7360( 9) - 08/22/97 15:43 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7360 Version: 9 Check-in Date: 22-Aug-1997 15:42:37 1.Proposal Title: A Search for Broad Absorption Lines in Narrow-Line Seyfert 1 Galaxies ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle AGN/QUASARS GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: KAREN M. LEIGHLY COLUMBIA UNIVERSITY CoI: Dr. Jules Halpern Columbia University N CoI: Dr. Chiko Otani RIKEN N ------------------------------------------------------------------------------------ 6. Abstract Recent ASCA X-ray spectra of several narrow-line Seyfert 1 galaxies (NLS1s) show a feature near 1 keV that can be described as an absorption edge. If it is due to ionized oxygen, the principal absorber in the X-ray spectra of broad- line Seyfert 1s, a blueshift of 0.2-0.3 c is implied. This is reminiscent of the UV absorption lines seen in broad absorption line quasars (BALQSOs). To investigate this possible connection, we propose to obtain UV spectra to search for blueshifted absorption lines in two of the NLS1s that show the X-ray absorption feature, IRAS 13224-3809 and H0707-495. NLS1s are bright X-ray sources, while BALQSOs are quite weak, but evidence points toward extreme X-ray absorption in the latter. Discovery of absorption lines in the UV spectra of NLS1s would demonstrate a continuity between NLS1s and BALQSOs that is based upon the degree of absorption. Hints of a relationship are already present in terms other properties shared by both classes, including strong or extreme Fe II emission, weak [O III] emission, red optical continua, and strong infrared emission. If we can establish the existence of BALs in NLS1s, we can use them to address open questions such as: Is the continuum of BALQSOs intrinsically red? Why is extreme ionFe2 emission found preferentially in NLS1s and BALQSOs? What is the origin of the remarkable X-ray variability of NLS1s, and what is its effect upon the BALs? ------------------------------------------------------------------------------------ 7360( 9) - 08/22/97 15:43 - [ 2] Observations Description ------------------------ Scientific Goals The Search for BAL in Two NLS1s We propose to make a sensitive search for absorption lines and troughs in the UV spectra of the narrow-line Seyfert 1 galaxies IRAS 13224-3809 and H0707-495. These objects were chosen because they show strong X-ray evidence for blueshifted absorption edges in the ASCA spectra (Leighly et al. 1997). IRAS 13224-3809 was observed several times with IUE (Mas-Hesse et al. 1994). No broad absorption lines are seen in those spectra; however, IRAS 13224-3809 is a fairly faint UV source, so the existence of features at or below the level of the continuum, including the low- ionization emission and absorption lines of Fe II and Mg II longward of 2000 A (e.g., Halpern et al. 1996), cannot be established using IUE. Furthermore, because of the strong soft X-ray emission observed from these objects, we expect their absorbing column densities to be moderate, and thus the equivalent widths of the absorption lines to be small. Nevertheless, they should be detectable. For example, Mathur, Elvis & Wilkes (1995) show that associated absorption features in NGC 5548 are consistent with an origin in the same material as the warm absorber that is apparent in the X-ray spectrum. The optical depths of O(+6) and O(+7) measured in IRAS 13224-3809 are 2-6 times larger than those of NGC 5548 (depending on the ion), so we might expect larger equivalent widths in the UV spectrum, although that depends on the ionization parameter of the absorbing material and differences between the ionizing continuum shape of IRAS 13224-3809 and NGC 5548. If we detect the broad absorption lines in the UV spectrum at the same blueshift at the X-ray absorption edges, it would suggest that they occur in the same material. Then we can use methods pioneered by Mathur and collaborators (Mathur, Elvis & Wilkes 1995 and references therein) which employ the photoionization code CLOUDY by G. Ferland to determine whether the column densities in different ions are indeed consistent with an origin in the same material. If so, we can estimate the ionization state of the UV absorption region, and compare with that predicted by the photoionization model to determine the abundances (e.g. Turnshek et al. 1996). We will have the advantage that we have a better idea of the actual photoionization spectrum, since the X-ray spectrum is observed. Implied velocities of 0.2-0.3 c are measured from the ASCA spectra of IRAS 13224-3809 and H0707-495. These are suggestively close to 0.26 c, the velocity of the jets in SS 433. This could indicate that line locking contributes to the acceleration