17083( 4) - 10-Oct-2022 18:04:26 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17083 Version: 4 Check-in Time: 10-Oct-2022 18:04:26 STScI Edit Number: 0 Title In search of the remnant of SN 2021fcg : detonation, deflagration or merger? ------------------------------------------------------------------------------------ Type Cycle GO 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Viraj Karambelkar California Institute of Technology Y CoI: Dr. Mansi Kasliwal California Institute of Technology N CoI: Dr. Kate Maguire University of Dublin, Trinity College N ------------------------------------------------------------------------------------ Abstract Type Ia supernovae are thermonuclear explosions that result in the detonation of a white dwarf. Type Iax supernovae are a peculiar, less energetic sub-class of SNe Ia in which the white dwarf is believed to survive the explosion. This leaves behind a bound remnant, that is detectable at late-times when the supernova emission has faded. SN 2021fcg is a recently discovered unique member of this class. It is the lowest luminosity type Iax supernova as well as the least luminous thermonuclear explosion of any kind discovered to date. SN 2021fcg challenges the picture that SNe Iax originate in white dwarf deflagrations, and may hint towards a white dwarf merger origin. SN 2021fcg is also the nearest SN Iax discovered in the last decade, and provides an excellent opportunity to directly test the hypothesis that SNe Iax leave behind a bound remnant. Theoretical models predict that emission from the remnant will peak during HST Cycle 30. The supernova luminosity is also expected to be significantly lower than the predicted remnant luminosity during Cycle 30, making it feasible to detect the bound remnant in this cycle. We propose to conduct late-time multi-band optical and near-infrared imaging of SN 2021fcg using HST WFC3 to search for the bound remnant and determine the remnant properties. ------------------------------------------------------------------------------------ Observations Description ------------------------ The aim of this proposal is to use two HST orbits to image the location of SN 2021fcg using WFC3 UVIS F625W, F814W and IR F125W filters to search for a possible bound remnant. We plan to conduct dithered observations in these three filters, with exposure times of 1800 sec, 1700 sec and 2000 sec respectively. Using the WFC3 Exposure Time Calculator, we estimate depths of ~27 mag with S/N ~ 5 in each filter. These exposures together with all observing overheads amounts to 2 HST orbits. As shown in Fig. 2 (Phase I proposal), this sensitivity will be sufficient to detect the SN remnant based on model predictions as well as previous observations of the similar SN 2008ha. In particular, the remnant will be detected in all three filters if it has a high envelope entropy, but F125W observations are crucial to detect it if the envelope entropy is low. As shown in Fig 3, the multi-band observations are necessary to accurately identify the nature of the detected source and determine the mass and entropy of the remnant. Both detections and non-detections will help us constrain these properties of the remnant. 17083( 4) - 10-Oct-2022 18:04:26 - [ 2] We emphasize that Cycle 30 is an ideal time to search for the remnant of SN 2021fcg. First, on account of the extremely low luminosity and fast evolution rate of SN 2021fcg, the supernova emission is expected to fade below the remnant luminosities during Cycle 30 - merely 500 days since explosion. This is in stark contrast to brighter SNe Iax like SN2012Z, where significant supernova emission was seen even 3 years since explosion (McCully et al. 2022). Secondly, several theoretical models predict that the emission from the remnant should peak during Cycle 30 (Fig. 2). Throughout Cycle 30, SN 2021fcg is schedulable for several windows of ~2 week duration each. Therefore we do not place any constraints on the timing of HST observations. We do not expect a reduced gyro mode to affect our observations significantly. ------------------------------------------------------------------------------------ 17083( 4) - 10-Oct-2022 18:04:26 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SN2021FCG EXT-STAR, SUPERNOVA, RA=09H04M32.5700S +/- 0.5", J2000 Z = V = 27 SUPERNOVA TYPE IA DEC=+85D29'48.51" +/- 0.5" 0.0054 Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 17083( 4) - 10-Oct-2022 18:04:26 - [ 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-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17083( 4) - 10-Oct-2022 18:04:26 - [ 5] Visit: 01 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 SN2021FCG WFC3/UVI ACCUM UVIS2-FIX F625W FLASH=2 1 600 S PATTERN 1 1 S (1732 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN2021FCG WFC3/UVI ACCUM UVIS2-FIX F814W FLASH=7.0 1 436 S (436 POS TARG 0.000, 0.000 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN2021FCG WFC3/UVI ACCUM UVIS2-FIX F814W FLASH=7.0 1 435 S (435 POS TARG 0.092, 0.098 S S) ------------------------------------------------------------------------------------------------------------------------------------ 4 SN2021FCG WFC3/UVI ACCUM UVIS2-FIX F814W 1 769 S (769 POS TARG 0.185, 0.197 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 SN2021FCG WFC3/IR MULTIAC IR F125W NSAMP=11, SAMP-SEQ=STEP100 1 DEF PATTERN 2 5 CUM (1996.928 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN2021FCG 1 WFC3/UVI ACCUM UVIS2-FI F625W 1 none none none 1 N/A S X SN2021FCG 1 WFC3/UVI ACCUM UVIS2-FI F625W 2 none none none 1 N/A S X SN2021FCG 1 WFC3/UVI ACCUM UVIS2-FI F625W 3 none none none 1 532.0 S S X SN2021FCG 2 WFC3/UVI ACCUM UVIS2-FI F814W none none none none 1 N/A S X SN2021FCG 3 WFC3/UVI ACCUM UVIS2-FI F814W none none none none 1 N/A S X SN2021FCG 4 WFC3/UVI ACCUM UVIS2-FI F814W none none none none 2 N/A S X SN2021FCG 5 WFC3/IR MULTIAC IR F125W 1 none none none 2 N/A CUM SN2021FCG 5 WFC3/IR MULTIAC IR F125W 2 none none none 2 N/A CUM SN2021FCG 5 WFC3/IR MULTIAC IR F125W 3 none none none 2 N/A CUM SN2021FCG 5 WFC3/IR MULTIAC IR F125W 4 none none none 2 N/A CUM 17083( 4) - 10-Oct-2022 18:04:26 - [ 6] Summary Form for Proposal 17083 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, UVIS2-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=2, FLASH=7.0, NSAMP=11, SAMP-SEQ=STEP100 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 2 5, POS TARG 0.000, 0.000, POS TARG 0.092, 0.098, POS TARG 0.185, 0.197 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125W, F625W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN2021FCG ------------------------------------------------------------------------------------------------------------------------------------