8109( 8) - 12/23/99 14:17 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8109 Version: 8 Check-in Date: 23-Dec-1999 14:16:48 1.Proposal Title: Determination of the SED for TON S180: A Direct Probe of the Big Blue Bump ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Jane Turner NASA Goddard Space Flight Center CoI: Dr. Steven Kraemer Catholic University of America/STIS N Science team CoI: Dr. Michael Crenshaw Catholic University of America/STIS N Science team CoI: Dr. Ian George NASA/Goddard Space Flight Center N CoI: Dr. Gerard Kriss Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract The Seyfert 1 galaxy, TON S180, is the brightest AGN in the extreme UV regime, there is a low Galactic column along the line-of-sight and no evidence for intrinsic absorption. This offers a rare opportunity to obtain the spectral-energy- distribution (SED) of the source, including data from the vital soft X-ray to UV range which is generally difficult to observe due to absorption of those photons by Galactic material. TON S180 has a strong soft X-ray excess, and may be the best case in which to confirm the presence of a Big Blue Bump (BBB). The existence of a BBB in the EUV continuum is extremely controversial. For example, although the SEDs derived from QSO spectra appear to be power-laws, photoionization models based on these fits greatly underpredict the strength of the He II emission lines. This apparent deficit of He II ionizing photons could be explained if a BBB were indeed present. We request a STIS observation of TON S180, to be made simultaneous with our approved AXAF and FUSE observations. The combined data will allow us to determine the SED and test the presence of a BBB, addressing the photon deficit problem in detail. ------------------------------------------------------------------------------------ 8109( 8) - 12/23/99 14:17 - [ 2] Observations Description ------------------------ We propose a single orbit exposure on TON S180 splitting the time between G140L and G230L. Continuum variations in this source are thought to be slow in the optical regime, with significant variations occuring on timescales of a year (Winkler 1997). However, the source is highly variable in the EUVE bandpass (Hwang and Bowyer 1996) and the X-ray data indicate a strong dependence of variability amplitude on photon energy, such that factor-of-several variations seem to be observed in the XUV regime down to timescales of a few thousand seconds (Turner et al. 1998). As the source has never been monitored in the STIS bandpass, its variability properties in that band can be considered highly uncertain. For this reason, we request simultaneous observation by STIS, with AXAF, FUSE and (we intend) support by a ground-based observatory, to ensure an accurate SED will be obtained for a single epoch. We used archival IUE spectra (Fig. 1) to estimate the signal-to-noise which will be ac hieved in the proposed STIS exposure. The visibility for TON S180 is 53 min. The time overheads from V2.0 of the STIS Instrument Handbook are: beginitemize em Guide Star Acquisition 7 min em Target Acquisition 6 min em 1st MAMA exp. 8 min em 2nd MAMA exp. 4 min enditemize This leaves 28 min for science exposures. The STIS exposure time calculator gives the following estimates. For G140L/FUV- MAMA, 0.5x52 slit, a 600 s exposure gives a signal-to-noise > 20 across the spectrum, with a peak over 50. The G230L/NUV-MAMA, 0.5x52 slit, with a 1000 s exposure also gives a signal-to-noise > 20 across the spectrum, with a peak over 50. Thus we can obtain a high-quality spectrum in a very modest exposure time. Real Time Justification ----------------------- None The approved AXAF observations utilize the ACIS/LETG combination, for an accurate X-ray spectrum down to ~ 0.2 keV. The AXAF exposure time will be 80 ks, this relatively long exposure will help the scheduling of three simultaneous satellites. FUSE will cover 912-1180 Angstrom at ~ 0.03 Angstrom resolution and a 27 ks observation is planned. We also plan to obtain contemporaneous optical spectra from ground based observatories. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8109( 8) - 12/23/99 14:17 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 TONS180 GALAXY, SEYFERT, RA=00H 57M 20.09S +/- 0.02S, J2000 Z = V = 14.4 NUCLEUS DEC=-22D 22' 56.2" +/- 0.5", 0.062 PLATE-ID=011P 8109( 8) - 12/23/99 14:17 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 01-Jan-2000 AND 08-Feb-2000 On Hold Comments: Additional Comments: Coordinated with Chandra. Target enters solar avoidance zone on 8-Feb-2000. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 TONS180 STIS/C ACQ F28X50L MIRROR 1 1.0 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 TONS180 STIS/F ACCUM 52X0.2 G140L 1425 1 1260 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 TONS180 STIS/N ACCUM 52X0.2 G230L 2376 1 720 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8109( 8) - 12/23/99 14:17 - [ 5] Summary Form for Proposal 8109 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-Jan-2000 AND 08-Feb-2000 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names TONS180 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2376 ------------------------------------------------------------------------------------------------------------------------------------