of the material, as was once hypothesized for SS 433 (e.g. Shapiro et al. 1986, although the radiation in that case was not intense enough). If so, we might see an absorption feature which is fairly narrow, as the lines are in SS 433, indicating the termination of the acceleration at v=0.26c. Recently, an isolated broad absorption feature at 0.19c was found in HST spectra from PG2302+029 (Jannuzi et al. 1996), offering a very interesting precedent for what we may see. Other Goals There are some other problems we will address with the spectra from these NLS1s. We will be able to measure the UV continuum and lines accurately for the first time in IRAS 13224-3809, and for the first time ever in H0707-495. The continuum will be essential to estimate the broad band spectrum for photoionization modeling. A full complement of UV lines is necessary to understand the ways, if any, in which the emission-line clouds of NLS1s are different from those of ordinary Seyfert 1 galaxies, apart from their apparent velocities. The various lines in the UV from different ions of carbon and other elements provide excellent diagnostics of the ionization parameter and density in the BLR that are not available in the optical. Since these objects are strong, narrow Fe II emitters, they are best suited for resolving the complexes of blended lines that dominate the near UV spectral region, and are responsible for a large fraction of the cooling. The mystery of the excitation mechanism of the strong Fe II emission in AGNs will probably not be understood without better diagnostics that might be discovered among these dominant UV Fe II lines. The objectives of this proposal are to obtain spectra of the ultraviolet emission lines, absorption lines, and continuum of two narrow-line Seyfert 1 galaxies, IRAS 13224-3809 and 1H 0707-495. Our special emphasis is a search for broad absorption lines. We propose to accomplish this using the STIS UV MAMA detectors and the two overlapping gratings G140L and G230L, which cover the wavelength range 1150-3180A. Four IUE spectra of IRAS 13224-3809 are available that can be used to calculate required exposure times. Variability is the main uncertainty, as the IUE spectra show that the flux in the far UV varies by a factor of 4-5 on time scales of months. Accordingly, we estimate exposure times conservatively, based on the weakest of the IUE spectra. There were no IUE observations of H0707-495, but the optical spectrum and photometry of Remillard et al. (1986) show that it is quite blue, with V=15.70, B-V = 0.32, and U-B=-0.71. Its flux at 3200 A is 4 x 10(-15) ergs/cm2/s/A, about twice that of IRAS 13224-3809. We calculate exposure times for H0707-495 assuming that in the ultraviolet it is twice as bright as the low state of IRAS 13224-3809. The limiting factor in determining the exposure times is the low throughput of both gratings at the wavelength of C IV, the principal line in which to search for a BAL. We require a signal-to-noise ratio of at least 20 in the continuum around C IV. In the case of IRAS 13224-3809 (z = 0.0667), the C IV line falls at 1653 A, so it will be included in both the G140L and G230L gratings. But at the lower redshift of H0707-495 (z = 0.0411), a useful detection of the C IV line will be made only in the G140L spectrum, so the exposure must be longer. There will be several other lines in which to look for BALs, principally Ly alpha, N V (1240A), and Mg II (2800A). Each of these lines will be well exposed in these spectra, with Ly alpha shifted significantly away from the geocoronal feature, especially in IRAS 13224-3809. We were awarded 8 orbits in the Phase I proposal review, which is half of what we had requested. Accordingly, we have designed an efficient program observations so that both objects will observed, as was recommended to us by the proposal review panel. We propose to use a 0.5" wide slit, which offers the best compromise between far-UV throughput and spectral resolution, and which does not require acquisition/peakup. The accompanying Table shows the predicted fluxes in the continuum near the important lines, and the signal-to-noise ratios that can be expected for the revised exposure times. We took into account the sensitivity curves and dark count of the MAMA detectors, and a slit thoughput ranging from 76-84% in the UV was assumed, as indicated in the STIS manual. To calculate signal-to-noise ratios, it was assumed that a resolution element in the FUV MAMA detector consists of 2 pixels in the dispersion direction times 7 pixels in the spatial direction, the latter enclosing 80% of the transmitted flux. In the NUV MAMA, the resolution element is 2 X 5 pixels. In all cases, sky background is negligible. Because it is