Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548

M. Dehghanian, G. J. Ferland, G. A. Kriss, B. M. Peterson, S. Mathur, M. Mehdipour, F. Guzmán, M. Chatzikos, P. A.M. Van Hoof, R. J.R. Williams, N. Arav, A. J. Barth, M. C. Bentz, S. Bisogni, William Nielsen Brandt, D. M. Crenshaw, E. Dalla Bonta, G. De Rosa, M. M. Fausnaugh, J. M. Gelbord & 10 others M. R. Goad, A. Gupta, Keith Horne, J. Kaastra, C. Knigge, K. T. Korista, I. M. McHardy, R. W. Pogge, D. A. Starkey, M. Vestergaard

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60-70 day "holiday," suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a "holiday." It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.

Original languageEnglish (US)
Article number119
JournalAstrophysical Journal
Volume877
Issue number2
DOIs
StatePublished - Jun 1 2019

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reverberation
telescopes
continuums
ionization
helium
coverings
physics
cycles
project
holiday
ion
Hubble Space Telescope
ionizing radiation
line of sight
monitoring
x rays
time lag
ions

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Dehghanian, M., Ferland, G. J., Kriss, G. A., Peterson, B. M., Mathur, S., Mehdipour, M., ... Vestergaard, M. (2019). Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548. Astrophysical Journal, 877(2), [119]. https://doi.org/10.3847/1538-4357/ab1b48
Dehghanian, M. ; Ferland, G. J. ; Kriss, G. A. ; Peterson, B. M. ; Mathur, S. ; Mehdipour, M. ; Guzmán, F. ; Chatzikos, M. ; Van Hoof, P. A.M. ; Williams, R. J.R. ; Arav, N. ; Barth, A. J. ; Bentz, M. C. ; Bisogni, S. ; Brandt, William Nielsen ; Crenshaw, D. M. ; Bonta, E. Dalla ; De Rosa, G. ; Fausnaugh, M. M. ; Gelbord, J. M. ; Goad, M. R. ; Gupta, A. ; Horne, Keith ; Kaastra, J. ; Knigge, C. ; Korista, K. T. ; McHardy, I. M. ; Pogge, R. W. ; Starkey, D. A. ; Vestergaard, M. / Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548. In: Astrophysical Journal. 2019 ; Vol. 877, No. 2.
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abstract = "The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60-70 day {"}holiday,{"} suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a {"}holiday.{"} It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.",
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Dehghanian, M, Ferland, GJ, Kriss, GA, Peterson, BM, Mathur, S, Mehdipour, M, Guzmán, F, Chatzikos, M, Van Hoof, PAM, Williams, RJR, Arav, N, Barth, AJ, Bentz, MC, Bisogni, S, Brandt, WN, Crenshaw, DM, Bonta, ED, De Rosa, G, Fausnaugh, MM, Gelbord, JM, Goad, MR, Gupta, A, Horne, K, Kaastra, J, Knigge, C, Korista, KT, McHardy, IM, Pogge, RW, Starkey, DA & Vestergaard, M 2019, 'Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548', Astrophysical Journal, vol. 877, no. 2, 119. https://doi.org/10.3847/1538-4357/ab1b48

Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548. / Dehghanian, M.; Ferland, G. J.; Kriss, G. A.; Peterson, B. M.; Mathur, S.; Mehdipour, M.; Guzmán, F.; Chatzikos, M.; Van Hoof, P. A.M.; Williams, R. J.R.; Arav, N.; Barth, A. J.; Bentz, M. C.; Bisogni, S.; Brandt, William Nielsen; Crenshaw, D. M.; Bonta, E. Dalla; De Rosa, G.; Fausnaugh, M. M.; Gelbord, J. M.; Goad, M. R.; Gupta, A.; Horne, Keith; Kaastra, J.; Knigge, C.; Korista, K. T.; McHardy, I. M.; Pogge, R. W.; Starkey, D. A.; Vestergaard, M.

In: Astrophysical Journal, Vol. 877, No. 2, 119, 01.06.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548

AU - Dehghanian, M.

AU - Ferland, G. J.

AU - Kriss, G. A.

AU - Peterson, B. M.

AU - Mathur, S.

AU - Mehdipour, M.

AU - Guzmán, F.

AU - Chatzikos, M.

AU - Van Hoof, P. A.M.

AU - Williams, R. J.R.

AU - Arav, N.

AU - Barth, A. J.

AU - Bentz, M. C.

AU - Bisogni, S.

AU - Brandt, William Nielsen

AU - Crenshaw, D. M.

AU - Bonta, E. Dalla

AU - De Rosa, G.

AU - Fausnaugh, M. M.

AU - Gelbord, J. M.

AU - Goad, M. R.

AU - Gupta, A.

AU - Horne, Keith

AU - Kaastra, J.

AU - Knigge, C.

AU - Korista, K. T.

AU - McHardy, I. M.

AU - Pogge, R. W.

AU - Starkey, D. A.

AU - Vestergaard, M.

PY - 2019/6/1

Y1 - 2019/6/1

N2 - The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60-70 day "holiday," suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a "holiday." It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.

AB - The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60-70 day "holiday," suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a "holiday." It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.

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