14484( 2) - 10-Feb-2016 21:31:49 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14484 Version: 2 Check-in Time: 10-Feb-2016 21:31:49 STScI Edit Number: 1 Title PS15dpn - a very unusual transient discovered by Pan-STARRS. ------------------------------------------------------------------------------------ Type Cycle GO/DD 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kenneth Chambers University of Hawaii Y CoI: Dr. Stephen J. Smartt The Queen's University of Belfast Y CoI: Dr. Armin Rest Space Telescope Science Institute Y CoI: Prof. Christopher W. Stubbs Harvard University N ------------------------------------------------------------------------------------ Abstract We have discovered a most unusual transient PS15dpn, which is quite unlike any other SN that Pan-STARRS or PESSTO has seen in several years of surveying. It has a fast rise (less than 8 days) has a hot blackbody spectrum (Teff ~15000K) for more than 20 days which remains featureless apart from transitory helium lines. The spectrum has not cooled, which is very unusual for a supernova, even as it fades it remains blue. It has been detected at radio wavelengths with a luminosity similar to supernovae with relativistic outflows. It is 2 arcsec offset from a host galaxy at z=0.175, and hence is not an AGN or a tidal disruption event. We propose HST imaging as it rapidly fades to constrain the energetics and determine the physical origin. ------------------------------------------------------------------------------------ Observations Description ------------------------ PS15dpn is currently fading rapidly at 0.1 Mag per day. Unless there is some late time powering or change in SED (which would be exactly the type of behavior that we need to investigate), this will fade to around r=24 when it disappears behind the Sun and becomes inaccessible to HST on 11-Mar-2016. The luminosity evolution beyond this is quite uncertain, but if powered by 56Ni then it may hit the 56Co tail and decay at 1 mag per 100 days. There are other r-processed elements which may power GW counterparts (as discussed above), and again the lightcurve decline rate needs to be quantified to determine if there is radioactive powering or luminosity from another source such as internal engine. Engine driven, luminous supernovae are known to occur (e.g. Nicholl et al. 2015), but the central engine may be an accreting stellar mass black hole or a highly magnetized neutron star (a magnetar). To quantify this decline rate and constrain these possibilities we request three epochs 1. Epoch 1 (Two orbits with WFC3): 25-Feb -2016 to 11-Mar-2106. F475W (g-band) with a 4 point dither pattern will provide 4x300 seconds to give S/N=60 @ mag=24.0. Followed by F814W (i-band) 4x280 seconds giving S/N=76 for ABmag = 24.0. A second orbit is requested for H-band with WFC3, again using a 4-point dither, 4x700 seconds gives S/N = 26 at H=25 (ABmag). 2. Epoch 2 (One orbit with WFC3) : 28-June-2016 to 14-Jul-2016. This is the 14484( 2) - 10-Feb-2016 21:31:49 - [ 2] next window of observability. .We will repeat the F475W and F814W filter sequence exactlyt as above. This will recover the object down to a S/N=10 at magnitudes g= (ABmag) and i- (ABmag) 3. Epoch 3 (Two orbits with WFC3) : 22-Aug-2016 to 06-Sep-2016. Dependng on the outcome of Epoch 2. We will either repeat Epoch 1, or chose to drop g or H-band and put more time into the other two filters. We can not predict how this transient may evolve, and that is part of the justification for asking for this DDT. We will assume for the purposes of this proposal that we will repeat Epoch 1. We have been awarded 2 orbits for Epoch 1 in the first instance. ------------------------------------------------------------------------------------ 14484( 2) - 10-Feb-2016 21:31:49 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PS15DPN EXT-STAR, SUPERNOVA RA=02H32M59.7700S, J2000 V = 24 +/- 1 DEC=+18D38'7.10" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 14484( 2) - 10-Feb-2016 21:31:49 - [ 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: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 14484( 2) - 10-Feb-2016 21:31:49 - [ 5] Visit: 01 Visit Requirements: BETWEEN 31-JAN-2016:00:00:00 AND 11-MAR-2016:00:00:00 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 PS15DPN WFC3/UVI ACCUM UVIS2-C1K F475W FLASH=7 1 265 S PATTERN 1 1-2 S 1C-SUB (1060 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 PS15DPN WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=8 1 250 S S 1C-SUB (1000 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PS15DPN WFC3/IR MULTIAC IR-FIX F160W NSAMP=14, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 3 CUM (2611.753 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 | ------------------------------------------------------------------------------------------------------------------------------------ PS15DPN 1 WFC3/UVI ACCUM UVIS2-C1 F475W 1 none none none 1 N/A S K1C-SUB PS15DPN 1 WFC3/UVI ACCUM UVIS2-C1 F475W 2 none none none 1 N/A S K1C-SUB PS15DPN 1 WFC3/UVI ACCUM UVIS2-C1 F475W 3 none none none 1 N/A S K1C-SUB PS15DPN 1 WFC3/UVI ACCUM UVIS2-C1 F475W 4 none none none 1 N/A S K1C-SUB PS15DPN 2 WFC3/UVI ACCUM UVIS2-C1 F814W 1 none none none 1 N/A S K1C-SUB PS15DPN 2 WFC3/UVI ACCUM UVIS2-C1 F814W 2 none none none 1 N/A S K1C-SUB PS15DPN 2 WFC3/UVI ACCUM UVIS2-C1 F814W 3 none none none 1 N/A S K1C-SUB PS15DPN 2 WFC3/UVI ACCUM UVIS2-C1 F814W 4 none none none 1 N/A S K1C-SUB PS15DPN 3 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 2 N/A CUM PS15DPN 3 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 2 N/A CUM PS15DPN 3 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 2 N/A CUM PS15DPN 3 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 2 N/A CUM 14484( 2) - 10-Feb-2016 21:31:49 - [ 6] Summary Form for Proposal 14484 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-FIX, UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=7, FLASH=8, NSAMP=14, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 31-JAN-2016:00:00:00 AND 11-MAR-2016:00:00:00, PATTERN 1 1-2, PATTERN 2 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W, F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PS15DPN ------------------------------------------------------------------------------------------------------------------------------------