Luminosity dependent accretion state change in GRO J1008–57

¹ Dr. Karl Remeis-Observatory & ECAP, Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
² Space Radiation Lab, California Institute of Technology, MC 290-17 Cahill, 1200 E. California Blvd., Pasadena, CA 91125, USA
³ CRESST, Center for Space Science and Technology, UMBC, Baltimore, MD 21250, USA
⁴ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁵ Center for Astronomy and Space Sciences, University of California, San Diego, La Jolla, CA 92093, USA
⁶ CEA Saclay, DSM/IRFU/SAp-UMR AIM (7158) CNRS/CEA/Université Paris 7, Diderot, 91191 Gif sur Yvette, France
⁷ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁸ Universities Space Research Association, Columbia, MD 21044, USA
⁹ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
¹⁰ ISDC Data Center for Astrophysics, Chemin d’Écogia 16, 1290 Versoix, Switzerland
¹¹ Instituto de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante, 03080 Alicante, Spain

^a e-mail: matthias.kuehnel@sternwarte.uni-erlangen.de

Published online: 8 January 2014

Abstract

In a former publication, we have analyzed the transient neutron star X-ray binary GRO J1008–57 using all available RXTE-, Swift-, and Suzaku-data. As we have found, the source’s spectral components, i.e., a power-law with high exponential cutoff and a black-body, are strongly correlated with the hard X-ray flux (15–50 keV). We update the analytical description of these dependence, including a change in the photon index behaviour from a flat to a logarithmic function. The flux, where the change occurs, is consistent with the onset of the black-body emission. Thus, a change of the accretion state always occurs in GRO J1008–57 at a particular flux level.