A good long look at the black hole candidates LMC X-1 and LMC X-3 |
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Authors: | M. A. Nowak J. Wilms W. A. Heindl K. Pottschmidt J. B. Dove M. C. Begelman |
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Affiliation: | JILA, University of Colorado, Campus Box 440, Boulder, CO 80309-0440, USA;Institut für Astronomie und Astrophysik, Abt. Astronomie, Waldhäuser Str. 64, D-72076 Tübingen, Germany;Center for Astronomy and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA;Center for Astronomy and Space Astrophysics, University of Colorado, Boulder, CO 80309-389, USA;Department of Physics, Metropolitan State College of Denver, C. B. 69, PO Box 173362, Denver, CO 80217-3362, USA;Department of Astrophysics and Planetary Sciences, University of Colorado, Boulder 80309, USA |
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Abstract: | LMC X-1 and LMC X-3 are the only known persistent stellar-mass black-hole candidates that have almost always shown spectra that are dominated by a soft, thermal component. We present here results from 170-ks-long Rossi X-ray Timing Explorer ( RXTE ) observations of these objects, taken in 1996 December, where their spectra can be described by a disc blackbody plus an additional soft high-energy power law (detected up to energies of 50 keV in LMC X-3). These observations, as well as archival Advanced Satellite for Cosmology and Astrophysics ( ASCA ) observations, constrain any narrow Fe line present in the spectra to have an equivalent width ≲90 eV. Stronger, broad lines (≈150 eV EW, are permitted. We also study the variability of LMC X-1. Its X-ray power spectral density (PSD) is approximately proportional to between 10−3 and 0.3 Hz with a root-mean-square (rms) variability of ≈7 per cent. At energies >5 keV, the PSD shows evidence of a break at possibly indicating an outer disc radius of ≲1000 GM c 2 in this likely wind-fed system. Furthermore, the coherence function a measure of the degree of linear correlation between variability in the >5 keV band and variability in the lower energy bands, is extremely low (≲50 per cent). We discuss the implications of these observations for the mechanisms that might be producing the soft and hard X-rays in these systems. |
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Keywords: | accretion, accretion discs black hole physics binaries: spectroscopic stars: individual: LMC X-1 stars: individual: LMC X-3 X-rays: stars |
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