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Super-Eddington accretion on to the neutron star NGC 7793 P13: Broad-band X-ray spectroscopy and ultraluminous X-ray sources

Walton, D. J. and Fürst, F. and Harrison, F. A. and Stern, D. and Bachetti, M. and Barret, D. and Brightman, M. and Fabian, A. C. and Middleton, M. J. and Ptak, A. and Tao, L. (2018) Super-Eddington accretion on to the neutron star NGC 7793 P13: Broad-band X-ray spectroscopy and ultraluminous X-ray sources. Monthly Notices of the Royal Astronomical Society, 473 (4). pp. 4360-4376. ISSN 0035-8711. http://resolver.caltech.edu/CaltechAUTHORS:20180221-134250534

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Abstract

We present a detailed, broad-band X-ray spectral analysis of the ultraluminous X-ray source (ULX) pulsar NGC 7793 P13, a known super-Eddington source, utilizing data from the XMM–Newton, NuSTAR and Chandra observatories. The broad-band XMM–Newton+NuSTAR spectrum of P13 is qualitatively similar to the rest of the ULX sample with broad-band coverage, suggesting that additional ULXs in the known population may host neutron star accretors. Through time-averaged, phase-resolved and multi-epoch studies, we find that two non-pulsed thermal blackbody components with temperatures ∼0.5 and 1.5 keV are required to fit the data below 10 keV, in addition to a third continuum component which extends to higher energies and is associated with the pulsed emission from the accretion column. The characteristic radii of the thermal components appear to be comparable, and are too large to be associated with the neutron star itself, so the need for two components likely indicates the accretion flow outside the magnetosphere is complex. We suggest a scenario in which the thick inner disc expected for super-Eddington accretion begins to form, but is terminated by the neutron star's magnetic field soon after its onset, implying a limit of B ≲ 6 × 10^(12) G for the dipolar component of the central neutron star's magnetic field. Evidence of similar termination of the disc in other sources may offer a further means of identifying additional neutron star ULXs. Finally, we examine the spectrum exhibited by P13 during one of its unusual ‘off’ states. These data require both a hard power-law component, suggesting residual accretion on to the neutron star, and emission from a thermal plasma, which we argue is likely associated with the P13 system.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1093/mnras/stx2650DOIArticle
https://academic.oup.com/mnras/article/473/4/4360/4443211PublisherArticle
https://arxiv.org/abs/1705.10297arXivDiscussion Paper
ORCID:
AuthorORCID
Walton, D. J.0000-0001-5819-3552
Harrison, F. A.0000-0003-2992-8024
Stern, D.0000-0003-2686-9241
Bachetti, M.0000-0002-4576-9337
Ptak, A.0000-0001-5655-1440
Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 October 9. Received 2017 October 9; in original form 2017 May 29. Published: 11 October 2017. The authors would like to thank the reviewer for the feedback provided, which helped to improve the final version of the manuscript. DJW and MJM acknowledge support from an STFC Ernest Rutherford fellowship, ACF acknowledges support from ERC Advanced Grant 340442 and DB acknowledges financial support from the French Space Agency (CNES). This research has made use of data obtained with NuSTAR, a project led by Caltech, funded by NASA and managed by NASA/JPL, and has utilized the NUSTARDAS software package, jointly developed by the ASDC (Italy) and Caltech (USA). This work 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:Space Radiation Laboratory, NuSTAR
Funders:
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
European Research Council (ERC)340442
Centre National d'Études Spatiales (CNES)UNSPECIFIED
NASA/JPL/CaltechUNSPECIFIED
Subject Keywords:stars: neutron – X-rays: binaries – X-rays: individual: NGC7793 P13
Record Number:CaltechAUTHORS:20180221-134250534
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180221-134250534
Official Citation:D. J. Walton, F. Fürst, F. A. Harrison, D. Stern, M. Bachetti, D. Barret, M. Brightman, A. C. Fabian, M. J. Middleton, A. Ptak, L. Tao; Super-Eddington accretion on to the neutron star NGC 7793 P13: Broad-band X-ray spectroscopy and ultraluminous X-ray sources, Monthly Notices of the Royal Astronomical Society, Volume 473, Issue 4, 1 February 2018, Pages 4360–4376, https://doi.org/10.1093/mnras/stx2650
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84908
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:21 Feb 2018 22:06
Last Modified:21 Feb 2018 22:06

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