Heavy X-ray absorption in soft X-ray-weak active galactic nuclei

S. C. Gallagher, W. N. Brandt, A. Laor, M. Elvis, S. Mathur, Beverley J. Wills, N. Iyomoto

Research output: Contribution to journalArticle

66 Citations (Scopus)

Abstract

Recent ROSAT studies have identified a significant population of active galactic nuclei (AGNs) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGNs intrinsically X-ray weak or are they highly absorbed? Brandt, Laor, & Wills have systematically examined the optical and UV spectral properties of a well-defined sample of these soft X-ray-weak (SXW) AGNs drawn from the Boroson & Green sample of all the Palomar Green AGNs with z < 0.5. We present ASCA observations of three of these SXW AGNs: PG 1011-040, PG 1535+547 (Mrk 486), and PG 2112+059. In general, our ASCA observations support the intrinsic absorption scenario for explaining soft X-ray weakness; both PG 1535+547 and PG 2112+059 show significant column densities (NH ≈ 1022-1023 cm-2) of absorbing gas. Interestingly, PG 1011-040 shows no spectral evidence for X-ray absorption. The weak X-ray emission may result from very strong absorption of a partially covered source, or this AGN may be intrinsically X-ray weak. PG 2112+059 is a broad absorption line (BAL) QSO, and we find it to have the highest X-ray flux known of this class. It shows a typical power-law X-ray continuum above 3 keV; this is the first direct evidence that BAL QSOs indeed have normal X-ray continua underlying their intrinsic absorption. Finally, marked variability between the ROSAT and ASCA observations of PG 1535+547 and PG 2112+059 suggests that the soft X-ray-weak designation may be transient, and multiepoch 0.1-10.0 keV X-ray observations are required to constrain variability of the absorber and continuum.

Original languageEnglish (US)
Pages (from-to)795-804
Number of pages10
JournalAstrophysical Journal
Volume546
Issue number2 PART 1
DOIs
StatePublished - Jan 10 2001

Fingerprint

active galactic nuclei
x rays
continuums
quasars
absorbers
power law

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Gallagher, S. C., Brandt, W. N., Laor, A., Elvis, M., Mathur, S., Wills, B. J., & Iyomoto, N. (2001). Heavy X-ray absorption in soft X-ray-weak active galactic nuclei. Astrophysical Journal, 546(2 PART 1), 795-804. https://doi.org/10.1086/318294
Gallagher, S. C. ; Brandt, W. N. ; Laor, A. ; Elvis, M. ; Mathur, S. ; Wills, Beverley J. ; Iyomoto, N. / Heavy X-ray absorption in soft X-ray-weak active galactic nuclei. In: Astrophysical Journal. 2001 ; Vol. 546, No. 2 PART 1. pp. 795-804.
@article{edf0626e2d5d4bfd80658cb8367798a1,
title = "Heavy X-ray absorption in soft X-ray-weak active galactic nuclei",
abstract = "Recent ROSAT studies have identified a significant population of active galactic nuclei (AGNs) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGNs intrinsically X-ray weak or are they highly absorbed? Brandt, Laor, & Wills have systematically examined the optical and UV spectral properties of a well-defined sample of these soft X-ray-weak (SXW) AGNs drawn from the Boroson & Green sample of all the Palomar Green AGNs with z < 0.5. We present ASCA observations of three of these SXW AGNs: PG 1011-040, PG 1535+547 (Mrk 486), and PG 2112+059. In general, our ASCA observations support the intrinsic absorption scenario for explaining soft X-ray weakness; both PG 1535+547 and PG 2112+059 show significant column densities (NH ≈ 1022-1023 cm-2) of absorbing gas. Interestingly, PG 1011-040 shows no spectral evidence for X-ray absorption. The weak X-ray emission may result from very strong absorption of a partially covered source, or this AGN may be intrinsically X-ray weak. PG 2112+059 is a broad absorption line (BAL) QSO, and we find it to have the highest X-ray flux known of this class. It shows a typical power-law X-ray continuum above 3 keV; this is the first direct evidence that BAL QSOs indeed have normal X-ray continua underlying their intrinsic absorption. Finally, marked variability between the ROSAT and ASCA observations of PG 1535+547 and PG 2112+059 suggests that the soft X-ray-weak designation may be transient, and multiepoch 0.1-10.0 keV X-ray observations are required to constrain variability of the absorber and continuum.",
author = "Gallagher, {S. C.} and Brandt, {W. N.} and A. Laor and M. Elvis and S. Mathur and Wills, {Beverley J.} and N. Iyomoto",
year = "2001",
month = "1",
day = "10",
doi = "10.1086/318294",
language = "English (US)",
volume = "546",
pages = "795--804",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2 PART 1",

}

Gallagher, SC, Brandt, WN, Laor, A, Elvis, M, Mathur, S, Wills, BJ & Iyomoto, N 2001, 'Heavy X-ray absorption in soft X-ray-weak active galactic nuclei', Astrophysical Journal, vol. 546, no. 2 PART 1, pp. 795-804. https://doi.org/10.1086/318294

Heavy X-ray absorption in soft X-ray-weak active galactic nuclei. / Gallagher, S. C.; Brandt, W. N.; Laor, A.; Elvis, M.; Mathur, S.; Wills, Beverley J.; Iyomoto, N.

