0 Assigned ID: 3195 ----- Attempting Submission 1 (Fri Mar 25 12:05:36 GMT 2022) ----- HST Phase I Proposal 3195 successfully submitted. Receipt: # 3195-1 ----- Attempting Submission 2 (Fri Mar 25 20:25:05 GMT 2022) ----- HST Phase I Proposal 3195 successfully submitted. Receipt: # 3195-2 Split the F814W dither-pattern into three separate exposures with different FLASH levels. -474785343 ----- Attempting Submission 1 (Thu Jul 14 17:07:54 GMT 2022) ----- HST Phase II Proposal 17083 successfully submitted. Receipt: # 17083-1 ----- Attempting Submission 2 (Fri Sep 30 19:30:41 GMT 2022) ----- HST Phase II Proposal 17083 successfully submitted. Receipt: # 17083-2 ----- Attempting Submission 3 (Thu Oct 06 20:13:41 GMT 2022) ----- 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. 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. 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. Viraj Karambelkar - a third year graduate student at Caltech. Discovered and was the first author on the paper about the supernova. This project is part of his PhD thesis. Mansi Kasliwal - Professor of Astronomy at Caltech is Viraj's thesis advisor and has led various projects in time domain astronomy. Kate Maguire - Associate Professor of Physics at Trinity College Dublin is a world-expert on type Ia supernovae. The larger Zwicky Transient Facility team has the theoretical expertise to develop models of thermonuclear supernovae remnants to analyze and interpret the proposed observations. Stellar Physics and Stellar Types Stellar Populations and the Interstellar Medium 6 false false false false false false false SUPPORTED EXT-STAR SUPERNOVA SUPERNOVA TYPE IA J2000 J2000 WFC3/UVIS Imaging No No F625W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F125W POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 2 false 1665019179680 /Users/viraj/Documents/OP-cache/SN2021fcg_HST-v01.xml The scheduling data was generated by CASM 30.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17083 :visit-id "01" :proposal-version -1 :trans-version "20220516" :date "05-Oct-2022 18:19:39.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 2568112 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17083 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17083 :visit-id "01" :orbit-number 1 :pcs-time 383 :si-vis-utilization 3157 :al-overhead-at-end 121 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3540 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17083 :visit-id "01" :orbit-number 2 :pcs-time 392 :si-vis-utilization 3148 :al-overhead-at-end 0 :internal-dur-at-end 443 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3540 :pcs-gap 0 ) true 2 0