Assigned ID: 2029 ----- Attempting Submission 1 (Fri Jan 07 17:47:04 GMT 2011) ----- This is a resubmission which updates our submission yesterday since we believe we incorrectly specified orient constraints for a nearby bright star. The new submisison does include constraints closer to the available roll angles for HST over the next few days, however, they are also quite conservative and could potentially be shrunk to improve the visibility windows if necessary. ----- Attempting Submission 1 (Sat Jan 08 23:58:05 GMT 2011) ----- HST Phase II Proposal 12438 (12438_al.apt) successfully submitted. ----- Attempting Submission 2 (Sun Jan 09 22:09:34 GMT 2011) ----- On Christmas day 2010, Swift detected one of the most unusual gamma-ray bursts (GRBs) ever seen. It apparently persisted for well over 1000s, had an extremely bright, and long lived X-ray afterglow, followed by a remarkably rapid decay, and exhibited an even longer slow decline in its (very blue) optical lightcurve. Recent observations establish a spectroscopic redshift z=0.4, and so GRB 101225 is not a member of the low-luminosity (and hence low-redshift) class as had been suggested. This leads to the natural question of what can produce such an event? Is this a classical GRB from core collapse or an phenomena involving a galactic nucleus (its early lightcurve and optical spectral were reminscent of Blazars)? Could it be an unusual progenitor in a low density medium (e.g. stellar halo), or a chemically extremely unusual system (e.g. ultra-low metallicity). Our proposed HST observations will help to directly address these questions. We will i) track the light curve to late times, directly measuring the total energy of the explosions, and searching for any evidence of an associated supernova - a supernova comparable to those seen in many long-GRBs is already ruled out by the ground data, but is of course the key to definitely associating this burst with a core-collapse event; ii) precisely position the afterglow on its host galaxy using the invariant PSF of HST to obtain positions much more accurately than is possible from the ground, this will allow us to ascertain if the burst is coincident with the galactic nucleus with far greater confidence and relate the burst to any star-forming regions; iii) characterize the nature of the host galaxy in comparison with those of other GRBs, and hence provide critical clues to the nature of the progenitor.

The aim of this proposal is to obtain HST observations of GRB 101225A utilizing ACS in B and V. We will use observations in F435W and F606W and a three point dither (#13 from ISR 2001-07) to give us a total of 1020s and 880s in each filter respectively. We have shortened the first F606W exposure to avoid issues of buffer dumps within the single orbit observations, while the dither will allow us to remove cosmic rays and ensure against bad pixels etc. We have included a modest range of orient constraints to avoid diffraction spikes from a nearby bright star (R~19), although in practice these are not close to the available orients for the visit. COSMOLOGY 0 false 0.0 0.0 false false false false false false SUPPORTED UNIDENTIFIED ACCRETION DISK X-RAY EMITTER J2000 00 00 0.0000 +00 00 0.00 J2000 ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F606W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.138 LINE false false 3 32.99 ACS-WFC-DITHER-LINE 1 false The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1294609402607 /Users/levan/OP-cache/12438_orient-v01.xml (Tic-Visit :proposal-id 12438 :visit-id "01" :proposal-version -1 :trans-version "20100902" :date "09-Jan-2011 21:43:22.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1705344 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12438 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12438 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2973 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3341 :pcs-gap 0 ) true 1 0