Simultaneous ultraviolet and X-ray observations of seyfert galaxy NGC 4151. I. Physical conditions in the X-ray absorbers

S. B. Kraemer, I. M. George, D. M. Crenshaw, Jack Gabel, T. J. Turner, T. R. Gull, J. B. Hutchings, G. A. Kriss, R. F. Mushotzky, H. Netzer, B. M. Peterson, Ehud Behar

Research output: Contribution to journalArticle

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Abstract

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

Original languageEnglish
Pages (from-to)693-705
Number of pages13
JournalAstrophysical Journal
Volume633
Issue number2 I
DOIs
StatePublished - Nov 10 2005
Externally publishedYes

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Seyfert galaxies
absorbers
ionization
gas ionization
gases
gas
cosmology
astrophysics
x rays
ultraviolet absorption
ultraviolet spectra
outflow
Hubble Space Telescope
accretion disks
magnetohydrodynamics
line of sight
spectrographs
photoionization
coverings
luminosity

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Space and Planetary Science

Cite this

Simultaneous ultraviolet and X-ray observations of seyfert galaxy NGC 4151. I. Physical conditions in the X-ray absorbers. / Kraemer, S. B.; George, I. M.; Crenshaw, D. M.; Gabel, Jack; Turner, T. J.; Gull, T. R.; Hutchings, J. B.; Kriss, G. A.; Mushotzky, R. F.; Netzer, H.; Peterson, B. M.; Behar, Ehud.

In: Astrophysical Journal, Vol. 633, No. 2 I, 10.11.2005, p. 693-705.

Research output: Contribution to journalArticle

Kraemer, SB, George, IM, Crenshaw, DM, Gabel, J, Turner, TJ, Gull, TR, Hutchings, JB, Kriss, GA, Mushotzky, RF, Netzer, H, Peterson, BM & Behar, E 2005, 'Simultaneous ultraviolet and X-ray observations of seyfert galaxy NGC 4151. I. Physical conditions in the X-ray absorbers', Astrophysical Journal, vol. 633, no. 2 I, pp. 693-705. https://doi.org/10.1086/466522
Kraemer, S. B. ; George, I. M. ; Crenshaw, D. M. ; Gabel, Jack ; Turner, T. J. ; Gull, T. R. ; Hutchings, J. B. ; Kriss, G. A. ; Mushotzky, R. F. ; Netzer, H. ; Peterson, B. M. ; Behar, Ehud. / Simultaneous ultraviolet and X-ray observations of seyfert galaxy NGC 4151. I. Physical conditions in the X-ray absorbers. In: Astrophysical Journal. 2005 ; Vol. 633, No. 2 I. pp. 693-705.
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abstract = "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",
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T1 - Simultaneous ultraviolet and X-ray observations of seyfert galaxy NGC 4151. I. Physical conditions in the X-ray absorbers

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AU - George, I. M.

AU - Crenshaw, D. M.

AU - Gabel, Jack

AU - Turner, T. J.

AU - Gull, T. R.

AU - Hutchings, J. B.

AU - Kriss, G. A.

AU - Mushotzky, R. F.

AU - Netzer, H.

AU - Peterson, B. M.

AU - Behar, Ehud

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N2 - 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

AB - 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

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