skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: DETERMINING THE COVERING FACTOR OF COMPTON-THICK ACTIVE GALACTIC NUCLEI WITH NuSTAR

Abstract

The covering factor of Compton-thick (CT) obscuring material associated with the torus in active galactic nuclei (AGNs) is at present best understood through the fraction of sources exhibiting CT absorption along the line of sight (N{sub H} > 1.5 × 10{sup 24} cm{sup −2}) in the X-ray band, which reveals the average covering factor. Determining this CT fraction is difficult, however, due to the extreme obscuration. With its spectral coverage at hard X-rays (>10 keV), Nuclear Spectroscopic Telescope Array (NuSTAR) is sensitive to the AGNs covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGNs observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so-called CT AGNs. We use the torus models of Brightman and Nandra that predict the X-ray spectrum from reprocessing in a torus and include the torus opening angle as a free parameter and aim to determine the covering factor of the CT gas in these sources individually. Across the sample we find mild to heavy CT columns, with N{sub H} measured from 10{sup 24} to 10{sup 26} cm{sup −2}, and a wide range of covering factors, where individual measurements range frommore » 0.2 to 0.9. We find that the covering factor, f{sub c}, is a strongly decreasing function of the intrinsic 2–10 keV luminosity, L{sub X}, where f{sub c} = (−0.41 ± 0.13)log{sub 10}(L{sub X}/erg s{sup −1})+18.31 ± 5.33, across more than two orders of magnitude in L{sub X} (10{sup 41.5}–10{sup 44} erg s{sup −1}). The covering factors measured here agree well with the obscured fraction as a function of L{sub X} as determined by studies of local AGNs with L{sub X} > 10{sup 42.5} erg s{sup −1}.« less

Authors:
; ; ;  [1];  [2];  [3];  [4];  [5]; ;  [6];  [7];  [8];  [9];  [10];  [11];  [12];  [13];
  1. Cahill Center for Astrophysics, California Institute of Technology, 1216 East California Boulevard, Pasadena, CA 91125 (United States)
  2. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109 (United States)
  3. Instituto de Física y Astronoma, Facultad de Ciencias, Universidad de Valparaíso, Gran Bretana N 1111, Playa Ancha, Valparaíso (Chile)
  4. Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States)
  5. Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)
  6. Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
  7. DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
  8. INAF Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
  9. Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)
  10. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
  11. Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States)
  12. SNSF Ambizione Fellow, Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich (Switzerland)
  13. Yale Center for Astronomy and Astrophysics, Yale University, P.O. Box 208120, New Haven, CT 06520 (United States)
Publication Date:
OSTI Identifier:
22522404
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 805; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPTON EFFECT; COMPUTERIZED TOMOGRAPHY; GALAXY NUCLEI; HARD X RADIATION; KEV RANGE; LUMINOSITY; REPROCESSING; TELESCOPES; X-RAY GALAXIES; X-RAY SPECTRA

Citation Formats

Brightman, M., Baloković, M., Fuerst, F., Harrison, F. A., Stern, D., Arévalo, P., Ballantyne, D. R., Bauer, F. E., Boggs, S. E., Craig, W. W., Christensen, F. E., Comastri, A., Gandhi, P., Hailey, C. J., Hickox, R. C., Koss, M., LaMassa, S., and and others. DETERMINING THE COVERING FACTOR OF COMPTON-THICK ACTIVE GALACTIC NUCLEI WITH NuSTAR. United States: N. p., 2015. Web. doi:10.1088/0004-637X/805/1/41.
Brightman, M., Baloković, M., Fuerst, F., Harrison, F. A., Stern, D., Arévalo, P., Ballantyne, D. R., Bauer, F. E., Boggs, S. E., Craig, W. W., Christensen, F. E., Comastri, A., Gandhi, P., Hailey, C. J., Hickox, R. C., Koss, M., LaMassa, S., & and others. DETERMINING THE COVERING FACTOR OF COMPTON-THICK ACTIVE GALACTIC NUCLEI WITH NuSTAR. United States. doi:10.1088/0004-637X/805/1/41.
Brightman, M., Baloković, M., Fuerst, F., Harrison, F. A., Stern, D., Arévalo, P., Ballantyne, D. R., Bauer, F. E., Boggs, S. E., Craig, W. W., Christensen, F. E., Comastri, A., Gandhi, P., Hailey, C. J., Hickox, R. C., Koss, M., LaMassa, S., and and others. Wed . "DETERMINING THE COVERING FACTOR OF COMPTON-THICK ACTIVE GALACTIC NUCLEI WITH NuSTAR". United States. doi:10.1088/0004-637X/805/1/41.
@article{osti_22522404,
title = {DETERMINING THE COVERING FACTOR OF COMPTON-THICK ACTIVE GALACTIC NUCLEI WITH NuSTAR},
author = {Brightman, M. and Baloković, M. and Fuerst, F. and Harrison, F. A. and Stern, D. and Arévalo, P. and Ballantyne, D. R. and Bauer, F. E. and Boggs, S. E. and Craig, W. W. and Christensen, F. E. and Comastri, A. and Gandhi, P. and Hailey, C. J. and Hickox, R. C. and Koss, M. and LaMassa, S. and and others},
abstractNote = {The covering factor of Compton-thick (CT) obscuring material associated with the torus in active galactic nuclei (AGNs) is at present best understood through the fraction of sources exhibiting CT absorption along the line of sight (N{sub H} > 1.5 × 10{sup 24} cm{sup −2}) in the X-ray band, which reveals the average covering factor. Determining this CT fraction is difficult, however, due to the extreme obscuration. With its spectral coverage at hard X-rays (>10 keV), Nuclear Spectroscopic Telescope Array (NuSTAR) is sensitive to the AGNs covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGNs observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so-called CT AGNs. We use the torus models of Brightman and Nandra that predict the X-ray spectrum from reprocessing in a torus and include the torus opening angle as a free parameter and aim to determine the covering factor of the CT gas in these sources individually. Across the sample we find mild to heavy CT columns, with N{sub H} measured from 10{sup 24} to 10{sup 26} cm{sup −2}, and a wide range of covering factors, where individual measurements range from 0.2 to 0.9. We find that the covering factor, f{sub c}, is a strongly decreasing function of the intrinsic 2–10 keV luminosity, L{sub X}, where f{sub c} = (−0.41 ± 0.13)log{sub 10}(L{sub X}/erg s{sup −1})+18.31 ± 5.33, across more than two orders of magnitude in L{sub X} (10{sup 41.5}–10{sup 44} erg s{sup −1}). The covering factors measured here agree well with the obscured fraction as a function of L{sub X} as determined by studies of local AGNs with L{sub X} > 10{sup 42.5} erg s{sup −1}.},
doi = {10.1088/0004-637X/805/1/41},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 805,
place = {United States},
year = {2015},
month = {5}
}