Application of a relativistic accretion disc model to X-ray spectra of LMC X-1 and GRO J1655-40
Abstract
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 0.68<=a<=0.88. Accretion discs in both sources are radiation-pressure dominated. We do not find Compton reflection features in the spectra of any of these objects.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2001
- DOI:
- 10.1046/j.1365-8711.2001.04540.x
- arXiv:
- arXiv:astro-ph/0103362
- Bibcode:
- 2001MNRAS.325.1253G
- Keywords:
-
- ACCRETION;
- ACCRETION DISCS;
- RELATIVITY;
- STARS: INDIVIDUAL: GRO J1655-40;
- STARS: INDIVIDUAL: LMC X-1;
- X-RAYS: STARS;
- Astrophysics
- E-Print:
- 13 pages, 8 figures, accepted for publication in MNRAS