Simultaneous Ultraviolet and X-Ray Observations of Seyfert Galaxy NGC 4151. I. Physical Conditions in the X-Ray Absorbers

We present a detailed analysis of the intrinsic X-ray absorption in the Seyfert 1 galaxy NGC 4151 using Chandra High Energy Transmission Grating Spectrometer data obtained in 2002 May as part of a program that included simultaneous ultraviolet (UV) spectra using the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectrographic Explorer. Previous studies, most recently using Advanced Satellite for Cosmology and Astrophysics (ASCA) spectra, revealed a large (>1022 cm-2) column of intervening gas, which has varied both in ionization state and total column density. NGC 4151 was in a relatively low flux state during the observations reported here (~25% of its historic maximum), although roughly 2.5 times as bright in the 2-10 keV band as during a Chandra observation in 2000. At both epochs, the soft X-ray band was dominated by emission lines, which show no discernible variation in flux between the two observations. The 2002 Chandra data show the presence of a very highly ionized absorber, in the form of H-like and He-like Mg, Si, and S lines, as well as lower ionization gas via the presence of inner-shell absorption lines from lower ionization species of these elements. The latter accounts for both the bulk of the soft X-ray absorption and the high covering factor UV absorption lines of O VI, C IV, and N V with outflow velocities ≈500 km s-1. The presence of high-ionization gas, which is not easily detected at low resolution (e.g., with ASCA), appears common among Seyfert galaxies. Since this gas is too highly ionized to be radiatively accelerated in sources such as NGC 4151, which is radiating at a small fraction of its Eddington Luminosity, it may be key to understanding the dynamics of mass outflow. We find that the deeper broadband absorption detected in the 2000 Chandra data is the result of both (1) lower ionization of the intervening gas due to the lower ionizing flux and (2) a factor of ~3 higher column density of the lower ionization component. To account for this bulk motion, we estimate that this component must have a velocity ≳1250 km s-1 transverse to our line of sight. This is consistent with the rotational velocity of gas arising from the putative accretion disk. While both thermal wind and magnetohydrodynamic models predict large nonradial motions, we suggest that the latter mechanism is more consistent with the results of the photoionization models of the absorbers

[1]  Hagai Netzer,et al.  Dynamical and Spectral Modeling of the Ionized Gas and Nuclear Environment in NGC 3783 , 2005, astro-ph/0502272.

[2]  D. Crenshaw,et al.  The Connection between the Narrow-Line Region and the UV Absorbers in Seyfert Galaxies , 2005, astro-ph/0501257.

[3]  M. Bottorff,et al.  Complex X-Ray Absorption and the Fe Kα Profile in NGC 3516 , 2004, astro-ph/0409091.

[4]  T.J.Turner,et al.  Complex X-ray Absorption and the Fe Kalpha Profile in NGC 3516 , 2004, astro-ph/0409091.

[5]  B. M. Peterson,et al.  Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database , 2004, astro-ph/0407299.

[6]  G. Ferland,et al.  The Effects of Low-Temperature Dielectronic Recombination on the Relative Populations of the Fe M-Shell States , 2003, astro-ph/0311568.

[7]  Kazunori Ishibashi,et al.  In-flight calibration of the Chandra high-energy transmission grating spectrometer , 2003, SPIE Optics + Photonics.

[8]  Adam P. Hitchcock,et al.  Composition of the Chandra ACIS contaminant , 2003, SPIE Optics + Photonics.

[9]  D. Crenshaw,et al.  Mass Loss from the Nuclei of Active Galaxies , 2003 .

[10]  J. C. Shields,et al.  The Ionized Gas and Nuclear Environment in NGC 3783. IV. Variability and Modeling of the 900 Kilosecond Chandra Spectrum , 2003, astro-ph/0309096.

[11]  M. Sako,et al.  A Long Look at NGC 3783 with the XMM-Newton Reflection Grating Spectrometer , 2003, astro-ph/0307467.

[12]  M. Gu,et al.  Dielectronic Recombination Rate Coefficients for H-like through Ne-like Isosequences of Mg, Si, S, Ar, Ca, Fe, and Ni , 2003 .

[13]  Mark W. Bautz,et al.  Advanced CCD imaging spectrometer (ACIS) instrument on the Chandra X-ray Observatory , 2003, SPIE Astronomical Telescopes + Instrumentation.

