transients for which the trigger is unknown. One popular model is IMBH TDEs. AT 2024puz may represent the bridge between LFBOTs and more typical TDEs: it is consistent with being an LFBOT definitively produced by an IMBH TDE. However, it is also consistent with stellar LFBOT models. There are two questions that we must answer to distinguish between stellar LFBOT and TDE models for AT 2024puz: (1) where is AT 2024puz located within its host galaxy and (2) how does the late-time optical/UV emission evolve? If AT 2024puz is nuclear or located away from star formation, it is may be a TDE. If it is off-nuclear and in a star-forming region, it may be associated with a massive star. The rate of the late-time optical/UV luminosity decline is predicted to be different for stellar and TDE models. These questions cannot be answered with ground based telescopes: HST imaging in four bands spanning the transient SED is required. ------------------------------------------------------------------------------------ Observations Description ------------------------ These are observations of a candidate LFBOT - TDE intermediate spanning two orbits using WFC3/IR and WFC3/UVIS. The combined IR and UVIS observations will 1) measure the transient position (using UVIS/F336W and IR/F160W) and 2) measure the late-time transient SED (using UVIS/F606W and IR/F105W), to be performed at the beginning of the scheduling window on Sept 19 or at the latest by Oct 7 (making this a non-disruptive ToO). Assuming the total observation time available (excluding overheads) is 2200s 17854( 3) - 14-Sep-2024 03:07:52 - [ 2] per orbit, our observations are as follows for a total of two orbits in a single visit: IR observations will include an 1100s observation (3-point dither) with F160W and an 1100s observation (3-point dither) with F105W. UVIS observations will include an 1100s observation with F336W (3-point dither) and an 1100s observation with F606W (3-point dither). ------------------------------------------------------------------------------------ 17854( 3) - 14-Sep-2024 03:07:52 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AT2024PUZ UNIDENTIFIED, ACCRETION RA=17H31M20.6371S +/- 0.1", J2000 V = 25 DISK, ULTRAVIOLET DEC=+53D24'14.94" +/- 0.1" EMITTER, WIND, 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 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17854( 3) - 14-Sep-2024 03:07:52 - [ 4] 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 ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.605 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 41.788 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17854( 3) - 14-Sep-2024 03:07:52 - [ 5] Visit: 01 Visit Requirements: TOO RESPONSE TIME 24.0D 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 AT2024PUZ WFC3/IR MULTIAC IR-UVIS-C F160W NSAMP=15, SAMP-SEQ=SPARS25 1 DEF PATTERN 2 1-2 CUM ENTER (1058.819 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2024PUZ WFC3/IR MULTIAC IR-UVIS-C F105W NSAMP=15, SAMP-SEQ=SPARS25 1 DEF CUM ENTER (1058.819 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 AT2024PUZ WFC3/UVI ACCUM UVIS2-2K2 F336W FLASH=20 1 364 S PATTERN 1 3-4 S C-SUB see below (1073 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 AT2024PUZ WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=5 1 364 S S C-SUB see below (994 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2024PUZ 1 WFC3/IR MULTIAC IR-UVIS- F160W 1 none none none 1 N/A CUM CENTER AT2024PUZ 1 WFC3/IR MULTIAC IR-UVIS- F160W 2 none none none 1 N/A CUM CENTER AT2024PUZ 1 WFC3/IR MULTIAC IR-UVIS- F160W 3 none none none 1 N/A CUM CENTER AT2024PUZ 2 WFC3/IR MULTIAC IR-UVIS- F105W 1 none none none 1 N/A CUM CENTER AT2024PUZ 2 WFC3/IR MULTIAC IR-UVIS- F105W 2 none none none 1 N/A CUM CENTER AT2024PUZ 2 WFC3/IR MULTIAC IR-UVIS- F105W 3 none none none 1 N/A CUM CENTER AT2024PUZ 3 WFC3/UVI ACCUM UVIS2-2K F336W 1 none none none 1 209.0 S S 2C-SUB AT2024PUZ 3 WFC3/UVI ACCUM UVIS2-2K F336W 2 none none none 2 664.0 S S 2C-SUB AT2024PUZ 3 WFC3/UVI ACCUM UVIS2-2K F336W 3 none none none 2 200.0 S S 2C-SUB AT2024PUZ 4 WFC3/UVI ACCUM UVIS2-2K F606W 1 none none none 2 348.0 S S 2C-SUB 17854( 3) - 14-Sep-2024 03:07:52 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2024PUZ 4 WFC3/UVI ACCUM UVIS2-2K F606W 2 none none none 2 346.0 S S 2C-SUB AT2024PUZ 4 WFC3/UVI ACCUM UVIS2-2K F606W 3 none none none 2 300.0 S S 2C-SUB 17854( 3) - 14-Sep-2024 03:07:52 - [ 7] Summary Form for Proposal 17854 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-UVIS-CENTER, UVIS2-2K2C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=20, FLASH=5, NSAMP=15, SAMP-SEQ=SPARS25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 3-4, PATTERN 2 1-2, TOO RESPONSE TIME 24.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F105W, F160W, F336W, F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2024PUZ ------------------------------------------------------------------------------------------------------------------------------------