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The Variable Hard X-Ray Emission of NGC4945 as Observed by NuSTARWe present a broadband (approx. 0.5 - 79 keV) spectral and temporal analysis of multiple NuSTAR observations combined with archival Suzaku and Chandra data of NGC4945, the brightest extragalactic source at 100 keV. We observe hard X-ray (> 10 keV) flux and spectral variability, with flux variations of a factor 2 on timescales of 20 ksec. A variable primary continuum dominates the high energy spectrum (> 10 keV) in all the states, while the reflected/scattered flux which dominates at E< 10 keV stays approximately constant. From modelling the complex reflection/transmission spectrum we derive a Compton depth along the line of sight of Thomson approx.2.9, and a global covering factor for the circumnuclear gas of approx. 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 that Compton-scattered. This demonstrates the effectiveness of spectral analysis in constraining the geometric properties of the circumnuclear gas, and validates similar methods used for analyzing the spectra of other bright, Compton-thick AGN. The lower limits on the e-folding energy are between 200 − 300 keV, consistent with previous BeppoSAX, Suzaku and Swift BAT observations. The accretion rate, estimated from the X-ray luminosity and assuming a bolometric correction typical of type 2 AGN, is in the range approx. 0.1 − 0.3 lambda(sub Edd) depending on the flux state. The substantial observed X-ray luminosity variability of NGC4945 implies that large errors can arise from using single-epoch X-ray data to derive L/L(sub Edd) values for obscured AGNs.
Document ID
20150023316
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Puccetti, Simonetta
(Istituto di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Rome, Italy)
Comastri, Andrea
(Istituto Nazionale di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Bologna, Italy)
Fiore, Fabrizio
(Istituto di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Rome, Italy)
Arevalo, Patricia
(Pontifical Catholic Univ. of Chile Santiago, Chile)
Risaliti, Guido
(Istituto di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Rome, Italy)
Bauer, Franz E.
(Pontifical Catholic Univ. of Chile Santiago, Chile)
Brandt, William N.
(Pennsylvania State Univ. University Park, PA, United States)
Stern, Daniel
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Harrison, Fiona A.
(California Inst. of Tech. Pasadena, CA, United States)
Alexander, David M.
(Durham Univ. United Kingdom)
Boggs, Steve E.
(California Univ. Berkeley, CA, United States)
Christensen, Finn E.
(Technical Univ. of Denmark Lyngby, Denmark)
Craig, William W.
(California Univ. Berkeley, CA, United States)
Gandhi, Poshak
(Durham Univ. United Kingdom)
Hailey, Charles J.
(Columbia Univ. New York, NY, United States)
Koss, Michael R.
(Eidgenoessische Technische Hochschule Zurich, Switzerland)
Lansbury, George B.
(Durham Univ. United Kingdom)
Luo, Bin
(Pennsylvania State Univ. University Park, PA, United States)
Madejski, Greg M.
(Stanford Linear Accelerator Center Menlo Park, CA, United States)
Matt, Giorgio
(Rome III Univ. Rome, Italy)
Walton, Dominic J.
(California Inst. of Tech. Pasadena, CA, United States)
Zhang, Will
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
December 18, 2015
Publication Date
July 15, 2014
Publication Information
Publication: Astrophysical journal
Publisher: IOP Publishing
Volume: 793
Issue: 1
Subject Category
Astronomy
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN24305
Funding Number(s)
CONTRACT_GRANT: NNG12FA45C
Distribution Limits
Public
Copyright
Other
Keywords
galaxies: active aEuro" galaxies: individual (NGC4945) aEuro" XaEuro"rays: galax

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