0 Assigned ID: 1276 ----- Attempting Submission 1 (Thu Feb 04 17:04:19 GMT 2016) ----- HST Phase I Proposal 1276 (PS15dpn.apt) successfully submitted. Receipt: # 1276-1 ----- Attempting Submission 2 (Thu Feb 04 22:13:25 GMT 2016) ----- 0 0 ----- Attempting Submission 1 (Tue Feb 09 20:54:49 GMT 2016) ----- 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. 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 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. HOT STARS 0 SUPPORTED EXT-STAR SUPERNOVA NO J2000 J2000 WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 2 false 1455050949890 The scheduling data was generated by CASM 24.0. CASM was run in Phase II mode. /private/var/folders/fr/k6bfhfb52531wzb48c8t4kq80000gp/T/OPVisit4951434333920935832.xml (Tic-Visit :proposal-id 14484 :visit-id "01" :proposal-version -1 :trans-version "20160129" :date "09-Feb-2016 20:49:09.0" :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 1187120 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14484 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14484 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2866 :al-overhead-at-end 80 :internal-dur-at-end 31 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3221 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14484 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2840 :al-overhead-at-end 0 :internal-dur-at-end 652 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3221 :pcs-gap 0 ) true 2 0