2012ApJ...745L...7S

During its 2003 outburst, the black hole X-ray transient H1743-322 produced two-sided radio and X-ray jets. Applying a simple and symmetric kinematic model to the trajectories of these jets, we determine the source distance, 8.5±0.8 kpc, and the inclination angle of the jets, 75°±3°. Using these values, we estimate the spin of the black hole by fitting its Rossi X-ray Timing Explorer spectra, obtained during the 2003 outburst, to a standard relativistic accretion-disk model. For its spin, we find a_*= 0.2±0.3 (68% limits), -0.3 < a_*< 0.7 at 90% confidence. We strongly rule against an extreme value of spin: a_*< 0.92 at 99.7% confidence. H1743-322 is the third known microquasar (after A0620-00 and XTE J1550-564) that displays large-scale ballistic jets and has a moderate value of spin. Our result, which depends on an empirical distribution of black hole masses, takes into account all known sources of measurement error.