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The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR

Walton, D. J. and Pinto, C. and Nowak, M. and Bachetti, M. and Sathyaprakash, R. and Kara, E. and Roberts, T. P. and Soria, R. and Brightman, M. and Canizares, C. R. and Earnshaw, H. P. and Fürst, F. and Heida, M. and Middleton, M. J. and Stern, D. and Tao, L. and Webb, N. and Alston, W. N. and Barret, D. and Fabian, A. C. and Harrison, F. A. and Kosec, P. (2020) The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR. Monthly Notices of the Royal Astronomical Society, 494 (4). pp. 6012-6029. ISSN 0035-8711. doi:10.1093/mnras/staa1129.

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We present results from the major coordinated X-ray observing programme on the ULX NGC 1313 X-1 performed in 2017, combining XMM–Newton, Chandra, and NuSTAR, focusing on the evolution of the broad-band (∼0.3–30.0 keV) continuum emission. Clear and unusual spectral variability is observed, but this is markedly suppressed above ∼10–15 keV, qualitatively similar to the ULX Holmberg IX X-1. We model the multi-epoch data with two-component accretion disc models designed to approximate super-Eddington accretion, allowing for both a black hole and a neutron star accretor. With regards to the hotter disc component, the data trace out two distinct tracks in the luminosity–temperature plane, with larger emitting radii and lower temperatures seen at higher observed fluxes. Despite this apparent anticorrelation, each of these tracks individually shows a positive luminosity–temperature relation. Both are broadly consistent with L ∝ T⁴, as expected for blackbody emission with a constant area, and also with L ∝ T², as may be expected for an advection-dominated disc around a black hole. We consider a variety of possibilities for this unusual behaviour. Scenarios in which the innermost flow is suddenly blocked from view by outer regions of the super-Eddington disc/wind can explain the luminosity–temperature behaviour, but are difficult to reconcile with the lack of strong variability at higher energies, assuming this emission arises from the most compact regions. Instead, we may be seeing evidence for further radial stratification of the accretion flow than is included in the simple models considered, with a combination of winds and advection resulting in the suppressed high-energy variability.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Walton, D. J.0000-0001-5819-3552
Pinto, C.0000-0003-2532-7379
Nowak, M.0000-0001-6923-1315
Bachetti, M.0000-0002-4576-9337
Sathyaprakash, R.0000-0002-5254-3969
Kara, E.0000-0003-0172-0854
Roberts, T. P.0000-0001-8252-6337
Soria, R.0000-0002-4622-796X
Brightman, M.0000-0002-8147-2602
Earnshaw, H. P.0000-0001-5857-5622
Fürst, F.0000-0003-0388-0560
Heida, M.0000-0002-1082-7496
Middleton, M. J.0000-0002-8183-2970
Stern, D.0000-0003-2686-9241
Alston, W. N.0000-0003-2658-6559
Barret, D.0000-0002-0393-9190
Fabian, A. C.0000-0002-9378-4072
Harrison, F. A.0000-0003-2992-8024
Alternate Title:The Unusual Broadband X-ray Spectral Variability of NGC 1313 X-1 seen with XMM-Newton, Chandra and NuSTAR
Additional Information:© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 April 20. Received 2020 April 20; in original form 2019 November 20. Published: 26 April 2020. The authors would like to thank the reviewer for their positive and thorough feedback, which helped to improve the final version of this manuscript. DJW and MJM acknowledge support from Science and Technology Facilities Council (STFC) Ernest Rutherford Fellowships. CP and FF acknowledge support from European Space Agency (ESA) Research Fellowships. HPE acknowledges support under National Aeronautics and Space Administration (NASA) contract NNG08FD60C. TPR was funded as part of the STFC consolidated grant ST/K000861/1. NW acknowledges support from Centre National d'Etudes Spatiales (CNES) for this work. CRC and MN acknowledge support from the Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 to the Massachusetts Institute of Technology (MIT), which is in turn supported by NASA under contract NAS8-03060 for the Chandra X-ray Center (CXC). This research has made use of data obtained with NuSTAR, a project led by Caltech, funded by NASA and managed by NASA Jet Propulsion Laboratory (JPL), and has utilized the NUSTARDAS software package, jointly developed by the Space Science Data Centre (SSDC; Italy) and Caltech (USA). This research has also made use of data obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States.
Group:Astronomy Department, NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)ST/K000861/1
European Space Agency (ESA)UNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Smithsonian Astrophysical ObservatorySV3-73016
Subject Keywords:X-rays: binaries – X-rays: individual: NGC1313 X-1
Issue or Number:4
Record Number:CaltechAUTHORS:20200413-153610462
Persistent URL:
Official Citation:D J Walton, C Pinto, M Nowak, M Bachetti, R Sathyaprakash, E Kara, T P Roberts, R Soria, M Brightman, C R Canizares, H P Earnshaw, F Fürst, M Heida, M J Middleton, D Stern, L Tao, N Webb, W N Alston, D Barret, A C Fabian, F A Harrison, P Kosec, The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR, Monthly Notices of the Royal Astronomical Society, Volume 494, Issue 4, June 2020, Pages 6012–6029,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102512
Deposited By: Tony Diaz
Deposited On:13 Apr 2020 22:44
Last Modified:16 Nov 2021 18:12

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