Evidence for different accretion regimes in GRO J1008-57

Kühnel M, Furst F, Pottschmidt K, Kreykenbohm I, Ballhausen R, Falkner S, Rothschild RE, Klochkov D, Wilms J (2017)

Publication Status: Published

Publication Type: Journal article

Publication year: 2017

Journal

Publisher: EDP SCIENCES S A

Book Volume: 607

Article Number: ARTN A88

DOI: 10.1051/0004-6361/201629131

Abstract

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 3.7 sigma. 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.

Authors with CRIS profile

Involved external institutions

Eberhard Karls Universität Tübingen Germany (DE) University of California, San Diego United States (USA) (US) University of Maryland, Baltimore County United States (USA) (US) California Institute of Technology (Caltech) United States (USA) (US)

How to cite

APA:

Kühnel, M., Furst, F., Pottschmidt, K., Kreykenbohm, I., Ballhausen, R., Falkner, S.,... Wilms, J. (2017). Evidence for different accretion regimes in GRO J1008-57. Astronomy & Astrophysics, 607. https://dx.doi.org/10.1051/0004-6361/201629131

MLA:

Kühnel, Matthias, et al. "Evidence for different accretion regimes in GRO J1008-57." Astronomy & Astrophysics 607 (2017).

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