journal contribution posted on 03.07.2019, 11:01 by M Dehghanian, GJ Ferland, GA Kriss, BM Peterson, S Mathur, M Mehdipour, F Guzman, M Chatzikos, PAM van Hoof, RJR Williams, N Arav, AJ Barth, MC Bentz, S Bisogni, WN Brandt, DM Crenshaw, E Dalla Bonta, G De Rosa, MM Fausnaugh, JM Gelbord, MR Goad, A Gupta, K Horne, J Kaastra, C Knigge, KT Korista, IM McHardy, RW Pogge, DA Starkey, M Vestergaard
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.
Support for HST program number GO-13330 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We thank NSF (1816537), NASA (ATP 17-0141), and STScI (HST-AR.13914, HST-AR-15018) for their support and Huffaker scholarship for funding the trip to Atlanta to attend the annual AGN STORM meeting, 2017. M.C. acknowledges support from NASA through STScI grant HST-AR-14556.001-A and STScI grant HST-AR-14286. M.D., G.F., and F.G. acknowledge support from the NSF (AST-1816537), NASA (ATP 17-0141), and STScI (HST-AR-13914, HST-AR-15018), and the Huffaker Scholarship. B.M.P., G.D.R., M.M.F, C.J.G., and R.W.P. are grateful for the support of the National Science Foundation through grant AST-1008882 to The Ohio State University. A.J.B. has been supported by NSF grant AST-1412693. M.C.B. gratefully acknowledges support through NSF CAREER grant AST-1253702 to Georgia State University. S.B. is supported by NASA through the Chandra award no. AR7-18013X issued by the Chandra X-ray Observatory Center, operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. S.B. was also partially supported by grant HST-AR-13240.009. E.D.B. acknowledge support from Padua University through grants DOR1699945/16, DOR1715817/17, DOR1885254/18, and BIRD164402/16. K.D.D. is supported by an NSF Fellowship awarded under grant AST-1302093. R.E. gratefully acknowledges support from NASA under the ADAP award 80NSSC17K0126. K.H. acknowledges support from STFC grant ST/R000824/1. SRON is financially supported by NWO, the Netherlands Organization for Scientific Research. C.S.K. acknowledges the support of NSF grant AST-1009756. A.P. is supported by NASA through Einstein Postdoctoral Fellowship grant number PF5-160141 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA
CitationAstrophysical Journal, 2019, 877 (2)
Author affiliation/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
VersionVoR (Version of Record)
Published inAstrophysical Journal
PublisherAmerican Astronomical Society, IOP Publishing