9182( 5) - 02/04/02 10:37 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9182 Version: 5 Check-in Date: 04-Feb-2002 10:35:08 1.Proposal Title: The Thermal Glow of Gamma Ray Pulsars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Roger Romani Stanford University CoI: Dr. George Pavlov The Pennsylvania State University N CoI: Prof. Jules Halpern Columbia University N ------------------------------------------------------------------------------------ 5. Abstract We propose time- and energy- resolved UV observations of two young Gamma-ray pulsars using the HST STIS/MAMA detectors. Our targets, the Vela and Geminga pulsars, are the brightest neutron stars spanning the critical 10^4-10^6y age range, where the thermal surface emission is detectable. The UV lightcurves we obtain will provide phase-resolved colors that will isolate this thermal emission and test the Equation of State and fundamental interactions of matter at supernuclear densities. In addition, combining the UV results with our IR/optical and X-ray data we will map spectral variations in the non-thermal pulsations and probe the acceleration physics of these GeV gamma-ray machines. ------------------------------------------------------------------------------------ 9182( 5) - 02/04/02 10:37 - [ 2] Observations Description ------------------------ These are faint targets, so we have carefully simulated the various techniques to extract the required phase resolved colors in the UV. To best separate and measure the thermal and magnetospheric spectra in minimum exposure time we require a combination of NUV and FUV TIME-TAG MAMA integrations. The strategies differ in the two cameras. For the FUV the very low dark current confirmed on orbit means that maximal S/N on faint point sources with known positions is obtained by imaging through the 52X0.5 aperture and the G140L grating. This resolves the dominant geocoronal background to 65 of the 967 dispersion pixels. The source count decrease due to grating losses is more than compensated by the background suppression and, binning heavily over the remaining pixels, we obtain faint target sensitivities near the source count limit. We have confirmed that this gives a dramatic improvement over any direct FUV imaging, with the added bonus of significant color information. Figure 2 gives the total flux 10Sigma source sensitivities. We have requested sufficient exposure to obtain ~ 1300--1700 FUV counts each from PSR B0833--45 (2 orbits) and Geminga (4 orbits). Although the detailed split is different for the two pulsars (Figure 3) this suffices to cleanly separate the thermal emission, giving pulse profiles in at least two spectral bands, with S/N~ 10 per phase bin in a 10-bin light curve. Alternatively, we can separately sum all thermal and non-thermal phases. For Vela this should provide ~ 7 S/N~ 10 spectral bands each for the thermal and non-thermal components. For Geminga, we extract ~ 11 thermal bands and ~ 3 non-thermal bands. These will measure the phase dependence of the non- thermal index Alpha$ and can isolate large equivalence width features, if any, in the thermal continuum. Figure 2 includes the spectral edges predicted from the Rajagopal et al. (1997) magnetic Fe surface spectra. These are not expected to give a strong signal in our data set, but our measured fluxes, in addition to confirming the R-J nature of the thermal continuum, set the required sensitivity for any future search for redshifted surface absorption edges. \medskip In the NUV, direct imaging in TIME-TAG mode through the F25SRF2 filter provides the best combination of band definition and S/N. Here our proposed exposures collect ~ 1000--1200 counts each for Vela and Geminga. This suffices to provide a 10 bin light curve with S/N ~ 7/bin, the minimum needed for a clean separation of the (fainter) thermal component. As Figure 2 demonstrates, the spectral leverage provided by this NUV detection greatly improves the measurement of the R-J component and provides additional sensitivity to surface composition. Since our light curve provides a ~ 7\ also enhance the FUV measurements of spectral index variation in this component. Placement into the FUV 0.5" slit requires on-board target acquisition, but no PEAKUP. This is straightforward as we have confirmed with existing HST images that there are suitable offset stars with accurately known separation for each pulsar. The coordinates and proper motion are known with great precision for both objects. We also have checked that the MAMA bright limits are not violated in either target field. Our combination of exposures is tuned to best achieve our primary science goals, the measurement of the neutron star thermal bolometric luminosity at these two critical ages and the detection of the non-thermal pulsation and its spectral variation. Further, if spectral features with an EW as large as that implied by the Geminga optical data exist in the UV, we will measure these and isolate these in pulse phase. Some synchrotron models do in fact predict higher resonances in this band. Also, for Vela, our NUV direct image and FUV slit sample offer the chance to probe the spectral index of the `wisp'; the relativistic shock in the compact synchrotron nebula surrounding the pulsar recently discovered in an early Chandra HRC image (Pavlov et al 2000). Our team has appreciable experience studying such `pulsar wind nebulae'. