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NuSTAR Observations of the Compton-thick Active Galactic Nucleus and Ultraluminous X-Ray Source Candidate in NGC 5643

Annuar, A.; Gandhi, P.; Alexander, D.M.; Lansbury, G.B.; Arevalo, P.; Ballantyne, D.R.; Balokovic, M.; Bauer, F.E.; Boggs, S.E.; Brandt, W.N.; Brightman, M.; Christensen, F.E.; Craig, W.W.; Del Moro, A.; Hailey, C.J.; Harrison, F.A.; Hickox, R.C.; Matt, G.; Puccetti, S.; Ricci, C.; Rigby, J.R.; Stern, D.; Walton, D.J.; Zappacosta, L.; Zhang, W.

NuSTAR Observations of the Compton-thick Active Galactic Nucleus and Ultraluminous X-Ray Source Candidate in NGC 5643 Thumbnail


A. Annuar

P. Gandhi

G.B. Lansbury

P. Arevalo

D.R. Ballantyne

M. Balokovic

F.E. Bauer

S.E. Boggs

W.N. Brandt

M. Brightman

F.E. Christensen

W.W. Craig

A. Del Moro

C.J. Hailey

F.A. Harrison

R.C. Hickox

G. Matt

S. Puccetti

C. Ricci

J.R. Rigby

D. Stern

D.J. Walton

L. Zappacosta

W. Zhang


We present two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the local Seyfert 2 active galactic nucleus (AGN) and an ultraluminous X-ray source (ULX) candidate in NGC 5643. Together with archival data from Chandra, XMM-Newton, and Swift-BAT, we perform a high-quality broadband spectral analysis of the AGN over two decades in energy (~0.5–100 keV). Previous X-ray observations suggested that the AGN is obscured by a Compton-thick (CT) column of obscuring gas along our line of sight. However, the lack of high-quality gsim10 keV observations, together with the presence of a nearby X-ray luminous source, NGC 5643 X–1, have left significant uncertainties in the characterization of the nuclear spectrum. NuSTAR now enables the AGN and NGC 5643 X–1 to be separately resolved above 10 keV for the first time and allows a direct measurement of the absorbing column density toward the nucleus. The new data show that the nucleus is indeed obscured by a CT column of NH gsim 5 × 1024 cm−2. The range of 2–10 keV absorption-corrected luminosity inferred from the best-fitting models is L2–10,int = (0.8–1.7) × 1042 erg s−1, consistent with that predicted from multiwavelength intrinsic luminosity indicators. In addition, we also study the NuSTAR data for NGC 5643 X–1 and show that it exhibits evidence of a spectral cutoff at energy E ~ 10 keV, similar to that seen in other ULXs observed by NuSTAR. Along with the evidence for significant X-ray luminosity variations in the 3–8 keV band from 2003 to 2014, our results further strengthen the ULX classification of NGC 5643 X–1.

Journal Article Type Article
Acceptance Date Oct 4, 2015
Online Publication Date Dec 4, 2015
Publication Date Dec 10, 2015
Deposit Date May 11, 2016
Publicly Available Date May 12, 2016
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 815
Issue 1
Article Number 36
Public URL


Published Journal Article (1.7 Mb)

Copyright Statement
© 2015. The American Astronomical Society. All rights reserved.

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