9063( 4) - 01/16/02 10:13 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9063 Version: 4 Check-in Date: 16-Jan-2002 10:12:45 1.Proposal Title: Optical Counterparts of Isolated Neutron Stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Marten Van Kerkwijk Universiteit Utrecht, Sterrekundig Instituut CoI: Mr. David Kaplan California Institute of Technology N CoI: Prof. S. Kulkarni California Institute of Technology N CoI: Dr. Dale Frail National Radio Astronomy Observatory N CoI: Dr. Chris Thompson Canadian Institute for Theoretical N Astrophysics ------------------------------------------------------------------------------------ 5. Abstract There has been gradual recognition of neutron stars as laboratories to test our understanding of both quantum chromodynamics (QCD) and quantum electrodynamics (QED). Specifically, the measurement of radii of neutron stars can test QCD at high density. This is being realized through intensive X-ray observations of bright nearby neutron stars. However, the natures of these important sources are not clear and to this end we propose a simple proper motion program as a means to obtain their ages and potential association with star-forming regions. One of the sources is RX J0720.4-3125 which has been argued to be an old magnetar --- a highly magnetized neutron star --- and thanks to its high count rate is already a choice object for X- ray missions. Magnetars, with their extreme magnetic field strengths, are excellent laboratories for testing out some expectation of QED. We show how UV observations can be combined with optical and X-ray observations to demonstrate the magnetar nature of the source. The other sources are the brightest of the nearby neutron stars that currently lack optical identifications. For these we will first detect them and then perform accurate astrometry so that future observations will yield birth locations. ------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 2] Observations Description ------------------------ RX J1308+2127 & RX J1605+3249: Our primary goal is to detect these sources and determine optical fluxes and rough colors. Second, we wish to detect the sources well enough (at least 10Sigma) to perform accurate astrometry, with the eventual goal of measuring proper motions and parallaxes ( e.g. Walter 2000). In Table reftab_sum, we present our estimates of the observing time required to do this along with the data used to make the estimates. To estimate required integration times, we used two separate source models (Expected B 1 & 2 in Table reftab_sum). Model (1) assumes a constant log(f_X/f_ opt)=5, based on RX J0720.4-3125 and RX J1856-3754 (Kulkarni & van Kerkwijk 1998; Motch 2000). f_X (5--5000 eV) was calculated using PIMMS ( http://heasarc.gsfc.nasa.gov/Tools/w3pimms.html), assuming a thermal spectrum normalized to the PSPC count rate. The actual f_X values found in the literature (often 0.1--2.4 keV) differ by a factor of ~ 1.5, but there does not appear to be a systematic bias, and we wished for uniform calculations. Model (2) assumes thermal emission of the form f_ opt=K * 4PI R^2 2 k T/Lambda^2, where R=10 km and K~ 5* 10^-29mbox s^-1mbox cm^-2 accounts for intrinsic luminosity, distance, and bandwidth, and was again calculated using values from RX J0720-3125 and RX J1856-3754. We then applied extinction corrections to the B magnitudes using A_B=N_H/1.2* 10^21 mbox cm^-2, but these were very minor. We note that all of the predicted magnitudes are fainter than the current upper limits. We then inserted the fainter of the two estimated fluxes (worst case) into the STIS imaging exposure time calculator. For a source model we assumed a blackbody spectrum in the Rayleigh-Jeans regime (f_Nu\propto nu^2). The reddening that we used was quite small (E_B-V=N_H/5* 10^21 mbox cm^-2). The observing times listed in Table reftab_sum are those required for a 10Sigma detection using STIS/50CCD. Of the sources in Motch (2000), only RX J1605+3249 and RX J1308+2127 are detectable in reasonable numbers of orbits. To determine colors we also request STIS/LP observations, but only for RX J1605+3249 (as noted in Table reftab_sum) as the other sources would require prohibitively long integration times. For these sources, at Delta=+32degrees and Delta=+21degrees, the orbital visibilities are 53 min. We also take into account guide- star acquisition and startup times: 6 min and 6 min respectively for the first orbit, and 5 min and 1 