The advent of wide-field optical time-domain surveys is providing an opportunity to discover and decipher new classes of astronomical transient phenomena. One of the most unexpected results from Pan-STARRS and other time-domain surveys is the discovery of ultra-luminous supernovae (ULSNe), with bolometric luminosities up to 100 times higher than normal core-collapse and Type Ia supernovae (SNe), and with spectra that do not match known SN classes. These ULSNe represent a new challenge to our understanding of the deaths of massive stars, the standard core-collapse picture, and the mechanism for powering optical emission in SNe. Progress in our understanding of these mysterious explosions requires detailed studies of their light curves and spectra (available from our Pan-STARRS data and ground-based follow-up), and studies of their galactic and sub-galactic environments - the focus of this HST proposal. We propose to take advantage of HST's superb angular resolution to study the locations of the ULSNe relative to their host UV light distribution as a probe of the progenitor population (similar studies of GRBs and core-collapse SNe suggest distinct types of massive star progenitors). Seven Pan-STARRS ULSN hosts will have HST imaging through our existing Cycle 19 and 20 programs, and here we propose to essentially double that sample and obtain rest-frame UV imaging of another 6 ULSN hosts (ranging in brightness from 22-25.5 mag). This will bring the Pan-STARRS sample to a comparable number as the GOODS core-collapse SNe and GRB hosts, which are also well-matched to the Pan-STARRS sample in redshift, allowing for a detailed statistical comparison between the populations. We wish to image six ULSN host galaxies with HST/ACS, in filters corresponding to rest-frame UV emission. For the three lower-redshift (z~0.6) targets, we use F475W, and for the three higher-redshift targets (z~1.4) we use F814W. The magnitudes of our targets are known from ground-based imaging range from 22-25.5, and so one orbit per target is sufficient. We use a standard four-point dither pattern for better PSF subsampling. UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE Default false false false false false SUPPORTED GALAXY UNDESIGNATED J2000 J2000 GALAXY UNDESIGNATED J2000 J2000 GALAXY UNDESIGNATED J2000 J2000 GALAXY UNDESIGNATED J2000 J2000 GALAXY UNDESIGNATED J2000 J2000 GALAXY UNDESIGNATED J2000 J2000 ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F814W POS-TARG DITHER 0.265 LINE 0.187 false false 69.05 4 20.67 ACS-WFC-DITHER-BOX 1 false The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13326 :visit-id "01" :proposal-version -1 :trans-version "20130502" :date "21-Jun-2013 15:48:13.0" :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 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13326 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13326 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2894 :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 3229 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13326 :visit-id "02" :proposal-version -1 :trans-version "20130502" :date "21-Jun-2013 15:48:35.0" :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 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13326 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13326 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3158 :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 3491 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13326 :visit-id "03" :proposal-version -1 :trans-version "20130502" :date "21-Jun-2013 15:49:01.0" :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 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13326 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13326 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2998 :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 3333 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13326 :visit-id "04" :proposal-version -1 :trans-version "20130502" :date "18-Jun-2013 14:44:02.0" :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 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13326 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13326 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2894 :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 ) false 1 0 The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13326 :visit-id "05" :proposal-version -1 :trans-version "20130502" :date "18-Jun-2013 14:45:04.0" :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 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13326 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13326 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2894 :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 3229 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13326 :visit-id "06" :proposal-version -1 :trans-version "20130502" :date "21-Jun-2013 15:49:23.0" :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 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13326 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13326 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2918 :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 3253 :pcs-gap 0 ) true 1 0