1. X-Ray and Near-Infrared Observations of GX 339−4 in the Low/Hard State with Suzaku and IRSF
- Author
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Shidatsu, Megumi, Ueda, Yoshihiro, Tazaki, Fumie, Yoshikawa, Tatsuhito, Nagayama, Takahiro, Nagata, Tetsuya, Oi, Nagisa, Yamaoka, Kazutaka, Takahashi, Hiromitsu, Kubota, Aya, Cottam, Jean, Remillard, Ronald, and Negoro, Hitoshi
- Abstract
X-ray and near-infrared ( $J$– $H$– $K_{\rm s}$) 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 $\approx$175 keV. The Comptonizing corona has at least two optical depths, $\tau$$\approx$1, 0.4. Analysis of the iron-K line profile yields an inner-disk radius of (13.3 $^{+6.4}_{-6.0}$) $\ R_{\rm g}$( $\ R_{\rm g}$represents the gravitational radius $GM/c^2$), with the best-fit inclination angle of $\approx$50 $^\circ$. This radius is consistent with that estimated from the continuum fit by assuming the conservation of photon numbers in Comptonization. Our results suggest that the standard disk of GX 339 $-$4 is likely truncated before reaching the innermost stable circular orbit (for a non-rotating black hole) in the low/hard states at $\sim\ $1% of the Eddington luminosity. The one-day averaged near-infrared light curves are found to be correlated with hard X-ray flux with $F_{\rm Ks}$$\propto$$F_{\rm X}^{0.45}$. The flatter near-infrared $\nu F_{\nu}$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 $\times$10 $^{4}\ $G and 6 $\times$10 $^{8}\ $cm, respectively. The synchrotron self Compton component is estimated to be approximately 0.4% of the total X-ray flux.
- Published
- 2011
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