0 Assigned ID: 1304 ----- Attempting Submission 1 (Mon Nov 28 20:51:14 GMT 2016) ----- 0 ----- Attempting Submission 1 (Mon Dec 05 23:11:18 GMT 2016) ----- The Dark Energy Survey (DES) has discovered DES16C2nm, a superluminous supernova (SLSN) at redshift of 1.998. DES16C2nm is the highest-redshift spectroscopically-classified supernova of any type ever discovered. The griz photometry from DES shows a flat, slightly rising light curve over the past 80 days (27 days rest-frame), and we estimate that DES16C2nm may be the most luminous SLSN ever discovered (Mu < -23). But our DES photometry only covers the rest-frame UV, making it impossible to accurately measure the bolometric luminosity of this event. Furthermore, the high redshift of this SN makes it possible to obtain photometry of the FUV region, essential for understanding how to find SLSNe at even higher redshifts. Finally, while we can confirm the classification and redshift of this object with our optical photometry, to fully compare with low-redshift SLSNe we need to obtain rest-frame optical spectra. We propose to use cadenced HST UV photometry along with NIR photometry and spectroscopy to obtain a complete picture of this unique, most distant ever supernova. We observe the z=1.9985 Superluminous Supernova DES16C2nm (H~23.2) with the F160W filter and take a spectrum using the G141 grism in order to constrain the rest-frame optical properties of this highest-redshift-ever spectroscopically-classified supernova. We assume the spectral shape of a blackbody with T=10000 K to estimate observing times. The G141 filter is 46.5A per pixel, which is 15.5A per pixel in the rest-frame. For a 'classifiable' spectrum, we want to obtain a minimum SNR of 3 per 10A resolution element, thus a minimum SNR of 3.7 per resolution element across the spectrum. This is achievable across the entirety of the sensitive range of the G141 filter (1.1-1.65 um) with an exposure of 2369s, with the peak SNR 50% higher than this minimum value. We conservatively suppose the SN may fade by ~ 0.5 mag by the time of our requested observations. To obtain 20-sigma detections (mag uncertainty 0.05) in the F160W filter, we estimate a 285s integration time. We use a two-point WFC3-IR-DITHER-BLOB dither pattern with a set of F160W and G141 spectra taken in each dither. This allows the F160W exposure to serve as a pointing constraint for the spectrum. The total exposure time in F160W in this visit is 306s, and the G141 spectrum is 2406s, exceeding both of our exposure time requirements. Stellar Physics Intergalactic Medium and Cosmology 12 SUPPORTED EXT-STAR SUPERNOVA The H-band flux is rather uncertain, as it is derived by fitting a blackbody to the observed griz data and extrapolating a blackbody into the H-band (superluminous supernovae do not have very well-defined templates). The current magnitude could span from 22.9 - 23.6. The host galaxy is 1.5 magnitudes fainter in the both the DES i and z filters than the target. The galaxy's H-band magnitude is unknown. J2000 J2000 H = 23.2 WFC3/UVIS Imaging No No F390W WFC3/IR Imaging No No F160W WFC3/IR Spectroscopic No No G141 WFC3/UVIS Imaging No No F390W POS-TARG DITHER DITHER 4 5.183 WFC3-IR-DITHER-BOX-MIN false 74.653 true 0.365 0.572 2 41.859 POS-TARG WFC3-IR-DITHER-BLOB 18.528 2 false 1480966858930 /private/var/folders/m6/d113mjdd3nj6_m36qwtljxqw0000gn/T/OPVisit1244199468823026738.xml The scheduling data was generated by CASM 24.2. CASM was run in Phase II mode. A dithered set of exposures using the F160W filter followed by G141 spectra. (Tic-Visit :proposal-id 14899 :visit-id "01" :proposal-version -1 :trans-version "20160601" :date "05-Dec-2016 19:40:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 765984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14899 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14899 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2881 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3229 :pcs-gap 0 ) true 1 0