0 Assigned ID: 5462 ----- Attempting Submission 1 (Tue Mar 26 16:03:30 GMT 2024) ----- I am resubmitting this proposal with the following changes: 1. The dither pattern has been changed from approximately 5 pixels to approximately 10 pixels 2. F160W observations (unaffected by airglow lines) have been placed before and after the F110W observations to mitigate the effects of He I contamination 3. NSAMP has been increased to provide sufficient datapoints to remove cosmic rays and other sources of bad pixels -996867098 ----- Attempting Submission 2 (Thu Oct 17 11:03:38 GMT 2024) ----- HST Phase II Proposal 17784 successfully submitted. Receipt: # 17784-2 ----- Attempting Submission 3 (Fri Oct 18 08:45:14 GMT 2024) ----- 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. 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 with 2x515s exposures over one orbit. The team have comprehensive expertise in the reduction and analysis of HST data, as well as data modelling. Dr. Morgan Fraser is an expert on core collapse supernovae and other optical transients, including gap transients. Beth Fitzpatrick is currently in the 3rd year of a PhD, supervised by Dr. Morgan Fraser. Her research is focused on gap transients. Stellar Physics and Stellar Types 6 false false false false false false false false SUPPORTED STAR LUMINOUS BLUE VARIABLE SUPERNOVA 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. J2000 J2000 WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 1 false POS-TARG DITHER 1.908 LINE false false 2 41.788 WFC3-IR-DITHER-LINE 2 false 1721297765456 /Users/bethfitzpatrick/Downloads/OP-cache/HST_phase2_edited-v01.xml The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 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(Tic-Visit :proposal-id 17784 :visit-id "02" :proposal-version -1 :trans-version "20240604" :date "18-Oct-2024 09:41:38.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 800800 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17784 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17784 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2580 :al-overhead-at-end 0 :internal-dur-at-end 500 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3023 :pcs-gap 0 ) true 1 0