We propose deep Chandra observations of ACT-CL J0102-4915, the brightest Sunyaev-Zeldovich effect cluster discovered by the Atacama Cosmology Telescope and South Pole Telescope surveys. These surveys covered approximately 3000 square degrees and are essentially complete to high redshift. Our recent Chandra and VLT optical data reveal ACL-CL J0102-4915 to be undergoing a major merger. It is likely a high redshift (z=0.870) counterpart to the famous ‘‘bullet’’ cluster. New Chandra data will determine the properties of the merger shock and the HST/ACS data will provide a weak lensing mass map.

The target is a rich cluster of galaxies at a redshift of 0.87. The observation goals are to obtain a weak lensing mass measurement and to map the dark matter distribution for comparison with Chandra X-ray data. The cluster is clearly undergoing a major merger and there are two main galaxy distributions separated by 1.2 arcminutes. We will perform a 2 point mosaic in order to cover both galaxy distributions and most of the extent of the X-ray emission. Each pointing is approximately centered on a peak in the galaxy distribution which also allows for a significant region of overlap between the 2 pointings. As clearly stated in our proposal, the alignment of the two galaxy peaks requires us to restrict the orientation angle of the WFC/ACS pointings. The required values are 324 deg for the NW pointing and 322 deg for the SE pointing with an acceptable range of +/- 5 degrees. The given "Fixed Targets" coordinates were optimised for these roll angles. At each point in the mosaic we use one orbit per filter (F625W, F773W, and F850LP). To ensure optimal overlap between these images for color segregation of the galaxies, we schedule each pointing as a separate visit consisting of 3 orbits. We use a 4-point box dither pattern intended to perform 1/2 subpixel sampling and cover the chip gaps of ACS/WFC. COSMOLOGY 12 false 0.0 0.0 false false false false SUPPORTED CLUSTER OF GALAXIES GRAVITATIONAL LENS HIGH REDSHIFT CLUSTER RICH CLUSTER J2000 J2000 CLUSTER OF GALAXIES GRAVITATIONAL LENS HIGH REDSHIFT CLUSTER RICH CLUSTER J2000 J2000 ACS/WFC Imaging No No F625W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F850LP POS-TARG DITHER 5.943 LINE 3.077 false false 166.993 4 91.429 ACS-WFC-DITHER-BOX 1 false The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12755 :visit-id "01" :proposal-version -1 :trans-version "20110811" :date "03-Oct-2011 18:42:47.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 3410688 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12755 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12755 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3056 :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 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12755 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3168 :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 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12755 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3167 :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 3391 :pcs-gap 0 ) false 3 0 The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12755 :visit-id "02" :proposal-version -1 :trans-version "20110811" :date "03-Oct-2011 18:42:51.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 3410688 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12755 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12755 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3056 :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 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12755 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3168 :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 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12755 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3167 :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 3391 :pcs-gap 0 ) true 3 0