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The Variable Hard X-Ray Emission of NGC 4945 as Observed by NuSTAR

Puccetti, Simonetta and Comastri, Andrea and Fiore, Fabrizio and Arévalo, Patricia and Risaliti, Guido and Bauer, Franz E. and Brandt, William N. and Stern, Daniel and Harrison, Fiona A. and Alexander, David M. and Boggs, Steven E. and Christensen, Finn E. and Craig, William W. and Gandhi, Poshak and Hailey, Charles J. and Koss, Michael J. and Lansbury, George B. and Luo, Bin and Madejski, Greg M. and Matt, Giorgio and Walton, Dominic J. and Zhang, Will (2014) The Variable Hard X-Ray Emission of NGC 4945 as Observed by NuSTAR. Astrophysical Journal, 793 (1). Art. No. 26. ISSN 0004-637X. doi:10.1088/0004-637X/793/1/26.

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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 τ_(Thomson) ~ 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 λ_(Edd) depending on the flux state. 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Puccetti, Simonetta0000-0002-2734-7835
Comastri, Andrea0000-0003-3451-9970
Bauer, Franz E.0000-0002-8686-8737
Brandt, William N.0000-0002-0167-2453
Stern, Daniel0000-0003-2686-9241
Harrison, Fiona A.0000-0003-2992-8024
Alexander, David M.0000-0002-5896-6313
Boggs, Steven E.0000-0001-9567-4224
Christensen, Finn E.0000-0001-5679-1946
Gandhi, Poshak0000-0003-3105-2615
Koss, Michael J.0000-0002-7998-9581
Lansbury, George B.0000-0002-5328-9827
Luo, Bin0000-0002-9036-0063
Matt, Giorgio0000-0002-2152-0916
Walton, Dominic J.0000-0001-5819-3552
Zhang, Will0000-0002-1426-9698
Additional Information:© 2014 American Astronomical Society. Received 2014 April 15; accepted 2014 July 14; published 2014 September 2. This work was supported under NASA Contract NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). S.P., A.C., F.F., and G.M. acknowledge support from the ASI/INAF grant I/037/12/0–011/13. A.C. acknowledges the Caltech Kingsley visitor program. P.G. acknowledges support from STFC (grant reference ST/J003697/ 1). G.B.L. acknowledges support from STFC (grant reference ST/K501979/1). D.M.A. acknowledges support from STFC (grant reference ST/I001573/1) and from the Leverhulme Trust. P.A. acknowledges financial support from Fondecyt grant 11100449 and Anillo ACT1101. G.R. acknowledges financial support from grant NASA GO3–14109X. M.K. gratefully acknowledges support from Swiss National Science Foundation Grant PP00P2_138979/1. W.N.B. and B.L. acknowledge support from California Institute of Technology NuSTAR subcontract 44A–1092750 and NASA ADP Grant NNX10AC99G. F.E.B. acknowledges support from Basal–CATA PFB–06/2007, CONICYT–Chile (grants FONDECYT 1101024 and “EMBIGGEN” Anillo ACT1101), and Project IC120009 “Millennium Institute of Astrophysics (MAS)” of Iniciativa Científica Milenio del Ministerio de Economía, Fomento y Turismo. S.P. is grateful to Tahir Yaqoob for useful discussions on the mytorus model.
Group:Space Radiation Laboratory, NuSTAR
Funding AgencyGrant Number
Agenzia Spaziale Italiana (ASI)I/037/12/0–011/13
Science and Technology Facilities Council (STFC)ST/J003697/ 1
Science and Technology Facilities Council (STFC)ST/K501979/1
Science and Technology Facilities Council (STFC)ST/I001573/1
Leverhulme TrustUNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)11100449
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)ACT1101
Swiss National Science Foundation (SNSF)PP00P2_138979/1
Caltech NuSTAR subcontract44A-1092750
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1101024
Anillo projectACT1101
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y Turismo Millennium Institute of Astrophysics (MAS)IC120009
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:galaxies: active; galaxies: individual (NGC 4945); X-rays: galaxies
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2014-33
Issue or Number:1
Record Number:CaltechAUTHORS:20141003-074456235
Persistent URL:
Official Citation:The Variable Hard X-Ray Emission of NGC 4945 as Observed by NuSTAR Simonetta Puccetti et al. 2014 ApJ 793 26
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50185
Deposited By: Ruth Sustaita
Deposited On:06 Oct 2014 02:44
Last Modified:10 Nov 2021 18:53

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