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Title: Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing

Abstract

Swift monitoring of NGC 4151 with an ∼6 hr sampling over a total of 69 days in early 2016 is used to construct light curves covering five bands in the X-rays (0.3–50 keV) and six in the ultraviolet (UV)/optical (1900–5500 Å). The three hardest X-ray bands (>2.5 keV) are all strongly correlated with no measurable interband lag, while the two softer bands show lower variability and weaker correlations. The UV/optical bands are significantly correlated with the X-rays, lagging ∼3–4 days behind the hard X-rays. The variability within the UV/optical bands is also strongly correlated, with the UV appearing to lead the optical by ∼0.5–1 days. This combination of ≳3 day lags between the X-rays and UV and ≲1 day lags within the UV/optical appears to rule out the “lamp-post” reprocessing model in which a hot, X-ray emitting corona directly illuminates the accretion disk, which then reprocesses the energy in the UV/optical. Instead, these results appear consistent with the Gardner and Done picture in which two separate reprocessings occur: first, emission from the corona illuminates an extreme-UV-emitting toroidal component that shields the disk from the corona; this then heats the extreme-UV component, which illuminates the disk and drives its variability.

Authors:
 [1];  [2];  [3]; ;  [4]; ;  [5]; ;  [6];  [7]; ;  [8];  [9];  [10];  [11];  [12];  [13];  [14];  [15];  [16] more »; « less
  1. University of Maryland, Department of Astronomy, College Park, MD 20742-2421 (United States)
  2. Spectral Sciences Inc., 4 Fourth Avenue, Burlington, MA 01803 (United States)
  3. Department of Physics and Astronomy, Wayne State University, 666 W. Hancock Street, Detroit, MI 48201 (United States)
  4. University of Southampton, Highfield, Southampton, SO17 1BJ (United Kingdom)
  5. University of Durham, Center for Extragalactic Astronomy, Department of Physics, South Road, Durham, DH1 3LE (United Kingdom)
  6. The Ohio State University, Department of Astronomy, 140 W 18th Avenue, Columbus, OH 43210 (United States)
  7. Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  8. University of Leicester, Department of Physics and Astronomy, Leicester, LE1 7RH (United Kingdom)
  9. SUPA Physics and Astronomy, University of St. Andrews, Fife, KY16 9SS Scotland (United Kingdom)
  10. Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark)
  11. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom)
  12. Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697 (United States)
  13. Department of Physics and Astronomy, Georgia State University, 25 Park Place, Suite 605, Atlanta, GA 30303 (United States)
  14. Physics Department, Southwestern University, Georgetown, TX 78626 (United States)
  15. Department of Astronomy and Astrophysics, Eberly College of Science, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802 (United States)
  16. South African Astronomical Observatory, P.O. Box 9, Observatory 7935, Cape Town (South Africa)
Publication Date:
OSTI Identifier:
22663652
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 840; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; CORRELATIONS; EMISSION; GALAXIES; GALAXY CLUSTERS; GALAXY NUCLEI; HARD X RADIATION; HEAT; KEV RANGE; REPROCESSING; ULTRAVIOLET RADIATION; VISIBLE RADIATION

