15908( 3) - 04-Oct-2019 15:15:25 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15908 Version: 3 Check-in Time: 04-Oct-2019 15:15:25 STScI Edit Number: 0 Title Probing the inner accretion disk in NGC3147 ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Stefano Bianchi Universita' degli Studi Roma Tre Y CoI: Prof. Robert Antonucci University of California - Santa Barbara N CoI: Dr. Alessandro Capetti Osservatorio Astronomico di Torino N CoI: Dr. Marco Chiaberge Space Telescope Science Institute - ESA N CoI: Dr. Ari Laor Technion-Israel Institute of Technology N ------------------------------------------------------------------------------------ Abstract NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the background host galaxy. Narrow (0.1"x0.1") slit HST spectroscopy allowed excluding the host galaxy light, and revealed a remarkably strong and extremely broad Halpha line. The line profile shows a very steep blue wing and an extended red wing, the signature of a mildly relativistic thin accretion disk line profile. The line profile is well fit with a nearly face on thin disk (i=23 degrees), with an inner radius at 77 gravitational radii, as expected from the R-L^1/2 relation. This result critically questions the very existence of true type 2 AGN, and is likely to change our current view of the accretion flow at low accretion rates. Here we propose to get the first C IV emission line profile of NGC 3147. Reverberation mapping campaigns indicate that the C IV line is produced in a region which is about half the size of the Balmer line emitting region. This means that the C IV line in NGC 3147 can potentially probe the accretion disk well below 50 gravitational radii, a region currently probed only with X-ray line spectroscopy. Optical detections of relativistic line profiles may provide a new and powerful tool for precision measurements of the innermost accretion disk structure and the BH properties, as the optical photons detection rate is >10^5 higher than in the X-rays. ------------------------------------------------------------------------------------ Observations Description ------------------------ We observe the target using STIS/CCD for 4 orbits with the G750L and the G750M gratings, and the FUV/MAMA with G140L. The observations are aimed at characterizing the expected very broad profile of the C iv line, and getting a higher spectral resolution view of the Halpha emission disk line profile previously detected by STIS G750L. In ground based spectra, the emission of these lines is heavily contaminated by the host galaxy stellar emission. We will use the 52x0.1" slit in order to reduce such a contamination by a factor of ~10 with respect to ground 15908( 3) - 04-Oct-2019 15:15:25 - [ 2] based observations. This choice proved extremely effective with the past STIS G750L observation (GO 15225), which revealed for the first time an extremely broad Halpha in this source. The pointing strategy is the same as in our previous program 15225. We will aim at the host galaxy photocenter. A target acquisition image will be taken to allow recentering on the brightest region, which we know coincides with the AGN, as shown by the previous STIS G750L observation. As recommended in the STIS handbook, we will use the F28X50LP lter for the acquisition image and an exposure time of 60s, as in our previous program that observed the very same target. We performed accurate S/N simulations using the STIS ETC: G750M: the most efficient choice is to use the 6295-6867A band, which covers most of the observed disk line Halpha profile and all the bright NLR lines. Using the observed average flux density of the broad Halpha (0.2x10^-15 erg cm^2 s^-1 A^-1, the ETC returns a S/N ~12 per resolution element in 2000 s, which will be accommodated in the first orbit, after the acquisition image. G750L: a very short repetition of the low resolution Halpha profile is important, since the restricted band of G750M does not allow for a proper determination of the continuum level. It will also be used for a direct comparison of the disk line profile measured in the earlier observation. An exposure of 800s will be accommodated at the beginning of orbit 2. G140L: the C iv line is expected to have about the same flux of the Halpha line, as derived from the SDSS QSO template (Vanden Berk et al., 2001), while the continuum is higher by a factor of 5. The E(B-V) of NGC 3147 is fairly low, being 0.02 mag. Adopting a flux density of 5 x0.15 x10^-15 erg cm^-2 s^-1 A^-1 (5 times the observed continuum level around Halpha), the ETC returns a S/N of 12 per resolution element on the continuum, for an exposure time of 8500 s. The required exposure will be split in three orbits (2100s in orbit 2, and 3200 s in orbit 3 and 4). We use the 52x01E1 aperture to mitigate CTE losses, as suggested by the IHB. For the MAMA observations, we will use the D1 aperture, as recommended in the IHB. We use two CR-SPLIT images at each slit position to eliminate cosmic rays in 15908( 3) - 04-Oct-2019 15:15:25 - [ 3] the CCD exposures. We also include simultaneous flat fields to perform de-fringing at long wavelengths, as recommended by the IHB in Sect. 7.2.6. These flats are taken during occultation, immediately after the last on-target exposure in orbits 1 and 2. ------------------------------------------------------------------------------------ 15908( 3) - 04-Oct-2019 15:15:25 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-3147 GALAXY, SEYFERT RA=10H16M53.6509S, J2000 V = 11.43 DEC=+73D24'2.70" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the NED database. The magnitude is the magnitude of the entire galaxy, not the nucleus. Expected nuclear fluxes are given in the Phase I proposal and in the description of the Observations ------------------------------------------------------------------------------------------------------------------------------------ 15908( 3) - 04-Oct-2019 15:15:25 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-3147 STIS/CCD ACQ F28X50LP MIRROR 1 60 S (60 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-3147 STIS/CCD ACCUM 52X0.1E1 G750M 6581 1 2335 S (2335 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 CCDFLAT STIS/CCD ACCUM 52X0.1 G750L 7751 2 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-3147 STIS/CCD ACCUM 52X0.1E1 G750L 7751 1 800 S (800 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-3147 STIS/FUV TIME-TA 52X0.1D1 G140L 1425 BUFFER-TIME=1000 1 1988 S -MAMA G (1988 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC-3147 STIS/FUV TIME-TA 52X0.1D1 G140L 1425 BUFFER-TIME=1597 1 3195 S -MAMA G (3195 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC-3147 STIS/FUV TIME-TA 52X0.1D1 G140L 1425 BUFFER-TIME=1597 1 3195 S -MAMA G (3195 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC-3147 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A NGC-3147 2 STIS/CCD ACCUM 52X0.1E1 G750M 6581 none none none 1 1 N/A NGC-3147 2 STIS/CCD ACCUM 52X0.1E1 G750M 6581 none none none 2 1 N/A CCDFLAT 3 STIS/CCD ACCUM 52X0.1 G750L 7751 none none 1 none 1 N/A CCDFLAT 3 STIS/CCD ACCUM 52X0.1 G750L 7751 none none 2 none 1 N/A NGC-3147 4 STIS/CCD ACCUM 52X0.1E1 G750L 7751 none none none 1 2 N/A NGC-3147 4 STIS/CCD ACCUM 52X0.1E1 G750L 7751 none none none 2 2 N/A NGC-3147 5 STIS/FUV TIME-TA 52X0.1D1 G140L 1425 none none none none 2 N/A -MAMA G NGC-3147 6 STIS/FUV TIME-TA 52X0.1D1 G140L 1425 none none none none 3 N/A -MAMA G NGC-3147 7 STIS/FUV TIME-TA 52X0.1D1 G140L 1425 none none none none 4 N/A -MAMA G 15908( 3) - 04-Oct-2019 15:15:25 - [ 6] Summary Form for Proposal 15908 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.1, 52X0.1D1, 52X0.1E1, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1000, BUFFER-TIME=1597 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G750L, G750M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names CCDFLAT, NGC-3147 ------------------------------------------------------------------------------------------------------------------------------------