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Application of a relativistic accretion disc model to X-ray spectra of LMC X-1 and GRO J1655-40


  • Marek Gierliński,

    Corresponding author
    1. 1Astronomical Observatory, Jagiellonian University, Orla 171, 30-244 Cracow, Poland
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    • †Present address: University of Durham, Department of Physics, Science Laboratories, South Road, Durham DH1 3LE.

  • Andrzej Maciołek-Niedźwiecki,

    1. 3Łódź University, Department of Physics, Pomorska 149/153, 90-236 Łódź, Poland
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  • Ken Ebisawa

    1. 4Code 660.2, Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
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    • ‡Also at Universities Space Research Association.


We present a general relativistic accretion disc model and its application to the soft-state X-ray spectra of black hole binaries. The model assumes a flat, optically thick disc around a rotating Kerr black hole. The disc locally radiates away the dissipated energy as a blackbody. Special and general relativistic effects influencing photons emitted by the disc are taken into account. The emerging spectrum, as seen by a distant observer, is parametrized by the black hole mass and spin, the accretion rate, the disc inclination angle and the inner disc radius.

We fit the ASCA soft-state X-ray spectra of LMC X-1 and GRO J1655-40 by this model. We find that, having additional limits on the black hole mass and inclination angle from optical/UV observations, we can constrain the black hole spin from X-ray data. In LMC X-1 the constraint is weak, and we can only rule out the maximally rotating black hole. In GRO J1655-40 we can limit the spin much better, and we find 0.68leqslant R: less-than-or-eq, slantaleqslant R: less-than-or-eq, slant0.88. Accretion discs in both sources are radiation-pressure dominated. We do not find Compton reflection features in the spectra of any of these objects.