5874( 17) - 04/30/96 13:33 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5874 Version: 17 Check-in Date: 30-Apr-1996 13:20:48 1.Proposal Title: UV echoes in X-ray Pulsars: LMC X-4 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Saeqa Vrtilek University of Maryland CoI: Richard McCray Joint Institute for Laboratory N Astrophysics CoI: Bram Boroson Joint Institute for Laboratory N Astrophysics CoI: Francis Primini Smithsonian Astrophysical Observatory N CoI: Fu-Hua Cheng University of Maryland N CoI: Richard Kelley Goddard Space Flight Center N CoI: Fumiaki Nagase Institute for Space and Advanced Studies N ------------------------------------------------------------------------------------ 6. Abstract UV emission in many X-ray binaries is dominated by X-rays reprocessed in the accretion disk. For pulsars illumination of the accretion disk by a rotating beam of X-rays should result in pulsed UV emission lines with Doppler shifts corresponding to projected gas velocities. Simultaneous high time resolution UV and X-ray spectra thus offer a fundamentally new approach to understanding gas flows in these systems. We propose to observe pulsations and rapid variations in the spectra of the 13.5s pulsar LMC X-4. We will use the GHRS G160M in the RAPID mode to look for spectrum variability at timescales ranging from 0.5s - 30m. The HST observations will be coordinated with ASCA to look for correlations of UV variability with X- ray variability and to look for lags in pulse waveforms. By observing UV echoes of X-ray variations with the GHRS, we can map the dynamics of a precessing accretion disk and other structures in the accretion flow. The UV lines, X-ray Fe lines at 6-7 keV, and soft X-ray lines will complement each other as plasma diagnostics. ------------------------------------------------------------------------------------ 5874( 17) - 04/30/96 13:33 - [ 2] Observations Description ------------------------ We will observe LMC X-4 during the high state of the 30 day cycle. We would like to schedule observations to cover the binary phases 0.5 - 0.9 which will permit us to observe the eclipse ingress and will give us a good chance of catching a pre-eclipse ``dip'' in the X-ray light curve. We will coordinate simultaneous X-ray observations with the ASCA telescope. Observations will be taken with the GHRS G160M grating centered alternately at 1240 Angstrom (N V) and 1550 Angstrom (C IV) in the RAPID mode with a time resolution of 0.5s. The observed flux from N V Lambda 1240 measured with IUE (van der Klis Etal 1982) ranges from F ~ 3 * 10^-12ergs cm^-2 s^-1 at maximum (orbital phase Phi ~ 0.9) to F ~ 1 * 10^-12 ergs cm^-2 s^-1 at minimum (Phi ~ 0.5). We obtain count rates R ~ 0.25 counts/s/diode at Phi~ 0.9 for the measured line width of 7Angstrom. One spectral resolution element corresponds to ~ 1 diode, giving a resolution DeltaLambda ~ 0.08 Angstrom at 1240 Angstrom, or velocity resolution Delta V ~ 19 km s^-1. Thus, in a 40 minute observation at Phi ~ 0.9 one can expect ~ 5.8 * 10^4 counts in the line which spans ~ 95 diodes. A 60-minute observation at Phi ~ 0.5 will give us 2.9 * 10^4 counts. The number of counts required to detect pulsations at the 5Sigma level is roughly (depending on the assumed waveform) N ~ 25 f^-2, where f is the fractional pulse amplitude. Thus, we see that it should be possible in a 40 minute observation at Phi ~ 0.9 to detect (5Sigma) pulsations with amplitude f ~ 0.02 in the net line flux and f ~ 0.2 in a single 19 km s^-1 resolution element. At Phi ~ 0.5 the values for a 60 minute integration are f ~ 0.03 in the net line flux and f ~ 0.09 in a single 19 km s^ -1 resolution element. The number of counts required to determine the UV pulse phase will be greater, depending on the pulse waveform, which we do not know a priori, and on the desired accuracy of the phase. However, we note that since the line width measured by IUE is an upper limit our estimated count rates are a lower limit. For the CIV (Lambda1550) line with a measured flux F ~ 6.6 * 10^ -13ergs cm^-2 s^-1 roughly constant over orbital phase, a 60 minute observation would give a count rate of ~ 1.7 * 10^4 in the line with a corresponding f ~ 0.04 in the net line flux and f ~ 0.4 in a single 19 km s^-1 resolution element. We would like a total of 8 observations: 2 each for each of the lines at each of 2 binary phases. The total time on source would be 440 minutes. Assuming a 60-minute viewing window for LMC X-4, with one guide star acquisition (12 minutes), one target acquisition (11 minutes), 8 target re- acquisitions of 6 minutes each, and 8 instrument read-outs of 4 minutes each, the total number of satellite orbits we require is 9. Real Time Justification ----------------------- There are four times during the year (for a total of 160 days) when LMC X-4 falls in a CVZ. While we do not need the CVZ to accomplish our goals, the