min for the second (if there is no change in the observing setup). With this overhead, we calculate the number of orbits required for each source, and list these in Table reftab_sum. RX J0720.4-3125: Here the goal is to obtain precise UV and optical fluxes as well as UV light curves. For this purpose, we propose to use STIS with the FUV MAMA without filter and with the SrF2 filter, the NUV MAMA with the Quartz filter, and the CCD without filter (we verified from our Keck images that no source in the field will be above the brightness limits for the MAMAs). This will give flux measurements at a range of effective wavelengths (1340, 1400, 2140, and 4400 Angstrom\ for a lambda^-4 spectrum), and allow a check for LyAlpha by combining the two FUV images. We require (i) fluxes to better than 5\ (the latter in Clear and SrF2, with and without LyAlpha); (ii) in the UV, light curves with better than 10\ the optical, an accurate position of the optical counterpart of \rxj\ relative to stars in the field, for future proper motion measurements and possible future FUV spectroscopy. Requirement (iii) is a subset of (i): with a >\.20Sigma detection, we obtain a position accurate to <\.2.5 mas, which is sufficient. Requirement (ii) is stronger than (i): it requires 28Sigma detections in the UV bands. In the far UV, however, we would not compromise our science by combining the with-and-without LyAlpha measurements for the determination of the light curve. We used the STIS imaging exposure time calculator (v.2.1.4) to estimate sensitivities. For our estimates, we assume a black-body with T_rmeff=10^6 K (i.e., very hot), reddening E_B-V=0.04, and flux normalized to B=26.6. The normalization may be slightly optimistic for the UV, since the optical flux is a factor five above the flux expected from the X-ray black-body fit, and it might be a little less in the UV. On the other hand, the estimate of the reddening is an upper limit, and hence is conservative. For our source, at Delta=-31^degrees, the orbital visibility is 53 minutes. For a first orbit, the overhead is 6 minutes guide-star acquisition, 6 minutes imaging startup; for a second, 5 minutes guide-star reacquisition, 1 minute imaging startup if the configuration is not changed. For two, three, and five orbits with the same setup, one therefore has a total of 88, 135, and 229 minutes available for integration (minus further start-ups). For observations requiring shadow time, 25 minutes every orbit are available. For STIS/FUV with F25SrF2, the signal-to-noise is improved greatly by using shadow time. For the SrF2 filter, a 21Sigma detection is made in 2*25 minutes in shadow time, while using the full two orbits out of the shadow results in a 15Sigma detection. Thus, we request shadow time for this observation. We will, however, observe the whole orbit, as the extra 37 minutes out of shadow still lead to a slightly improved total signal-to- noise ratio of 23Sigma. Since we will be using time-tag mode, we can select the time in the shadow later if that out of the shadow turns out to be worse than expected. For STIS/FUV without filter, again shadow time is better. Because of the higher background, three orbits are required. In 75 minutes, one obtains a 22Sigma detection. Combined, like above, with the out-of -shadow time, this becomes 24Sigma. For the combined FUV lightcurve, we obtain 12Sigma detections in 8 bins. For STIS/NUV, the F25QTZ and F25SrF2 filters give approximately equal signal-to-noise ratios. In order to have the NUV band be as separate as possible from the FUV bands, we prefer the F25QTZ filter. It is insensitive whether or not one observes in shadow time. Due to the higher detector background and the smaller number of source counts in the NUV, a relatively long exposure is required. In 5 orbits (229 minutes), a 25Sigma detection is expected; the light curve will have 9Sigma detections in 8 bins, which should still be sufficient. For STIS/CCD, Clear, one expects a 21Sigma detection. Here, we assumed 6 exposures over 2 orbits (with a total exposure time of 83 minutes). We will obtain a slight gain if we can observe in the shadow (~\.27Sigma), but this is not critical. