17996( 2) - 15-Aug-2025 17:24:31 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17996 Version: 2 Check-in Time: 15-Aug-2025 17:24:31 STScI Edit Number: 0 Title Expanding shocks and the emergence of the compact object in Supernova 1987A ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Josefin Larsson Royal Institute of Technology Y CoI: Prof. Claes Fransson Stockholm University N CoI: Prof. Robert P. Kirshner Harvard University N CoI: Mr. Peter Challis Harvard University N CoI: Dr. Roger A. Chevalier The University of Virginia 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. Seppo Mattila University of Turku N CoI: Dr. Bruno Leibundgut European Southern Observatory - Germany N CoI: Dr. Nicholas B. Suntzeff Texas A & M University 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: Dr. Tea Temim Columbia University in the City of New N York CoI: Dr. Alec S. Hirschauer Morgan State University N CoI: Dr. Patrick Kavanagh National University of Ireland, Maynooth N ------------------------------------------------------------------------------------ Abstract By a fortunate turn of events, SN 1987A, the brightest supernova (SN) since 1604, exploded just a few years before the launch of HST. This has allowed HST to monitor the evolution from the very beginning as the SN evolves into a remnant, proving astronomers with a unique laboratory for SN physics. The most recent observations show major changes in the interaction with the iconic triple-ring nebula of circumstellar material. The dense, inner ejecta are just starting 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, as well as a COS spectrum in Cycle 31, to study the shock interaction and compact object. The observations will be used to determine the conditions in the shock region, the properties of the circumstellar medium, and constrain the main competing scenarios for the compact object. Annual observations are needed to track the rapid evolution of the shocks and the emerging emission from the compact object. Taken together, this will allow the properties of the progenitor and compact object to be connected for the first time. The HST observations are also indispensable for interpreting other multiwavelength observations of SN 1987A. 17996( 2) - 15-Aug-2025 17:24:31 - [ 2] ------------------------------------------------------------------------------------ Observations Description ------------------------ The requested observervations include 6 orbits with WFC3/UVIS and 11 orbits with COS. WFC3 Imaging: We request imaging in F625W, F502N, F657N and F763M in cycle 31. The first three filters are needed to measure the propagation of all the shock components and connect to the previous monitoring, while F763M will be used to search for signs of the compact object. To obtain a similar S/N as the previous observations, considering the fading of the system, we require one orbit each for F625W and F657N, and two orbits for F502N. The most interesting line from the compact object in the F763M filter is the [Ar III] 7753 line. Model predictions give a typical luminosity ~0.1* the [Ar II] 6.99 um luminosity, which results in a flux of 9 * 10^-17 erg cm^-2 s^-1. With a FWHM of 200 km s^-1, this results in a S/N ~14 in 6000 s. We therefore request two orbits with F763M to search for the compact object. Since 2003, all ACS and WFC3 imaging have used a fixed dither strategy to improve the spatial resolution, which will be repeated for consistency. COS spectrum: We will observe SN 1987A using central wavelength settings of the G130M (1291, 1318) and G160M (1600, 1611, 1623) gratings, which ensures continuous wavelength coverage at relatively constant S/N, and effectively performs a focal plane split to minimize fixed pattern noise. The 1318 setting for G130M is needed to provide continuous wavelength coverage across the full G130M spectral region and to compare with previous epochs of COS data. The limited spatial resolution of COS (about 1" in a 2.5" aperture) leaves some spatialspectral ambiguity in the deep spectral data. However, different emission components can be separated based on different line widths and Doppler shifts. While STIS would provide spatial information, its lower sensitivity makes it unsuitable for our objectives. We require a similar S/N as in the COS spectrum from 2017 (Fig. 7) to model the shocked emission from the ring and search for possible new lines from the compact object. Assuming that the UV flux from the ring has faded by 30% since 2017 (as in the optical), we require 3.5 orbits with G130M and 7 orbits with G160M. Combining these, and including extra time to account for the overheads introduced in Cycle 30 by the extra wavelength calibration at LP6, we require 11 orbits for the COS observations. We have run the Bright Object Tools and no bright object violations are detected. This, combined with the offset acquisition, makes the observations safe to execute. ------------------------------------------------------------------------------------ 17996( 2) - 15-Aug-2025 17:24:31 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 17996( 2) - 15-Aug-2025 17:24:31 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 17996( 2) - 15-Aug-2025 17:24:31 - [ 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 10-MAY-2026:00:00:00 AND 15-OCT-2026:00:00:00; SEQ 01, 02 WITHIN 14 D On Hold Comments: Additional Comments: The orienation constraints are set to make sure that the diffraction spikes from "Star 3" (Fig. 1 of the proposal) do not overlap with the emission from the SN. 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 CR-SPLIT=NO, FLASH=16 1 560 S PATTERN 1 1-3 S 1C-CTE (2240 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F502N CR-SPLIT=NO, FLASH=16 1 560 S S 1C-CTE (2240 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F657N CR-SPLIT=NO, FLASH=15 1 560 S S 1C-CTE (2240 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 N/A S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F502N 2 none none none 1 N/A S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F502N 3 none none none 2 N/A S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F502N 4 none none none 3 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 1 none none none 1 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 2 none none none 2 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 3 none none none 2 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F502N 4 none none none 3 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F657N 1 none none none 1 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F657N 2 none none none 2 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F657N 3 none none none 3 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F657N 4 none none none 3 N/A S K1C-CTE 17996( 2) - 15-Aug-2025 17:24:31 - [ 6] Visit: 02 Visit Requirements: ORIENT 78D TO 82 D; ORIENT 168D TO 172 D; ORIENT 258D TO 262 D; ORIENT 348D TO 352 D; SEQ 01, 02 WITHIN 14 D On Hold Comments: Additional Comments: The orienation constraints are set to make sure that the diffraction spikes from "Star 3" (Fig. 1 of the proposal) do not overlap with the emission from the SN. 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 F625W CR-SPLIT=NO, FLASH=5 1 562 S PATTERN 1 1-3 S 1C-CTE (2248 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F763M CR-SPLIT=NO, FLASH=11 1 562 S S 1C-CTE (2248 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN-1987A WFC3/UVI ACCUM UVIS2-C1K F763M CR-SPLIT=NO, FLASH=11 1 562 S S 1C-CTE (2248 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 F625W 1 none none none 1 N/A S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F625W 2 none none none 1 N/A S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F625W 3 none none none 2 N/A S K1C-CTE SN-1987A 1 WFC3/UVI ACCUM UVIS2-C1 F625W 4 none none none 3 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F763M 1 none none none 1 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F763M 2 none none none 2 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F763M 3 none none none 2 N/A S K1C-CTE SN-1987A 2 WFC3/UVI ACCUM UVIS2-C1 F763M 4 none none none 3 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F763M 1 none none none 1 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F763M 2 none none none 2 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F763M 3 none none none 3 N/A S K1C-CTE SN-1987A 3 WFC3/UVI ACCUM UVIS2-C1 F763M 4 none none none 3 N/A S K1C-CTE 17996( 2) - 15-Aug-2025 17:24:31 - [ 7] Summary Form for Proposal 17996 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-CTE ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO, FLASH=11, FLASH=15, FLASH=16, FLASH=5 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 10-MAY-2026:00:00:00 AND 15-OCT-2026:00:00:00, ORIENT 168D TO 172 D, ORIENT 258D TO 262 D, ORIENT 348D TO 352 D, ORIENT 78D TO 82 D, PATTERN 1 1-3, SEQ 01, 02 WITHIN 14 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F502N, F625W, F657N, F763M ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN-1987A ------------------------------------------------------------------------------------------------------------------------------------