opportunity exists to utilize the HST at high efficiency. If we are allocated time during a CVZ interval we will be able to observe the SIV line in addition to the NV and CIV lines. We have submitted a proposal to obtain simultaneous time on LMC X-4 with the ASCA X-ray satellite. We are only asking for HST time if simultaneous X-ray observations can be scheduled. LMC X-4 is always visible to ASCA and HST has four CVZ opportunities for a total of 160 days during the year so scheduling coordinated times should not be a problem. Simultaneous X- ray observations with ASCA are intrinsic to this proposal and add a vital dimension to the proposed program. By observing brightness and phase correlations among the X-ray continuum, Fe-K lines, and UV line profiles, we can measure the light-travel times and angles from the neutron star to the fluorescing gas. We have obtained high quality data on LMC X-4 during an ASCA AO1 observation in April 1994. The analysis of the high time resolution data is yet to be accomplished, however, a 6.4 keV Fe-K line is seen that comes from X- ray illumination of cold gas in the system, part of which may be the same gas that is responsible for the UV fluorescence (Vrtilek Etal 1994). We can test this conjecture by comparing the phase shift of the pulsation of the Fe-K line with that of the UV line pulsations. We are proposing for more time on ASCA since simultaneous observations with HST will yield far more scientific return. Calibration Justification ------------------------- Additional Comments ------------------- SIMULTANEOUS OBSERVATIONS WILL BE TAKEN BY THE ASCA X-RAY TELESCOPE. LMC X-4 is always visible to ASCA. There is a second period (30.33D) To= JD2449727.33 with a phase restriction of 0.5-0.9. We are coordinating with ASCA. The ASCA observations will last for 100,000s. We will need at least a one-month lead time on the week in which the observations takes place and a two weeks lead time on the exact time. ------------------------------------------------------------------------------------ 5874( 17) - 04/30/96 13:33 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5874( 17) - 04/30/96 13:33 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 4U0532-664 STAR, MXB, Giant O RA = 5H 32M 49.61S +/- 0.08S, J2000 V = 14.0+/-0.1 DEC = -66D 22' 13.6" +/- 0.5", B-V = -0.1+/-0.01 PLATE-ID = 06B0 TYPE=O7III-V F-LINE(1240)=2.0+/-1.0e-12 W-LINE(1240)=7.0+/-2.0 F-LINE(1550)=6.6+/-2.0e-13 W-LINE(1550)=7.0+/-2.0 Comments: Coordinates are from a parabolic centroid GASP measurement 5874( 17) - 04/30/96 13:33 - [ 5] Visit: 01 Visit Requirements: PCS MODE F PERIOD 33.80H AND ZERO-PHASE JD2447742.4904 On Hold Comments: Additional Comments: SIMULTANEOUS OBSERVATIONS WILL BE TAKEN BY THE ASCA X-RAY TELESCOPE. LMC X- 4 is always visible to ASCA. There is a second period (30.33D) To= JD2449727.33 with a phase restriction of 0.5-0.9. We are coordinating with ASCA. The ASCA observations will last for 100,000s. We will need at least a one-month lead time on the week in which the observations takes place and a two weeks lead time on the exact time. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 4U0532-664 HRS ACQ 2.0 MIRROR-N2 SAA-CONTOUR=HIGH-NOISE 1 4.95S ONBOARD ACQ FOR 2-15 PHASE 0.15 to 0.40 SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 4U0532-664 HRS RAPID 2.0 G160M 1225-12 SAMPLE-TIME = 0.5, 1 4445S 55 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 3 4U0532-664 HRS RAPID 2.0 G160M 1535-15 SAMPLE-TIME = 0.5, 1 4600S 65 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 5 4U0532-664 HRS RAPID 2.0 G160M 1225-12 SAMPLE-TIME = 0.5, 1 4380S 55 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 7 4U0532-664 HRS RAPID 2.0 G160M 1535-15 SAMPLE-TIME = 0.5, 1 4320S 65 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 9 4U0532-664 HRS RAPID 2.0 G160M 1225-12 SAMPLE-TIME = 0.5, 1 4320S 55 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 11 4U0532-664 HRS RAPID 2.0 G160M 1535-15 SAMPLE-TIME = 0.5, 1 4440S 65 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 13 4U0532-664 HRS RAPID 2.0 G160M 1225-12 SAMPLE-TIME = 0.5, 1 4620S 55 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 15 4U0532-664 HRS RAPID 2.0 G160M 1535-15 SAMPLE-TIME = 0.5, 1 6540S 65 SAA-CONTOUR=HIGH-NOISE ------------------------------------------------------------------------------------------------------------------------------------ 5874( 17) - 04/30/96 13:33 - [ 6] Summary Form for Proposal 5874 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SAA-CONTOUR=HIGH-NOISE SAMPLE-TIME = 0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE F PERIOD 33.80H AND ZERO-PHASE JD2447742.4904 ONBOARD ACQ FOR 2-15 PHASE 0.15 to 0.40 SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names 4U0532-664 ------------------------------------------------------------------------------------------------------------------------------------