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Evidence for different accretion regimes in GRO J1008−57

Kühnel, Matthias and Fürst, Felix and Pottschmidt, Katja and Kreykenbohm, Ingo and Ballhausen, Ralf and Falkner, Sebastian and Rothschild, Richard E. and Klochkov, Dmitry and Wilms, Jörn (2017) Evidence for different accretion regimes in GRO J1008−57. Astronomy and Astrophysics, 607 . Art. No. A88. ISSN 0004-6361. doi:10.1051/0004-6361/201629131.

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We present a comprehensive spectral analysis of the BeXRB GRO J1008−57 over a luminosity range of three orders of magnitude using NuSTAR, Suzaku, and RXTE data. We find significant evolution of the spectral parameters with luminosity. In particular, the photon index hardens with increasing luminosity at intermediate luminosities in the range 10^(36)–10^(37) erg s^(-1). This evolution is stable and repeatedly observed over different outbursts. However, at the extreme ends of the observed luminosity range, we find that the correlation breaks down, with a significance level of at least 3.7σ. We conclude that these changes indicate transitions to different accretion regimes, which are characterized by different deceleration processes, such as Coulomb or radiation breaking. We compare our observed luminosity levels of these transitions to theoretical predications and discuss the variation of those theoretical luminosity values with fundamental neutron star parameters. Finally, we present detailed spectroscopy of the unique “triple peaked” outburst in 2014/15 which does not fit in the general parameter evolution with luminosity. The pulse profile on the other hand is consistent with what is expected at this luminosity level, arguing against a change in accretion geometry. In summary, GRO J1008−57 is an ideal target to study different accretion regimes due to the well-constrained evolution of its broad-band spectral continuum over several orders of magnitude in luminosity.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fürst, Felix0000-0003-0388-0560
Pottschmidt, Katja0000-0002-4656-6881
Kreykenbohm, Ingo0000-0001-7335-1803
Falkner, Sebastian0000-0001-5209-991X
Wilms, Jörn0000-0003-2065-5410
Additional Information:© 2017 ESO. Article published by EDP Sciences. Received 16 June 2016; Accepted 14 August 2017; Published online 20 November 2017. M.K. acknowledges support by the Bundesministerium für Wirtschaft und Technologie under Deutsches Zentrum für Luft- und Raumfahrt grants 50OR1113 and 50OR1207. We appreciate the useful discussions with K. Postnov and M. Gornostaev about accretion column physics. All figures shown in this paper were produced using the SLXfig module, developed by John E. Davis. We thank the Suzaku and NuSTAR teams for accepting our proposals and performing the observations. Finally, we thank the referee for her/his valuable comments, which helped improving the quality of our paper.
Funding AgencyGrant Number
Bundesministerium für Wirtschaft und Technologie (BMWi)UNSPECIFIED
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50OR1113
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50OR1207
Subject Keywords:X-rays: binaries – stars: neutron – stars: emission-line, Be – pulsars: individual: GRO J1008-57
Record Number:CaltechAUTHORS:20171211-133120974
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Official Citation:Evidence for different accretion regimes in GRO J1008−57. Matthias Kühnel, Felix Fürst, Katja Pottschmidt, Ingo Kreykenbohm, Ralf Ballhausen, Sebastian Falkner, Richard E. Rothschild, Dmitry Klochkov and Jörn Wilms. A&A, 607 (2017) A88. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83806
Deposited By: Tony Diaz
Deposited On:12 Dec 2017 21:59
Last Modified:15 Nov 2021 20:14

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