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9182( 5) - 02/04/02 10:37 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PSR0833--45- STAR, UNDESIGNATED RA=08H 35M 19.834S +/- 0.5", J2000 V = 18.6 OFFSET DEC=-45D 10' 27.76" +/- 0.5", PLATE-ID=01FB Coordinate Source: HST_IMAGE 2 PSR0833--45 STAR, PULSAR, NEUTRON RA-OFF=0.7093S+/- 0.0015S, DEC- J2000 V = 23.6+/-0.1 STAR, ISM, SNR OFF=-7.230"+/- 0.0013", FROM 1, PLATE-ID=01FB Coordinate Source: HST_IMAGE Comments: Vela has a proper motion of (-41,+24)mas/y = (-0.0039 s/y, 0.024"/y). The positions have been measured from a 2000.04 PC image and the offset has been computed for 2002.0. May update for actual observation date, but not needed. Bright Star Check -- only flag is GSC2 S133121341356 (V=13.89, B-V=1.75 i.e. ~M5) this is 28" away from pointing center, i.e. ~16" from any aperture -- Should be safe; B-V would need to be 0.9mag too large for even an O5 to be of concern if _in_ aperture. Brightest Star in aperture is K w/ WFPC2 V=18.6 (B-R~1.2 i.e. ~G5) color needs to be 1.5mag in error for even 05 to be of concern. 3 GEMINGA- STAR, G V-IV RA=6H 33M 54.359S +/- 0.002S, J2000 V = 21.3+/-0.1 OFFSET DEC=17D 46' 9.23" +/- 0.01", PLATE-ID=001S Coordinate Source: HST_IMAGE 4 GEMINGA STAR, PULSAR RA-OFF=-0.1509S+/- 0.0036S, DEC- J2000 V = 25.5+/-0.1 OFF=4.405"+/- 0.051", FROM 3, PLATE-ID=001S Coordinate Source: HST_IMAGE Comments: Last PC plate was 1995.75 (gem-G was -3022+/-8, +3736+/-7 mas) using PM (+137+/-7,+107+/-7 mas/y), correct to 2002.0= New offset (-2166+/-52,+4405+/- 51)==(-0.1509+/-0.0036s, 4.405+/-0.051"). Note: NICMOS (1998.25) gives within 10mas the same offset. VTT Bright Object check has no flags -- only star GSC2 N223132112522 V=17.24 B-V=0.94 (Sp K0) well outside of field. Brightest Star (USNO A2 check) -- 06 33 52.8553 +17 46 13.500 R=16.2 B-R=1.8 -- this color would need to be 1.6mag bluer for an O5 star to reach the bright object limit. Downes confirms that GSC2 colors are red enough to pass. 9182( 5) - 02/04/02 10:37 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 10D TO 165D ORIENT 190D TO 345D On Hold Comments: Additional Comments: Orient to exclude Star K from slit. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 20 PSR0833--45 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 14 S -OFFSET CD P ------------------------------------------------------------------------------------------------------------------------------------ 21 PSR0833--45 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=400 1 2359 S POS TARG 0,-7 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 22 PSR0833--45 STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=400 1 3014 S POS TARG 0,-7 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 31 PSR0833--45 STIS/N TIME-TA F25SRF2 MIRROR BUFFER-TIME=512 1 2895 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 32 PSR0833--45 STIS/N TIME-TA F25SRF2 MIRROR BUFFER-TIME=512 1 3056 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9182( 5) - 02/04/02 10:37 - [ 5] Visit: 02 Visit Priority: Visit Requirements: BEFORE 28-FEB-2002 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 ------------------------------------------------------------------------------------------------------------------------------------ 20 GEMINGA-OFF STIS/C ACQ 50CCD MIRROR 1 45 S SET CD Comments: Dj & Kul -- `Moderately Reddened G5' ------------------------------------------------------------------------------------------------------------------------------------ 21 GEMINGA STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=400 1 2070 S POS TARG 0,-7 UV-MAM G A Comments: Buffer time estimates from Max count rate (Lya at 30kR) - 5kHz. ------------------------------------------------------------------------------------------------------------------------------------ 22 GEMINGA STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=400 1 2890 S POS TARG 0,-7 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 23 GEMINGA STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=400 1 2857 S POS TARG 0,-7 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 24 GEMINGA STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=400 1 2857 S POS TARG 0,-7 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9182( 5) - 02/04/02 10:37 - [ 6] Visit: 03 Visit Priority: Visit Requirements: BEFORE 28-FEB-2002 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 GEMINGA STIS/N TIME-TA F25SRF2 MIRROR BUFFER-TIME=512 1 2670 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 312 GEMINGA STIS/N TIME-TA F25SRF2 MIRROR BUFFER-TIME=512 1 2899 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 313 GEMINGA STIS/N TIME-TA F25SRF2 MIRROR BUFFER-TIME=512 1 2899 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 314 GEMINGA STIS/N TIME-TA F25SRF2 MIRROR BUFFER-TIME=512 1 2899 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9182( 5) - 02/04/02 10:37 - [ 7] Summary Form for Proposal 9182 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.5 F25SRF2 50CCD ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT BUFFER-TIME=400 BUFFER-TIME=512 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 10D TO 165D ORIENT 190D TO 345D POS TARG 0,-7 BEFORE 28-FEB-2002 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names PSR0833--45-OFFSET PSR0833--45 GEMINGA-OFFSET GEMINGA ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------