Spectral and Timing Properties of the Black Hole X-ray Binary H 1743-322 in the Low/hard State Studied with Suzaku

Abstract

We report on the results from Suzaku observations of the Galactic black hole X-ray binary H 1743-322 in the low/hard state during its outburst in 2012 October. We appropriately take into account the effects of dust-scattering to accurately analyze the X-ray spectra. The time-averaged spectra in the 1-200 keV band are dominated by a hard power-law component of a photon index of \approx 1.6 with a high-energy cutoff at \approx 60 keV, which is well described with Comptonization of the disk emission by hot corona. We estimate the inner disk radius from the multi-color disk component, and find that it is 1.3-2.3 times larger than the radius in the high/soft state. This suggests that the standard disk was not extended to the innermost stable circular orbit. A reflection component from the disk is detected with R = \Omega/2\pi \approx 0.6 (\Omega is the solid angle). We also successfully estimate the stable disk component in a way independent of the time-averaged spectral modeling, by analyzing short-term spectral variability on the \sim 1-sec timescale. A weak low-frequency quasi-periodic oscillation (LF QPO) at 0.1-0.2 Hz is detected, whose frequency is found to correlate with the X-ray luminosity and photon index. This result may be explained by the evolution of the disk truncation radius.