14743( 5) - 13-Mar-2017 14:18:44 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14743 Version: 5 Check-in Time: 13-Mar-2017 14:18:44 STScI Edit Number: 3 Title Determining the explosion mechanism of a superluminous supernova through the deepest ever late-time study ------------------------------------------------------------------------------------ Type Cycle GO 24 ------------------------------------------------------------------------------------ Investigators Contact? PI: Matt Nicholl Harvard University Y CoI: Prof. Edo Berger Harvard University N CoI: Prof. Ryan Chornock Ohio University N CoI: Mr. Peter Blanchard Harvard University N ------------------------------------------------------------------------------------ Abstract The superluminous supernova (SLSN) SN 2015bn is one of the three nearest objects of its kind to date, and is now the best studied. However, despite a wealth of observations within ~1 year of peak light, the explosion mechanism remains elusive. Here we propose to distinguish between the popular scenarios of magnetar spin-down, circumstellar interaction and pair-instability explosion, by obtaining the latest and deepest ever images of a SLSN at around 2 years after explosion. At this phase, competing models predict robust colour differences, which we can detect in 3 orbits of HST+ACS observations (with 3 more orbits in the following cycle required for host galaxy template subtraction, also leading to a detailed host analysis). In the decade or so since the first SLSNe were discovered, no event has had the combination of late-time luminosity, proximity and a sufficiently faint host to be able to follow to such a late phase. We stress that these observations are new, timely, and only possible for ~1 SLSN per decade. Furthermore, we have a robust magnitude prediction based on extensive data, and the colour test we wish to perform is powerful yet relatively straightforward, and only possible using HST. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will use 3 orbits in Cycle 24 to observe SN 2015bn with the Advanced Camera for Surveys in the F475W, F625W and F775W filters, and 3 orbits in Cycle 25 to obtain images of the host galaxy in the same filters and with the same depth, after the SN has disappeared (during the same months in Cycle 25, the SN flux will be negligible, at r >30). These filters have been specifically chosen to cover the wavelength range where we expect most of the SN light to be concentrated. Taking into account the visibility window per orbit of ~54 min based on the target declination, and the time needed for guide star acquisition, dithering (in a standard 4 point pattern) and per-exposure overheads, the available time for integration on the target is ~2100 s in each orbit. Using this exposure time in each filter (i.e. 3 orbits total), the SN should be detectable with S/N >~ 5. If it has faded faster than expected, we will stack the exposures in a deep 'white-light' image to recover the SN. ------------------------------------------------------------------------------------ 14743( 5) - 13-Mar-2017 14:18:44 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SN2015BN+HOS GALAXY, DWARF COMPACT RA=11H33M41.5500S, J2000 Z = supernova: r = 28 AB mag, host: r = 22 T DEC=+00D43'33.40" 0.1136 AB mag Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 14743( 5) - 13-Mar-2017 14:18:44 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.262 Line_Spacing 0.192 Coordinate_Frame POS-TARG Pattern_Orient 18.39 Angle_Between_Sides 68.14 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 14743( 5) - 13-Mar-2017 14:18:44 - [ 4] 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 SN2015BN+HO ACS/WFC ACCUM WFC1 F775W 1 500 S GS ACQ SCENARIO BASE1B3; ST see below PATTERN 1 1 (2180 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN2015BN+HO ACS/WFC ACCUM WFC1 F625W 1 525 S PATTERN 1 2 ST see below (2356 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN2015BN+HO ACS/WFC ACCUM WFC1 F475W 1 525 S PATTERN 1 3 ST see below (2344 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN2015BN+HOST 1 ACS/WFC ACCUM WFC1 F775W 1 none none none 1 545.0 S SN2015BN+HOST 1 ACS/WFC ACCUM WFC1 F775W 2 none none none 1 545.0 S SN2015BN+HOST 1 ACS/WFC ACCUM WFC1 F775W 3 none none none 1 545.0 S SN2015BN+HOST 1 ACS/WFC ACCUM WFC1 F775W 4 none none none 1 545.0 S SN2015BN+HOST 2 ACS/WFC ACCUM WFC1 F625W 1 none none none 2 589.0 S SN2015BN+HOST 2 ACS/WFC ACCUM WFC1 F625W 2 none none none 2 589.0 S SN2015BN+HOST 2 ACS/WFC ACCUM WFC1 F625W 3 none none none 2 589.0 S SN2015BN+HOST 2 ACS/WFC ACCUM WFC1 F625W 4 none none none 2 589.0 S SN2015BN+HOST 3 ACS/WFC ACCUM WFC1 F475W 1 none none none 3 586.0 S SN2015BN+HOST 3 ACS/WFC ACCUM WFC1 F475W 2 none none none 3 586.0 S SN2015BN+HOST 3 ACS/WFC ACCUM WFC1 F475W 3 none none none 3 586.0 S SN2015BN+HOST 3 ACS/WFC ACCUM WFC1 F475W 4 none none none 3 586.0 S 14743( 5) - 13-Mar-2017 14:18:44 - [ 5] Summary Form for Proposal 14743 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO BASE1B3, PATTERN 1 1, PATTERN 1 2, PATTERN 1 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F625W, F775W ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN2015BN+HOST ------------------------------------------------------------------------------------------------------------------------------------