17784( 4) - 18-Oct-2024 14:49:32 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17784 Version: 4 Check-in Time: 18-Oct-2024 14:49:32 STScI Edit Number: 0 Title AT2019krl: Did a star die? ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Beth Fitzpatrick University College Dublin Y CoI: Dr. Morgan Fraser University College Dublin N ------------------------------------------------------------------------------------ Abstract AT2019krl is gap transient which exploded in 2019 in M74. Originally classified as an LBV, recent HST observations suggest that it may have dimmed to a luminosity fainter than that of the progenitor. This implies a terminal explosion, i.e., AT2019krl is a peculiarly faint core collapse supernova. AT2019krl would in fact be the faintest core collapse supernova ever observed. To explain such a low luminosity, AT2019krl must be a "failed supernova", the result of the collapse of a massive star to a black hole. This would be the first observational evidence of a "failed supernova", which have been theoretically predicted and are a solution to the "Red Supergiant Problem" (the lack of supernova progenitors above 16 solar masses, despite red supergiants existing with these masses). Unfortunately, AT2019krl was located near the edge of the chip in this recent image, meaning that the apparent dimming may not be genuine. We have conducted an analysis of the magnitudes of other sources in close proximaty to the chip edge and conclude that it is likely that our observations are real and AT2019krl was a "failed supernova". New HST observations at the site of the transient are required for confirmation. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose new imaging of AT2019krl to be taken using WFPC3/UVIS with a total exposure time of 1090s in each of the F555W and F814W filters, which will fill one orbit (53 min duration). In addition to this, we wish to obtain 2060s of WFPC3/IR imaging (1030s in each of the F110W and F160W filters), which will also take one orbit. We hence request two orbits of HST time. We wish to at least match the depth of the pre-explosion images covering the site of AT2019krl, which were 780 s in the F555W and F814W filters. Allowing 6 min for guide star acquisition, 0.5 min for filter change, 2.1 min for readout, and 0.5 min for small dithers; we will require 16.4 min for overheads to obtain 2 images in each of the F555W and F814W filters. This leaves 36.6 min of open shutter time, implying 2x545 s exposures per filter. We will use a two-point dither pattern to help remove bad pixels. As our exposures are longer than 339s we do not incur extra overheads associated with dumping the images. These observations will reach a limiting Vega magnitude of 26.8 and 26.1 mag in F555W and F814W respectively. To rule out the possibility that AT2019krl is obsucred by dust, observations in the IR are required. Using DUSTY, we calculate that if AT2019krl is indeed enshrouded in dust, but has comparable luminosity to the progenitor star, then it must have both F110W and F160W magnitudes <24.0. We will reach limiting magnitudes of 25.6 and 24.4 respectively, in these filters 17784( 4) - 18-Oct-2024 14:49:32 - [ 2] with 2x515s exposures over one orbit. ------------------------------------------------------------------------------------ 17784( 4) - 18-Oct-2024 14:49:32 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AT2019KRL STAR, LUMINOUS BLUE RA=01H36M49.6510S, J2000 V = 24 +/- 2 VARIABLE, SUPERNOVA DEC=+15D46'46.21" Reference Frame: ICRS Comments: Coordinates updated with values from Transient Name Server. The magnitude of the target is uncertain and is what we wish to test as part of this proposal. In V we expect it to be between 24-26 mag. In the IR the brightest the target could be is 24th mag. However, even if the source is not observed in the IR, the limiting magnitudes coupled with the optical photometry, will allow us to determine the nature of the target. 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 ------------------------------------------------------------------------------------------------------------------------------------ 17784( 4) - 18-Oct-2024 14:49:32 - [ 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 WFC3-IR-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 1.908 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 41.788 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17784( 4) - 18-Oct-2024 14:49:32 - [ 5] Visit: 01 (Optical) Visit Requirements: 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 AT2019KRL WFC3/UVI ACCUM UVIS1-FIX F555W FLASH=2 1 555 S PATTERN 1 1 S (1110 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2019KRL WFC3/UVI ACCUM UVIS1-FIX F814W FLASH=4 1 555 S PATTERN 1 2 S (1110 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2019KRL 1 WFC3/UVI ACCUM UVIS1-FI F555W 1 none none none 1 N/A S X AT2019KRL 1 WFC3/UVI ACCUM UVIS1-FI F555W 2 none none none 1 N/A S X AT2019KRL 2 WFC3/UVI ACCUM UVIS1-FI F814W 1 none none none 1 N/A S X AT2019KRL 2 WFC3/UVI ACCUM UVIS1-FI F814W 2 none none none 1 N/A S X 17784( 4) - 18-Oct-2024 14:49:32 - [ 6] Visit: 02 (IR) Visit Requirements: 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 AT2019KRL WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS50, NSAMP=7 1 DEF SEQ 1-3 NON-INT; PATTERN CUM (605.87 S) 2 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2019KRL WFC3/IR MULTIAC IR-FIX F110W SAMP-SEQ=SPARS100, NSAMP=6 1 DEF PATTERN 2 2 CUM (1005.868 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 AT2019KRL WFC3/IR MULTIAC IR-FIX F160W SAMP-SEQ=SPARS50, NSAMP=7 1 DEF PATTERN 2 3 CUM (605.87 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2019KRL 1 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 1 N/A CUM AT2019KRL 1 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 1 N/A CUM AT2019KRL 2 WFC3/IR MULTIAC IR-FIX F110W 1 none none none 1 N/A CUM AT2019KRL 2 WFC3/IR MULTIAC IR-FIX F110W 2 none none none 1 N/A CUM AT2019KRL 3 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 1 N/A CUM AT2019KRL 3 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 1 N/A CUM 17784( 4) - 18-Oct-2024 14:49:32 - [ 7] Summary Form for Proposal 17784 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-FIX, UVIS1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=2, FLASH=4, NSAMP=6, NSAMP=7, SAMP-SEQ=SPARS100, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2, PATTERN 2 1, PATTERN 2 2, PATTERN 2 3, SEQ 1-3 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W, F160W, F555W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2019KRL ------------------------------------------------------------------------------------------------------------------------------------