The contemporaneous Chandra observations show that this burst is declining slowly. Our HST observations appear to confirm this -- though getting an optical magnitude without knowing the luminosity of the undertlying host galaxy leaves more room for error. We have therefore decided to go back to our original plan of three visits. The slow decay means we can afford to divide our remaining four orbits in half to accomplish this. ----- Attempting Submission 3 (Thu Aug 25 21:16:20 GMT 2011) ----- ----- Attempting Submission 4 (Fri Mar 02 22:59:59 GMT 2012) ----- We appreciate that we are not using one of the available patterns. The Astrophysics of the Most Energetic Gamma-Ray Bursts The Large Area Telescope (LAT) of Fermi has found a sample of highly relativistic gamma-ray bursts (GRBs), which may be among the most energetic bursts ever discovered. Here we propose to use Chandra and HST to follow the late time X-ray and optical light curves of a LAT detected burst that also has excellent early multiwavelength coverage. Our observations, in conjunction with the Fermi data, will allow us to measure the energy and the bulk Lorentz factor of the explosion. Recent work on some of the most powerful GRBs begins to substantially constrain physical models of the progenitors. The energetics of the highly relativistic LAT bursts may greatly strengthen these constraints and provide new insight into the currently unknown mechanism that determines the energy in a GRB. We plan three visits with HST: the first an orbit long, a second two orbits long, and a third four orbits long. The first visit will occur about around twenty days after outburst. The second will be around forty days after outburst. The exact times will be scaled according to the decay seen from the ground. The third visit will be taken at least six months after the burst to allow an accurate host subtraction. We will use the UVIS camera on WFC3 because WFC3 easily has as good sensitivity on point sources as ACS with smaller detector-induced noise sources (CTE, bias-striping, etc). We will choose the filter at the time of the ToO to match one of the best observed bands from the ground (most likely a red band). If the OT and host are sufficiently bright in the first two epochs we will divide the last epoch into 3 orbits with WFC3/UVIS and one orbit with WFC3/IR, in order to better study the environment underlying this extremely energetic burst. 12 false 0.0 0.0 false false false false SUPPORTED EXT-STAR GAMMA RAY BURSTER J2000 WFC3/UVIS Imaging No No WFC3/UVIS Imaging No No WFC3/UVIS Imaging No No POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER DITHER 2 0.173 WFC3-UVIS-DITHER-LINE 0.112 false false 81.785 0.145 4 23.884 POS-TARG BOX 46.84 2 true The scheduling data was generated by CASM 20.0. 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