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 RXJ0720.4- STAR, Neutron Star RA=7H 20M 24.59S +/- 0.02S, DEC= J2000 V = 26.8 3125 -31D 25' 55.0" +/- 0.2" B-V = -0.2 Coordinate Source: OTHER_SOURCE Comments: spectrum likely roughly like Raileigh-Jeans tail; position offset 4.1 arcsec S, 4.1 arcsec W in order to avoid bright stars to the NE. 2 RXJ1605.3+32 STAR, Neutron Star RA=16H 05M 18.66S +/- 0.05S, J2000 V = 27 49 DEC=+32D 49' 19.7" +/- 0.7" B-V = -0.2 Coordinate Source: OTHER_SOURCE Comments: Optical flux not known; spectrum likely Raileigh-Jeans 3 RXJ1308.6+21 STAR, Neutron Star RA=13H 08M 48.17S +/- 0.1S, J2000 V = 28 27 DEC=+21D 27' 07.5" +/- 1.6" B-V = -0.2 Coordinate Source: OTHER_SOURCE Comments: Optical flux not known; spectrum likely Raileigh-Jeans 9063( 4) - 01/16/02 10:13 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-CCD-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.567 Coordinate_Frame POS-TARG Pattern_Orient 26.6 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 5] Visit: 10 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 101 RXJ0720.4-3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 657.0 S PATTERN 1 125 CD ------------------------------------------------------------------------------------------------------------------------------------ 102 RXJ0720.4-3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 678.0 S POSITION TARGET -0.506, 125 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 6] Visit: 11 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 111 RXJ0720.4-3 STIS/N TIME-TA F25QTZ MIRROR BUFFER-TIME=685 1 2741.0 125 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 112 RXJ0720.4-3 STIS/N TIME-TA F25QTZ MIRROR BUFFER-TIME=685 1 2947.0 POSITION TARGET 0.246, 125 UV-MAM G 0.123 A ------------------------------------------------------------------------------------------------------------------------------------ 113 RXJ0720.4-3 STIS/N TIME-TA F25QTZ MIRROR BUFFER-TIME=685 1 2947.0 POSITION TARGET 0.123, 125 UV-MAM G 0.246 A ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 7] Visit: 12 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 121 RXJ0720.4-3 STIS/N TIME-TA F25QTZ MIRROR BUFFER-TIME=685 1 2741.0 POSITION TARGET 0.246, 125 UV-MAM G -0.123 A ------------------------------------------------------------------------------------------------------------------------------------ 122 RXJ0720.4-3 STIS/N TIME-TA F25QTZ MIRROR BUFFER-TIME=685 1 2947.0 POSITION TARGET 0.123, 125 UV-MAM G -0.246 A ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 8] Visit: 13 Visit Priority: Visit Requirements: BETWEEN 10-JAN-2002:12 AND 30-JAN-2002:12 On Hold Comments: Additional Comments: The FUV/SrF2 observations require shadow time in order to reduce background. However, the time out of shadow is still useful. Therefore, we did not use the SHADOW requirement, but selected dates near opposition in which the requirement is fulfilled, so that we can expose for the whole orbit and select the shadow time off-line. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 131 RXJ0720.4-3 STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=342 1 2741.0 125 UV-MAM G A Comments: Expose for whole orbit. Shadow time will be selected off-line. Buffer time appropriate for non-shadow time. ------------------------------------------------------------------------------------------------------------------------------------ 132 RXJ0720.4-3 STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=342 1 2947.0 POSITION TARGET 0.246, 125 UV-MAM G 0.123 A Comments: Expose for whole orbit. Shadow time will be selected off-line. Buffer time appropriate for non-shadow time. ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 9] Visit: 14 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background. Unlike for FUV/SrF2, the out-of-shadow background is so high that collecting data over a whole visibility period and selecting shadow- time off-line is not useful. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 141 RXJ0720.4-3 STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=245 1 1735.0 SHADOW 125 UV-MAM G A Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background ------------------------------------------------------------------------------------------------------------------------------------ 142 RXJ0720.4-3 STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=245 1 1892.0 SHADOW; POSITION TARGET 125 UV-MAM G 0.246, 0.123 A Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background ------------------------------------------------------------------------------------------------------------------------------------ 143 RXJ0720.4-3 STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=245 1 1892.0 SHADOW; POSITION TARGET 125 