8608( 2) - 03/13/00 17:25 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8608 Version: 2 Check-in Date: 04-Jan-2000 17:11:10 1.Proposal Title: Simultaneous HST, Chandra, and FUSE Spectroscopy of NGC 4151 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Gerard Kriss Space Telescope Science Institute CoI: Dr. Andrew Wilson University of Maryland N CoI: Dr. Patrick Shopbell University of Maryland N CoI: Dr. Claude Canizares Massachusetts Institute of Technology N CoI: Dr. Herman Marshall Massachusetts Institute of Technology N ------------------------------------------------------------------------------------ 5. Abstract Absorption by warm, ionized gas at UV and X-ray wavelengths is proving to be a common feature in Seyfert 1 galaxies, showing its presence in well over half the galaxies observed. In some cases, like NGC 4151 and NGC 3516, the absorption is seen over a wide range of ionization states, and it is optically thick at the Lyman limit, thick enough to potentially collimate the ionizing radiation in these objects and produce ``ionization cones" visible in emission-line images. Thus understanding this warm absorbing gas and its origin may help us to understand how radiation is collimated in AGN, and it may provide additional clues to the differences and similarities between Type 1 and Type 2 AGN. The proximity and brightness of NGC 4151 make it a key object for understanding the structure of AGN. We propose to obtain simultaneous spectroscopy of the absorbing gas in NGC 4151 using the STIS echelle modes on HST, FUSE, and Chandra. These observations will allow us to determine the ionization states of each of the 8 kinematic components present in the absorbing gas in NGC 4151, and to resolve the persistent discrepancies between the gas columns inferred for the UV and X-ray absorption over the past two decades. The simultaneity will avoid any ambiguity due to the known variability in the UV and X-ray absorption. ------------------------------------------------------------------------------------ 8608( 2) - 03/13/00 17:25 - [ 2] Observations Description ------------------------ Our proposed observations will obtain medium-resolution echelle spectra of all UV resonance lines in NGC 4151 longward of 1200 A using the STIS MAMAs and gratings E140M and E230M. One wavelength setting for E140M covers Lyalpha, N V, Si IV, and C IV; the Mg II doublet requires the NUV-MAMA and a single setting of E230M. As our goal, we aim for S/N comparable to that obtained by Weymann et al. (1997) in their GHRS observations of the C IV profile as illustrated in Figure 1. Those spectra have a S/N of ~50 per 0.072 Angstrom resolution element. The higher resolution STIS echelle spectra (0.033 Angstrom per resolution element) therefore will require a S/N of 34 per resolution element for comparable quality. (The lower resolution GHRS spectra were adequate to resolve all features intrinsic to NGC 4151, so our proposed STIS spectra can be binned to lower resolution to improve S/N, if necessary.) Although NGC 4151 is variable, the UV continuum flux has been well above the historical average for the past five years. The lowest recently observed flux was 2.85 * 10^-13 erg cm^-2 s^-1 AA^-1 at 1000 Angstrom, observed with ORFEUS on 3 December 1996. We use this as our baseline for estimating the required exposure times. For the 0.2X0.2 aperture, the STIS exposure time calculator then gives a required exposure time of 10, 600 s for E140M, and 2450 s for E230M if the NGC 4151 spectrum is normalized to these flux levels. (The highest observed flux is less than 2 * this value, which is still more than an order of magnitude below the level at which there would be any bright-object protection concerns.) We note that our proposed spectra of the Mg II line region will have a higher S/N than that shown in Figure 1, and will be comparable in quality to the C IV profile. Allowing for overheads as given in Chapter 16 of the Cycle 9 Call for Proposals, these exposures can be carried out in one visit with a total allocation of 5 orbits. NGC 4151 has a total visibility of 54 m. This allows time for science exposures as follows: Orbit 1: GSAcq+TargAcq+MAMAovhd = 20 m; 2080 s exposure with E140M., Orbit 2: GSReAcq = 5 m; 2460 s exposure with E140M., Orbit 3: GSReAcq = 5 m; 2460 s exposure with E140M., Orbit 4: GSReAcq = 5 m; 2460 s exposure with E140M. (Total of 9, 460 s for E140M.) Orbit 5: GSReAcq+MAMAovhd = 13 m; 2560 s exposure with E230M. Real Time Justification ----------------------- The proposed HST observations will be coordinated with Chandra observations and with FUSE observations. Both the Chandra and FUSE observing times have already been allocated as part of the respective observatories GTO time awarded to Andrew Wilson (Chandra ACIS), Claude Canizares (Chandra HETG) and Gerard Kriss (FUSE). The primary scheduling constraint on our observations is a roll restriction on the Chandra observations that will prevent the extended X-ray emission in NGC 4151 and a nearby source from contaminating the dispersed HETG spectra. Acceptable rolls for the Chandra observations are 145 +10/-25 and 296 +/- 4 degrees; observations in these ranges are possible between January 31, 2000, and March 16, 2000, and July 24, 2000, and August 5, 2000. The latter range of possible dates is narrowed by the HST sun avoidance constraint, which is violated by NGC 4151 starting on July 31. FUSE observations are not impacted by sun constraints until August 10, but the entirety of the second window is at high beta angles, where FUSE now exhibits thermal mechanical instabilities that make it difficult to keep a target in the observing apertures. Thus the preferred time for scheduling these observations is in the January 31 to March 16 window. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8608( 2) - 03/13/00 17:25 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4151 GALAXY, SEYFERT RA=12H 10M 32.65S +/- 0.1S, J2000 Z=0.0033 V = 12.5 DEC=+39D 24' 20.6" +/- 1.0", B-V = 0.7 PLATE-ID=01QY F-CONT(1450)=2.9+/-2.4e-13 Comments: UV flux is variable by factors of several. 8608( 2) - 03/13/00 17:25 - [ 4] Visit: 01 Visit Priority: Visit Requirements: SCHED 100% On Hold Comments: Additional Comments: To be coordinated to within +/- 3 days with FUSE and Chandra Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4151 STIS/C ACQ F28X50L MIRROR 1 0.1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4151 STIS/F ACCUM 0.2X0.2 E140M 1425 2 1040 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4151 STIS/F ACCUM 0.2X0.2 E140M 1425 6 1230 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4151 STIS/N ACCUM 0.2X0.2 E230M 2707 2 1280 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8608( 2) - 03/13/00 17:25 - [ 5] Summary Form for Proposal 8608 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHED 100% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4151 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2707 ------------------------------------------------------------------------------------------------------------------------------------