15482( 2) - 17-May-2018 16:11:47 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15482 Version: 2 Check-in Time: 17-May-2018 16:11:47 STScI Edit Number: 0 Title Unveiling the nature of GW170817 through late-time observations: A normal short GRB viewed off-axis or a unique event? ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Joseph Lyman The University of Warwick Y CoI: Prof. Andrew James Levan The University of Warwick N CoI: Prof. Nial Rahil Tanvir University of Leicester N CoI: Dr. Gavin Lamb University of Leicester N CoI: Dr. Ilya Mandel University of Birmingham N CoI: Dr. Andrew S. Fruchter Space Telescope Science Institute N CoI: Prof. Jens Hjorth University of Copenhagen, Niels Bohr N Institute CoI: Dr. Danny Steeghs The University of Warwick N CoI: Dr. Benjamin Paul Gompertz The University of Warwick N CoI: Dr. Samantha Oates The University of Warwick N CoI: Dr. Klaas Wiersema The University of Warwick N CoI: Tuomas Kangas Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract The first multi-messenger gravitational wave event, GW170817, continues to intrigue long after the fading of the fabled kilonova. The source is now detectable as a gamma-ray burst (GRB) afterglow, emitting synchrotron radiation across a wide range of electromagnetic frequencies. The continued, long rise of the afterglow thus far has shown the canonical beamed jet model, often used to interpret cosmological GRBs, is not correct for this event. Currently, competing models are able to reproduce the observed afterglow - these include the 'cocoon' and 'structured-jet' models. Distinguishing between these scenarios is vital to understanding the intrinsically subluminous GRB that accompanied GW170817, by either reconciling it with cosmological short GRBs (due to it being viewed off-axis), or confirming an entirely new means of gamma-ray production for this event. The coming months represent a crucial period of evolution for the afterglow light curve, where we have predicted it will peak and begin to decay. Observing the time of peak and the steepness of the decay are a means to directly distinguish between the competing models. Our proposed cadenced deep mid-cycle observations will provide the necessary coverage over this opportune epoch and will answer one of the outstanding mysteries of this unique event: the nature of the emission mechanism responsible for the GRB and afterglow. These results will shape future theoretical and observational effort in the new field of multi-messenger GW astrophysics. ------------------------------------------------------------------------------------ Observations Description ------------------------ This proposal will perform 2 deep observations of GW170817 at very late times to constrain its optical flux and investigate the associated GRB afterglow emission mechanism. 15482( 2) - 17-May-2018 16:11:47 - [ 2] Deep multi-orbit WFC3/UVIS imaging will be performed in the F606W filter utilising dithers. The strategy differs slightly from phase I in that we will perform 2 epochs of observations for 5 orbits each. We favour less epochs and better depth compared to phase I, owing to the increased fading of the source since proposal submission. Each observation will be split into 2+3 orbit visits. The 2-orbit visits have a window of 1 week and the subsequent associated 3-orbit visit can be performed anytime within several days afterward, to aid scheduability. Note CTE aperture will be used owing to the desire to cover the whole galaxy, and the fact that the object is in a region of reasonable background brightness. The WFC3-UVIS-MOS-DITH-LINE dither pattern has been used with adjusted point spacing to create a 6-point dither pattern since psf sampling, rather than chip gap coverage is desired. Observation 1 (to be scheduled around start of July) Visit 1A: 2 orbits - F606W - 4 point box dither spread over visit, 2 exposures per orbit Visit 1B: 3 orbits - F606W - 6 point dither (3 line x 2 point) spread over visit, 2 exposures per orbit Observation 2 (to be scheduled around middle of August) Visit 2A: 2 orbits - F606W - 4 point box dither spread over visit, 2 exposures per orbit Visit 2B: 3 orbits - F606W - 6 point dither (3 line x 2 point) spread over visit, 2 exposures per orbit ------------------------------------------------------------------------------------ 15482( 2) - 17-May-2018 16:11:47 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 GW170817 GALAXY, UNDESIGNATED RA=13H09M48.0800S, J2000 V = 26.4 +/- 0.1 DEC=-23D22'53.20" Reference Frame: ICRS Comments: Actual flux at time of observations not known, is likely to be fading and will be somewhere 26.5-27 in V. ------------------------------------------------------------------------------------------------------------------------------------ 15482( 2) - 17-May-2018 16:11:47 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-MOS-DITH-LINE WFC3-UVIS-MOS-DITH-LINE Pattern_Purpose DITHER DITHER Number_Of_Points 3 2 Point_Spacing 0.135 0.119 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.754 33.606 Angle_Between_Sides Center_Pattern YES NO ------------------------------------------------------------------------------------------------------------------------------------ 15482( 2) - 17-May-2018 16:11:47 - [ 5] Visit: 1A Visit Requirements: BETWEEN 08-JUL-2018:00:00:00 AND 15-JUL-2018:00:00:00 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 GW170817 WFC3/UVI ACCUM UVIS2 F606W 1 600 S PATTERN 1 1 S see below (5606 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 | ------------------------------------------------------------------------------------------------------------------------------------ GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 1 none none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 2 none none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 3 none none none 2 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 4 none none none 2 1429.0 S S 15482( 2) - 17-May-2018 16:11:47 - [ 6] Visit: 1B Visit Requirements: SAME ORIENT AS 1A; AFTER 1A BY 0 Orbits TO 4 D 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 GW170817 WFC3/UVI ACCUM UVIS2 F606W 1 600 S PATTERN 3 1 S see below (8464 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 | ------------------------------------------------------------------------------------------------------------------------------------ GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 1 1 none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 1 2 none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 2 1 none none 2 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 2 2 none none 2 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 3 1 none none 3 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 3 2 none none 3 1429.0 S S 15482( 2) - 17-May-2018 16:11:47 - [ 7] Visit: 2A Visit Requirements: BETWEEN 14-AUG-2018:00:00:00 AND 21-AUG-2018:00:00:00 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 GW170817 WFC3/UVI ACCUM UVIS2 F606W 1 600 S PATTERN 1 1 S see below (5606 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 | ------------------------------------------------------------------------------------------------------------------------------------ GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 1 none none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 2 none none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 3 none none none 2 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 4 none none none 2 1429.0 S S 15482( 2) - 17-May-2018 16:11:47 - [ 8] Visit: 2B Visit Requirements: SAME ORIENT AS 2A; AFTER 2A BY 0 Orbits TO 4 D 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 GW170817 WFC3/UVI ACCUM UVIS2 F606W 1 600 S PATTERN 3 1 S see below (8464 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 | ------------------------------------------------------------------------------------------------------------------------------------ GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 1 1 none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 1 2 none none 1 1374.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 2 1 none none 2 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 2 2 none none 2 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 3 1 none none 3 1429.0 S S GW170817 1 WFC3/UVI ACCUM UVIS2 F606W 3 2 none none 3 1429.0 S S 15482( 2) - 17-May-2018 16:11:47 - [ 9] Summary Form for Proposal 15482 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 1A BY 0 Orbits TO 4 D, AFTER 2A BY 0 Orbits TO 4 D, BETWEEN 08-JUL-2018:00:00:00 AND 15-JUL-2018:00:00:00, BETWEEN 14-AUG-2018:00:00:00 AND 21-AUG-2018:00:00:00, PATTERN 1 1, PATTERN 3 1, SAME ORIENT AS 1A, SAME ORIENT AS 2A ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names GW170817 ------------------------------------------------------------------------------------------------------------------------------------