As an initial step in the analysis, we fit the full data set to our spectral model using fiducial values for and (Section 1) and a distance kpc (Orosz et al. 2009), and adopting a viscosity . We include limb darkening and returning radiation effects, adopt zero torque at the inner-disk boundary, and make the standard assumption that the black hole’s spin axis is aligned with the orbital angular momentum (Steiner & McClintock 2012; McClintock et al. 2013). There are just four free fit parameters: , mass accretion rate , photon spectral index , and the scattering fraction (the fraction of disk photons scattered in the corona). We constrained the photon index to lie in the range ; the three other parameters are unconstrained.