15974( 2) - 25-Jul-2019 11:39:40 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15974 Version: 2 Check-in Time: 25-Jul-2019 11:39:40 STScI Edit Number: 0 Title Unmasking the cow: Distinguishing models for the unique transient AT2018cow ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Andrew James Levan Radboud Universiteit Nijmegen Y CoI: Dr. Daniel Perley Liverpool John Moores University N CoI: Prof. Nial Rahil Tanvir University of Leicester N CoI: Dr. Andrew S. Fruchter Space Telescope Science Institute N CoI: Tuomas Kangas Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract AT2018 is a transient unlike any seen before, unprecedented in its rapid rise time and high luminosity. It may well be a manifestation of one of two long sought after astrophysical phenomena: either an intermediate mass black hole, or a direct view to the central engine in a collapsing star. Here we propose a modest set of HST imaging observations to answer a vital question relating to AT2018cow -- where was it born? If it was created in the tidal disruption of a white dwarf star by an intermediate-mass black hole, we might expect to uncover a globular cluster at its location, since it is in these locations that IMBHs may exist with a sufficiently high stellar density for white dwarfs to be scattered into their loss cone. Alternatively, if the source of AT2018cow is a massive star, we should see signs of ongoing star formation. Our observations in H-alpha and the UV will probe very young, extremely massive (tens of solar masses) stars and distinguish them from somewhat older, less massive (~10 Msol) stars. Deep optical observations will uncover any underlying globular cluster directly. Through these observations, we will measure the environment in which AT2018cow was born, and through that environment, we will determine its origin. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to obtain three orbits of observations of AT2018cow after is has faded with the aim of understandings its environment. We will obtain images in two UV filters (F225W and F606W), two optical filters (F555W and F814W) and two narrow band filters (F665N and F657N, the first of these will be off-band at the redshift of AT2018cow, while the second will match with H-alpha). For each filter we will obtain 3 exposures along a standard line dither with an observation time of half an orbit. In order to fit within the orbit our UV and narrow band observations will use the UVIS2-C1K1C-SUB aperture to reduce overheads. For F555W and F814W it is possible to fit the observations within a single orbit while still using the full chip. We have requested that the observations be scheduled approximately within 1 month of eachother since if there is any residual transient flux the data will be most useful if they are approximately taken at the same time. 15974( 2) - 25-Jul-2019 11:39:40 - [ 2] ------------------------------------------------------------------------------------ 15974( 2) - 25-Jul-2019 11:39:40 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AT2018COWHOS UNIDENTIFIED, GAMMA RAY RA=16H16M0.2242S, J2000 V = 16 +/- 1 T EMITTER, RADIO EMITTER, DEC=+22D16'4.38" X-RAY EMITTER Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 15974( 2) - 25-Jul-2019 11:39:40 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 15974( 2) - 25-Jul-2019 11:39:40 - [ 5] Visit: 01 Visit Requirements: GROUP 01, 02, 03 WITHIN 30D 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 AT2018COWHO WFC3/UVI ACCUM UVIS2-C1K F665N FLASH=11 1 348 S PATTERN 1 1-2 ST S 1C-SUB see below (1119 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2018COWHO WFC3/UVI ACCUM UVIS2-C1K F657N FLASH=11 1 348 S ST S 1C-SUB see below (1119 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2-C1 F665N 1 none none none 1 373.0 S S K1C-SUB AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2-C1 F665N 2 none none none 1 373.0 S S K1C-SUB AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2-C1 F665N 3 none none none 1 373.0 S S K1C-SUB AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2-C1 F657N 1 none none none 1 373.0 S S K1C-SUB AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2-C1 F657N 2 none none none 1 373.0 S S K1C-SUB AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2-C1 F657N 3 none none none 1 373.0 S S K1C-SUB 15974( 2) - 25-Jul-2019 11:39:40 - [ 6] Visit: 02 Visit Requirements: GROUP 02, 01, 03 WITHIN 30D 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 AT2018COWHO WFC3/UVI ACCUM UVIS2-C1K F225W FLASH=11 1 348 S PATTERN 1 1-2 ST S 1C-SUB see below (1116 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2018COWHO WFC3/UVI ACCUM UVIS2-C1K F336W FLASH=11 1 348 S ST S 1C-SUB see below (1116 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2-C1 F225W 1 none none none 1 372.0 S S K1C-SUB AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2-C1 F225W 2 none none none 1 372.0 S S K1C-SUB AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2-C1 F225W 3 none none none 1 372.0 S S K1C-SUB AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2-C1 F336W 1 none none none 1 372.0 S S K1C-SUB AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2-C1 F336W 2 none none none 1 372.0 S S K1C-SUB AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2-C1 F336W 3 none none none 1 372.0 S S K1C-SUB 15974( 2) - 25-Jul-2019 11:39:40 - [ 7] Visit: 03 Visit Requirements: GROUP 03, 01, 02 WITHIN 30D 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 AT2018COWHO WFC3/UVI ACCUM UVIS2 F555W FLASH=4 1 348 S PATTERN 1 1-2 ST S (1044 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2018COWHO WFC3/UVI ACCUM UVIS2 F814W FLASH=5 1 348 S ST S (1044 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2 F555W 1 none none none 1 N/A S AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2 F555W 2 none none none 1 N/A S AT2018COWHOST 1 WFC3/UVI ACCUM UVIS2 F555W 3 none none none 1 N/A S AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2 F814W 1 none none none 1 N/A S AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2 F814W 2 none none none 1 N/A S AT2018COWHOST 2 WFC3/UVI ACCUM UVIS2 F814W 3 none none none 1 N/A S 15974( 2) - 25-Jul-2019 11:39:40 - [ 8] Summary Form for Proposal 15974 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2, UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=11, FLASH=4, FLASH=5 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 01, 02, 03 WITHIN 30D, GROUP 02, 01, 03 WITHIN 30D, GROUP 03, 01, 02 WITHIN 30D, PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F225W, F336W, F555W, F657N, F665N, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2018COWHOST ------------------------------------------------------------------------------------------------------------------------------------