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Browsing by Author "Peterson, B. M."

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    A fast and long-lived outflow from the supermassive black hole in NGC 5548
    Kaastra, J. S.; Kriss, G. A.; Cappi, M.; Mehdipour, M.; Petrucci, P. O.; Steenbrugge, K. C.; Arav, Nahum; Behar, E.; Bianchi, S.; Boissay, R.; Branduardi-Raymont, G.; Chamberlain, C.; Costantini, E.; Ely, J. C.; Ebrero, J.; Di Gesu, L.; Harrison, F. A.; Kaspi, S.; Malzac, J.; De Marco, B.; Matt, G.; Nandra, K.; Paltani, S.; Person, R.; Peterson, B. M.; Pinto, C.; Ponti, G.; Nunez, F. P.; De Rosa, A.; Seta, H.; Ursini, F.; de Vries, C. P.; Walton, D. J.; Whewell, M. (Amer Assoc Advancement Science, 2014-07-04)
    Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution X-ray and UV observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas never seen before. It blocks 90% of the soft X-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.
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    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.; Guzman, F.; Chatzikos, M.; van Hoof, P. A. M.; Williams, R. J. R.; Arav, Nahum; Barth, A. J.; Bentz, M. C.; Bisogni, S.; Brandt, W. N.; Crenshaw, D. M.; Dalla Bonta, E.; 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. (2019-06-01)
    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.