6777( 6) - 03/18/99 16:55 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6777 Version: 6 Check-in Date: 18-Mar-1999 16:55:15 1.Proposal Title: A Counterpart Search for SGR 0526-66 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 6 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Richard Rothschild University of California, San Diego CoI: David Marsden University of California, San Diego N CoI: Ross Cohen University of California, San Diego N ------------------------------------------------------------------------------------ 5. Abstract Soft gamma-ray repeaters are a class of bursting X-ray sources which are characterized by short durations, relatively soft spectra, and lack of spectral evolution during outburst. Thought to be due to neutron stars, optical counterparts have yet to be confirmed for any of the three known SGRs. We propose to use the WFPC2 to search for an optical counterpart to the X-ray point source which is coincident with the gamma- ray error box for SGR 0526-66. Detection of an optical counterpart is crucial to advancing our understanding of these remarkable objects. The proposed search will be made possible by the fine resolution of the WFPC2, which will allow for significantly more sensitive searches than presently available. ------------------------------------------------------------------------------------ 6777( 6) - 03/18/99 16:55 - [ 2] Observations Description ------------------------ The observation will take one orbit in the CVZ, and will use the PC and F814W. After quide star acquisition and overhead, time remains for 4 exposures of 1100s each. This allows for two exposures (to remove cosmic rays) at each of two locations separated by 11 pixels (to correct for hot pixels and other defects). To calculate the expected optical flux of a typical low mass X-ray binary (LMXRB) in the field of view, we use a relationship between the optical and X-ray fluxes for these systems F_optsimF_x/500, where F_opt and F_x are the integrated optical (3000-7000Angstrom) and X-ray (2-11 keV) fluxes, respectively (Van Paradijs, 1995). To obtain the X-ray flux we integrated a power law model with photon index 1.4 (White et al, 1988) and neutral hydrogen column density of 10^22 cm^2 (Dickel, 1995) over the 2-11 keV range using the PIMMS software package and the normalization from the ROSAT HRI observations of the N49 point source (Rothschild et al, 1994). The X-ray flux found was 8.5 X 10^-12 erg cm^-2 s^-1, which yielded an integrated optical flux of 3.0 X 10^-14 erg cm^-2 s^-1. Because the optical flux per frequency f_nu of LMXRB is approximately flat over the wavelengths of interest (Van Paradijs, 1995), we then obtained the predicted (unreddened) differential flux F_nu=3 X 10^-29 erg cm^-2 s^-1 hz^-1 for a putative LMXRB in the N49 point source. Because the X- ray point source coincides with the N49 supernova remnant, the background is dominated by emission lines and nebular continuum emission. To minimize both the background due to emission lines and the extinction, we will use the PC with the F814W filter for the proposed observation. We estimate the reddening using N_H= 10^22 cm^2 derived from the ROSAT PSPC observations of the N49 point source (Dickel, 1995) and the relationship between neutral H column and extinction (Diplas & Savage, 1994). We derive 3.6 magnitudes of extinction at 8140 Angstroms, for an estimated observed magnitude m_nu(8140)=26.35. The mean nebular background was estimated from data in Vancura et al (1992) as m_nu=21.2 per square arcsecond. Object count rates, nebular and sky background (at the south ecliptic pole), dark count rates, and read noise were estimated from "Exposure Time Estimation for WFPC2 Images of Stellar Targets". The count rates are 0.13 counts/sec, 0.031 counts/sec/pixel, and 0.0075 counts/sec/pixel for the source, nebula, and sky, respectively. For the PC, in a 4680 s exposure we obtain a S/N of 8 on the target, assuming that the object falls at a pixel corner (sharpness=0.045). Because read noise is not dominant, we can split the exposures to allow cosmic ray removal. Real Time Justification ----------------------- Continuous viewing zone observation (CVZ) Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6777( 6) - 03/18/99 16:55 - [ 3] Data Distribution Paper Products: Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6777( 6) - 03/18/99 16:55 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 N49-052601- Unidentified, X-ray RA=5H 26M 0.44S +/- 1.72S, DEC=- 2000 I = 25.6 660435 Emitter, Gamma Ray 66D 4' 35.56"+/-5.0" F(8140)=5e-20 Emitter, Star, X-ray SURF-BKG(8140)=5.5e-18 Burster, X-ray Comments: These fluxes are calculated for the filter F814W 6777( 6) - 03/18/99 16:55 - [ 5] 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 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S 660435 ------------------------------------------------------------------------------------------------------------------------------------ 2 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S POS TARG 5, 5 660435 ------------------------------------------------------------------------------------------------------------------------------------ 3 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S 660435 ------------------------------------------------------------------------------------------------------------------------------------ 4 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S POS TARG 5, 5 660435 ------------------------------------------------------------------------------------------------------------------------------------ 6777( 6) - 03/18/99 16:55 - [ 6] Visit: 51 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: This is a repeat of visit 1 which failed GS ACQ. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S 660435 ------------------------------------------------------------------------------------------------------------------------------------ 2 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S POS TARG 5, 5 660435 ------------------------------------------------------------------------------------------------------------------------------------ 3 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S 660435 ------------------------------------------------------------------------------------------------------------------------------------ 4 N49-052601- WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 1100 S POS TARG 5, 5 660435 ------------------------------------------------------------------------------------------------------------------------------------ 6777( 6) - 03/18/99 16:55 - [ 7] Summary Form for Proposal 6777 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ POS TARG 5, 5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names N49-052601-660435 ------------------------------------------------------------------------------------------------------------------------------------