Evidence for different accretion regimes in GRO J1008-57

Journal article

Publication Details

Author(s): Kühnel M, Furst F, Pottschmidt K, Kreykenbohm I, Ballhausen R, Falkner S, Rothschild RE, Klochkov D, Wilms J
Journal: Astronomy & Astrophysics
Publication year: 2017
Volume: 607
ISSN: 1432-0746


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.

FAU Authors / FAU Editors

Ballhausen, Ralf
Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut
Falkner, Sebastian Dr.
Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut
Kreykenbohm, Ingo Dr.
Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut
Wilms, Jörn Prof. Dr.
Professur für Astronomie und Astrophysik

External institutions with authors

California Institute of Technology (Caltech)
Eberhard Karls Universität Tübingen
University of California, San Diego
University of Maryland, Baltimore County

How to cite

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

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


Last updated on 2019-04-06 at 02:08