0 Assigned ID: 441 ----- Attempting Submission 1 (Fri Apr 11 12:32:15 GMT 2014) ----- 0 ----- Attempting Submission 1 (Thu Jul 17 12:28:51 GMT 2014) ----- The evolutionary link between low-mass X-ray binaries and millisecond radio pulsars Low-mass X-ray binaries (LMXBs) and millisecond radio pulsars (MSRPs) are two different manifestations of neutron stars in binary systems. They are thought to be evolutionary linked, but many questions about their connection remain. Recent discoveries have opened up a new vista to investigate the LMXB/MSRP link. The neutron star XSS J12270-4859 was recently observed to switch between the two different manifestations. Here, we propose to exploit the unique UV capabilities of the HST to search for the presence of a quiescent accretion disk and to test if the neutron star is hot. This will give insight into its accretion history and the mechanism driving its metamorphosis, which will have direct implications for our understanding of the LMXB/MSRP evolutionary link. Detecting a quiescent accretion disk or a hot neutron star in our target requires observations in the NUV/FUV bands. Observations with the Swift/UVOT (during the current MSRP state) are not sensitive enough to detect the source in the NUV: uvw1 > 19.7 mag (lambda_c~2600 A), uvm2 > 19.7 mag (lambda_c~2246 A), and uvw2 > 20.2 mag (lambda_c~1928 A). This corresponds to NUV fluxes of <5E-17 erg/cm2/s/A, which is well above that expected for a quiescent accretion disk or a hot neutron star (~1-5E-18 erg/cm2/s/A). Our science goals therefore require the unprecedented UV sensitivity of the HST. Given the unknown NUV/FUV magnitude of our target, we propose HST imaging observations. To be able to determine the shape of the UV spectral energy distribution and to measure UV colors, we request observations using different NUV/FUV filters. To achieve the best sensitivity (our target is not in a crowded field), we chose the WFC3/UVIS for the NUV, and the ACS/SBC for the FUV. For the WFC3/UVIS we will use 3 filters: F218W (lambda_c~2224 A), F225W (lambda_c~2359 A), and F275W (lambda_c~2704 A), and for the ACS/SBC we use 1 filter: F150LP (lambda_c~1500 A). We used the online WFC3/UVIS and ACS/SBC exposure time calculators (v. 22.2). The distance to our target is 3.6 kpc, and the reddening is E(B-V)=0.577. Detecting a hot neutron star poses the strongest constraints on the science exposures. We assumed a black body of ~3.5E5 K (corresponding to the lowest neutron star temperatures in LMXBs), which yields a flux of ~1E-18 (NUV) and ~1.5E-18 erg/cm2/s/A (FUV). We aim for a SNR>10 at these fluxes. For a remnant accretion disk we expect a higher flux (a black body with a temperature of ~1E4 K, or a luminosity of ~8E30 erg/s, the coldest detected in quiescent LMXBs, would lead to FUV/NUV fluxes of ~5E-18 erg/cm2/s/A), and hence a higher SNR. We used dither patterns for all science observations and for the WFC2/UVIS exposure time calculation we took into account lamp flashes to ensure that the minimum background for proper CTE is reached. Some of the required UVIS exposures were >3600 s, which we then split into two. We require 2 orbits of ACS/SBC observations, and 4 orbits of WFC3/UVIS observations, together totalling 6 orbits. These are combined into a single visit. HOT STARS Default false true false false false SUPPORTED STAR LMXB NEUTRON STAR PULSAR J2000 J2000 ACS/SBC Imaging No No F150LP WFC3/UVIS Imaging No No F218W WFC3/UVIS Imaging No No F225W WFC3/UVIS Imaging No No F275W POS-TARG DITHER 0.472 LINE false false 3 44.4 ACS-SBC-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 /private/var/folders/kw/ptyqv6_j40v4zcxg60051shc0054qb/T/OPVisit6563953164043989635.xml The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13642 :visit-id "01" :proposal-version -1 :trans-version "20140605" :date "17-Jul-2014 14:24:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 111088 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13642 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13642 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3025 :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 3358 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13642 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3134 :al-overhead-at-end 0 :internal-dur-at-end 158 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) true 2 0 /Users/degenaar/Work/Proposals/HST/Cycle22/hybrid/PHASE_2/OP-cache/GO13642_phase2-v02.xml The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13642 :visit-id "02" :proposal-version -1 :trans-version "20140605" :date "17-Jul-2014 14:22:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 4619984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13642 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13642 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3024 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13642 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3134 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13642 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3135 :al-overhead-at-end 121 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13642 :visit-id "02" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3135 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3358 :pcs-gap 0 ) true 4 0