Resubmitting to correct proprietary period to 3 months -682895461 Assigned ID: 658 ----- Attempting Submission 1 (Wed Jan 30 17:21:51 GMT 2019) ----- HST Phase I Proposal 658 (16aqy-prop.apt) successfully submitted. Receipt: # 658-1 ----- Attempting Submission 2 (Wed Jan 30 17:31:17 GMT 2019) ----- Target is fading, so sooner observations can be scheduled the better. FLASH was recommended for UVIS observations. I read the handbook, but have not used FLASH before, so please check that I am using it correctly to minimise CTE losses. Thanks! 2000345954 ----- Attempting Submission 1 (Mon Mar 18 13:07:18 GMT 2019) ----- Supernovae that strongly interact with their immediate environments offer a unique way to probe mass loss from very massive stars, with critical implications for understanding stellar evolution and the expected distribution of remnant masses. We have discovered one of the most extreme interacting supernovae to date, PS16aqy, at a redshift of 0.265 but with no detectable host galaxy in ground-based imaging. We have conducted a multi-year follow-up campaign revealing a very slowly fading light curve and a radiated energy well in excess of the canonical 1e51 erg supernova explosion energy. It may in fact exceed the electromagnetic output of any previous SN. Spectroscopy shows narrow and intermediate Balmer emission lines that persist throughout its evolution. The combination suggests ongoing interaction with several tens of solar masses of circumstellar medium. This requirement for very high mass and explosion energy may be indicative of an extremely massive star and possibly a pair instability or pulsational pair instability supernova, critical for our understanding of stellar evolution. The transient is now sufficiently faint that it can only be studied using HST. A single optical image will extend our temporal baseline for light curve modelling by 50%, enabling much tighter constraints on the properties of the CSM, which is the key to understanding this event. At the same time a high resolution UV image of the host galaxy will allow us to determine the star-formation rate at the explosion site as a clue to the progenitor mass. This proposal could not be submitted during the regular Call for Proposals as no Small Programs were permitted in the original Cycle 26 call. We propose to obtain an optical image of supernova PS16aqy in Cycle 26 using the Advanced Camera for Surveys (ACS) in the F775W filter, where we expect the transient to be brightest due to the presence of H-alpha emission, and a UV image of the host galaxy using Wide Field Camera 3 (WFC3) in the F390W filter, corresponding to rest-frame 3000 Angstroms. Taking into account the visibility window per orbit of 60 min, and the time needed for guide star acquisition, dithering (in a standard 4 point pattern) and per-exposure overheads for each instrument, the available time per orbit for integration on the target is about 2500s for ACS, and 2700s for WFC3. We expect to detect the transient with S/N > 20 and the galaxy with S/N > 10. Stellar Physics 3 false false false false false false false SUPPORTED EXT-STAR SUPERNOVA NO J2000 J2000 The scheduling data was generated by CASM 26.0. CASM was run in Phase I mode. WFC3/UVIS Imaging No No F390W The scheduling data was generated by CASM 26.2.2. CASM was run in Phase I mode. ACS/WFC Imaging No No F775W POS-TARG DITHER 0.262 LINE 0.192 false false 68.14 4 18.39 ACS-WFC-DITHER-BOX 1 false POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 2 false 1552914303541 /private/var/folders/ns/25q469zs20l23n94vz7hz99m0000gn/T/OPVisit6008776601664447095.xml The scheduling data was generated by CASM 26.2.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15709 :visit-id "01" :proposal-version -1 :trans-version "20181130" :date "18-Mar-2019 13:05:03.0" :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 2291872 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15709 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 15709 :visit-id "01" :obset-id "A1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15709 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3190 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3525 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15709 :visit-id "01" :orbit-number 2 :pcs-time 333 :si-vis-utilization 3191 :al-overhead-at-end 121 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3525 :pcs-gap 0 ) true 2 0