9098( 3) - 05/07/01 13:16 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9098 Version: 3 Check-in Date: 07-May-2001 13:15:31 1.Proposal Title: The Spectrum and the Light Curve of the Nearest Millisecond Pulsar ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: George Pavlov The Pennsylvania State University CoI: Prof. Jules Halpern Columbia University N CoI: Dr. Vyacheslav Zavlin Max-Planck-Institut fuer Extraterr. Physik N CoI: Prof. Roger Romani Stanford University N ------------------------------------------------------------------------------------ 5. Abstract PSR J0437--4715 is the nearest and the brightest millisecond (recycled) pulsar, and the only one that has been well studied at X-ray/EUV energies, where it has a strong pulsed signal. It is the most promising candidate for detecting the first optical counterpart of a millisecond pulsar. The HST has the unique ability to detect the cyclotron spectral line in the far UV from this weakly magnetized neutron star and to measure directly, for the first time, the magnetic field of a rotation-powered pulsar. The cyclotron line would be recognized by its sharp pulse profile in the FUV MAMA detector. The spectral and timing analysis of the far-UV continuum will allow us to study synchrotron radiation from the pulsar magnetosphere and thermal radiation from the surface of the neutron star. The magnetospheric and thermal components will be distinguished by their different pulse shapes and spectral slopes. ------------------------------------------------------------------------------------ 9098( 3) - 05/07/01 13:16 - [ 2] Observations Description ------------------------ The FUV MAMA detector operated in TIME-TAG mode will be used to measure the flux and low-resolution spectrum and to examine the pulse shape of PSR J0437-- 4715, free of contamination by its cool white dwarf companion. The 21st magnitude white dwarf, known to have a temperature of ~4000 K, prevents this study from being made at longer wavelengths, including in the NUV MAMA. To obtain the spectrum and, particularly, to search for the cyclotron line, we will use the G140L grating with the 52X0.5 slit. By dispersing, we isolate the dominant geocoronal background to 65 of the 967 dispersion pixels. With the very low dark current confirmed on-orbit for the FUV detector, we can then achieve photon-limited sensitivity by binning the spectra heavily after exclusion of the geocoronal features. Simulations confirm that this gives a dramatic improvement over direct FUV MAMA imaging of this isolated point source. We estimate a lower limit on the expected count rate of 0.015 cnts/s, based on an empirical extrapolation of the observed thermal X-ray spectrum, which is presumed to be coming from the pulsar's hot polar caps. To detect the pulsar at this lower limit and measure its flux with S/N=~10, we need five HST orbits (230 min exposure time, with allowance for overheads and target acquisition). A full-surface blackbody at T=1*10^5 K would give the continuum count rate of 0.08 cnts/s, corresponding to S/N=~30 for the time-integrated FUV flux (~10 per 1/10 phase bin or wavelength bin; ~7 per bin for phase-resolved spectroscopy with six phase bins and three wavelength bins). If the magnetic field is in the range of (6--9)*10^8 G, we expect to detect a strong cyclotron line. Its actual strength and position are unknown --- measuring these properties is one of the important goals of our proposal. For L_cyc=1*10^28 erg s^-1, we will be able to resolve the line in 12 wavelength bins with S/N>~8. Detectability of the line depends on the continuum level; at the accepted lower limit on the continuum the line would be detected at a 5Sigma level if L_cyc >~ 3* 10^26 erg s^-1. The FUV 0.5 arcsec slit requires on-board target acquisition, but no PEAKUP. The cool white dwarf companion of PSR J0437--4715 is bright enough in the visible to be acquired directly. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9098( 3) - 05/07/01 13:16 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PSRJ0437- STAR, BINARY PULSAR RA=4H 37M 15.72S +/- 0.04S, DEC= J2000 V = 20.9+/-0.1 4715 -47D 15' 8.3" +/- 0.5", PLATE- B-V = 1.2+/-0.1 ID=03C1 R = 20.1+/-0.1 I = 19.4+/-0.1 Coordinate Source: HST_IMAGE Comments: This binary pulsar has a proper motion (+121.3,-72.5) mas/yr. The position has been measured from a 1996.38 PC1 image and computed for 2002.0. It differs by 1.1 arcsec from the position calculated from the radio data (Sandhu et al. 1997). Bright Star Check -- the only nearby bright star is USNO-A2 0375-01566299 (B=13.5, R=13.4, may correspond to A0-A3), this is 27" away from the pointing center, i.e. ~15" away from our 25x0.5 aperture at a most unfavorable roll angle; should be safe if even gets in the aperture (3 magnitudes fainter than the V=10.3 limit for an A1V star). 9098( 3) - 05/07/01 13:16 - [ 4] Visit: 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 PSRJ0437-47 STIS/C ACQ 50CCD MIRROR ACQTYPE=POINT 1 60 S 15 CD ------------------------------------------------------------------------------------------------------------------------------------ 2 PSRJ0437-47 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=500 1 2150 S 15 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 PSRJ0437-47 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=500 1 3000 S 15 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 4 PSRJ0437-47 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=500 1 3000 S 15 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 5 PSRJ0437-47 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=500 1 3000 S 15 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 6 PSRJ0437-47 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=500 1 3000 S 15 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9098( 3) - 05/07/01 13:16 - [ 5] Summary Form for Proposal 9098 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT BUFFER-TIME=500 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names PSRJ0437-4715 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------