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

Authors :
Dom Walton
Hannah P. Earnshaw
Murray Brightman
Fiona A. Harrison
R. Sathyaprakash
Timothy P.L. Roberts
A. C. Fabian
Lian Tao
Matthew J. Middleton
Didier Barret
D. Stern
P. Kosec
Felix Fürst
Ciro Pinto
Claude R. Canizares
Erin Kara
William Alston
N. A. Webb
Roberto Soria
Matteo Bachetti
M. Heida
Michael A. Nowak
Institut de recherche en astrophysique et planétologie (IRAP)
Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3)
Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP)
Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Université Toulouse III - Paul Sabatier (UT3)
Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)
Source :
Mon.Not.Roy.Astron.Soc., Mon.Not.Roy.Astron.Soc., 2020, 494 (4), pp.6012-6029. ⟨10.1093/mnras/staa1129⟩, arXiv, Monthly notices of the Royal Astronomical Society, 2020, Vol.494(4), pp.6012-6029 [Peer Reviewed Journal]
Publication Year :
2020
Publisher :
HAL CCSD, 2020.

Abstract

We present results from the major coordinated X-ray observing program on the ULX NGC 1313 X-1 performed in 2017, combining $XMM$-$Newton$, $Chandra$ and $NuSTAR$, focusing on the evolution of the broadband ($\sim$0.3-30.0 keV) continuum emission. Clear and unusual spectral variability is observed, but this is markedly suppressed above $\sim$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 anti-correlation, each of these tracks individually shows a positive luminosity-temperature relation. Both are broadly consistent with $L\propto{T}^{4}$, as expected for blackbody emission with a constant area, and also with $L\propto{T}^{2}$, 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.<br />Comment: 18 pages, 7 figures, accepted for publication in MNRAS

Details

Language :
English
Database :
OpenAIRE
Journal :
Mon.Not.Roy.Astron.Soc., Mon.Not.Roy.Astron.Soc., 2020, 494 (4), pp.6012-6029. ⟨10.1093/mnras/staa1129⟩, arXiv, Monthly notices of the Royal Astronomical Society, 2020, Vol.494(4), pp.6012-6029 [Peer Reviewed Journal]
Accession number :
edsair.doi.dedup.....c74be96edc533908852edbf6688eb9a4