Resubmission. Changed aperture to WFC1-CTE, and center check box in dithering pattern. 219594968 ----- Attempting Submission 2 (Thu Aug 30 08:25:32 GMT 2012) ----- Pair-instability supernovae (PISN) may be the brightest and most energetic explosions in the Universe, arising from the most massive stars. However, they are rare! Only a single promising candidate has been published to date (SN 2007bi; Gal-Yam et al. 2009, Nature, 462, 624). During the last two years we have been monitoring a second good candidate, discovered by the Palomar Transient Factory - PTF10nmn, whose observed features (both light curve and spectra) closely resemble those of SN 2007bi. The SN, at redshift z=0.123, is now more than 1.5 years after peak brightness, but became nebular only around 100 days ago and is still visible; its late-time emission powered by the huge synthesized 56Ni mass and slowly declining. We propose to obtain accurate late-time photometry of the SN in order to measure the late-time decay rate and constrain the relevant physics (continued decline following the 56Co rate vs. possible contribution from late CSM interaction). We will acquire accurate photometry of the dwarf host galaxy (an important clue to the origin of these explosions) and determine the exact location of the SN within its host. This should serve future studies (after the SN light has completely disappeared) that will be able to unveil in detail the immediate surrounding of this SN, and test recent theoretical work concerning the nature of PISNe at low redshift galaxies. Two orbits imaging using ACS/WFC with optical band F625W. Scheduling requirement: We stress again that due to the fact that our target is already 2 years post maximum light and is fading away, and because a major goal is to obtain a precise localization within the host, we have requested that the observations will take place as early as possible within the cycle. This constraint has been reviewed and approved by the panel, and it would be of tremendous value if this observation is indeed scheduled to the very beginning (1st month) of the cycle! HOT STARS 12 false 0.0 0.0 false false false false SUPPORTED EXT-STAR SUPERNOVA J2000 J2000 ACS/WFC Imaging No No F625W POS-TARG DITHER 0.265 LINE 0.187 false true 69.05 4 20.67 ACS-WFC-DITHER-BOX 1 false The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. /private/var/folders/1y/bl53zcws0_l1hcr_g20v7h2m0000gn/T/OPVisit5784140481271777415.xml 1346314535719 (Tic-Visit :proposal-id 12983 :visit-id "01" :proposal-version -1 :trans-version "20120802" :date "30-Aug-2012 11:15:35.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12983 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12983 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2894 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3233 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12983 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3008 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3233 :pcs-gap 0 ) true 2 0