18404( 2) - 11-Aug-2026 16:27:26 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18404 Version: 2 Check-in Time: 11-Aug-2026 16:27:26 STScI Edit Number: 0 Title It keeps getting better: Supernova 1987A entering its fourth decade ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Josefin Larsson KTH - Royal Institute of Technology Y CoI: Prof. Claes Fransson Stockholm University N CoI: Prof. Robert P. Kirshner Harvard University N CoI: Prof. Kevin France University of Colorado at Boulder N CoI: Prof. Kevin Heng Ludwig Maximilian Universitat of Munich N CoI: Dr. Stephen S. Lawrence Hofstra University N CoI: Prof. Peter Lundqvist Stockholm University N CoI: Dr. Bruno Leibundgut European Southern Observatory - Germany N CoI: Dr. Jesper Sollerman Stockholm University N CoI: Dr. Mikako Matsuura Cardiff University N CoI: Dr. Sophie ROSU University of Geneva, Department of N Astronomy CoI: Dr. Jason Spyromilio European Southern Observatory - Germany N CoI: Christos Tegkelidis KTH - Royal Institute of Technology N CoI: Dr. Patrick Kavanagh National University of Ireland, Maynooth N ------------------------------------------------------------------------------------ Abstract SN 1987A, the brightest supernova (SN) since 1604, is the great supernova (SN) of the HST era. HST has monitored the evolution from the very beginning, providing astronomers with a unique observational record of a SN evolving into a remnant. The most recent observations show major changes in the interaction with the iconic triple-ring nebula of circumstellar material on a time scale of one year. A strong increase of flux has been observed as the dense, inner ejecta of processed material have started to crash into the equatorial ring, while the shocks further out in the system are gradually revealing the mass-loss history of the progenitor star. Furthermore, JWST has recently detected the first clear electromagnetic signal from the compact object created in the explosion, though its properties are yet to be determined. We request imaging in narrow and broad filters over the next three cycles to study the evolution of the shock interaction and compact object. The observations will be used to measure the density profile of the inner ejecta, determine the mass-loss history of the progenitor, and constrain the main competing scenarios for the compact object (thermally emitting neutron star or pulsar-wind nebula). These investigations offer a unique avenue for connecting late stellar evolution, SN physics and compact objects. The HST observations are also indispensable for interpreting other multiwavelength observations of SN 1987A. ------------------------------------------------------------------------------------ Observations Description ------------------------ These observations are a part of a 3-year mointioring program of SN 1987A (cycles 34, 35 and 36) using WFC3/UVIS. 18404( 2) - 11-Aug-2026 16:27:26 - [ 2] We will use the narrow filters F502N and F657N in all three cycles, where F502N will primarily be used to monitor the new interaction region in [O III] and F657N to track the expansion of the reverse shock. We will also use F625W in all three cycles, which probes the overall evolution of the structure of the remnant and connects to the previous long-term monitoring. The F438W filter will be used every 2nd year (Cycles 34 and 36) to monitor the color evolution. We will use the F763M filter in Cycle 35 to search for emerging emission from the compact object. To obtain a similar or better S/N as the previous observations, considering the fading of most regions of the remnant, we require two orbits each for F438W, F625W, F657N, and F763M, and four orbits for F502N. This amounts to 10 orbits per cycle with the cadences described above. Since 2003, all HST imaging have used a fixed dither strategy to improve spatial resolution, which will be repeated for consistency. We have placed an ORIENT constraint on the WFC3 imaging to make sure that the diffraction spikes from Stars 2 and 3 (Fig 1) do not overlap with the emission from the SN. The spikes are brightest in F438W, F502N, and F625W, but having the same orientation in all imaging observations will reduce systematic effects in the comparison between filters and epochs. ------------------------------------------------------------------------------------ 18404( 2) - 11-Aug-2026 16:27:26 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SN-1987A EXT-MEDIUM, SNR RA=05H35M28.0200S, J2000 V = 22 DEC=-69D16'11.07" Reference Frame: Other: SIMBAD Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 18404( 2) - 11-Aug-2026 16:27:26 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18404( 2) - 11-Aug-2026 16:27:26 - [ 5] Visit: 01 Visit Requirements: ORIENT 78D TO 82 D; ORIENT 168D TO 172 D; ORIENT 258D TO 262 D; ORIENT 348D TO 352 D; BETWEEN 01-MAY-2027:00:00:00 AND 31-OCT-2027:00:00:00; SEQ 01, 02, 03 WITHIN 30 D On Hold Comments: Additional Comments: The orienation constraints are set to make sure that the diffraction spikes from the bright nearby stars do not overlap with the emission from the SN. The timing requirement is to keep the appximate one year cadence of the monitoring. 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 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F502N FLASH=16 1 580 S PATTERN 1 1-4 S 1C-CTE see below (2357 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F502N FLASH=16 1 580 S S 1C-CTE see below (2357 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F502N FLASH=16 1 580 S S 1C-CTE see below (2357 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F502N FLASH=16 1 580 S S 1C-CTE see below (2357 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F502N 1 none none none 1 593.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F502N 2 none none none 2 588.