One orbit was approved for GO/DD 12447. The PI was given permission to use time under his related approved GRB program, 12370, for subsequent observations of this GRB. To allow the second visit to go forward quickly, it was kept on the schedule as GO/DD 12447, but the orbit was charged to GO 12370. As a result, THE SECOND VISIT OF 12447 HAS THE PROPRIETARY PERIOD ASSOCIATED WITH 12370. We apologize for the confusion caused by this change. However, it was done to allow rapid observations of an unusual astrophysical object. We propose HST observations of the extraordinary transient, GRB 110328A. This object triggered the Swift automatic burst detection twice over the course of about ninety minutes, and has continued to be a bright X-ray source for the two days since. While this behavior might typically suggest a Galactic source, the high Galactic latitude of the object, and its coincidence with a star-forming galaxy at z=0.35 instead suggests a new type of extragalactic transient. WFC3 imaging in the optical and NIR will allow us to search for a varying point source to far greater depth than could be done from the ground, given the presence of an apparent host, and the use of the F160W filter may allow us to pierce enshrouding dust, if extinction is the reason for the present lack of a detection in the optical. While we do not yet know the astrophysical source of this transient, it appears unique among the hundreds of transients so far detected by Swift. This alone should provide strong grounds for HST observations of this unusual and potentially important object.

tbd COSMOLOGY 0 false 0.0 0.0 false false false false SUPPORTED EXT-STAR X-RAY TRANSIENT This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 16 44 49.9300 +57 34 59.70 J2000 WFC3/UVIS Imaging No No F606W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F160W WFC3/UVIS Imaging No No F606W POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false POS-TARG DITHER 1.908 LINE false false 2 41.788 WFC3-IR-DITHER-LINE 2 false POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 3 false POS-TARG DITHER 1.716 LINE 1.095 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 4 false The scheduling data was generated by CASM 19.0. CASM was run in Phase II mode. 1301886180000 237.0 (Tic-Visit :proposal-id 12447 :visit-id "01" :proposal-version -1 :trans-version "20100902" :date "06-Apr-2011 17:45:59.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1632256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12447 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12447 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2853 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3511 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 19.0. CASM was run in Phase II mode. 1303305851000 237.0 (Tic-Visit :proposal-id 12447 :visit-id "02" :proposal-version -1 :trans-version "20100902" :date "06-Apr-2011 18:57:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1632256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12447 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12447 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2853 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3511 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 19.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12447 :visit-id "03" :proposal-version -1 :trans-version "20100902" :date "06-Apr-2011 17:29:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1632256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12447 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12447 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2853 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3511 :pcs-gap 0 ) true 1 0