[14]  Shai Kaspi,et al.  The Ionized Gas and Nuclear Environment in NGC 3783. II. Averaged Hubble Space Telescope/STIS and Far Ultraviolet Spectroscopic Explorer Spectra , 2003, astro-ph/0506323.

[15]  B. Krauskopf,et al.  Proc of SPIE , 2003 .

[16]  D. Crenshaw,et al.  Variable Ultraviolet Absorption in the Seyfert 1 Galaxy NGC 3516: The Case for Associated Ultraviolet and X-Ray Absorption , 2002, astro-ph/0205389.

[17]  Astronomy,et al.  Characterizing the complex absorber in NGC 4151 , 2002, astro-ph/0204057.

[18]  W. Brandt,et al.  The Ionized Gas and Nuclear Environment in NGC 3783. I. Time-averaged 900 Kilosecond Chandra Grating Spectroscopy , 2002, astro-ph/0203263.

[19]  R. V. Meer,et al.  X-ray spectroscopy of NGC 5548 , 2002, astro-ph/0202481.

[20]  H. Netzer,et al.  Inner-Shell 1s-2p Soft X-Ray Absorption Lines , 2002, astro-ph/0201416.

[21]  D. Crenshaw,et al.  Mass Outflow in Active Galactic Nuclei: New Perspectives , 2002 .

[22]  Gerard A. Kriss,et al.  Warm Absorbers in Active Galactic Nuclei: A Multitemperature Wind , 2001 .

[23]  H. Netzer,et al.  Radiation pressure acceleration by X-rays in active galactic nuclei , 2001, astro-ph/0104260.

[24]  Shai Kaspi,et al.  High-Resolution X-Ray Spectroscopy and Modeling of the Absorbing and Emitting Outflow in NGC 3783 , 2001, astro-ph/0101540.

[25]  J. Hutchings,et al.  Space Telescope Imaging Spectrograph Echelle Observations of the Seyfert Galaxy NGC 4151: Physical Conditions in the Ultraviolet Absorbers , 2001, astro-ph/0101037.

[26]  J. Lee,et al.  Chandra Observations of the X-Ray Narrow-Line Region in NGC 4151 , 2000, astro-ph/0010314.

[27]  J. Hutchings,et al.  Space Telescope Imaging Spectrograph Echelle Observations of NGC 4151: Variable Ionization of the Intrinsic UV Absorbers , 2000, astro-ph/0009356.

[28]  G. Ferland,et al.  Magnetic Confinement, Magnetohydrodynamic Waves and Smooth Line Profiles in Active Galactic Nuclei , 2000 .

[29]  J. Nousek,et al.  Discovery of Narrow X-Ray Absorption Lines from NGC 3783 with the Chandra High Energy Transmission Grating Spectrometer , 2000, The Astrophysical journal.

[30]  G. Ferland,et al.  Magnetic Confinement, MHD Waves, and Smooth Line Profiles in AGN , 2000, astro-ph/0001532.

[31]  K. Korista,et al.  Dynamics of Warm Absorbing Gas in Seyfert Galaxies: NGC 5548 , 2000, astro-ph/0001514.

[32]  Paul S. Smith,et al.  Reverberation Measurements for 17 Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei , 1999, astro-ph/9911476.

[33]  D. Crenshaw,et al.  Intrinsic Absorption Lines in the Seyfert 1 Galaxy NGC 5548: Ultraviolet Echelle Spectra from the Space Telescope Imaging Spectrograph , 1999, astro-ph/9903439.

[34]  Stephen P. Maran,et al.  Intrinsic Absorption Lines in Seyfert 1 Galaxies. I. Ultraviolet Spectra from the Hubble Space Telescope , 1998, astro-ph/9812265.

[35]  G. Ferland,et al.  CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra , 1998 .

[36]  K. Nandra,et al.  ASCA Observations of Seyfert 1 Galaxies. III. The Evidence for Absorption and Emission Due to Photoionized Gas , 1997, astro-ph/9708046.

[37]  A. Fabian,et al.  Geometrical and chemical dependence of K-shell X-ray features , 1997 .

[38]  Herman L. Marshall,et al.  Preliminary test results on spectral resolution of the Low Energy Transmission Grating Spectrometer on board of AXAF , 1997, Optics & Photonics.

