Long-Term Monitoring of the Black Hole Binary GX 339-4 in the High/Soft State during the 2010 Outburst with MAXI/GSC

We present the results of monitoring the galactic black hole candidate GX 339-4 with the Monitor of All-sky X-ray Image (MAXI)/Gas Slit Camera in the high/soft state during an outburst in 2010. All of the spectra throughout the 8-month period were well reproduced with a model consisting of multi-color disk emission and its Comptonization component, whose fraction is <= 25% in the total flux. In spite of the flux variability over a factor of 3, the innermost disk radius is constant at R-in = 61 +/- 2 km for an inclination angle of i = 46 degrees and a distance of d = 8 kpc. This R-in, value is consistent with those of past measurements with Tenma in the high/soft state. Assuming that the disk extends to the innermost stable circular orbit of a non-spinning black hole, we estimate the black hole mass to be M = 6.8 +/- 0.2 M-circle dot for i = 46 degrees and d = 8 kpc, which is consistent with that estimated from the Suzaku observation of the previous low/hard state. Further combined with the mass function, we obtained a mass constraint of 4.3 M-circle dot < M < 13.3 M-circle dot for the allowed range of d = 6-15 kpc and i < 60 degrees. We also discuss the spin parameter of the black hole in GX 339-4 by applying relativistic accretion disk models to the Swift/XRT data.