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The Ultraluminous X-Ray Sources NGC 1313 X-1 and X-2: A Broadband Study with NuSTAR and XMM-Newton

Bachetti, Matteo and Rana, Vikram and Walton, Dominic J. and Barret, Didier and Harrison, Fiona A. and Boggs, Steven E. and Christensen, Finn E. and Craig, William W. and Fabian, Andrew C. and Fürst, Felix and Grefenstette, Brian W. and Hailey, Charles J. and Hornschemeier, Ann and Madsen, Kristin K. and Miller, Jon M. and Ptak, Andrew F. and Stern, Daniel and Webb, Natalie A. and Zhang, William W. (2013) The Ultraluminous X-Ray Sources NGC 1313 X-1 and X-2: A Broadband Study with NuSTAR and XMM-Newton. Astrophysical Journal, 778 (2). Art. No. 163. ISSN 0004-637X. doi:10.1088/0004-637X/778/2/163.

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We present the results of NuSTAR and XMM-Newton observations of the two ultraluminous X-ray sources: NGC 1313 X-1 and X-2. The combined spectral bandpass of the two satellites enables us to produce the first spectrum of X-1 between 0.3 and 30 keV, while X-2 is not significantly detected by NuSTAR above 10 keV. The NuSTAR data demonstrate that X-1 has a clear cutoff above 10 keV, whose presence was only marginally detectable with previous X-ray observations. This cutoff rules out the interpretation of X-1 as a black hole in a standard low/hard state, and it is deeper than predicted for the downturn of a broadened iron line in a reflection-dominated regime. The cutoff differs from the prediction of a single-temperature Comptonization model. Further, a cold disk-like blackbody component at ~0.3 keV is required by the data, confirming previous measurements by XMM-Newton only. We observe a spectral transition in X-2, from a state with high luminosity and strong variability to a lower-luminosity state with no detectable variability, and we link this behavior to a transition from a super-Eddington to a sub-Eddington regime.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bachetti, Matteo0000-0002-4576-9337
Rana, Vikram0000-0003-1703-8796
Walton, Dominic J.0000-0001-5819-3552
Barret, Didier0000-0002-0393-9190
Harrison, Fiona A.0000-0003-2992-8024
Boggs, Steven E.0000-0001-9567-4224
Christensen, Finn E.0000-0001-5679-1946
Fabian, Andrew C.0000-0002-9378-4072
Fürst, Felix0000-0003-0388-0560
Grefenstette, Brian W.0000-0002-1984-2932
Hornschemeier, Ann0000-0001-8667-2681
Madsen, Kristin K.0000-0003-1252-4891
Ptak, Andrew F.0000-0001-5655-1440
Stern, Daniel0000-0003-2686-9241
Zhang, William W.0000-0002-1426-9698
Additional Information:© 2013 American Astronomical Society. Received 2013 July 25; accepted 2013 October 2; published 2013 November 13. M.B. wishes to acknowledge the support from the Centre National d'Études Spatiales (CNES). 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 work also makes use of observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA, and of observations made by the Chandra X-ray Observatory. For timing analysis and plotting, a set of Python codes making use of the NumPy and Scipy libraries was used. For some plots, we used the Veusz software. The authors wish to thank Olivier Godet and Chris Done for interesting discussions, and the referee Matt Middleton, whose comments and suggestions substantively improved the quality of the manuscript.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Centre National d’Études Spatiales (CNES)UNSPECIFIED
Subject Keywords:accretion, accretion disks; black hole physics; stars: black holes; X-rays: individual (NGC 1313 X-1, NGC 1313 X-2); X-rays: stars
Issue or Number:2
Record Number:CaltechAUTHORS:20140106-152234543
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Official Citation:The Ultraluminous X-Ray Sources NGC 1313 X-1 and X-2: A Broadband Study with NuSTAR and XMM-Newton Matteo Bachetti et al. 2013 ApJ 778 163
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43235
Deposited By: Ruth Sustaita
Deposited On:06 Jan 2014 23:50
Last Modified:10 Nov 2021 16:34

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