In: Astrophysical Journal, Vol. 546, No. 2 PART 1, 10.01.2001, p. 795-804.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Heavy X-ray absorption in soft X-ray-weak active galactic nuclei

AU - Gallagher, S. C.

AU - Brandt, W. N.

AU - Laor, A.

AU - Elvis, M.

AU - Mathur, S.

AU - Wills, Beverley J.

AU - Iyomoto, N.

PY - 2001/1/10

Y1 - 2001/1/10

N2 - Recent ROSAT studies have identified a significant population of active galactic nuclei (AGNs) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGNs intrinsically X-ray weak or are they highly absorbed? Brandt, Laor, & Wills have systematically examined the optical and UV spectral properties of a well-defined sample of these soft X-ray-weak (SXW) AGNs drawn from the Boroson & Green sample of all the Palomar Green AGNs with z < 0.5. We present ASCA observations of three of these SXW AGNs: PG 1011-040, PG 1535+547 (Mrk 486), and PG 2112+059. In general, our ASCA observations support the intrinsic absorption scenario for explaining soft X-ray weakness; both PG 1535+547 and PG 2112+059 show significant column densities (NH ≈ 1022-1023 cm-2) of absorbing gas. Interestingly, PG 1011-040 shows no spectral evidence for X-ray absorption. The weak X-ray emission may result from very strong absorption of a partially covered source, or this AGN may be intrinsically X-ray weak. PG 2112+059 is a broad absorption line (BAL) QSO, and we find it to have the highest X-ray flux known of this class. It shows a typical power-law X-ray continuum above 3 keV; this is the first direct evidence that BAL QSOs indeed have normal X-ray continua underlying their intrinsic absorption. Finally, marked variability between the ROSAT and ASCA observations of PG 1535+547 and PG 2112+059 suggests that the soft X-ray-weak designation may be transient, and multiepoch 0.1-10.0 keV X-ray observations are required to constrain variability of the absorber and continuum.

AB - Recent ROSAT studies have identified a significant population of active galactic nuclei (AGNs) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGNs intrinsically X-ray weak or are they highly absorbed? Brandt, Laor, & Wills have systematically examined the optical and UV spectral properties of a well-defined sample of these soft X-ray-weak (SXW) AGNs drawn from the Boroson & Green sample of all the Palomar Green AGNs with z < 0.5. We present ASCA observations of three of these SXW AGNs: PG 1011-040, PG 1535+547 (Mrk 486), and PG 2112+059. In general, our ASCA observations support the intrinsic absorption scenario for explaining soft X-ray weakness; both PG 1535+547 and PG 2112+059 show significant column densities (NH ≈ 1022-1023 cm-2) of absorbing gas. Interestingly, PG 1011-040 shows no spectral evidence for X-ray absorption. The weak X-ray emission may result from very strong absorption of a partially covered source, or this AGN may be intrinsically X-ray weak. PG 2112+059 is a broad absorption line (BAL) QSO, and we find it to have the highest X-ray flux known of this class. It shows a typical power-law X-ray continuum above 3 keV; this is the first direct evidence that BAL QSOs indeed have normal X-ray continua underlying their intrinsic absorption. Finally, marked variability between the ROSAT and ASCA observations of PG 1535+547 and PG 2112+059 suggests that the soft X-ray-weak designation may be transient, and multiepoch 0.1-10.0 keV X-ray observations are required to constrain variability of the absorber and continuum.

UR - http://www.scopus.com/inward/record.url?scp=0035835130&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0035835130&partnerID=8YFLogxK

U2 - 10.1086/318294

DO - 10.1086/318294

M3 - Article

AN - SCOPUS:0035835130

VL - 546

SP - 795

EP - 804

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 PART 1

ER -

Gallagher SC, Brandt WN, Laor A, Elvis M, Mathur S, Wills BJ et al. Heavy X-ray absorption in soft X-ray-weak active galactic nuclei. Astrophysical Journal. 2001 Jan 10;546(2 PART 1):795-804. https://doi.org/10.1086/318294