[39]  C. Reynolds,et al.  An X-ray spectral study of 24 type 1 active galactic nuclei , 1997 .

[40]  R. Weymann,et al.  GHRS Monitoring of the Outflowing Material in NGC 4151 , 1996, astro-ph/9610227.

[41]  Edward M. Murphy,et al.  Galactic H i Column Densities toward Quasars and Active Galactic Nuclei , 1996 .

[42]  A. Zdziarski,et al.  Broad-band γ-ray and X-ray spectra of NGC 4151 and their implications for physical processes and geometry , 1996, astro-ph/9607015.

[43]  Gerard A. Kriss,et al.  Multiwavelength observations of short-timescale variability in NGC 4151 .4. Analysis of multiwavelength continuum variability , 1996 .

[44]  Shai Kaspi,et al.  Multiwavelength observations of short-timescale variability in NGC 4151 .1. Ultraviolet observations , 1996 .

[45]  Riken,et al.  ASCA observations of the composite warm absorber in NGC 3516 , 1996, astro-ph/9603057.

[46]  D. A. Verner,et al.  Atomic data for astrophysics. II. New analytic fits for photoionization cross sections of atoms and ions , 1996 .

[47]  J. Chiang,et al.  Accretion Disk Winds from Active Galactic Nuclei , 1995 .

[48]  Wei Zheng,et al.  The Far-Ultraviolet Spectrum of NGC 4151 as Observed with the Hopkins Ultraviolet Telescope on Astro-2 , 1995 .

[49]  J. Krolik,et al.  Observable Properties of X-Ray--heated Winds in Active Galactic Nuclei: Warm Reflectors and Warm Absorbers: Erratum , 1995, astro-ph/9501089.

[50]  Masaru Matsuoka,et al.  New X-ray spectral observations of NGC 4151 with ASCA , 1994 .

[51]  A. Königl,et al.  DISK-DRIVEN HYDROMAGNETIC WINDS AS A KEY INGREDIENT OF ACTIVE GALACTIC NUCLEI UNIFICATION SCHEMES , 1994 .

[52]  S. Mathur,et al.  The X-ray and ultraviolet absorbing outflow in 3C 351 , 1994 .

[53]  Zhi-Yun Li,et al.  Radiative acceleration in outflows from broad absorption line quasi-stellar objects. 2: Wind models , 1994 .

[54]  D. Balsara,et al.  Numerical simulation of X-ray-heated winds in Seyfert galaxies. I - The case of zero angular momentum , 1993 .

[55]  H. Ferguson,et al.  Hopkins ultraviolet telescope observations of the far-ultraviolet spectrum of NGC 4151 , 1992 .

[56]  R. Blandford,et al.  Magnetic acceleration of broad emission-line clouds in active galactic nuclei , 1992 .

[57]  Andrew C. Fabian,et al.  X-ray reflection from cold matter in Active Galactic Nuclei and X-ray binaries , 1991 .

[58]  Robert S. Warwick,et al.  The X-ray spectral variability of NGC 4151 , 1991 .

[59]  Robert S. Warwick,et al.  Variable X-Ray Absorption in NGC 4151 , 1989 .

[60]  Julian H. Krolik,et al.  Molecular tori in Seyfert galaxies - Feeding the monster and hiding it , 1988 .

[61]  M. Rees.  Magnetic confinement of broad-line clouds in active galactic nuclei , 1987 .

[62]  Julian H. Krolik,et al.  An X-ray heated wind in NGC 1068 , 1986 .

[63]  M. Ulrich,et al.  Detailed observations of NGC 4151 with IUE – IV. Absorption line spectrum and variability , 1985 .

[64]  C. McKee,et al.  Compton heated winds and coronae above accretion disks. I. Dynamics , 1983 .

[65]  R. Blandford,et al.  Hydromagnetic flows from accretion discs and the production of radio jets , 1982 .

[66]  J. Krolik,et al.  Two-phase models of quasar emission line regions , 1981 .

[67]  C. C. Wu,et al.  IUE observations of extragalactic objects , 1978, Nature.

[68]  P. Barr,et al.  An increase in the X-ray absorption of NGC 4151 , 1977 .

[69]  J. Ives,et al.  The variability and absorption of the X-ray emission from NGC 4151. , 1976 .

[70]  John I. Castor,et al.  Radiation-driven winds in Of stars. , 1975 .