Volume 555, July 2013
|Number of page(s)||15|
|Published online||08 July 2013|
GRO J1008−57: an (almost) predictable transient X-ray binary⋆
Dr. Karl Remeis-Observatory & ECAP, Universität
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
Accepted: 9 May 2013
A study of archival RXTE, Swift, and Suzaku pointed observations of the transient high-mass X-ray binary GRO J1008−57 is presented. A new orbital ephemeris based on pulse arrival-timing shows the times of maximum luminosities during outbursts of GRO J1008−57 to be close to periastron at orbital phase − 0.03. This makes the source one of a few for which outburst dates can be predicted with very high precision. Spectra of the source in 2005, 2007, and 2011 can be well described by a simple power law with high-energy cutoff and an additional black body at lower energies. The photon index of the power law and the black-body flux only depend on the 15–50 keV source flux. No apparent hysteresis effects are seen. These correlations allow us to predict the evolution of the pulsar’s X-ray spectral shape over all outbursts as a function of just one parameter, the source’s flux. If modified by an additional soft component, this prediction even holds during GRO J1008−57’s 2012 type II outburst.
Key words: X-rays: binaries / pulsars: individual: GRO J1008-57 / accretion, accretion disks / ephemerides
Table 1 is available in electronic form at http://www.aanda.org
© ESO, 2013
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