changed cycle ----- Attempting Submission 3 (Fri Jul 01 17:55:35 GMT 2011) ----- We propose to obtain two epochs of WFC3/IR imaging of the counterpart of the soft gamma-repeater, SGR 0501+4516 to measure its proper motion and hence identify its birth place and constrain its age in a model independent manner. Our ground based observations have already located the optical/IR counterpart, and provided proper motion limits of <70 mas/yr. The source has now faded significantly since its first discovery and is becoming too faint for detailed ground based study. Using the excellent point spread function, wide field of view, astrometric stability, and sensitivity of WFC3, we can now make use of HST to directly measure the proper motion of an SGR for the first time. The location of SGR 0501+4516 in the Galactic anti-centre direction, with a likely low distance (~1.5 kpc), coupled with moderate foreground extinction, and no issues of crowding makes it the only SGR source for which such observations are plausible with current technology. Our proposed observations (one in Cycle 18 and one in Cycle 19) with a baseline of ~2 years should constrain the proper motion to better than 3-4 milliarcseconds per year (3 sigma), corresponding to spatial velocities of less than 25 km/s, smaller than the velocities observed for many radio pulsars. Hence we can place the first direct constraints on the kick velocities given to magnetars at their birth, as well as testing models for their age and evolution, and informing estimates of their rate of creation.

We propose to obtain a proper motion for SGR 0501+4516 via two epochs of observations. One will be taken early in Cycle 18, with a second visit to follow towards the end of Cycle 19, providing a time baseline of ~2 years. We will use the WFC3 IR channel and the F160W observations. We will use a 4 point dither pattern, but have multiplied the standard offsets by a factor of 3 to enable bright stars (which may leave persistence) to be well removed from eachother and hence possible to centroid with accuracy. Additionally we have specified a restricted range of roll angles, such that diffraction spikes from a bright object in the field at large angular spearation, and from fainter, but closer, objects will not overlap our target position. HOT STARS 12 false 0.0 0.0 false false false false SUPPORTED STAR NEUTRON STAR J2000 J2000 K=20.2 WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F160W POS-TARG DITHER 1.716 LINE 1.095 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. 1309530783033 (Tic-Visit :proposal-id 12672 :visit-id "01" :proposal-version -1 :trans-version "20110509" :date "01-Jul-2011 15:33:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 974880 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12672 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12672 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3028 :al-overhead-at-end 0 :internal-dur-at-end 711 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) false 1 0