GRO J1008−57: an almost predictable transient X-ray binaryReport as inadecuate

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* Corresponding author 1 ECAP - Erlangen Centre for Astroparticle Physics 2 CALTECH - California Institute of Technology 3 CRESST - Center for Research and Exploration in Space Science and Technology GSFC 4 AIM - UMR 7158 - UMR E 9005 - Astrophysique Interactions Multi-échelles 5 Leibniz-Institut für Astrophysik Potsdam

Abstract : 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.

Keywords : accretion pulsars: individual: GRO J1008-57 X-rays: binaries accretion disks ephemerides

Author: M. Kühnel - S. Müller - I. Kreykenbohm - F. Fürst - K. Pottschmidt - R. E. Rothschild I. Caballero - V. Grinberg - G. Schönhe



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