9868( 6) - 02/04/04 10:16 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9868 Version: 6 Check-in Date: 04-Feb-2004 10:15:19 1.Proposal Title: Timing of the proposed optical counterpart of the 16 ms LMC X-ray pulsar PSR J0537- 6910 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Dr. Roberto Mignani European Southern Observatory - Germany CoI: Dr. George G. Pavlov The Pennsylvania State University N CoI: Dr. Leisa Townsley The Pennsylvania State University N ------------------------------------------------------------------------------------ 5. Abstract PSR J0537-6910 is a fast, young (~ 5, 000 yrs) X-ray pulsar -still undetected in radio- at the the center of the SNR N157B in the LMC. PSR J0537-6910 is a champion pulsar - with a period of 16 ms it is the fastest rotator among ordinary pulsars, with the sharpest X-ray pulse among young pulsars. It is the most energetic one (together with the Crab), with a rotational energy loss log(dE/dt) ~ 38.7 erg/s, and its space velocity (> 1, 000 km/s), inferred from the shape of its X-ray bow-shock nebula, is probably one of the highest in the pulsar family. Taking advantage of the refined Chandra position of the X-ray pulsar, we have recently performed multi-band high-resolution imaging with the ACS (GO 9471) and we found a potential counterpart, characterized by unusual colours. Here, we propose to observe the candidate counterpart with the STIS/NUV-MAMA in its TIME-TAG mode to search for pulsations at the X-ray period, which would unambiguously confirm the proposed identification. ------------------------------------------------------------------------------------ 9868( 6) - 02/04/04 10:16 - [ 2] Observations Description ------------------------ After analyzing our ACS multi-band images of the field, we realized that there are 3 objects (mag=15-16), which are likely early type spectral stars and possibly violate the BOP limits for NUV-MAMA/F25QTZ imaging i.e. the observing configuration selected during Phase I. We thus decided to change our observing strategy, switching to NUV/MAMA spectroscopy with the PRISM. Because of the roll angle range imposed by the CVZ-visibility constraint, two of these stars may fall close to the shorter edges of the slit. However, according to the ETC, none of these objects violates the BOP limits for the selected observing configuration. With the newly selected observing configuration, we can still fulfill the original goals of our proposal. We plan to use the STIS/NUV-MAMA detector in TIMETAG mode to obtain a time-resolved spectrum around the {\sl Chandra}/HRC error box ($r \sim 2 ~ \arcsec$) of PSRJ0537$-$6910. The time resolution (125 $\mu s$) of the MAMA is precise enough to allow the detection of a signal pulsed at 16 ms even at a small ($\sim 20\%$) duty cycle. We propose to use the PRISM and thge 52x2 aperture. Taking as a reference the magnitudes of our candidate ($m_{342W} = 25.4$) and an E(B-V)=0.32 (Wang and Gotthelf, 1998) -- and assuming for PSRJ0537$-$6910 the flat optical flux distribution typical of young pulsars (Nasuti et al. 1997; Mignani and Caraveo 2001), we have used the STScI ETC tools to estimate the exposure time required to achieve a high S/N in the planned observation and enough photon counting statistics to perform a precise timing analysis of our target. For the above parameters and instrument configuration, we obtained a net of $\simeq$ 350 source counts per orbit ($\sim$ 4600 s--accounting for target visibility, GS acquisition and instrumental overheads), yielding a S/N $\sim$ 3 a t 2990 Angstrom The confidence level $C$ of pulsation detection can be estimated as $C=\left(1-\exp\{-S^2 p^2/[4 (S+B)]\}\right)\times 100\%$, where $S$ and $B$ are the numbers of source and background counts and $p$ is the pulsed fraction. The expected number of counts vs the background level will allow us to detect pulsations with a pulsed fraction as low as 30%, with a confidence level of 99.9998%, corresponding to a significance at the 5 sigma level. As a reference for the timing analysis, we will make use the pulsar's ephemerides obtained from quasi-simultaneous X-ray observations to be collected by our group. Thus, we will not need to apply FFT alghoritms for periodicity search but we will rather fold the photon times of arrival, transformed to the solar systen barycenter, with the expected period minimizing the number of trials. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9868( 6) - 02/04/04 10:16 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PSRJ0537- STAR, PULSAR RA-OFF=0.795S +/- 0.025S, DEC- J2000 V = 25.4+/-0.2 6910 OFF=-11.36" +/- 0.35", FROM 2, PLATE-ID=05ZW Coordinate Source: HST_IMAGE Comments: The slit orientation has been chossen so that there are no stars in the slit which violate the BOP limits. 2 PSRJ0537- STAR, UNDESIGNATED RA=05H37M46.56S +/- 0.35", DEC=- J2000 V = 16.0+/-0.1 6910-OFFSET 69D10'9.04" +/- 0.35", PLATE- ID=05ZW Coordinate Source: HST_IMAGE Comments: The coordinates of the star used for the offset have been obtained from our ACS images of the field obtained during cycle11 (prog. 9471) We note that the V band magnitude of this star, as given in the GSC2 is probably wrong. According to the PI's experience with the GSC2 pipeline, this is probably due to the crowding of the region which makes it difficult to derive accurate magnitudes from photographic plates. We measured the magnitude of this star both from our ground-based NTT images (Mignani et al, 2000, A&A 355, 603) and from recently acquired ACS images (GO-9471) and in both cases we got V~16. 9868( 6) - 02/04/04 10:16 - [ 4] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE; CVZ; ORIENT 45.0D TO 135.0 D; ORIENT 215.0D TO 315.0 D 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 PSRJ0537-69 STIS/C ACQ 50CCD MIRROR ACQTYPE=POINT 1 5 S 10-OFFSET CD Comments: Acquisition exposure ------------------------------------------------------------------------------------------------------------------------------------ 2 PSRJ0537-69 STIS/N TIME-TA 52X2 PRISM 2125 BUFFER-TIME=500 1 4400 S 10 UV-MAM G A Comments: Science exposure ------------------------------------------------------------------------------------------------------------------------------------ 3 PSRJ0537-69 STIS/N TIME-TA 52X2 PRISM 2125 BUFFER-TIME=500 1 5300 S 10 UV-MAM G A Comments: Science exposure ------------------------------------------------------------------------------------------------------------------------------------ 4 PSRJ0537-69 STIS/N TIME-TA 52X2 PRISM 2125 BUFFER-TIME=500 1 5300 S 10 UV-MAM G A Comments: Science exposure ------------------------------------------------------------------------------------------------------------------------------------ 5 PSRJ0537-69 STIS/N TIME-TA 52X2 PRISM 2125 BUFFER-TIME=500 1 5200 S 10 UV-MAM G A Comments: Science exposure ------------------------------------------------------------------------------------------------------------------------------------ 6 PSRJ0537-69 STIS/N TIME-TA 52X2 PRISM 2125 BUFFER-TIME=500 1 5000 S 10 UV-MAM G A Comments: Science exposure ------------------------------------------------------------------------------------------------------------------------------------ 9868( 6) - 02/04/04 10:16 - [ 5] Summary Form for Proposal 9868 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD 52X2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT BUFFER-TIME=500 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE; CVZ; ORIENT 45.0D TO 135.0 D; ORIENT 215.0D TO 315.0 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR PRISM ------------------------------------------------------------------------------------------------------------------------------------ Target Names PSRJ0537-6910-OFFSET PSRJ0537-6910 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2125 ------------------------------------------------------------------------------------------------------------------------------------