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F502N 3 none none none 3 588.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F502N 4 none none none 4 588.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 1 none none none 1 593.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 2 none none none 2 588.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 3 none none none 3 588.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 4 none none none 4 588.0 S S K1C-CTE 18404( 2) - 11-Aug-2026 16:27:26 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F502N 1 none none none 1 593.0 S S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F502N 2 none none none 2 588.0 S S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F502N 3 none none none 3 588.0 S S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F502N 4 none none none 4 588.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F502N 1 none none none 1 593.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F502N 2 none none none 2 588.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F502N 3 none none none 3 588.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F502N 4 none none none 4 588.0 S S K1C-CTE 18404( 2) - 11-Aug-2026 16:27:26 - [ 7] Visit: 02 Visit Requirements: ORIENT 78D TO 82 D; ORIENT 168D TO 172 D; ORIENT 258D TO 262 D; ORIENT 348D TO 352 D; BETWEEN 01-MAY-2027:00:00:00 AND 31-OCT-2027:00:00:00; SEQ 01, 02, 03 WITHIN 30 D On Hold Comments: Additional Comments: The orienation constraints are set to make sure that the diffraction spikes from the bright nearby stars do not overlap with the emission from the SN. The timing requirement is to keep the appximate one year cadence of the monitoring. 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 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F657N FLASH=15 1 580 S PATTERN 1 1-4 S 1C-CTE see below (2329 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F657N FLASH=15 1 580 S S 1C-CTE see below (2329 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F625W FLASH=5 1 580 S S 1C-CTE see below (2329 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F625W FLASH=5 1 580 S S 1C-CTE see below (2329 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F657N 1 none none none 1 586.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F657N 2 none none none 2 581.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F657N 3 none none none 3 581.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F657N 4 none none none 4 581.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F657N 1 none none none 1 586.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F657N 2 none none none 2 581.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F657N 3 none none none 3 581.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F657N 4 none none none 4 581.0 S S K1C-CTE 18404( 2) - 11-Aug-2026 16:27:26 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F625W 1 none none none 1 586.0 S S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F625W 2 none none none 2 581.0 S S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F625W 3 none none none 3 581.0 S S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F625W 4 none none none 4 581.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F625W 1 none none none 1 586.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F625W 2 none none none 2 581.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F625W 3 none none none 3 581.0 S S K1C-CTE SN-1987A 4 WFC3/UVI ACCUM UVIS2-C1 F625W 4 none none none 4 581.0 S S K1C-CTE 18404( 2) - 11-Aug-2026 16:27:26 - [ 9] Visit: 03 Visit Requirements: ORIENT 78D TO 82 D; ORIENT 168D TO 172 D; ORIENT 258D TO 262 D; ORIENT 348D TO 352 D; BETWEEN 01-MAY-2027:00:00:00 AND 31-AUG-2027:00:00:00; SEQ 01, 02, 03 WITHIN 30 D On Hold Comments: Additional Comments: The orienation constraints are set to make sure that the diffraction spikes from the bright nearby stars do not overlap with the emission from the SN. The timing requirement is to keep the appximate one year cadence of the monitoring. 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 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F438W FLASH=12 1 585 S PATTERN 1 1-2 S 1C-CTE see below (2366 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F438W FLASH=12 1 585 S S 1C-CTE see below (2366 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F438W 1 none none none 1 594.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F438W 2 none none none 1 594.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F438W 3 none none none 2 589.0 S S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F438W 4 none none none 2 589.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F438W 1 none none none 1 594.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F438W 2 none none none 1 594.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F438W 3 none none none 2 589.0 S S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F438W 4 none none none 2 589.0 S S K1C-CTE 18404( 2) - 11-Aug-2026 16:27:26 - [ 10] Summary Form for Proposal 18404 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-CTE ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=12, FLASH=15, FLASH=16, FLASH=5 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-MAY-2027:00:00:00 AND 31-AUG-2027:00:00:00, BETWEEN 01-MAY-2027:00:00:00 AND 31-OCT-2027:00:00:00, ORIENT 168D TO 172 D, ORIENT 258D TO 262 D, ORIENT 348D TO 352 D, ORIENT 78D TO 82 D, PATTERN 1 1-2, PATTERN 1 1-4, SEQ 01, 02, 03 WITHIN 30 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F438W, F502N, F625W, F657N ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN-1987A ------------------------------------------------------------------------------------------------------------------------------------