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Title: The Variable Hard X-Ray Emission of NGC 4945 as Observed by NUSTAR

Journal Article · · The Astrophysical Journal (Online)
ORCiD logo [1];  [2];  [3];  [4];  [5];  [6];  [7]; ORCiD logo [8];  [8];  [9];  [10];  [11];  [12];  [9];  [13];  [14];  [9];  [7];  [15];  [16] more »;  [8];  [17] « less
  1. ASDC-ASI, Roma (Italy); INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone (RM) (Italy)
  2. INAF-Osservatorio Astronomico di Bologna, Bologna (Italy)
  3. INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone (RM) (Italy)
  4. Pontificia Univ. Catolica de Chile, Santiago (Chile)
  5. INAF-Osservatorio Astrofisico di Arcetri, Firenze (Italy); Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
  6. Pontificia Univ. Catolica de Chile, Santiago (Chile); Space Science Institute, Boulder, CO (United States)
  7. The Pennsylvania State Univ., University Park, PA (United States)
  8. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  9. Durham Univ., Durham (United Kingdom)
  10. Univ. of California, Berkeley, CA (United States)
  11. Technical Univ. of Denmark, Lyngby (Denmark)
  12. Univ. of California, Berkeley, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  13. Columbia Univ., New York, NY (United States)
  14. ETH Zurich, Zurich (Switzerland)
  15. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  16. Univ. 'a Roma Tre, Roma (Italy)
  17. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
+ Show Author Affiliations

Here, we present a broadband (~0.5-79 keV) spectral and temporal analysis of multiple NuSTAR observations combined with archival Suzaku and Chandra data of NGC 4945, the brightest extragalactic source at 100 keV. We observe hard X-ray (>10 keV) flux and spectral variability, with flux variations of a factor of two on timescales of 20 ks. A variable primary continuum dominates the high-energy spectrum (>10 keV) in all states, while the reflected/scattered flux that dominates at E <10 keV stays approximately constant. From modeling the complex reflection/transmission spectrum, we derive a Compton depth along the line of sight of τThomson ~ 2.9, and a global covering factor for the circumnuclear gas of ~0.15. This agrees with the constraints derived from the high-energy variability, which implies that most of the high-energy flux is transmitted rather than Compton-scattered. This demonstrates the effectiveness of spectral analysis at constraining the geometric properties of the circumnuclear gas, and validates similar methods used for analyzing the spectra of other bright, Compton-thick active galactic nuclei (AGNs). The lower limits on the e-folding energy are between 200 and 300 keV, consistent with previous BeppoSAX, Suzaku, and Swift Burst Alert Telescope observations. The accretion rate, estimated from the X-ray luminosity and assuming a bolometric correction typical of type 2 AGN, is in the range ~0.1-0.3 λEdd depending on the flux state. As a result, the substantial observed X-ray luminosity variability of NGC 4945 implies that large errors can arise from using single-epoch X-ray data to derive L/L Edd values for obscured AGNs.

Research Organization:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC); National Aeronautics and Space Administration (NASA)
Grant/Contract Number:
AC02-76SF00515
OSTI ID:
1165903
Report Number(s):
SLAC-PUB-16156; arXiv:1407.3974
Journal Information:
The Astrophysical Journal (Online), Vol. 793, Issue 1; ISSN 1538-4357
Publisher:
Institute of Physics (IOP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 56 works
Citation information provided by
Web of Science

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Cited By (19)

The subarcsecond mid-infrared view of local active galactic nuclei – II. The mid-infrared–X-ray correlation journal September 2015
An Iwasawa–Taniguchi effect for Compton-thick active galactic nuclei journal April 2018
The nuclear environment of the NLS1 Mrk 335: Obscuration of the X-ray line emission by a variable outflow journal September 2019
Long-Term X-Ray Variability of Typical Active Galactic Nuclei in the Distant Universe journal November 2016
Suzaku Observations of Heavily Obscured (Compton-thick) Active Galactic Nuclei Selected by the Swift /BAT Hard X-Ray Survey journal February 2018
New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei journal February 2018
Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR journal September 2018
Compton-thick AGNs in the NuSTAR Era. II. A Deep NuSTAR and XMM - Newton View of the Candidate Compton-thick AGN in NGC 1358 journal January 2019
Compton-thick AGN in the NuSTAR Era. IV. A Deep NuSTAR and XMM-Newton View of the Candidate Compton-thick AGN in ESO 116-G018 journal January 2019
Compton-thick AGNs in the NuSTAR Era. III. A Systematic Study of the Torus Covering Factor journal February 2019
Compton-thick AGNs in the NuSTAR Era. V. Joint NuSTAR and XMM-Newton Spectral Analysis of Three “Soft-gamma” Candidate CT-AGNs in the Swift /BAT 100-month Catalog journal September 2019
A NICER Look at Strong X-Ray Obscuration in the Seyfert-2 Galaxy NGC 4388 journal October 2019
NuSTAR Uncovers an Extremely Local Compton-thick AGN in NGC 4968 journal December 2019
The subarcsecond mid-infrared view of local active galactic nuclei: II. The mid-infrared--X-ray correlation text January 2015
Suzaku Observations of Heavily Obscured (Compton-thick) Active Galactic Nuclei selected by Swift/BAT Hard X-ray Survey text January 2018
Compton-thick AGN in the NuSTAR era II: A deep NuSTAR and XMM-Newton view of the candidate Compton thick AGN in NGC 1358 text January 2018
Compton-thick AGN in the NuSTAR era IV: A deep NuSTAR and XMM-Newton view of the candidate Compton thick AGN in ESO 116-G018 text January 2018
Compton-thick AGN in the NuSTAR era III: A systematic study of the torus covering factor text January 2018
A NICER Look at Strong X-ray Obscuration in the Seyfert-2 Galaxy NGC 4388 text January 2019

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Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
Astrophysics
ASTRO
GRQC
galaxies: active
galaxies: individual (NGC 4945)
X-rays: galaxies