X-ray and near-infrared observations of GX 339-4 in the low/hard state with Suzaku and IRSF

X-ray and near-infrared (J -H-K_s) observations of the galactic black-hole binary GX 339-4 in the low/hard state were performed with Suzaku and IRSF in 2009 March. The spectrum in the 0.5-300 keV band is dominated by thermal Comptonization of multicolor disk photons, with a small contribution from a direct disk component, indicating that the inner disk is almost fully covered by hot corona with an electron temperature of ≅175 keV. The Comptonizing corona has at least two optical depths, τ ≅ 1, 0.4. Analysis of the iron-K line profile yields an inner-disk radius of (13.3^+6.4 _-6.0)R_g (R_g represents the gravitational radius GM=c²), with the best-fit inclination angle of ≅50°. This radius is consistent with that estimated from the continuum fit by assuming the conservation of photon numbers in Comptonization. Our results suggest that the standard disk of GX 339-4 is likely truncated before reaching the innermost stable circular orbit (for a non-rotating black hole) in the low/hard states at ∼1% of the Eddington luminosity. The one-day averaged near-infrared light curves are found to be correlated with hard X-ray flux with F_Ks ∝ F ^0.45 _X . The flatter near-infrared νFν spectrum than the radio one suggests that the optically thin synchrotron radiation from the compact jets dominates the near-infrared flux. Based on a simple analysis, we estimate the magnetic field and size of the jet base to be 5 × 10⁴G and 6 × 10⁸ cm, respectively. The synchrotron self Compton component is estimated to be approximately 0.4% of the total X-ray flux.