Citation Formats

Edelson, R., Gelbord, J., Cackett, E., Connolly, S., McHardy, I., Done, C., Gardner, E., Fausnaugh, M., Peterson, B. M., Gehrels, N., Goad, M., Vaughan, S., Horne, K., Vestergaard, M., Breeveld, A., Barth, A. J., Bentz, M., Bottorff, M., Brandt, W. N., Crawford, S. M., and and others. Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6890.
Edelson, R., Gelbord, J., Cackett, E., Connolly, S., McHardy, I., Done, C., Gardner, E., Fausnaugh, M., Peterson, B. M., Gehrels, N., Goad, M., Vaughan, S., Horne, K., Vestergaard, M., Breeveld, A., Barth, A. J., Bentz, M., Bottorff, M., Brandt, W. N., Crawford, S. M., & and others. Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing. United States. doi:10.3847/1538-4357/AA6890.
Edelson, R., Gelbord, J., Cackett, E., Connolly, S., McHardy, I., Done, C., Gardner, E., Fausnaugh, M., Peterson, B. M., Gehrels, N., Goad, M., Vaughan, S., Horne, K., Vestergaard, M., Breeveld, A., Barth, A. J., Bentz, M., Bottorff, M., Brandt, W. N., Crawford, S. M., and and others. Mon . "Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing". United States. doi:10.3847/1538-4357/AA6890.
@article{osti_22663652,
title = {Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing},
author = {Edelson, R. and Gelbord, J. and Cackett, E. and Connolly, S. and McHardy, I. and Done, C. and Gardner, E. and Fausnaugh, M. and Peterson, B. M. and Gehrels, N. and Goad, M. and Vaughan, S. and Horne, K. and Vestergaard, M. and Breeveld, A. and Barth, A. J. and Bentz, M. and Bottorff, M. and Brandt, W. N. and Crawford, S. M. and and others},
abstractNote = {Swift monitoring of NGC 4151 with an ∼6 hr sampling over a total of 69 days in early 2016 is used to construct light curves covering five bands in the X-rays (0.3–50 keV) and six in the ultraviolet (UV)/optical (1900–5500 Å). The three hardest X-ray bands (>2.5 keV) are all strongly correlated with no measurable interband lag, while the two softer bands show lower variability and weaker correlations. The UV/optical bands are significantly correlated with the X-rays, lagging ∼3–4 days behind the hard X-rays. The variability within the UV/optical bands is also strongly correlated, with the UV appearing to lead the optical by ∼0.5–1 days. This combination of ≳3 day lags between the X-rays and UV and ≲1 day lags within the UV/optical appears to rule out the “lamp-post” reprocessing model in which a hot, X-ray emitting corona directly illuminates the accretion disk, which then reprocesses the energy in the UV/optical. Instead, these results appear consistent with the Gardner and Done picture in which two separate reprocessings occur: first, emission from the corona illuminates an extreme-UV-emitting toroidal component that shields the disk from the corona; this then heats the extreme-UV component, which illuminates the disk and drives its variability.},
doi = {10.3847/1538-4357/AA6890},
journal = {Astrophysical Journal},
number = 1,
volume = 840,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}
  • We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spinmore » $$a\gt 0.9$$ accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection (IDR) flux variation drives the spectral variability during the observations. We discuss various physical scenarios for the IDR model and we find that a compact corona is consistent with the observed features.« less
  • We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spinmore » $$a\gt 0.9$$ accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection (IDR) flux variation drives the spectral variability during the observations. As a result, we discuss various physical scenarios for the IDR model and we find that a compact corona is consistent with the observed features.« less
  • A search for ..gamma..-rays in the 35 keV to 8.7 MeV energy range from the Seyfert galaxy NGC 4151 was made using an actively collimated scintillation detector. Upper limits to the flux in the 100--200 keV energy range are inconsistent with previous observations. Variability on a time scale of several months is indicated. Implications in terms of current models of NGC 4151 are discussed.
  • The recently reported spectral features of NGC 4151 in the hard X-ray and ..gamma..-ray energy range are analyzed. A two-component emission model is suggested in which the ultraviolet and soft X-ray photons (E<20 keV) are scattered by relativistic electrons via the inverse Compton process into the hard X-ray and ..gamma..-ray regime. It is shown that the rather flat, hard X-ray spectrum can be explained if a low-energy cutoff in the relativistic electron distribution is postulated. The concept of a low-energy cutoff in the electron distribution is not inconsistent with the observed overall continuum emission of NGC 4151.
  • Recent studies have suggested that the short-timescale (≲ 7 days) variability of the broad (∼10,000 km s{sup –1}) double-peaked Hα profile of the LINER nucleus of NGC 1097 could be driven by a variable X-ray emission from a central radiatively inefficient accretion flow. To test this scenario, we have monitored the NGC 1097 nucleus in X-ray and UV continuum with Swift and the Hα flux and profile in the optical spectrum using SOAR and Gemini-South from 2012 August to 2013 February. During the monitoring campaign, the Hα flux remained at a very low level—three times lower than the maximum flux observed in previousmore » campaigns and showing only limited (∼20%) variability. The X-ray variations were small, only ∼13% throughout the campaign, while the UV did not show significant variations. We concluded that the timescale of the Hα profile variation is close to the sampling interval of the optical observations, which results in only a marginal correlation between the X-ray and Hα fluxes. We have caught the active galaxy nucleus in NGC 1097 in a very low activity state, in which the ionizing source was very weak and capable of ionizing just the innermost part of the gas in the disk. Nonetheless, the data presented here still support the picture in which the gas that emits the broad double-peaked Balmer lines is illuminated/ionized by a source of high-energy photons which is located interior to the inner radius of the line-emitting part of the disk.« less