9471( 3) - 12/09/02 11:43 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9471 Version: 3 Check-in Date: 09-Dec-2002 11:42:46 1.Proposal Title: The Hunt for the Optical Counterpart of the Fastest Pulsar. ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Roberto Mignani European Southern Observatory - Germany CoI: Dr. George Pavlov Pennsylvania State University N CoI: Dr. Patrizia Caraveo Istituto di Fisica Cosmica/CNR N CoI: Dr. Leisa Townsley Pennsylvania State University N CoI: Dr. Stefan Wagner Landessternwarte N ------------------------------------------------------------------------------------ 5. Abstract PSR J0537-6910 is a fast, young (~ 5, 000 yrs) X-ray pulsar --still undetected in radio-- at 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 \dot E ~ 5 10^38 erg s^- 1, and its space velocity (>1, 000 km/s), inferred from the shape of its X-ray bow- shock nebula, is probably the highest in the pulsar family. Soon after its discovery, we performed multicolor observations with the ESO NTT to search for the optical counterpart. However, none of the several potential candidates detected within, or close to, the original ROSAT/HRI error circle (~eq 3 ") could be associated with the pulsar, which remained undetected down to V ~ 23.4. The results could not be improved by using the more accurate Chandra position (~eq 1 "). Since the crowding of the area, with a relatively bright star close to the pulsar position, makes the search for the PSR J0537-6910 optical counterpart virtually hopeless from the ground, we propose to obtain deep high-resolution multicolor imaging with ACS/WFC. The same data will allow us to study, for the first time, in the optical the compact nebula detected around the pulsar by Chandra. Since the target is in a CVZ, the whole program can be completed in two orbits. ------------------------------------------------------------------------------------ 9471( 3) - 12/09/02 11:43 - [ 2] Observations Description ------------------------ We plan to perform high-resolution multicolor imaging of the field around PSR J0537-6910 with ACS, the most sensitive imaging instrument aboard HST. The target will be observed with the ACS/WFC (50 mas/pixel), in the filters F435W, F555W and F814W, which have been chosen to maximize the spectral coverage and select objects with peculiar colors. Although both the NUV-MAMA detector of STIS and the ACS/HRC would provide an even sharper angular resolution, the significant amount of interstellar extinction towards the target admittedly discourages a ``blind'' observation in the UV. Observations in the optical with the ACS/WFC, favored with respect to the WFPC2 for its 3 times higher throughput, appear to be most suitable for a deep exploration. , Based on the above- described estimates, we can realistically bracket the magnitude of PSR J0537-6910 to be the range V =24.5--25.5. Taking conservatively a limit 1 magnitude fainter than the above minimum (i.e. V=26.5) as a reference -- with E(B- V)=0.32 (Wang and Gotthelf 1998) -- and assuming a flat optical flux distribution typical of young pulsars (e.g. Nasuti et al. 1997), we have used the ACS ETC to estimate the exposure time required to achieve a high S/N detection in all the selected passbands allowing at the same time for an efficient cr-splitting (CR-SPLIT=4). By setting the exposure time of each CR- SPLIT exposure to 400s, i.e. to avoid time losses due to buffer dumps, we can achieve the target detection with two integrations of 1600 s in the 435W (S/N ~ 8) and two of 1600 s each in the 555W (S/N ~ 7) and 814W (S/N ~ 8). Since the target can be observed in Continous Viewing Zone (CVZ), and our observations are not time-critical, all the planned exposures could be easily completed during two orbit, with allowance for Guide Stars acquisition and instrumental overheads. Real Time Justification ----------------------- We have checked that our LMC target can be observed in the Continuous Viewing Zone. Using the CVZ requirement will allow us to perform the observations in smaller number of orbits, increasing the HST observing efficiency. We have successfully used this approach in our observations of another LMC pulsar, 0540--69 (Caraveo et al. 2000). Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9471( 3) - 12/09/02 11:43 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-0537- STAR, PULSAR RA=05H 37M 47.36S +/- 1", DEC=- J2000 B-V = 0 6910 69D 10' 20.4" +/- 1", PLATE- V = 25+/-0.5 ID=05ZW Coordinate Source: GUIDE_STAR_CATALOG 9471( 3) - 12/09/02 11:43 - [ 4] Visit: 01 Visit Priority: Visit Requirements: CVZ 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 STAR-0537-6 ACS/WF ACCUM WFC1-FI F435W CR-SPLIT=4 1 3200 S 910 C X ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-0537-6 ACS/WF ACCUM WFC1-FI F555W CR-SPLIT=4 1 2800 S 910 C X ------------------------------------------------------------------------------------------------------------------------------------ 3 STAR-0537-6 ACS/WF ACCUM WFC1-FI F814W CR-SPLIT=4 1 2800 S 910 C X ------------------------------------------------------------------------------------------------------------------------------------ 9471( 3) - 12/09/02 11:43 - [ 5] Summary Form for Proposal 9471 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F435W F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names STAR-0537-6910 ------------------------------------------------------------------------------------------------------------------------------------