UV-MAM G 0.123, 0.246 A Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 10] Visit: 20 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 201 RXJ1605.3+3 STIS/C ACCUM F28X50L MIRROR CR-SPLIT=NO 1 662.0 S PATTERN 1 249 CD P ------------------------------------------------------------------------------------------------------------------------------------ 202 RXJ1605.3+3 STIS/C ACCUM F28X50L MIRROR CR-SPLIT=NO 1 678.0 S POSITION TARGET -0.506, 249 CD P 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 203 RXJ1605.3+3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 674.0 S POSITION TARGET -0.506, 249 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 11] Visit: 30 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 301 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 648.0 S PATTERN 1 127 CD ------------------------------------------------------------------------------------------------------------------------------------ 302 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 669.0 S POSITION TARGET -0.506, 127 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 303 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 669.0 S POSITION TARGET -1.012, 127 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 12] Visit: 31 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 311 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 648.0 S POSITION TARGET +0.506, 127 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 312 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 669.0 S POSITION TARGET +1.012, 127 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 313 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 669.0 S POSITION TARGET +1.518, 127 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 13] Visit: 32 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 321 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 648.0 S POSITION TARGET -1.518, 127 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 322 RXJ1308.6+2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 669.0 S POSITION TARGET -2.024, 127 CD 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 14] Visit: 54 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background. Unlike for FUV/SrF2, the out-of-shadow background is so high that collecting data over a whole visibility period and selecting shadow- time off-line is not useful. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 141 RXJ0720.4-3 STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=245 1 1735.0 SHADOW 125 UV-MAM G A Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background ------------------------------------------------------------------------------------------------------------------------------------ 142 RXJ0720.4-3 STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=245 1 1892.0 SHADOW; POSITION TARGET 125 UV-MAM G 0.246, 0.123 A Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background ------------------------------------------------------------------------------------------------------------------------------------ 143 RXJ0720.4-3 STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=245 1 1892.0 SHADOW; POSITION TARGET 125 UV-MAM G 0.123, 0.246 A Comments: The FUV/25MAMA observations require SHADOW time in order to reduce the background ------------------------------------------------------------------------------------------------------------------------------------ 9063( 4) - 01/16/02 10:13 - [ 15] Summary Form for Proposal 9063 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD F25QTZ F25SRF2 25MAMA F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO BUFFER-TIME=685 BUFFER-TIME=342 BUFFER-TIME=245 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 POSITION TARGET -0.506, 0.; PATTERN 1 POSITION TARGET 0.246, 0.123 POSITION TARGET 0.123, 0.246 POSITION TARGET 0.246, -0.123 POSITION TARGET 0.123, -0.246 BETWEEN 10-JAN-2002 12 AND 30-JAN-2002 12 SHADOW SHADOW; POSITION TARGET 0.246, 0.123 SHADOW; POSITION TARGET 0.123, 0.246 POSITION TARGET -1.012, 0.; PATTERN 1 POSITION TARGET +0.506, 0.; PATTERN 1 POSITION TARGET +1.012, 0.; PATTERN 1 POSITION TARGET +1.518, 0.; PATTERN 1 POSITION TARGET -1.518, 0.; PATTERN 1 POSITION TARGET -2.024, 0.; PATTERN 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names RXJ0720.4-3125 RXJ1605.3+3249 RXJ1308.6+2127 ------------------------------------------------------------------------------------------------------------------------------------