not yet known if signal-to-noise ratios much larger than 30 can be obtained with the MAMA detectors (due to fixed or time-dependent patterns in their flat fields), we will step the target along the slit several times during the exposure to reduce the effects of pattern noise. Taking into account the visibility period for each object, the observations of IRAS 13224-3809 can be completed in 5 orbits, while H0707--495 will require 3 orbits. RESULTS OF FEASIBILITY CALCULATIONS Target Grating Wavelength Flux(a) Counts/s(b) Exposure SNR Orbits (Angstroms) (minutes) --------------------------------------------------------------------- --------- IRAS G140L 1300 1.3 0.082 136 26 3 1650 0.8 0.013 10 IRAS G230L 1650 0.8 0.021 77 9 2 2035 1.0 0.156 26 3000 1.5 0.299 37 H0707 G140L 1265 2.6 0.164 92 30 2 1600 1.6 0.036 14 H0707 G230L 2000 2.0 0.285 31 22 1 2900 3.0 0.717 37 Notes: Multiple entries for a particular grating denote calculations for regions near different emission lines. (a) In units of 10E(-15)erg/cm2/s/A. (b) The counts per second per resolution element, defined in the text. References Halpern, J. P., et al. 1996, ApJ, 464, 704 Jannuzi, B. T. et al. 1996, preprint Leighly, K. M. 1997, submitted to ApJ Letters Mas-Hesse, J. M., et al. 1994, A&A, 283, L9 Mathur, S., Elvis, M., & Wilkes, B., 1995, ApJ, 452, 230 Remillard, R.A., et al. 1986, ApJ, 301, 742 Shapiro, P. R., et al. 1986, ApJS, 60, 393 Turnshek, D.A., et al. 1996, ApJ, 463, 110 Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7360( 9) - 08/22/97 15:43 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7360( 9) - 08/22/97 15:43 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IRAS13224- GALAXY, Seyfert RA=13H 25M 19.28S +/- 0.4", DEC= J2000 Z=0.0667 V = 15.9 3809 -38D 24' 53.5" +/- 0.4", PLATE- F-CONT(1300)=1.3e-15 ID=02EI F-CONT(3000)=1.5e-15 Comments: It is important to obtain high signal-to-noise so please make science exposures as long as possible. 2 1H0707-495 GALAXY, Seyfert RA=07H 08M 41.47S +/- 0.3", DEC= J2000 Z=0.0411 V = 15.7 -49D 33' 5.8" +/- 0.3", PLATE- B-V = 0.32 ID=019B U-B = -0.71 Comments: It is important to obtain high signal-to-noise so please reduce science exposures as little as possible. 7360( 9) - 08/22/97 15:43 - [ 5] Visit: 01 Visit Requirements: 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 IRAS13224-3 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 4.0 S ONBOARD ACQ for 2,3 809 CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 IRAS13224-3 STIS/N ACCUM 52X0.5 G230L 2376 PATTERN=ALONG-SLIT,NUM-POS=4, 1 1155 S 809 UV-MAM STEP-SIZE=1.0 A Comments: It is important to obtain high signal-to-noise so please make science exposures as long as possible. ------------------------------------------------------------------------------------------------------------------------------------ 3 IRAS13224-3 STIS/F ACCUM 52X0.5 G140L 1425 PATTERN=ALONG-SLIT,NUM-POS=3, 1 2300 S 809 UV-MAM STEP-SIZE=1.0 A Comments: It is important to obtain high signal-to-noise so please make science exposures as long as possible. ------------------------------------------------------------------------------------------------------------------------------------ 7360( 9) - 08/22/97 15:43 - [ 6] Visit: 02 Visit Requirements: 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 1H0707-495 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 4.0 S ONBOARD ACQ for 2,3 CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 1H0707-495 STIS/N ACCUM 52X0.5 G230L 2376 PATTERN=ALONG-SLIT,NUM-POS=4, 1 465 S UV-MAM STEP-SIZE=1.0 A Comments: It is important to obtain high signal-to-noise so please make science exposures as long as possible. ------------------------------------------------------------------------------------------------------------------------------------ 3 1H0707-495 STIS/F ACCUM 52X0.5 G140L 1425 PATTERN=ALONG-SLIT,NUM-POS=4, 1 1120 S MIN DUR UV-MAM STEP-SIZE=1.0 A Comments: It is important to obtain high signal-to-noise so please make science exposures as long as possible. ------------------------------------------------------------------------------------------------------------------------------------ 7360( 9) - 08/22/97 15:43 - [ 7] Summary Form for Proposal 7360 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT STEP-SIZE=1.0 NUM-POS=3 NUM-POS=4 PATTERN=ALONG-SLIT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category AGN/QUASARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ for 2,3 MIN DUR ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G230L G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names IRAS13224-3809 1H0707-495 ------------------------------------------------------------------------------------------------------------------------------------