NuSTAR Spectroscopy of Multi-component X-Ray Reflection from NGC 1068
Journal
Date Issued
2015
Author(s)
Bauer, Franz E.
•
Arévalo, Patricia
•
Walton, Dominic J.
•
Koss, Michael J.
•
Puccetti, Simonetta
•
Gandhi, Poshak
•
Stern, Daniel
•
Alexander, David M.
•
Baloković, Mislav
•
Boggs, Steve E.
•
Brandt, William N.
•
Brightman, Murray
•
Christensen, Finn E.
•
•
Craig, William W.
•
Del Moro, Agnese
•
Hailey, Charles J.
•
Harrison, Fiona A.
•
Hickox, Ryan
•
Luo, Bin
•
Markwardt, Craig B.
•
Marinucci, Andrea
•
•
Rigby, Jane R.
•
Rivers, Elizabeth
•
Saez, Cristian
•
Treister, Ezequiel
•
Urry, C. Megan
•
Zhang, William W.
Description
We thank the anonymous referee for useful comments, which improved the clarity of the paper. We acknowledge financial support from the following: CONICYT-Chile Basal-CATA PFB-06/2007 (FEB, ET), FONDECYT grants 1141218 (FEB), 1140304 (PA), 1120061 (ET), and Anillo grant ACT1101 (FEB, PA, ET); Project IC120009 “Millennium Institute of Astrophysics (MAS)” funded by the Iniciativa Científica Milenio del Ministerio de Economía, Fomento y Turismo (FEB); Swiss National Science Foundation through the Ambizione fellowship grant PZ00P2_154799/1 (MK); NuSTAR subcontract 44A-1092750 NASA ADP grant NNX10AC99G (WNB, BL); ASI/INAF grant I/037/12/0–011/13 (SP, AC, AM and GM); and STFC grant ST/J003697/1 (PG). This work was supported under NASA Contract No. 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). This research has made use of data obtained through the High Energy Astrophysics Science Archive Research Center (HEASARC) Online Service, provided by the NASA/Goddard Space Flight Center. Facilities: CXO (ACIS, HETG), XMM (pn, MOS), NuSTAR (FPMA, FPMB), Swift (XRT, BAT), BeppoSAX (MECS, PDS), Suzaku (XIS, PIN),
Abstract
We report on high-energy X-ray observations of the Compton-thick Seyfert 2 galaxy NGC 1068 with NuSTAR, which provide the best constraints to date on its >10 keV spectral shape. The NuSTAR data are consistent with those from past and current instruments to within cross-calibration uncertainties, and we find no strong continuum or line variability over the past two decades, which is in line with its X-ray classification as a reflection-dominated Compton-thick active galactic nucleus. The combined NuSTAR, Chandra, XMM-Newton, and Swift BAT spectral data set offers new insights into the complex secondary emission seen instead of the completely obscured transmitted nuclear continuum. The critical combination of the high signal-to-noise NuSTAR data and the decomposition of the nuclear and extranuclear emission with Chandra allow us to break several model degeneracies and greatly aid physical interpretation. When modeled as a monolithic (i.e., a single NH) reflector, none of the common Compton reflection models are able to match the neutral fluorescence lines and broad spectral shape of the Compton reflection hump without requiring unrealistic physical parameters (e.g., large Fe overabundances, inconsistent viewing angles, or poor fits to the spatially resolved spectra). A multi-component reflector with three distinct column densities (e.g., with best-fit values of NH of 1.4 × 1023, 5.0 × 1024, and 1025 cm-2) provides a more reasonable fit to the spectral lines and Compton hump, with near-solar Fe abundances. In this model, the higher NH component provides the bulk of the flux to the Compton hump, while the lower NH component produces much of the line emission, effectively decoupling two key features of Compton reflection. We find that ≈30% of the neutral Fe Kα line flux arises from >2″ (≈140 pc) and is clearly extended, implying that a significant fraction (and perhaps most) of the <10 keV reflected component arises from regions well outside a parsec-scale torus. These results likely have ramifications for the interpretation of Compton-thick spectra from observations with poorer signal-to-noise and/or more distant objects.
Volume
812
Issue
2
Start page
116
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...812..116B
Rights
open.access
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