Open AccessA good long look at the black hole candidates LMC X‐1 and LMC X‐3
Author(s) -
Nowak M. A.,
Wilms J.,
Heindl W. A.,
Pottschmidt K.,
Dove J. B.,
Begelman M. C.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.03984.x
Subject(s) - physics , astrophysics , black body radiation , spectral line , radius , large magellanic cloud , spectral density , black hole (networking) , power law , line (geometry) , root mean square , astronomy , radiation , stars , computer network , routing protocol , routing (electronic design automation) , computer science , link state routing protocol , statistics , computer security , mathematics , geometry , quantum mechanics
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.