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NuSTAR observations of the Compton-thick active galactic nucleus and ultraluminous X-ray source candidate in NGC 5643.

Annuar, A. and Gandhi, P. and Alexander, D. M. and Lansbury, G. B. and Arevalo, P. and Ballantyne, D. R. and Balokovic, M. and Bauer, F. E. and Boggs, S. E. and Brandt, W. N. and Brightman, M. and Christensen, F. E. and Craig, W. W. and Del Moro, A. and Hailey, C. J. and Harrison, F. A. and Hickox, R. C. and Matt, G. and Puccetti, S. and Ricci, C. and Rigby, J. R. and Stern, D. and Walton, D. J. and Zappacosta, L. and Zhang, W. (2015) 'NuSTAR observations of the Compton-thick active galactic nucleus and ultraluminous X-ray source candidate in NGC 5643.', Astrophysical journal., 815 (1). p. 36.


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.

Item Type:Article
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Publisher statement:© 2015. The American Astronomical Society. All rights reserved.
Date accepted:04 October 2015
Date deposited:12 May 2016
Date of first online publication:04 December 2015
Date first made open access:No date available

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