S. Puccetti
The Variable Hard X-Ray Emission of NGC 4945 as Observed by NuSTAR
Puccetti, S.; Comastri, A.; Fiore, F.; Arévalo, P.; Risaliti, G.; Bauer, F.E.; Brandt, W.N.; Stern, D.; Harrison, F.A.; Alexander, D.M.; Boggs, S.E.; Christensen, F.E.; Craig, W.W.; Gandhi, P.; Hailey, C.J.; Koss, M.J.; Lansbury, G.B.; Luo, B.; Madejski, G.M.; Matt, G.; Walton, D.J.; Zhang, W
Authors
A. Comastri
F. Fiore
P. Arévalo
G. Risaliti
F.E. Bauer
W.N. Brandt
D. Stern
F.A. Harrison
Professor David Alexander d.m.alexander@durham.ac.uk
Professor
S.E. Boggs
F.E. Christensen
W.W. Craig
P. Gandhi
C.J. Hailey
M.J. Koss
G.B. Lansbury
B. Luo
G.M. Madejski
G. Matt
D.J. Walton
W Zhang
Abstract
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. 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.
Citation
Puccetti, S., Comastri, A., Fiore, F., Arévalo, P., Risaliti, G., Bauer, F., …Zhang, W. (2014). The Variable Hard X-Ray Emission of NGC 4945 as Observed by NuSTAR. Astrophysical Journal, 793(1), Article 26. https://doi.org/10.1088/0004-637x/793/1/26
Journal Article Type | Article |
---|---|
Acceptance Date | Jul 14, 2014 |
Publication Date | Sep 20, 2014 |
Deposit Date | May 15, 2015 |
Publicly Available Date | May 21, 2015 |
Journal | Astrophysical Journal |
Print ISSN | 0004-637X |
Electronic ISSN | 1538-4357 |
Publisher | American Astronomical Society |
Peer Reviewed | Peer Reviewed |
Volume | 793 |
Issue | 1 |
Article Number | 26 |
DOI | https://doi.org/10.1088/0004-637x/793/1/26 |
Keywords | Galaxies: active, Galaxies: individual (NGC 4945), X-rays: galaxies. |
Related Public URLs | http://arxiv.org/pdf/1407.3974v1.pdf |
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Copyright Statement
© 2014. The American Astronomical Society. All rights reserved.
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