The Low-Spin Black Hole in LMC X-3

Building upon a new dynamical model for the X-ray binary LMC X-3, we measure the spin of its black hole primary via the continuum-fitting method. We consider over one thousand thermal-state RXTE X-ray spectra of LMC X-3. Using a large subset of these spectra, we constrain the spin parameter of the black hole to be spin = 0.21(+0.18,-0.22), 90% confidence. Our estimate of the uncertainty in spin takes into account a wide range of systematic errors. We discuss evidence for a correlation between a black hole's spin and the complexity of its X-ray spectrum.