X-Ray and Near-Infrared Observations of GX 339−4 in the Low/Hard State with Suzaku and IRSF

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.

No Evidence of Intrinsic Optical/Near-Infrared Linear Polarization for V404 Cygni During Its Bright Outburst in 2015: Broadband Modeling and Constraint on Jet Parameters

“…We also assume that the synchrotron peak flux is 2 Jy as observed by Kanata/HONIR (and also by RATAN-600 on MJD 57198.933). We can then derive the magnetic field B and the size of the emission region R by using the standard formulae for synchrotron absorption coefficient and emissitivity (e.g., Rybicki & Lightman 1979;Chaty et al 2011;Shidatsu et al 2011 where s is the power-law index of electron distribution (see below) and D is the distance to V404 Cyg. Here we assumed almost equipartition between magnetic field and electron energy density, which was confirmed by the following SED modeling.…”

SPECTRAL AND TIMING PROPERTIES OF THE BLACK HOLE X-RAY BINARY H1743–322 IN THE LOW/HARD STATE STUDIED WITHSUZAKU

“…It has been suggested that the Comptonization cloud in the low/hard state has a complex structure. Using Suzaku broadband X-ray data, Takahashi et al (2008), Makishima et al (2008), Shidatsu et al (2011b), and Yamada et al (2013) found that the time-averaged spectra can be described with two Comptonization components that have different optical depths. Moreover, Yamada et al (2013) detected the second Comptonization component by analyzing the spectral variability.…”

“…This spectral shape is generally described as unsaturated Compton scattering of the soft X-ray photons from the accretion disk by thermal electrons in hot inner flow or corona. Previous studies suggested that the standard disk is truncated in the low/hard state and eventually extends inward according to the increase of X-ray luminosity (Tomsick et al 2009;Shidatsu et al 2011b;Yamada et al 2013;Kolehmainen et al 2014). However, in what luminosity the standard disk reaches the ISCO is still controversial.…”

THE COMPLEX ACCRETION GEOMETRY OF GX 339–4 AS SEEN BYNuSTARANDSWIFT

“…Because GX 339-4 is a non-eclipsing system, the inclination has to be lower than 60 (Cowley et al 2002), and Zdziarski et al (2004) estimate from the secondary mass function a lower limit of 45. Shidatsu et al (2011) summarize all constraints and derive a best estimate of 50 » . The spin of the black hole in GX 339-4 is currently under debate in the literature.…”