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Hard X-ray emission of the luminous infrared galaxy NGC 6240 as observed by NuSTAR

Puccetti, S. and Comastri, A. and Bauer, F. E. and Brandt, W. N. and Fiore, F. and Harrison, F. A. and Luo, B. and Stern, D. and Urry, C. M. and Alexander, D. M. and Annuar, A. and Arévalo, P. and Baloković, M. and Boggs, S. E. and Brightman, M. and Christensen, F. E. and Craig, W. W. and Gandhi, P. and Hailey, C. J. and Koss, M. J. and La Massa, S. and Marinucci, A. and Ricci, C. and Walton, D. J. and Zappacosta, L. and Zhang, W. W. (2016) Hard X-ray emission of the luminous infrared galaxy NGC 6240 as observed by NuSTAR. Astronomy and Astrophysics, 585 . Art. No. A157. ISSN 0004-6361. http://resolver.caltech.edu/CaltechAUTHORS:20160204-180325331

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Abstract

We present a broadband (~0.3−70 keV) spectral and temporal analysis of NuSTAR observations of the luminous infrared galaxy NGC 6240 combined with archival Chandra, XMM-Newton, and BeppoSAX data. NGC 6240 is a galaxy in a relatively early merger state with two distinct nuclei separated by ~1.̋5. Previous Chandra observations resolved the two nuclei and showed that they are both active and obscured by Compton-thick material. Although they cannot be resolved by NuSTAR, we were able to clearly detect, for the first time, both the primary and the reflection continuum components thanks to the unprecedented quality of the NuSTAR data at energies >10 keV. The NuSTAR hard X-ray spectrum is dominated by the primary continuum piercing through an absorbing column density which is mildly optically thick to Compton scattering (τ ≃ 1.2, N_H ~ 1.5 × 10^(24) cm^(-2)). We detect moderately hard X-ray (>10 keV) flux variability up to 20% on short (15−20 ks) timescales. The amplitude of the variability is largest at ~30 keV and is likely to originate from the primary continuum of the southern nucleus. Nevertheless, the mean hard X-ray flux on longer timescales (years) is relatively constant. Moreover, the two nuclei remain Compton-thick, although we find evidence of variability in the material along the line of sight with column densities N_H ≤ 2 × 10^(23) cm^(-2) over long (~3−15 yr) timescales. The observed X-ray emission in the NuSTAR energy range is fully consistent with the sum of the best-fit models of the spatially resolved Chandra spectra of the two nuclei.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://www.aanda.org/articles/aa/abs/2016/01/aa27189-15/aa27189-15.htmlPublisherArticle
http://dx.doi.org/10.1051/0004-6361/201527189DOIArticle
ORCID:
AuthorORCID
Puccetti, S.0000-0002-2734-7835
Comastri, A.0000-0003-3451-9970
Bauer, F. E.0000-0002-8686-8737
Brandt, W. N.0000-0002-0167-2453
Harrison, F. A.0000-0003-2992-8024
Luo, B.0000-0002-9036-0063
Stern, D.0000-0003-2686-9241
Urry, C. M.0000-0002-0745-9792
Alexander, D. M.0000-0002-5896-6313
Boggs, S. E.0000-0001-9567-4224
Gandhi, P.0000-0003-3105-2615
Koss, M. J.0000-0002-7998-9581
Ricci, C.0000-0001-5231-2645
Walton, D. J.0000-0001-5819-3552
Additional Information:© ESO, 2016. Received 14 August 2015 / Accepted 14 October 2015. This work was supported under NASA Contract 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). A.C., A.M., F.F. and L.Z. acknowledge support from the ASI/INAF grant I/037/12/0 − 011/13. W.N.B. acknowledges support from Caltech NuSTAR sub-contract 44A-1092750. F.E.B. and C.R. acknowledge support from CONICYT−Chile grants Basal−CATA PFB−06/2007 and FONDECYT 1141218. F.E.B., C.R. and P.A. acknowledge support from “EMBIGGEN” Anillo ACT1101. FEB acknowledges support from the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. M.B. acknowledges support from NASA Headquarters under the NASA Earth and Space Science Fellowship Program, grant NNX14AQ07H.
Group:NuSTAR, Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASANNG08FD60C
Agenzia Spaziale Italiana (ASI)t I/037/12/0 − 011/13
Caltech NuSTAR subcontractt 44A-1092750
Basal-CATAPFB-06/2007
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1141218
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
NASANNX14AQ07H
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2016-27
Record Number:CaltechAUTHORS:20160204-180325331
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160204-180325331
Official Citation:Hard X-ray emission of the luminous infrared galaxy NGC 6240 as observed by NuSTAR S. Puccetti, A. Comastri, F. E. Bauer, W. N. Brandt, F. Fiore, F. A. Harrison, B. Luo, D. Stern, C. M. Urry, D. M. Alexander, A. Annuar, P. Arévalo, M. Baloković, S. E. Boggs, M. Brightman, F. E. Christensen, W. W. Craig, P. Gandhi, C. J. Hailey, M. J. Koss, S. La Massa, A. Marinucci, C. Ricci, D. J. Walton, L. ZappacostaS. Puccetti, A. Comastri, F. E. Bauer, W. N. Brandt, F. Fiore, F. A. Harrison, B. Luo, D. Stern, C. M. Urry, D. M. Alexander, A. Annuar, P. Arévalo, M. Baloković, S. E. Boggs, M. Brightman, F. E. Christensen, W. W. Craig, P. Gandhi, C. J. Hailey, M. J. Koss, S. La Massa, A. Marinucci, C. Ricci, D. J. Walton, L. Zappacosta and W. Zhang A&A, 585 (2016) A157 DOI: http://dx.doi.org/10.1051/0004-6361/201527189
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64253
Collection:CaltechAUTHORS
Deposited By: Joy Painter
Deposited On:05 Feb 2016 17:41
Last Modified:21 Mar 2019 18:55

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